Test Equipment Anonymous (TEA) group therapy thread

[mnementh]

The German Institute for Broadcast Technology (IRT) in Munich is being disbanded

of course, few months after I left Munich.

Wow... remind me never to piss you off. 

mnem

[mnementh]

Thanks for all the good info ! 

1) I wired +12V to the ACC wire. That meant I had to unplug the CAN bus box because the ACC wire goes straight to that box !
Result = no change, still no power, still does not draw even ONE mA... nothing at all.

2) Visual inspection leads nothing, damaged components or dislodged flat flex cables.

3) Probed main board for voltages... checked all electrolytic caps, all "SMPS" looking SMD coils, and all discrete components, diodes and what not, in the immediate vicinity of the main/power connector at the back of the unit. ZERO voltage everywhere. If the screen/front panel was at fault, the mainboard would still be running so I would be able to see supply VOLTAGES and theunit would draw at least SOME current ! But it draws absolutely zero, and zero voltage anywhere. So there is no point worrying about the display or flat flew cables at this point I think ! 

4) REGARDLESS of whatever magic the unit might perform to "decode" its numerous inputs, to decide if it will be so kind as to power up the unit... this smartness is embodied by circuitry, a CPU, or a dedicated power management chip or discrete circuitry or SOMETHING.... this means that even if the conditions for the unit to power up were not satisfied, the smarts inside the unit would be powered up anyway and therefore draw some current and need voltage to run.... but since I can't even witness the slightest current draw... it means the main board is just not "upset" with the way I wired it... it's more like it's simply not powered up AT ALL !

So I am now shifting from a "No display" fault, to a "No Power" fault.... not at all the same thing...

Zerto votlage and zero current... it's just like the main fuse was blown, as simple as that ! Yeah, I did check the fuse... it's fine...

Next step is to unscrew the main board from the chassis, so I can inspect the underside of it, and access the pins of the power connector. I will trace the +12V pin to see where it lands on the top/component side, then trace it there.

But it's too late now, going to bed.  Before I waste time on this thing, I will the owner who actually lives just 500m from me, so he can come with his car. I will ask that we  reconnect the stereo to his car, so he can show me if he really can get this thing to work.... as a quick sanity check. If it does power up and work, then I don't understand how that's possible 

More tomorrow then, good night ! 

Only one other thing to ask...
Have you connected the chassis to the supply 0V?
If you really have 0mA current draw there must be an open circuit somewere. Likely either a bad joint (soldered, crimped or loose connector) or a track on PCB or ribbon having been taken out by a short circuit.
If it poweres up with the chassis connected look to the 0V wiring.
Generally these do not need CAN for basic operation. CAN can save a bunch of auxillary wiring like the steering buttons, reversing and brake light. Some CARS need the CAN to stop warnings about the radio or make things like nav system work.
The CAN box with the AUX connetion is beause the car it's in does not have a switched 12V AUX to tell the unit the car is "on". The  CAN box decodes the signals and provides a switched 12V AUX supply. Commonly needed on Fiats for eample.

More generally, this unit is clearly a steamng turd. As it has no makers name, no E approval and an incorect CE mark it is clearly ILLEGAL to ue in the EU or install in a car. Technically fitting it invalidates the car's type approval and probably the insurance.* (Yes I know there is zero enforcement) Tell your friend to demand his mony back. If he paid with a credit card or PayPal they are also liable in most cases. If no joy tell him to talk to consumer protection or whoever enforces CE compline in France.

* Any electronic item that is installed in a car in the EU/UK that may affect the safety of the vehicle must be properly approved and "E" marked. Items that have displays or controls for the driver are explictly included as affecting safety.  CE marking does not apply to automotive parts.

Agreed it's a cheap shitbox. Sadly, these are all over Amazon, etc. 

The brand name and any alleged "compliance" markings are probably on the box it came in or a paper tag wrapped around the wire bundle; these are commonly batch-made for an importer/exporter to slap in a box with their own name on it. Sortof like all these cheap Android tablets over the last decade or so.

I'm not sure that the CANbus isn't necessary, tho... if it has been configured with a CANbus library with antitheft integration, I could see how the unit may not turn on even with the ACC wire connected as it's not getting the proper handshaking from the car's body computer/antitheft module. I can't say that I've ever run across this scenario, I'm just saying I can see how it could wind up bricking the device once removed from the car.

A lot of modern cars' antitheft systems are designed to do just that with the factory radio, and it may be that the CANbus libraries for some of those cars have to mimic that behavior to work with the car. I really don't know.

EDIT: Tho, agreed... if it really is not drawing ANY current... 0mA... there has to be something else wrong. While these units are supposed to be able to run entirely from vehicle wiring for both (B+) and GND as they are often screwed into an all-plastic dash, a lot of OEMs will also have a plug-in GND strap. If poor design, or something effed-up as you suggest, applying a GND to the metal chassis may reveal more. 


My gut is now saying to look inside the CANbus brick.

mnem
 

[Vince]

Car Stereo update !

Thanks again to everyone for all your comments while I was asleep 

I worked some more on the thing... I traced the GND and B+ pins from the input connector at the back , to the beefy looking through-hole power supply components on the mother board. A big coil, big Electrolytic cap, big diode. Found that GND is an uninterruipted path, so it's alwyas on so to speak. Well you would expect that...
Then I traced B+... and it TOO sneaked its way onto the board without interruption ! Nothing to cut the power path !
 So then it was clear I SHOULD get my B+ voltage on the fucking board NO MATTER WHAT ! But I was not !
So I was onto something  eh ! 

Eventually found it was just operator error ! The 12V from my lab power supply was getting to the stereo, but GND was not ! 
Turend out the alligator clip I shoved inside the back of the banana cable from the power supply, was NOT making contact, eventhough it was firmly gripping the jack !    I moved the alligator clip a bit, turning it 90° so as to grabv the side of the jack rather than the top of it, and now I get perfect electrical contact, power is getting to the stereo !!! 
Fuck me, can't believe it, how stupid, ridiculous !!! 

To my defense, I was using a new banana cable of a different model than I used before.. the old cable I could put the alligator clip in any orientation it would work fine, but somehow on the new cables it only works in one particular position ?! 

Anyway, now I have juice going to the board and I can play with it ! 

- With the ACC wire disconnected, it draws 5mA.
-  With the ACC wire connected, current ramps up as the CPU "boots" I guess (an ARM STM32), and after 3 seconds or so it stays at roughly 500mA, fluctuating a few tens of mA, it's not perfectly steady... which I find good. Means the operating system in this thing is actually alive and taking care of things.

Then I spent a bit of time looking at the board to try to identify all the power suppy stuff, so I can try and measure the various rails, see if it's looking or not.

See picture attached of the board with my annotations / findings.

Basically there is a beefy DC/DC converter that takes a lot of space, that takes B+ from the  power plug and produces 5V.
Then I found lots of linear 3 pin regulators that provides lower voltages all over the board. Circled on my picture.

Other than the main DC/DC converter that provides the bulk of the power in this thing, I found at least 5 other regulators, small/ local, 3 pin linear chips, basic stuff. 3 big D-PAK looking 78XX regulators (one 5V and two 9V), and two more but in tiny packages, each giving 3.3V for a couple tiny wireless third-party boards/modules. One of the has a thin coax cable going to a little antenna at the back of the stereo. The other module has a built-in / printed antenna. I guess one if for BT the other for WIfi... I don't know my wireless stuff.

They all output the expected voltage, with low ripple so that's fine... BUT ONE !

There is one regulator, a 7809 that ouptus absolute zero. Granted I didn't expect otherwise given that at its input I see only 300mV ! 
So either something is kakput here, or it's a supply that gets switched by the CPU nly in certain circumstances. So I can say as it stands, if it's normal or not. However, I find it interesting to note WHERE this 9V regulator is located on the board : as you can see, it's right next to one of the two falt flex connectors that interface to the front panel assembly, hence the LCD too !  And if you look at the traces and measure with the DMM, you can easily confirm that this 9V is connected to pads on this connector.

So I am making progress !   
If we assume that this 9V is NOT switched by the CPU, but is rather supposed to be on all the time, then this means we have a missing rail going to the front panel. So if this rail happens to be used to power the couple DC/DC converters I saw on the LCD display board... no wonder that there is no picture...
so now as someone suggested before, it's time to reconnect the front panel and shine a torch on the LCD panel to try to see if we have a picture but no backlight, or if we have no picture at all....

Hmmm this is getting exciting, I like that !!! 


ALSO : got news from the guy with the ASUS tablet and the two Somfy electric fence motors.... had him over the phone. He said he will pay the 50 euros I asked for the motor I fixed, no problemo, as well as the 30 Euros I spent for the used battery and charging board for his Asus tablet, and he even spontaneously said "yeah that's for the parts but don't forget to your labour !!! " .

WOW !!! First time I get a "client" like that ! I want more of them !!! 

Humanity is not 100% lost then, some bits of it out there are still worth saving ! 

[Cubdriver]

Vince, you need to get you some 'naner to agallator clip leads!


There's little more frustrating when troubleshooting something than to discover that the first part of your problem is in your setup.  At work, intermittent RF cables get cut in half immediately so they can't sneak back onto the rack to cause someone else grief and wasted time.  Good on you to find that problem with the setup - sometimes coming back after a break is a big help to a fresh start.

Good luck with your efforts now that the first hurdle has been cleared!

-Pat

[AVGresponding]

Car Stereo update !

There is one regulator, a 7809 that ouptus absolute zero. Granted I didn't expect otherwise given that at its input I see only 300mV ! 
So either something is kakput here, or it's a supply that gets switched by the CPU nly in certain circumstances. So I can say as it stands, if it's normal or not. However, I find it interesting to note WHERE this 9V regulator is located on the board : as you can see, it's right next to one of the two falt flex connectors that interface to the front panel assembly, hence the LCD too !  And if you look at the traces and measure with the DMM, you can easily confirm that this 9V is connected to pads on this connector.

So I am making progress !   
If we assume that this 9V is NOT switched by the CPU, but is rather supposed to be on all the time, then this means we have a missing rail going to the front panel. So if this rail happens to be used to power the couple DC/DC converters I saw on the LCD display board... no wonder that there is no picture...
so now as someone suggested before, it's time to reconnect the front panel and shine a torch on the LCD panel to try to see if we have a picture but no backlight, or if we have no picture at all....

Hmmm this is getting exciting, I like that !!! 

If the regulator has power at its input pin, it should have power at the output pin.

EDIT: Reread it lol. Where is the reg fed from? I'd be surprised if it's from anything other than the main power, maybe via a power mosfet I guess... disconnect the output pin and see if it comes up. It would be quite unusual to switch functionality via a regulator; they take time (a few micro/milli seconds) to come up, which can be a problem in itself.

[mnementh]

...It would be quite unusual to switch functionality via a regulator; they take time (a few micro/milli seconds) to come up, which can be a problem in itself.

Yeah, and that reg is a D-PAK package, so no EN pin. Got to be some fault in the supply to it; whether kaputski due to prior short downstream or just not being turned on for some reason.

I'd look for a short across Vout/GND and Vin/GND before I get too far down the rabbit-hole.

mnem

[capt bullshot]

Turend out the alligator clip I shoved inside the back of the banana cable from the power supply, was NOT making contact, eventhough it was firmly gripping the jack !    I moved the alligator clip a bit, turning it 90° so as to grabv the side of the jack rather than the top of it, and now I get perfect electrical contact, power is getting to the stereo !!! 
Fuck me, can't believe it, how stupid, ridiculous !!! 

To my defense, I was using a new banana cable of a different model than I used before.. the old cable I could put the alligator clip in any orientation it would work fine, but somehow on the new cables it only works in one particular position ?! 

Using an alligator clip and the banana plug this way, it's just pure luck wether it makes contact or not. Just clip the alligator to the other (non-isolated or business) end of the banana plug

Reminds me of one day wasted @work when I used a 10:1 oscilloscope probe and didn't notice it was switched to 1:1

[AVGresponding]

...It would be quite unusual to switch functionality via a regulator; they take time (a few micro/milli seconds) to come up, which can be a problem in itself.

Yeah, and that reg is a D-PAK package, so no EN pin. Got to be some fault in the supply to it; whether kaputski due to prior short downstream or just not being turned on for some reason.

I'd look for a short across Vout/GND and Vin/GND before I get too far down the rabbit-hole.

mnem

Quite an odd value in context, also. What with voltage drops through the wiring and pcb traces, that 7809 has got to be sailing close to the wind in terms of dropout voltage.

[Vince]

Stereo update :

Yeah Pat banana-crocodile leads would be nice indeed ! 

AVG yeah as you said your not reading properly ! 


MAKING PROGRESS --> reconnected the front panel assembly. Throw a torch light at the LCD for a few minutes, could see nothing. Did notice though, that every time I pressed one of the buttons on the front panel, that it yielded a brief current spike ! So that meant maybe CPU was reacting to the front panel hence not ignoring it due to CAN bus locking the unit or whatever, so was rather encouraging !
Then after a few minutes playing with the buttons randomly while shedding light onto the LCD, I could SWEAR that I briefly saw something being displayed, I think it read something like "Accès connecté " ! I am 100% sure I saw that, it was not garbage it was proper legible text !!!! 
Then it vanished and for the next 10 minutes I could not spot anything on the screen... weird.

But it was encouraging so I decided to take it a step further : I connected a small speaker to the unit. A tiny rectangular one that I recently salvaged from a flat TV I failed to fix. Then I pressed the "RADIO" push button. I could swear I could hear a very, very faint "shhhhhhh" sound. So I sticked a screw driver in the antenna socket, then also clipped a test lead onto the screw driver because why not, and the "shhhh" became much louder !   
Then I played with the volume knob/rotary encoder, and it would make the "shhh" noise more or less loud, and every time I would move the encoder a notch, I could hear a distinct "BIP" noise , yes !!!!
Then I played with the "BAND" and "memory/pre-select" buttons, and eventually managed to listen to FM station loud and clear !!!

YES !!!! 

So this thing is indeed working. No matter what CAN crap might be going on, there is no way it would let me play with the radio yet NOT display anything on the screen, it would be silly !

So it must be a backlight problem !!!   
Given that I managed to see a couple words  displayed on the LCD using the torch light, it means the CPU on the M/B can communicate just fine with the LCD, LCD can display stuff, no worries. It's purely a basic backlight problem, so there is hope it can be fixed, so let's get cracking !!!   

So I will check those two DC/DC converters on the LCD board to see if they are been fed any power, if not see if they use the missing 9V rail on the M/B, if so then try to probe around that 9V rail to figure out how it's put together, if it's switched with an upstream MOSFET possibly failed or whatever.... let's get cracking !!!   

[Atomillo]

A while back I posted photos of my first piece of vintage test equipmente, a Keithley 247 HV supply.

Back then I didn't have the proper HV BNC connector, but now thanks to the kindness of forum user Robert763 who gave a cable with the proper connector and a female extra conector for free now I do!

Look at that PERFECT fit!! Flawless!!

Once again, many thanks to Robert763 for his kindness

[mnementh]

Stereo update :

Yeah Pat banana-crocodile leads would be nice indeed ! 

AVG yeah as you said your not reading properly ! 


MAKING PROGRESS --> ....So it must be a backlight problem !!!   
Given that I managed to see a couple words  displayed on the LCD using the torch light, it means the CPU on the M/B can communicate just fine with the LCD, LCD can display stuff, no worries. It's purely a basic backlight problem, so there is hope it can be fixed, so let's get cracking !!!   

So I will check those two DC/DC converters on the LCD board to see if they are been fed any power, if not see if they use the missing 9V rail on the M/B, if so then try to probe around that 9V rail to figure out how it's put together, if it's switched with an upstream MOSFET possibly failed or whatever.... let's get cracking !!!   

Well, or a power to the LCD problem, which may or may not be caused by the backlight.

Check for continuity from that D-Pak regulator's Vout to the pins on the LCD connector. And again, check for a short on the Vin/Vout of that reg, both with the ribbon cable connected and disconnected. Power to that reg may have a fuse (some of which look like a SMD resistor), a PTC protector, or even a failed 0-ohm resistor in the path.

EDIT: Point being... you've found something that looks wrong, and that 9V reg has a high likelihood of being main power to the LCD. Figure that out first instead of jumping all around the thing. 

mnem
 

[Robert763]

<SNIP>
Agreed it's a cheap shitbox. Sadly, these are all over Amazon, etc. 

The brand name and any alleged "compliance" markings are probably on the box it came in or a paper tag wrapped around the wire bundle; these are commonly batch-made for an importer/exporter to slap in a box with their own name on it. Sortof like all these cheap Android tablets over the last decade or so.

<SNIP>
[/color][/color][/i][/b]

mnem
 

This is irrelevant. For the EU, UK and many other countries, this item must be compliant to UNECE Regulation 10 (ECE R10) if it is installed in a car.  The compliance has to confirmed by an approved body. The compliance mark must be applied TO THE UNIT. If it's not marked (E + country number in circle plus the number of the approved body)  then the unit is non compliant by default. Regulation 10 is for Electromagnetic Compatability (EMC). As the unit has a display and is in sight of the driver it has to comply with susceptability as well as emissions.

As I said before enforcement of this is virtually non-existent, that however does not make it legal. 

[mnementh]

Oh, for cryin' in the mud... I was agreeing with ya, man! All this Chinesium bulk-production generic electronics is a shitshow!

I was just relating some of what I've seen out in the wild. It's worse than it seems; way, way worse.

mnem

[25 CPS]

Happy Thanksgiving !  The date may be different elsewhere, but it is this weekend in the GWN.

It is actually a pretty good weekend.

SWMBO's nephew got married yesterday.  I missed out on it. 
Instead, I took the kiddo for a COVID test.
Results cam back negative 
School announced during the weekend that there are more cases ...    I figured that they should have already closed the school for a 14-day quarantine 

I am running on severe lack of sleep.  Last night was spent giving the dog a de-skunking bath with special shampoo.  This is where a smaller dog is easier to deal with ... dog still smells somewhat.  Garage, especially around the tractor door, stinks terribly.

Despite all this, I am making progress re-wiring a panel.  I will not be testing or plugging anything in this evening.  Turkey is in the oven for tomorrow, and I am not going to take anything to chance with the electrical supply.

Happy Thanksgiving!

My family got together yesterday at my aunt's house in Toronto so put away the stuff I'm working on here and go fulfil the family obligation.  The truth is, I very rarely get to see my relatives outside of gatherings like that and I do enjoy spending time and catching up with them except there's one problem:  My parents.  Of course, my lovely parents were there sucking the air out of the place, as usual which made it all pretty much impossible to have a decent conversation with anyone.  As soon as one started up, my mother or father would swoop on in and take over.  I got fed up with this so I started tweaking them.  Hard.  With the most bizzare off the wall stuff I could come up with and it went whooshing by.  I have no idea how they made it out of the 1950s without getting their eyes poked out by the tail fins on someone's car.

Mental notes have been made with an eye towards Christmas...

Anyways, I'm about to head out and mow the lawn and get some yard work done while it's nice, then it's back downstairs.  I'm not sure if I'm going to rip into that HP 8662A with the low output today or try to cycle some stuff through that hasn't had a chance to get on the bench yet.  Here's a better picture of the 8662A test setup:



Closer look at the military surplus 2235:



The HP 8447D amplifier was included with the Tektronix 547 I picked up a few weeks ago and the Tektronix 2235 is one of those military surplus units, which I hadn't yet used at home, so that was a good workout for equipment that's been waiting to go.

[mnementh]

And a Happy Thanksgiving to my fellow Canucks from the dwagon's household as well!

We've spent most of it moving stuff from the storage unit and doing yardwork ourselves... but the plan is to have a regular dinner with all of us at the table in one place tonight, just like a normal family.

We'll see how that works out. 

mnem
*toddles off to toddle off*

[med6753]

And I also want to extend a Happy Thanksgiving to the folks in the GWN. Ours is next month. I was planning on going to Colorado this year to visit Mother and Brother but then my medical issues intervened and I wasn't sure if I'd be well enough to travel. That turned out to be a non-issue but then my Mother's passing in July changed everything. Won't be the same, ever. But I think I'm going to go out there next Spring. I didn't go last year because of Covid and the year before it was a fun flight into Denver DIA landing (and having to do a go around) in the middle of a snow storm. Hundreds of flights were cancelled but we made it in....skidding and sliding on the runway.     

[med6753]

I need to stay off the bay of evil. Just bought one of these. Now I'll be able to fully utilize the full 500MHz B/W of the 7904. Tests and tear down when I get it. The one I bought was adverted as fully functional. We'll see.

https://w140.com/tekwiki/wiki/7A19

[mansaxel]

Closer look at the military surplus 2235:

Is there some kind of screening mesh in front of the CRT?

I really must be getting myself a signal generator. Played a bit with an ex-military 8640 this weekend. The old MTB base where we went for a ride with the museum missile/torpedo boat also has a working radio museum department, and as we were guided around on land I spotted a bunch of gentlemen manhandling a small 19" rack containing a 400W HF PA and a Standard Radio & Telephones exciter. They were setting up a mobile radio trailer with all-vintage HF gear. Tempting.

[Robert763]

Stereo update :

Yeah Pat banana-crocodile leads would be nice indeed ! 

AVG yeah as you said your not reading properly ! 


MAKING PROGRESS --> reconnected the front panel assembly. Throw a torch light at the LCD for a few minutes, could see nothing. Did notice though, that every time I pressed one of the buttons on the front panel, that it yielded a brief current spike ! So that meant maybe CPU was reacting to the front panel hence not ignoring it due to CAN bus locking the unit or whatever, so was rather encouraging !
Then after a few minutes playing with the buttons randomly while shedding light onto the LCD, I could SWEAR that I briefly saw something being displayed, I think it read something like "Accès connecté " ! I am 100% sure I saw that, it was not garbage it was proper legible text !!!! 
Then it vanished and for the next 10 minutes I could not spot anything on the screen... weird.

But it was encouraging so I decided to take it a step further : I connected a small speaker to the unit. A tiny rectangular one that I recently salvaged from a flat TV I failed to fix. Then I pressed the "RADIO" push button. I could swear I could hear a very, very faint "shhhhhhh" sound. So I sticked a screw driver in the antenna socket, then also clipped a test lead onto the screw driver because why not, and the "shhhh" became much louder !   
Then I played with the volume knob/rotary encoder, and it would make the "shhh" noise more or less loud, and every time I would move the encoder a notch, I could hear a distinct "BIP" noise , yes !!!!
Then I played with the "BAND" and "memory/pre-select" buttons, and eventually managed to listen to FM station loud and clear !!!

YES !!!! 

So this thing is indeed working. No matter what CAN crap might be going on, there is no way it would let me play with the radio yet NOT display anything on the screen, it would be silly !

So it must be a backlight problem !!!   
Given that I managed to see a couple words  displayed on the LCD using the torch light, it means the CPU on the M/B can communicate just fine with the LCD, LCD can display stuff, no worries. It's purely a basic backlight problem, so there is hope it can be fixed, so let's get cracking !!!   

So I will check those two DC/DC converters on the LCD board to see if they are been fed any power, if not see if they use the missing 9V rail on the M/B, if so then try to probe around that 9V rail to figure out how it's put together, if it's switched with an upstream MOSFET possibly failed or whatever.... let's get cracking !!!   

I suggest you lift the input pin to the 7809 and see if there is any voltage on he pad it connecs to. Don't prob it when it's powered, solder a small wire to the pad when the power is off and connect that to a meter. If there is voltage there then either the regulator is dead or there is a short on the circuit connected to it's output.
If no voltage on the pad, you will have to trace the circuit feeding it.
No point in jumping around when you don't have a circuit.

[Robert763]

Closer look at the military surplus 2235:

Is there some kind of screening mesh in front of the CRT?

I really must be getting myself a signal generator. Played a bit with an ex-military 8640 this weekend. The old MTB base where we went for a ride with the museum missile/torpedo boat also has a working radio museum department, and as we were guided around on land I spotted a bunch of gentlemen manhandling a small 19" rack containing a 400W HF PA and a Standard Radio & Telephones exciter. They were setting up a mobile radio trailer with all-vintage HF gear. Tempting.

Yes there is a mesh. It's needed on the military version to meet EMC requirements.

[med6753]

Is there some kind of screening mesh in front of the CRT?

Yes, X-Ray emission screen. Was an optional item for most portable Tek scopes. I have one which will fit a 465/475. My Type 535A also had one that has since been removed.   

[Robert763]

Is there some kind of screening mesh in front of the CRT?

Yes, X-Ray emission screen. Was an optional item for most portable Tek scopes. I have one which will fit a 465/475. My Type 535A also had one that has since been removed.

Nope,
A wire mesh you can see through wont stop x-rays.
The part number is 378-0237-00 NSN 5915012124417

FILTER,RADIO FREQUENCY INTERFERENCE
NSN: 5915012124417
MFG: TEKTRONIX INC. DBA TEKTRONIX
Description: FILTER,RADIO FREQUENCY INTERFERENCE

[Vince]

Stereo update :

Worked some more on the thing. Result is, I think the 9V might be a red herring.. I think it might not be used in this particular unit :

- Checked for resistance between the 78809 input and ground, and output to ground, VERY high impedance... too much to be even plausible...

- See picture for a annotated close up board view around the regulator.

- It looks like the input of the regulator IS INDEED switched by a FET transistor ! See on the left of the regulator, Q7. Marked  A79TF, actual P/N is TF3407, a P-channel MOSFET !

- there is a small SMD fuse, FB8, between the FET and the regulator input. Fuse is good. 300mV at the input of the regulator, and same at the FET drain. So the regulator is indeed not getting any juice to work with...

- Other pins of the FET, Gate and Source, both show B+ voltage. So Vgs being zero, I guess it's normal the FET is open circuit...

- Look further up the board : a bit farther north, there is another tranny, Q6, upstream the FET. Hard to see the tracks exactly but looks like the two Q could well be related ?!  Package is marked J3Y, actual P/N is S8050, an NPN tranny. So we might have a BJT commanding a FET commanding  7809 ?! 

- too hard to follow traces with my optivisor, need a microscope. So instead, knowing there was no short after the 7809, I cut the output pin of the regulator so as to isolate this rail, and instead soldered a wire to the now lone pad, so I can feed 9V directly with an external supply.  Result = still no backlight and the 9V rail drawing ZERO current.

- The 9V rail does indeed go to the LCD board but it looks like a low poer rail : uses only two adjacent pins, and the tracks are not even joined, it's not one fat trace, and the pins on the connector are not bridged either. 

- The only two "power" pins on this connector are Ground and +5V, not +9V.

- I probed the LCD board and saw that the two little DC/DC converters actually both run off of the 5V Supply not 9V !

- There is  A LOT of unpopulated stuff on the LCD board ! So since the backlight runs off of 5V not 9V, why would you need 9V for... there are only the keypads to read. Of course there must be the LCD driver chip somewhere in there, but it must run on a lower voltage I guess ??

- unneeded 9V + very high 9V rail impedance + lots of unpopulated stuff on that board = maybe the 9V is NOT required in this particular version of the device, hence the mainboard does not turn it on ?


SOOOOO... I moved away from the 9V stuff, and instead checked the backlight voltage. Now I know that both DC/DC converters do have power to get them going, I figured let's do a quick test... let's just see what voltage I have on the big backlight connector : +30V !!!  There is JUICE in there !

Can't believe a backlight with 30V doesn't come to life... so now I am targeting the backlight.  I don't even know if it's LED or CCFL. Given the unit is very recent, I guess it must be LED. 30V is a bit low for CCFL too, no ?

So my next move will be to take the front panel assembly apart to get at the backlight itself, maybe shine some light through the LCD if I can remove the backlight.

[factory]

The terms are 'eccentric' or 'delightfully quirky' 

I think 'fucking useless' is more appropriate. 

It's not just AVO that made meters without a range switch, here's one from Weston; https://www.ebay.com/itm/265188323058
I've seen Shango066 using a larger VOM similar to this in some of his resurrection videos.


David

[mnementh]

...I think the 9V might be a red herring.. I think it might not be used in this particular unit... (SNIP) So my next move will be to take the front panel assembly apart to get at the backlight itself, maybe shine some light through the LCD if I can remove the backlight.

You want to make taking the LCD apart your last resort; you will invariably get some bit of crap in there between the layers of the screen if you do open it up.

30V unloaded is not unusual; LED backlights are driven by a CC converter that will provide a fixed drive current no matter what the actual VFd of a LED string, as long as it is within a given operating voltage. The LED strip and converter are chosen to match vs voltage and desired drive current.

That 9V regulator output, if it is not to power the LCD, may be to power the BU Camera. This is why I suggested you check for continuity from the 9V Reg Vout to the LCD ribbon first. It may also run to the LCD as a signal to switch inputs to the analog camera line.

mnem