Author Topic: Test Equipment Anonymous (TEA) group therapy thread  (Read 2057144 times)

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Online bd139

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #19375 on: November 09, 2018, 01:30:28 pm »
Oh, doyt... yeah. Sorry... it was a perfect opportunity for a little snark, and I think I mentioned I'm a bit low on caffeine yet.  :-DD

mnem
*p00t!*

Go get some coffee.  :-DD :-DD :-DD

Coffee FTW. Cup number 5 here  :scared: and it's just gone lunch time.


How did you determine that the crystal was drifting? Did you have means to measure, or was it pure deduction and R&R empirical detective work?

mnem


The latter. Pure deduction. I figured it was the weakest link and the most likely to drift as components warmed up. And a bit of luck too.  :-DD

Old crystals are bastards, all of them. I was repairing an old counter for someone a few years ago, one of the very early LED heathkit ones and the damn thing just shot off all over the place occasionally. It took me three hours to identify the crystal. I was watching the supply lines and they'd spike heavily when the counter stalled so assumed it was power supply related (turned out to be Heathkit "economy decoupling"). Eventually I pulled every damn IC on the board out and added them back from the crystal oscillator forwards. Literally the moment I put poor little 7404 back in I could see it going mental. Looked at the crystal and it was a POS from 1958 that Heathkit had clearly bought in cheap. It was probably 15-18 years old when they shipped it in the kit. Replaced it with a modern one and changed the load caps so it was about right and it was fine after that.



Random rant: Typical UK parts buggering. I need 3x LM358 opamps as I used up the ones I had on that scope bouncy ball thing (and I dont want to take it to bits now). All prices including VAT / delivery:

1. Rapid: out of stock. Due in 2 months.
2. Bitsbox: £3.07 (no indication of brand/a revision etc)
3. Farnell: £6.59
4. CPC: £5.50
5. RS: £7.20

At that point it looks like I'm going to have to take the hooky bitsbox ones but no... did some digging around on RS

6. RS: tube of 50 for £7.44. SOLD (and I'll never buy another one ever again)!

Fuuuuuu why is this so hard. Perhaps I should write a comparison engine that goes and finds this shit out so you dont have to.
 

Offline mnementh

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #19376 on: November 09, 2018, 02:04:49 pm »
If you did that, a plagiarized version would find its way onto github in a week. Then every yo-yo with a smartphone would be buying your parts before you.

If you're talking about writing it just for yourself and not sharing... then *Shhhhhh...* the walls have ears.  ;)


mnem
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Offline med6753

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #19377 on: November 09, 2018, 02:23:57 pm »
Well done, old Bean.  :-+

My favorite kind of successful diag; where you do most of the work on the schematics and in your brain. So very satisfying. Although, I figured if anyone had devised a means to measure the crystal oscillation without disturbing the circuit, it would probably be you. ;)

mnem
*Currently enjoying a pants-free day*

I didn't even try measuring the crystal because I knew as soon as I hung any sort of probe on it the damn thing would shift frequency instantly. So I can't take credit for devising a way to measure it without making it go ape shit.  :P   
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Offline med6753

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #19378 on: November 09, 2018, 02:31:11 pm »

Old crystals are bastards, all of them. I was repairing an old counter for someone a few years ago, one of the very early LED heathkit ones and the damn thing just shot off all over the place occasionally. It took me three hours to identify the crystal. I was watching the supply lines and they'd spike heavily when the counter stalled so assumed it was power supply related (turned out to be Heathkit "economy decoupling"). Eventually I pulled every damn IC on the board out and added them back from the crystal oscillator forwards. Literally the moment I put poor little 7404 back in I could see it going mental. Looked at the crystal and it was a POS from 1958 that Heathkit had clearly bought in cheap. It was probably 15-18 years old when they shipped it in the kit. Replaced it with a modern one and changed the load caps so it was about right and it was fine after that.


I'll bet it was a 3.58Mhz color burst crystal, right? They were real cheap and a dime a dozen. I had a Heathkit frequency counter that used one. It was surprisingly stable and accurate right up to the day I sold it.
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Offline mnementh

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #19379 on: November 09, 2018, 02:41:21 pm »
Well done, old Bean.  :-+

My favorite kind of successful diag; where you do most of the work on the schematics and in your brain. So very satisfying. Although, I figured if anyone had devised a means to measure the crystal oscillation without disturbing the circuit, it would probably be you. ;)

mnem
*Currently enjoying a pants-free day*

I didn't even try measuring the crystal because I knew as soon as I hung any sort of probe on it the damn thing would shift frequency instantly. So I can't take credit for devising a way to measure it without making it go ape shit.  :P

That's why I said "If anyone"... ;)

I have to admit... now that you've got me thinking about it, there HAS to be some solution to this conundrum that has plagued tinkerers and repair techs alike for like... EVER.  |O  Maybe some misuse of one of those new micro inductive current probes?  :-//

mnem
Fuck.  >:(  I just realized that I HAVE TO do something this morning that requires pants... *Sigh*
« Last Edit: November 09, 2018, 02:43:10 pm by mnementh »
 

Online bd139

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #19380 on: November 09, 2018, 02:47:40 pm »
I'll bet it was a 3.58Mhz color burst crystal, right? They were real cheap and a dime a dozen. I had a Heathkit frequency counter that used one. It was surprisingly stable and accurate right up to the day I sold it.

Yep that was the one! They probably already had it in their inventory from their TV kits.
 

Offline mnementh

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #19381 on: November 09, 2018, 03:05:01 pm »
https://youtu.be/Q7LKJXvf_do

Why am I imagining this as their warehouse, and this guy writing up the BOM?   :-DD

mnem
Yup. I went there. Can I please come back?
« Last Edit: November 09, 2018, 03:13:37 pm by mnementh »
 

Offline Specmaster

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #19382 on: November 09, 2018, 04:26:14 pm »
@mnementh Yes it is a bloody power amplifier in a IC but only a 2 channel one that is as you correct assumed, BTL and it is the only item that takes the full supply rail voltage of 37V +ve and -ve. I don't believe that the IC is shorting out internally as the outputs are taken through speaker selector switches which are mounted on the front panel and are connected via that flat 7 core cable. It also connects the headphone socket, nothing else is carried via that 7 core cable, it's just output from the amp IC 2 channels in and then 2 x 2 channels coming out again to speakers A and B. No permanent voltage should be but I was reading 36V on right channel, on the A setting, B setting appears to be fine.

If the IC was internally shorted then operating the A B speaker selector would move this 36V from Ch1 R to Ch2 R but it isn't. Anyway, its late now and I'm toddling off to bed for some well earned sleep, got to be up early tomorrow to collect Mother in Laws flower plants for her, and then shoot off doing a 40 mile round trip collecting more audio gear and a set of speakers to replace my smoked ones. I'll look into this more tomorrow.


Does the 36VDC on the faulty A speaker output go away when switched to B Mode? A+B mode?

If not, I still suspect the IC.  You can confirm easily enough by tracing that hot channel back to the IC and desolder the leg to see if there's still 36VDC at the leg. If so, little doubt as to the culprit.

Cheers,

mnem
ZZZzzzZZZzzzZZZzzz...
I'm out shopping at the minute, I'll try that when I get back later. I expect personally it is going to be leaking onto the track from AB switches to speaker terminals. If it was on the input to the AB switches then selecting B speakers would switch the 37V connection from A to B but it isnt
« Last Edit: November 09, 2018, 06:12:38 pm by Specmaster »
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Offline med6753

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #19383 on: November 09, 2018, 05:40:29 pm »
https://youtu.be/Q7LKJXvf_do

Why am I imagining this as their warehouse, and this guy writing up the BOM?   :-DD

mnem
Yup. I went there. Can I please come back?

I like British humor (humour) but in this case the accents are too strong for me to understand it and fully appreciate it.   :-// To my Yankee ears it's almost as if he isn't speaking English.  :o
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Offline Specmaster

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #19384 on: November 09, 2018, 06:14:21 pm »
https://youtu.be/Q7LKJXvf_do

Why am I imagining this as their warehouse, and this guy writing up the BOM?   :-DD

mnem
Yup. I went there. Can I please come back?

I like British humor (humour) but in this case the accents are too strong for me to understand it and fully appreciate it.   :-// To my Yankee ears it's almost as if he isn't speaking English.  :o
Funny that we gave have much the same with some Americans as well [emoji23]
« Last Edit: November 09, 2018, 08:24:05 pm by Specmaster »
Who let Murphy in?
 

Online bd139

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #19385 on: November 09, 2018, 06:24:01 pm »
 

Offline med6753

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #19386 on: November 09, 2018, 06:25:05 pm »
Check this out. Genuine boatanchor. Very sensitive differential inputs but only about 1Mhz bandwidth. Appears to be in good shape but I see the upper right cover fubar.

$100? Maybe. $200? Are you nucking futs?  :palm:  I wish him good luck. I'll be watching to see if the price drops.
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Offline med6753

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #19387 on: November 09, 2018, 06:28:39 pm »
https://youtu.be/bIaUfBjHjpI

I don't understand that red neck either. After saying "911" it was pure gibberish.  :-DD
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Offline mnementh

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #19388 on: November 09, 2018, 07:58:39 pm »
Having spent some time living barely surviving in a little shithole town on the Georgia/Alabama border, I can tell you firsthand that not one of the characters in that show is in any way an exaggeration.  ::)  The only thing wrong with the show is the Hill family themselves; they're entirely too uptown.  :palm:

Okay... anybody on the other side of the pond gonna fess up and admit the same of their barely intelligible rednecks?

mnem
I barely escaped. That place, that life... it sucks you in like a black hole of despair. *shuddder*
 

Online bd139

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #19389 on: November 09, 2018, 08:09:21 pm »
Yeah we’ve got ours. Wanna buy a dag?



About to commence 8012A mods. Starting with power supply measurements. Fingers crossed :)
 

Offline tautech

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #19390 on: November 09, 2018, 08:22:43 pm »
About to commence 8012A mods. Starting with power supply measurements. Fingers crossed :)
Don't just cross it, tape that penis finger away so it can't be blamed.  :phew:
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Online bd139

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #19391 on: November 09, 2018, 08:32:10 pm »
I’ve got ten of those fingers  :-DD
 

Offline Specmaster

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #19392 on: November 09, 2018, 08:36:58 pm »
I’ve got ten of those fingers  :-DD
:-DD :-DD :-DD
Who let Murphy in?
 

Offline mnementh

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #19393 on: November 09, 2018, 08:39:35 pm »
Yeah we’ve got ours. Wanna buy a dag?

Umm... no thank you. All my sheep are vinyl, so highly dag-resistant.  :-DD

mnem
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Offline tautech

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #19394 on: November 09, 2018, 08:42:51 pm »
I’ve got ten of those fingers  :-DD
Some days.........me too !  :rant:

My deepest sympathies.
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Offline mnementh

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #19395 on: November 09, 2018, 09:47:11 pm »
I’ve got ten of those fingers  :-DD



They make a special prophylactic for guys like you...















...but in your case, these might be safer.  :-DD

mnem
You read my PS. That's enough interaction for one day.
« Last Edit: November 09, 2018, 09:49:55 pm by mnementh »
 

Offline factory

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #19396 on: November 09, 2018, 10:13:35 pm »
Check this out. Genuine boatanchor. Very sensitive differential inputs but only about 1Mhz bandwidth. Appears to be in good shape but I see the upper right cover fubar.

$100? Maybe. $200? Are you nucking futs?  :palm:  I wish him good luck. I'll be watching to see if the price drops.

Also the CRT is a proper dual beam one too & mostly vacuum-bulb based apart from a couple of transistors in the low voltage supply & another in the sweep circuit.

Mine followed me home from a local yesteryear steam rally last year, rescued from the local house clearer's stall, sadly it had been left out in the rain for the previous day and had clearly spent a long time in a damp shed too.
It dried out OK and after several cracked ex-vacuum bulbs were replaced I got a trace, unfortunately this was quickly lost after fixing the power supply & replacing the snapped intensity control.  |O
That transistor in the sweep lockout circuit was made the gold plated rust too.  :-DD Still haven't got round to replacing it yet.

David

PS. This was my first Tek purchase too, the price was a more sensible £20..
« Last Edit: November 09, 2018, 10:20:07 pm by factory »
 

Online bd139

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #19397 on: November 09, 2018, 11:03:56 pm »
Fluke 8012A update. ALL of the damn electrolytics have spewed their guts on the board. Major cleanup. Surprised it even came up.
 

Offline mnementh

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #19398 on: November 09, 2018, 11:08:38 pm »


Got you covered, bd.  :-DD


@factory:  Damn you... more hand-drafted schematics. And these have character out the yodel-ay-hee-hooo...  *wibble*

mnem
Remember when you could be in business and still have a soul?
« Last Edit: November 09, 2018, 11:10:24 pm by mnementh »
 

Offline Specmaster

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #19399 on: November 09, 2018, 11:52:24 pm »
Been working on the Technics amp tonight and I have no idea what I was doing / thinking last night, must have been distracted or someit  :palm:, pulled the main board out and checked all tracks for bridges, could I see any, nah.

Refitted it and powered up without speakers this , connected 4 meters up (internally this time) and checked to see if the 36V was being switched by the AB speaker switch and darn it, it was so WTF did I not spot that last night??? :palm:

Got a 5th meter and probed the main amp IC pins to see if there was an internal short when powered, and bugger it, there was (you were 100% bang on menmenth:-+ the right hand channel was instantly raised to 36V, left channel, not a problem.

New power amp IC on order, just got to wait for that slow boat to come now. Arh well onto the next item in line for the bench, an Aiwa XR-M500 whose CD player skips on tracks 1 and 2 and the tape drive doesn't work, otherwise performs really well.  :popcorn:
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