Test Equipment Anonymous (TEA) group therapy thread

[Vince]

Tek RM17 repair update

Thanks Robert and Papa smurf for your support !

17H30 here.. I have spent the entire afternoon on the thing, but it's fixed now.

Retrospectively, turns out I had already fixed it in the first 15 minutes, but then I spent the next 4 or 5 hours following red herrings needlessly, thinking there was still something wrong with it, when there was not.
More on that below.

Here is the schematic for the amplifier, so you can follow me.

So as I said I saw zero reason why me replacing that resistor in the attenuator, could make the trace disappear. Made zero sense.
So instead I grounded the signal input, and started tracing that in the amplifier. Schematic in one hand, the DMM probe in the other...
That's when I started screaming : all the tube designators on the schematic... could not find them in the scope ! The designators in the scope... NONE OF THEM match the schematic !   
WTF Tek ?! How a m I supposed to find stuff ! 
So had to try to figure things out. Luckily it was not too hard. The layout of the tubes follows a logical "flow", that matches the schematic. Plus, the tube types are marked on the chassis so it helps too.
Turns out what they did wqs modify the "section" indicator : the first digit of the 3 digits designator.. but the last 2 digits, the most important/meaning full ones, were preserved 
So I mean, on the schematic, all tubes for the amplifier are labeled V2XX . Well on my scope they changed that to V4XX or V5XX. 

Anyway, I was well pissed at Tek for doing that, as I don't see why they could need to do that... AND there is no manual specific to the rack mount version.


So anyway. I probed the grid of V183, I do get my 0V there, and 1.7V at cathode instead of 1.5V. Good enough. However the other tube, V203, should get 1.6V  and I get negative 150Volts !!!! 
Ah... good, found the problem ! 
I saw only two possible reasons for getting -150V :

1) Resistor R195 is shorted and tying the cathode straight to the -150V rail. Unlikely but well, I tested that resistor anyway, and it was good (enough, at 44.5K  instead of 39K ).

2) There is no current flowing through that resistor, which means the tube is not drawing any current. So probably dead. To be thorough, before incriminating that tub,  I first checked it's environment :

- Anode / Plate : I get +100V, check.

- Grid at 0V : was not. Schematic shows that it's set by the DC balance trim pot on the front panel, so I played with that. It allowed for an adjustment range of -1.1V up to +1.1V. I had no problem setting it to spot on 0.000V, happy.  Still no joy. So dead tube it is. Replaced it, now the cathode is at 1.5V, check. 


Soooo... I now look at the screen, and still no trace, bummer. I look at the output of the amplifier, V244/254 that drive the deflection plates. Should have +168V on both outputs. I don't. One output is 25V lower than that, and the other 25 higher. Hmm.... 50V difference, so a 50V offset at the deflection plates... enough to drive the trace off the screen maybe. So I play with the vertical position control, and yeah, trace was off screen at the bottom, and I can bring it back to the center line, juuust.  So I have a big offset problem.

I will spare you the headache that followed, which occupied the next 4 hours. Turns out, all was working fine, and the offset was simply due to the balance trim pot I had adjusted earlier to get 0V at the grid of V203, indicated on the schematic.... I eventually read the manual, calibration procedure. They DO NOT say to adjust the balance trimmer to get 0V at the grid, schematic was wrong (or I didn't understand the thinking behind it ?!  ). No, procedure says nothing about grid voltage having to be zero... all they say is to do as the operator would do : set the balance trimmer to cancel the vertical movements of the red variable attenuation knob. That's all.  So I tried that, and now the scope works just fine !  4 hours wasted for wanting to have that gird to Zero as shown on the schematic  !      

Once I adjusted the balance for proper operation, I measured voltages and that led to having the grid at -0.95V instead of the indicated zero, and the cathode at 0.8V instead of the indicated 1.6V.

However, I have to say that the balance control is pretty much all the way, next to zero head room... which does not feel right, makes me uncomfortable.... I guess that means the tube I replaced is a bit weak ? Might try another one... I guess that's the limit of using old parts form donors, you get what you get...

A basic tube tester would be nice to test emission levels, at least.  That's one of the duties of my Tek 575 transistor curve tracer... once it's restored. Will make an adapter to make it test vacuum tubes 

Anyway, it's fixed, and it was a tube that died on me at the exact same time that I replaced that resistor in the x2 attenuator ! What were the odds ?! 

So... now that the scope is working again... I can see if my work last night on the attenuator fixed my "differentiator" symptoms on all x2 ranges. Result : yes ! That fixed it !!! 

So now I am left with the last major problem : the 3 " AC ONLY " ranges, 50mV to 10mV / DIV... but I have a clue now as to what it might be ! 

I looked at the schematic in search of what these AC ONLY ranges might have in common... at first I failed, because I was following a red herring again : thinking well, they have " AC ONLY "in common, so must be the AC coupling cap ?!    But no, AC coupling works fine when I try it on all the other ranges.

Then the plain obvious, "right there you idiot ", eventually struck me : it's nothing to do with being  " AC ONLY " ! That was misleading.
What these AC ONLY ranges have in common is that... they are the 3 most sensitives ranges, and so are the only ones that route the input signal through the PRE-amp !

So... my problems must lie in the pre-amp, so I shall be probing in there shortly ! 


Now I will go take a well deserved shower and go get some groceries before the shop closes...

[mnementh]

Another victim of the "lamp maker".

https://www.ebay.com/

I could forgive this if the resistor decades were used to control the brightness of the lamp

Only if the decade box were kept intact and "plugged into" another structure that housed the actual lamp.

OTOH... If it were a smoked unit, with lots of hard-to-replace resistors, and/or damaged switches... maybe I could just make believe I didn't see it...? 

mnem
"They make new ones every day." ~mum, warning me not to fall in love with my junk

[Specmaster]

...Problem is that there are no sellers on eBay that has 2 of them, so I have submitted 2 offers, 1 one of which has been accepted and I've paid already, so I'm just waiting to hear if the one will be accepted, if not I may just try and get away with just the 1 speaker, after all, it will be far better than what I have currently

The power amp sits under the front passenger seat and judging by the huge multipin plug and loom going to it, it will be a tri-amp x 4.

At the moment I'm just fed up not being able to hear any bass coming from the left front door, especially when playing some of Pink Floyd and Phil Collins tracks where the stereo effect on bass is really pronounced.

Yeah, factory audio follows the same fundamental law of service-ability as all other technology:

"Good, Cheap, Easy. Pick any two."

Bet you a dollar that's because they replaced one that failed in exactly the same way as yours with a pair of aftermarket drivers and are trying to recoup a little of that investment.

It may very well be a "design flaw" with your vehicle; well, something that fails consistently in a certain way due to the design of the car or the speaker. I remember back in the day, the Chrysler K-cars would always blow out the left-front speaker; the other 3 almost never failed. 

mnem
 

Yeah possibly, but there is zero evidence of any water penetration into the door cavity at all, it all looks just like it left the factory yesterday, there are 3 large drainage slots in the bottom, and they have zero signs of rust or even watermarks on the paint so at the moment I have no idea what happened. I might just cut the cone out and investigate later.

[med6753]

...Problem is that there are no sellers on eBay that has 2 of them, so I have submitted 2 offers, 1 one of which has been accepted and I've paid already, so I'm just waiting to hear if the one will be accepted, if not I may just try and get away with just the 1 speaker, after all, it will be far better than what I have currently

The power amp sits under the front passenger seat and judging by the huge multipin plug and loom going to it, it will be a tri-amp x 4.

At the moment I'm just fed up not being able to hear any bass coming from the left front door, especially when playing some of Pink Floyd and Phil Collins tracks where the stereo effect on bass is really pronounced.

Yeah, factory audio follows the same fundamental law of service-ability as all other technology:

"Good, Cheap, Easy. Pick any two."

Bet you a dollar that's because they replaced one that failed in exactly the same way as yours with a pair of aftermarket drivers and are trying to recoup a little of that investment.

It may very well be a "design flaw" with your vehicle; well, something that fails consistently in a certain way due to the design of the car or the speaker. I remember back in the day, the Chrysler K-cars would always blow out the left-front speaker; the other 3 almost never failed. 

mnem
 

Listening to Pink Floyd on a less than optimal audio system is pure heresy and you should also be beaten with that resistor box lamp. 

[med6753]

It is here, at last. Much anticipated package from Deutschland. What is it you ask? A repaired HV assembly out of a Type 547. Apparently a Herr Felgendreher has found the secret sauce for fixing the leakage issue with the HV transformer. So this repaired unit will be installed and tested in one of the two Type 547's that need it. If successful I will relay that info back to Herr Felgendreher and proceed with the restoration/recap/calibration. I'm undecided at this point if I will have the 2nd HV assembly repaired or keep the other Type 547 as a potential parts mule. But other than a duff HV assembly that Type 547 powers up and seems to function too. We'll see.

I want to give a public THANK YOU to BU508A (Mounty) for functioning as an intermediary and translator in making this repair happen. Without his assistance this never would have been a reality. And as a bonus Mounty sent me a bunch of SS HV rectifiers if I chose to replace the 5642 HV rectifier vacuum tubes.     

[Specmaster]

<snip>
Listening to Pink Floyd on a less than optimal audio system is pure heresy and you should also be beaten with that resistor box lamp. 

Says the DRL disabler 

[mnementh]

Another victim of the "lamp maker".

https://www.ebay.com/

I could forgive this if the resistor decades were used to control the brightness of the lamp

You are too generous. They should be beaten to a pulp with the lamp. 

No, no, no. They should be allowed to choose which orifice it will be inserted into.

First one, then the other.

AFTER the lamp is removed, rewired as a standalone unit with incandescent blub, and plugged in so it gets nice and hot...   

mnem
"Let Law of Irony decide the punishment."

[med6753]

<snip>
Listening to Pink Floyd on a less than optimal audio system is pure heresy and you should also be beaten with that resistor box lamp. 

Says the DRL disabler 

And proud of it. 

[AVGresponding]

Just bagged myself a panaplex display boat anchor for slightly under £30 shipped. More info when it arrives...

[BU508A]

It is here, at last. Much anticipated package from Deutschland. What is it you ask? A repaired HV assembly out of a Type 547. Apparently a Herr Felgendreher has found the secret sauce for fixing the leakage issue with the HV transformer. So this repaired unit will be installed and tested in one of the two Type 547's that need it. If successful I will relay that info back to Herr Felgendreher and proceed with the restoration/recap/calibration. I'm undecided at this point if I will have the 2nd HV assembly repaired or keep the other Type 547 as a potential parts mule. But other than a duff HV assembly that Type 547 powers up and seems to function too. We'll see.

I want to give a public THANK YOU to BU508A (Mounty) for functioning as an intermediary and translator in making this repair happen. Without his assistance this never would have been a reality. And as a bonus Mounty sent me a bunch of SS HV rectifiers if I chose to replace the 5642 HV rectifier vacuum tubes.     

Ah. I thought, I'd heard a loud cheering from the other side of the Atlantic. 
Glad, that it finally arrived (hopefully) undamaged. 

Thanks for all the flowers, the pleasure was all on my side. 

[mnementh]

...I may just try and get away with just the 1 speaker, after all, it will be far better than what I have currently

The power amp sits under the front passenger seat and judging by the huge multipin plug and loom going to it, it will be a tri-amp x 4.

At the moment I'm just fed up not being able to hear any bass coming from the left front door, especially when playing some of Pink Floyd and Phil Collins tracks where the stereo effect on bass is really pronounced.

Listening to Pink Floyd on a less than optimal audio system is pure heresy and you should also be beaten with that resistor box lamp. 

To be fair, I knew many progressive rock junkies who would tell you that Floyd played through anything less than Sennheiser 580s or similar was an affront to the music gods.

mnem
 

[med6753]

...I may just try and get away with just the 1 speaker, after all, it will be far better than what I have currently

The power amp sits under the front passenger seat and judging by the huge multipin plug and loom going to it, it will be a tri-amp x 4.

At the moment I'm just fed up not being able to hear any bass coming from the left front door, especially when playing some of Pink Floyd and Phil Collins tracks where the stereo effect on bass is really pronounced.

Listening to Pink Floyd on a less than optimal audio system is pure heresy and you should also be beaten with that resistor box lamp. 

To be fair, I knew many progressive rock junkies who would tell you that Floyd played through anything less than Sennheiser 580s or similar was an affront to the music gods.

mnem
 

David Gilmour has admitted several times that he thought their early stuff sucked.

[AVGresponding]

...I may just try and get away with just the 1 speaker, after all, it will be far better than what I have currently

The power amp sits under the front passenger seat and judging by the huge multipin plug and loom going to it, it will be a tri-amp x 4.

At the moment I'm just fed up not being able to hear any bass coming from the left front door, especially when playing some of Pink Floyd and Phil Collins tracks where the stereo effect on bass is really pronounced.

Listening to Pink Floyd on a less than optimal audio system is pure heresy and you should also be beaten with that resistor box lamp. 

To be fair, I knew many progressive rock junkies who would tell you that Floyd played through anything less than Sennheiser 580s or similar was an affront to the music gods.

mnem
 

meh... second most overrated band of all time...



In experimental food news, I have installed baked beans on a pizza. Results will be reported in due course.

[AVGresponding]

...I may just try and get away with just the 1 speaker, after all, it will be far better than what I have currently

The power amp sits under the front passenger seat and judging by the huge multipin plug and loom going to it, it will be a tri-amp x 4.

At the moment I'm just fed up not being able to hear any bass coming from the left front door, especially when playing some of Pink Floyd and Phil Collins tracks where the stereo effect on bass is really pronounced.

Listening to Pink Floyd on a less than optimal audio system is pure heresy and you should also be beaten with that resistor box lamp. 

To be fair, I knew many progressive rock junkies who would tell you that Floyd played through anything less than Sennheiser 580s or similar was an affront to the music gods.

mnem
 

David Gilmour has admitted several times that he thought their early stuff sucked.

Gilmour's head has pushed further and further up his own arse in recent years. "Wish You Were Here" is the last excellent studio album they made. Other than that, "Animals" was decent, "The Wall" parts 1 and 2 are merely ok, and everything else pure repetition.

[BU508A]

In experimental food news, I have installed baked beans on a pizza. Results will be reported in due course.

You need to add some pieces of pineapple.

 

[med6753]

meh... second most overrated band of all time...



In experimental food news, I have installed baked beans on a pizza. Results will be reported in due course.

Point 1. Bite your tongue. 

Point 2. With that combination you are gonna have some nasty farts. Glad you are across the pond. 

[mnementh]

To be fair, I knew many progressive rock junkies who would tell you that Floyd played through anything less than Sennheiser 580s or similar was an affront to the music gods.

meh... second most overrated band of all time...

In experimental food news, I have installed baked beans on a pizza. Results will be retorted in due course.

There, FTFY.   

mnem
    
  L         R

[Specmaster]

...I may just try and get away with just the 1 speaker, after all, it will be far better than what I have currently

The power amp sits under the front passenger seat and judging by the huge multipin plug and loom going to it, it will be a tri-amp x 4.

At the moment I'm just fed up not being able to hear any bass coming from the left front door, especially when playing some of Pink Floyd and Phil Collins tracks where the stereo effect on bass is really pronounced.

Listening to Pink Floyd on a less than optimal audio system is pure heresy and you should also be beaten with that resistor box lamp. 

To be fair, I knew many progressive rock junkies who would tell you that Floyd played through anything less than Sennheiser 580s or similar was an affront to the music gods.

mnem
 

David Gilmour has admitted several times that he thought their early stuff sucked.

Speaking of David Gilmour, I've recently discovered that one of the engineers working in the hangar at North Weald with the Spitfires and the P51D, along with the vintage tractor that I'm helping to restore and some classic cars, actually used to work on David Gilmour's plane collection in another hangar at the airfield, small world ain't it.

[med6753]

Gilmour's head has pushed further and further up his own arse in recent years. "Wish You Were Here" is the last excellent studio album they made. Other than that, "Animals" was decent, "The Wall" parts 1 and 2 are merely ok, and everything else pure repetition.

He has a long way to go to catch up to Roger Waters.

[mnementh]

In experimental food news, I have installed baked beans on a pizza. Results will be reported in due course.

You need to add some pieces of pineapple.   

mnem
*toddles off to Discord*

[AVGresponding]

Gilmour's head has pushed further and further up his own arse in recent years. "Wish You Were Here" is the last excellent studio album they made. Other than that, "Animals" was decent, "The Wall" parts 1 and 2 are merely ok, and everything else pure repetition.

He has a long way to go to catch up to Roger Waters.

Possibly so. These ego-boys often seem to forget the other members, past and present, who create the ambience for their own creativity. Tracks like "Interstellar Overdrive" were decades ahead of their time.

To be honest, they aren't the second most overrated, probably somewhere in the top 20 though. Oasis are the No1 most overrated, beyond any doubt.

In experimental food news, I have installed baked beans on a pizza. Results will be reported in due course.[/color][/size][/b]

You need to add some pieces of pineapple.

 

For someone of your culinary skills, this is an astonishing and truly contrarian comment.

[med6753]

...I may just try and get away with just the 1 speaker, after all, it will be far better than what I have currently

The power amp sits under the front passenger seat and judging by the huge multipin plug and loom going to it, it will be a tri-amp x 4.

At the moment I'm just fed up not being able to hear any bass coming from the left front door, especially when playing some of Pink Floyd and Phil Collins tracks where the stereo effect on bass is really pronounced.

Listening to Pink Floyd on a less than optimal audio system is pure heresy and you should also be beaten with that resistor box lamp. 

To be fair, I knew many progressive rock junkies who would tell you that Floyd played through anything less than Sennheiser 580s or similar was an affront to the music gods.

mnem
 

David Gilmour has admitted several times that he thought their early stuff sucked.

Speaking of David Gilmour, I've recently discovered that one of the engineers working in the hangar at North Weald with the Spitfires and the P51D, along with the vintage tractor that I'm helping to restore and some classic cars, actually used to work on David Gilmour's plane collection in another hangar at the airfield, small world ain't it.

[BU508A]

In experimental food news, I have installed baked beans on a pizza. Results will be reported in due course.[/color][/size][/b]

You need to add some pieces of pineapple.

 

For someone of your culinary skills, this is an astonishing and truly contrarian comment.

Well, I wanted to improve your food experience. 

Imo, there are two possibilites as far as I can see:

- adding pineapple makes it better - win
- adding pineapple makes it not better - no worse than before

 

Because I'm having some Italian relatives, personally I would NOT add (never ever!) pineapple or baked beans to my pizza. Too dangerous!

[mnementh]

Pineapple and Bits o' Pig are a taste combination made in heaven... mixed with any form of tomato sauce, not so much.   

mnem
and fuck anchovies. with a shovel.   

[AVGresponding]

Pizza results are in, and it turns out it tastes quite good. It is however, one of the messiest pizzas ever; I need to clean my oven now, and had to use the pizza wheel cutter to make it manageable. Less bean juice next time for sure, and if I have any jalapenos, I feel they would go well with it.