Test Equipment Anonymous (TEA) group therapy thread

[Vince]

JUNK STEREO REPAIR UPDATE

Put the board back in the cabinet, reconnect the flat flex going to the front panel, was a bit short. So I was eyeing all around the bench for something suitable to prop the board a bit, which would also make it easier to work on. Look what I found, perfect !!!! 

Applied power. Checked all 3 power rails, 5/6/12V. All good. Pulled the plug. Spent 30 minutes buzzing the board. The 6V seems to be used by the audio section. 12V for the servo motors for the CD player.

5V for the CPU ? I buzzed all the 354 pins of the CPU and none of them appeared to be connected to any of the supplies ?! 

I just don't know 

So I checked a dozen tiny SMD caps in the vicinity of the USB/SD connectors, all good. Well I mean no super low ohms readings.
So I then checked all 245677 SOT 23 transistors. Found only a couple that tested weird and would have needed to be desoldered to test them. But they were far away from the USB/SD digital stuff. They looked more to do with the audio, so I left them alone, not wanting to waste time.

Then I applied power, tried my USB stick and what do you know, it works now !!! 
As you can see on the close up picture, the blue LED on the USB stick is lit, there is activity !
So I plugged the speakers, and hey presto music there was ! It was reading my MP3 files just fine ! I could switch from one track to the next as well, it was working perfectly.

Thrilled by this success, I immediately added an SD card to the mix to see if that would now work as well. Alas no.... so I then switch back the USB stick..... won't work anymore !!! 

So since it DID work once... it means there is nothing fundamentally broken in this stereo. CPU is fine at the least, which is the main relief. So must be an intermittent contact somewhere. Tried applying pressure with a pencil (plastic sharpie, non conductive    )on the USB connector and surrounding discrete components, the CPU even... no luck, it won't come back to life. 

But I guess it's got to be a dodgy joint somewhere. Logic would dictate the USB connector of course, since it takes all the mechanical stress every time she puts the stick in and out. At first glance I can't see any broken joints on its the 4 connector pins but well, I will look closer, and reflow those pins anyway, of course.

Wish me luck....

[med6753]

Here's the 8000A +5V PSU mod installed. Somewhat bodged into place but there isn't a lot of room to work with, especially when it came to installing a 2nd transformer. It's been in there for almost 5 years but if I had to do it over again I'd try to come up with a neater arrangement. The 7815/7915 regulators are just to the left of the heat sinked 7805 and didn't require heat sinks.

   

[Vince]

Oh OK ! So you replaced the transformer ! You didn't talk about that 

So OK, new transformer so you new what the specs for its windings were, and that it could supply the current comfortably.

I understand now !

[mnementh]

JUNK STEREO REPAIR UPDATE

...So since it DID work once... it means there is nothing fundamentally broken in this stereo. CPU is fine at the least, which is the main relief. So must be an intermittent contact somewhere. Tried applying pressure with a pencil (plastic sharpie, non conductive    )on the USB connector and surrounding discrete components, the CPU even... no luck, it won't come back to life. 

But I guess it's got to be a dodgy joint somewhere. Logic would dictate the USB connector of course, since it takes all the mechanical stress every time she puts the stick in and out. At first glance I can't see any broken joints on its the 4 connector pins but well, I will look closer, and reflow those pins anyway, of course.   Wish me luck....

You can't rule out the CPU yet, buddy. It's not obvious if the USB and the SD card use the same I/O pins; all you know for sure is that when the thing tries to access the SD card, all or part of the thing (I'm thinking USB controller, which usually has at least 2 USB ports) locks up.

This exact behavior is a very common failure mode in cheap digital picture frames; I suspect similar here. Time to scope out the SD slot itself:



mnem
*tzzzzzzt*

[med6753]

Oh OK ! So you replaced the transformer ! You didn't talk about that 

So OK, new transformer so you new what the specs for its windings were, and that it could supply the current comfortably.

I understand now !

I thought it was very obvious from the schematic I posted that a 2nd transformer was involved.

My bad. 

[Neomys Sapiens]

I was limiting the list intentionally at 3-terminal ones. Otherwise I would have not only included the L200, but also the LM104, LM106, LM2991, LR8K4, SG1501, SG1532, ....
LM150/250/350 is a 3A adjustable between the 117 and the 138.

That's an interesting one!
I've attached the datasheet of it. Is there a similar one of the SG1501A from Linear Technology?

An interesting one? I'll give you some more:

another scarcely known yet interesting voltage regulator: MC1466/MC1566. Oh, and the MC1561R too.
I can assume that everyone knows the high voltage derivatives of the LM117 and relatives?
And the LP2951 too?
Those that fancy the L200 will probably also like the LT3081.
Then there is the MIC29202 from Micrel and the SP1085 from Sipex.
As I mentioned the SG1532, I should also hint at the UCx834. And the TDB1146!

Interesting chips, you say? Outside of the VR category, there are more:
SAA1029 anyone?
AD5520 ? NE/SE592 ? LM195 ? LM12 ?
AM460 from Analog Microelectronics?
PKD01 from PMI? LTC1043 ?
TCA965 ? (of course the Germans know it, but do our friends from over the sea?)

I could give you some more, but then you would curse me or worse. So, not now..

Remark: the datasheet for the MC1561R is too large. Look it up on your own.

[tautech]

DOPAMIIIINNNNNEEEEEE!

I now have a fully working TDS794D!
I tracked down two bad acquisition RAM chips, U405 and U413 on channel 2. Replaced them with parts pulled from a scrap board (a smashed unit with a physically damaged acquisition board, well and truly for pulling parts..)

Now it passes all self-tests and no spurious spikes on the display. Yaaaaaaaaayyyyyy! 


Next step, find probes at a not-insane price.....

Actives or passives ?

[tautech]

Oh no...... oh help me..... it's JUNK CONSUMER ELECTRONICS REPAIR TIME again !!! 


She said that the problem is that when she puts a USB stick with MP3 files on it, it doesn't work anymore. Just nothing happens, as if she hadn't inserted the stick. I confirm that.
There is also an SD card reader with the same purpose... so I put some MP3 files on an SD card and... same result, nothing happens.

Don't overlook the stilly stuff.....is the USB port filled with something.....the sort of stuff unsupervised kiddies do ?
Are its pads/footprints/connections still in good order ?

[tautech]

JUNK STEREO REPAIR UPDATE

...So since it DID work once... it means there is nothing fundamentally broken in this stereo. CPU is fine at the least, which is the main relief. So must be an intermittent contact somewhere. Tried applying pressure with a pencil (plastic sharpie, non conductive    )on the USB connector and surrounding discrete components, the CPU even... no luck, it won't come back to life. 

But I guess it's got to be a dodgy joint somewhere. Logic would dictate the USB connector of course, since it takes all the mechanical stress every time she puts the stick in and out. At first glance I can't see any broken joints on its the 4 connector pins but well, I will look closer, and reflow those pins anyway, of course.   Wish me luck....

You can't rule out the CPU yet, buddy. It's not obvious if the USB and the SD card use the same I/O pins; all you know for sure is that when the thing tries to access the SD card, all or part of the thing (I'm thinking USB controller, which usually has at least 2 USB ports) locks up.

This exact behavior is a very common failure mode in cheap digital picture frames; I suspect similar here. Time to scope out the SD slot itself:



mnem
*tzzzzzzt*

Yeah but.......
The orientation of the MicroSD card holder suggests it's for uploading SW/FW/OS into the radio and not for use by the operator/user. 

[Neomys Sapiens]

JUNK STEREO REPAIR UPDATE

Wish me luck....

When it worked, I was shocked - now I am relieved.
Please don't pull an electronic Lourdes miracle on us!

[Vince]

JUNK STEREO REPAIR UPDATE

...So since it DID work once... it means there is nothing fundamentally broken in this stereo. CPU is fine at the least, which is the main relief. So must be an intermittent contact somewhere. Tried applying pressure with a pencil (plastic sharpie, non conductive    )on the USB connector and surrounding discrete components, the CPU even... no luck, it won't come back to life. 

But I guess it's got to be a dodgy joint somewhere. Logic would dictate the USB connector of course, since it takes all the mechanical stress every time she puts the stick in and out. At first glance I can't see any broken joints on its the 4 connector pins but well, I will look closer, and reflow those pins anyway, of course.   Wish me luck....

You can't rule out the CPU yet, buddy. It's not obvious if the USB and the SD card use the same I/O pins; all you know for sure is that when the thing tries to access the SD card, all or part of the thing (I'm thinking USB controller, which usually has at least 2 USB ports) locks up.

This exact behavior is a very common failure mode in cheap digital picture frames; I suspect similar here. Time to scope out the SD slot itself:



mnem
*tzzzzzzt*

Wow that's bad news  then !!!   

Thanks for the info, will warm up the scope....

[m k]

Who knew, who should have known.

At least, it looks quite similar to mine. But wasn't able to recognize because of the different case.

Pretty same.
Cursor missing?

01, 03 and 07 are single sided, 02, 06 and 08 are double sided.
03 LL has a special Log-Log slide.
(just learning)

BTW,
seems that Bentley's Auction have changed their view.
I tried to understand spring values but couldn't.

Some had more interest than others.
Tek 7k plugins were $6 and up, very few over $20.
Old HP were also passed, 4192A was $4.50, 5350B $75.
Fluke 8505A went for $37.50 and POWER DESIGNS 6050C was $20.
HP 34401A without a "name plate" was $32.50 and 3577A $42.50.
Enough.

[Vince]

JUNK STEREO REPAIR UPDATE

...So since it DID work once... it means there is nothing fundamentally broken in this stereo. CPU is fine at the least, which is the main relief. So must be an intermittent contact somewhere. Tried applying pressure with a pencil (plastic sharpie, non conductive    )on the USB connector and surrounding discrete components, the CPU even... no luck, it won't come back to life. 

But I guess it's got to be a dodgy joint somewhere. Logic would dictate the USB connector of course, since it takes all the mechanical stress every time she puts the stick in and out. At first glance I can't see any broken joints on its the 4 connector pins but well, I will look closer, and reflow those pins anyway, of course.   Wish me luck....

You can't rule out the CPU yet, buddy. It's not obvious if the USB and the SD card use the same I/O pins; all you know for sure is that when the thing tries to access the SD card, all or part of the thing (I'm thinking USB controller, which usually has at least 2 USB ports) locks up.

This exact behavior is a very common failure mode in cheap digital picture frames; I suspect similar here. Time to scope out the SD slot itself:



mnem
*tzzzzzzt*

Yeah but.......
The orientation of the MicroSD card holder suggests it's for uploading SW/FW/OS into the radio and not for use by the operator/user. 

Eh ? No the SD card is accessible on the front panel, user manual tells you what you can do with it. It's just like the USB stick :  you put MP3 files on the SD card (it's full size SD no micro SD), and it plays them. It can even copy an MP3 file from/to  SD / USB.

[Specmaster]

That digimess stuff is Chinese rebrand garbage. Not even decent Chinese garbage but rock bottom stuff 

Some of it might be, idk I've not had any in my hands. This however, does not look like Chinese made, it looks low volume, low R&D budget, low design budget, mid-quality euro-tryhard. In fact, it reminds me of early TTi stuff.  https://www.ebay.co.uk/itm/234578724312



It's from rchaudio so it's overpriced. Just to prove the Grundig lineage: https://www.farnell.com/datasheets/104629.pdf

I'd pay £50 shipped.

Hmm, I had a Grundig satellite box a few year back and that was utter crap, so I'd expect this to be no better, it has a certain rarity value and that's it.

[Specmaster]

Seriously? £80?

https://www.ebay.co.uk/itm/384932494888

Seriously, a wet dream on his part.  Bids should have started at $40 USD at most.

And then you have to modify the unregulated +5V supply for better stability. Once that's done it is a damn good DMM.

It's a terrible DMM full stop. Apart from the 5V problem it has mains routed badly on the main board, the display design and assembly stinks, the rest of the power supply stinks and the front end protection stinks.

So, when are you buying it?   

Had one. Hated it.

Quite happy with the 3465A. It’s 4.5 digits as well 

Yeah, but the 3466A is way better, though the 3465A looks to be almost a 3466A without the annunciators.

[bd139]

Seriously? £80?

https://www.ebay.co.uk/itm/384932494888

Seriously, a wet dream on his part.  Bids should have started at $40 USD at most.

And then you have to modify the unregulated +5V supply for better stability. Once that's done it is a damn good DMM.

It's a terrible DMM full stop. Apart from the 5V problem it has mains routed badly on the main board, the display design and assembly stinks, the rest of the power supply stinks and the front end protection stinks.

So, when are you buying it?   

Had one. Hated it.

Quite happy with the 3465A. It’s 4.5 digits as well 

Yeah, but the 3466A is way better, though the 3465A looks to be almost a 3466A without the annunciators.

It is and it’s not. The 3465A has about the same specifications but a lot less to go wrong inside it 

[Specmaster]

I see that our friend the Avo killer did not get a sale on his abortion and has relisted it again.

https://www.ebay.co.uk/itm/234578976853

[bd139]

Perhaps we should all offer him £1 for it 

[xrunner]

Agilent U1241A TRUE RMS 4-Digit Handheld Digital Multimeter AS IS 4 available

eBay auction: #144333972540

Sez "Item was plugged in but it does not power up"

Plugged in to what? 

Anyone wanna take a risk it works?


Here's more that do work for $79.99 Make Offer looks like a bunch that were obtained from some company

38 sold more than 10 available

eBay auction: #144324686429

[Vince]

JUNK STEREO REPAIR UPDATE


OK I think I might be getting somewhere. I touched up the 4 pins of the USB socket, no luck.

Then I started with the basics.... power supply. So for the past 20 minutes I have been playing in this area and found interesting things....

I measured USB Vdd then, expecting to find 5Volts isn't it, and instead found.... 800mV ! A second later... 600mV... a second later...400.... then 300mV... stayed there. I thought hey strange... so maybe that means USB power is not permanently supplied by the 5V rail, for some reason ? Maybe the CPU switches power to USB only when the input selector on the front panel is set to USB ? OK why not, even if I don't see the point of doing that but well...
Still, if the CPU switched the power off, I would expect to get Zero volt, not something as high as 800mV, and mysteriously dropping as I am watching it on the meter....


So, to test this hypothesis, I switch to different in puts : SD card, CD, Radio.... and... strange things again. For a split second, during the change of input, USB power pin goes up a bit, 1.2V say, then immediately drops back to 800mV and starts again dropping slowly.
So.... nah. not sure what happens with USB power but it doesn't look like the CPU is controlling / switching it.

So kept experimenting : I unplugged the USB stick, unplugged the stereo, plugged it back in while watching at the same time USB power. Oh !!!  Now we have something new ! USB power is now 3.28 Volt ! Much better.. but still a far cry from 5V.....
Then I plugged the USB stick, again while watching at the same time USB power : instantly the voltage drops to 800mV ! Same scenario as before !
Oh, so USB power is too weak, it can't stand ANY load whatsoever ?! So I unplugged the stick, to see if the voltage would climb back to 3.28V but it doesn't, it stays at 800mV.

SD card power pins : measured that. They get the same voltage that USB power does, it exhibits exactly the same symptoms, in unison. So that's good. That would explain why both USB and SD don't work.

So I have a power supply issue in the USB/SD area.

Noticed something else too : found a local 3.3V 3 pin linear regulator near the CPU, tiny one, you can see it on the picture I posted earlier.
OK so the CPU does run at 3.3V not 5V.  So the 5V must be only for USB and SD. but these get only 3.3V, why....
USB and SD do seem somehow to get the voltage from that 3.3V regulator : output of the regulator measured precisely 3.28V just like what I measured on the power pins of the USB and SD card connectors. Strange. Sure enough USB is only 5V right ? Or is there some standard somewhere that says it should also be compatible/work with 3.3V as well ?! 
Still, there IS a 5V rail on the board, so why not use it ?...

Anyway. Regardless, it looks like USB/SD are having power supply issues, be them with 3.3V or 5V doesn't matter. They don't get proper power and I need to investigate that don't I...  The CPU works fine and the output of the 3.3V regulator is solid, no issues there. So even if USB was indeed using 3.3V rather 5V, then the problem is not with the 3.3V regulator. There must be some discrete components in between the regulator and USB/SD connectors. That's plausible because when I do a continuity test, I don't get continuity between, the power pins of Sd and USB, nor do I get continuity between USB and 5V rail or SD and 5V rail.

tried looking at traces around the USB power pin. did some buzzing. I see an MLCC cap between that power pin and ground. But it's not shorted nor low impedance (could try removing it anyway just to see...). then there is an inductor in series with the pin, then it buggers off to I don't know where because the other side of the inductor goes to a burried via.. does not come out the other side of the board  .....

OK back to the bench, oh dear....

[DC1MC]

To risk or not to risk:

https://www.ebay-kleinanzeigen.de/s-anzeige/tektronix-577-d2-defekt-/2123531071-168-3793

[Vince]

JUNK STEREO REPAIR UPDATE

OK some more... I think I must have been confused in my previous message, have to take some of it back after the recent experiments of the past minute and a half...

USB power and SD power do not appear to be the same after all.... 

At power up, SD gets 3.280V exactly what the 3.3V regulator puts out, mV for mV, spot on.

However at the same time, for a split second, really right after pwoer, USB get a bit more : 3.5V not 3.3V ! Then again it drops and drops....  but SD power remains solid at 3.280V.

OK so that means that USB is indeed supposed to get 5V not 3.3... but not getting it, and plumetting.

But continuity check says this pin is not directly connected to to the 5V rail (and that rail is solid). So at least that reassures me that there must indeed be some components between the 5V trail and USB power pin, and these components are fishy.  But no schematic so good luck figuring out what the circuit is and what components no the board are concerned ! 

Oh boy....

[bd139]

The USB power will not be wired to the rail directly. There will be a host controller in the IC that handles all that faff including power negotiation.

3.3v is interesting through. It should be 5V. Check it with a scope to make sure it is actually that and not the average voltage you are reading.

[Vince]

To risk or not to risk:

https://www.ebay-kleinanzeigen.de/s-anzeige/tektronix-577-d2-defekt-/2123531071-168-3793

I guess it all depends if that's the model you were after, rather than one with storage/D1, or a its big brother the 576.

If you really want a 577 with no storage CRT, then I guess even as yellowed and defective as it is, given current prices, 200 Euros is "cheap"... so would go for it. Worse case it ends up being a parts donour for a another cheap one you might find later. Or you can flog it back for parts on Ebay for the price you paid....


So yeah if I were looking for that very specific model, I guess I would go for it at 200, had I the cash of course !.....

[Vince]

The USB power will not be wired to the rail directly. There will be a host controller in the IC that handles all that faff including power negotiation.

3.3v is interesting through. It should be 5V. Check it with a scope to make sure it is actually that and not the average voltage you are reading.

Thanks. OK that means we back again to incriminating that freaking CPU ! It's not looking good then 

OK so I really need to pull the datasheet for that CPU, see how it handles USB power. If it requires with some luck the help of external discrete components that might have failed... if not and it's the CPU direct, then it's toast 

23H56 here... will work a short while on it then