Test Equipment Anonymous (TEA) group therapy thread

[mnementh]

@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...

[mnementh]

   A quick heads-up... something that just blew me away.
A few days ago I needed a bunch of cheap extension cords; they were available as an "add-on" for a good price on Amazon, so I built up an order to get to the minimum. Among the many things I bought was the YinYoo KZ ZSE dual driver earbuds for the wallet-shattering price of $5.99.  I'd link to the page on Amazon for you, but since they sold out, it now links to a higher tier YinYoo product for $24. Chinglish ad copy set aside, they have some pretty impressive specs for any sub-$30 headphones, so I decided to give 'em a try for only $6. I got the blue ones.

...

but I haven't come across any as good as the ~$25 EP-630s for the money, and certainly not for $6-8.

Thanks. I may give these a shot. The 11/11 sale is coming up soon. Have you tried the version with microphone and control button?

Nope. I bought these on a chance, and specifically for my iPod use. I don't care for the audio processing of most phones very much; even the iPwns I've had.

mnem
*Toddles off to ded* No, fur reallz this time! 

[Specmaster]

I vote for MET as thats always happening to me 

[bitseeker]

Hehe. A good feature of NUTS is that it can be used in a sentence (or two): "Oh, NUTS! Now, where'd my frequency counter go?"

[med6753]

In other news....

The Rigol DMM with it's dead LCD display has been fully refunded.

The Siglent SDM3055 has been ordered from Saelig and will be here in a few days. I got the 6% EEVBlog discount however I didn't realize that Saeling was located in New York. And since I'm in New York had to pay sales tax which is 6.25% so it completely wiped out the discount. 

Bugger !
Maybe the USA shop price shipped from Ohio might have worked out better ? 

No, because the company has an office in New York State even if they shipped from Ohio they would have been obligated to charge sales tax. New York is real anal about that stuff. They want their money. They even have been pushing for years that ALL internet sales for NY residents should pay sales tax regardless if the origin has an office/outlet in the state. I say screw them.   

[tautech]

In other news....

The Rigol DMM with it's dead LCD display has been fully refunded.

The Siglent SDM3055 has been ordered from Saelig and will be here in a few days. I got the 6% EEVBlog discount however I didn't realize that Saeling was located in New York. And since I'm in New York had to pay sales tax which is 6.25% so it completely wiped out the discount. 

Bugger !
Maybe the USA shop price shipped from Ohio might have worked out better ? 

No, because the company has an office in New York State even if they shipped from Ohio they would have been obligated to charge sales tax. New York is real anal about that stuff. They want their money. They even have been pushing for years that ALL internet sales for NY residents should pay sales tax regardless if the origin has an office/outlet in the state. I say screw them. 

Sorry I wasn't clear; Siglent USA shop.
https://store.siglentamerica.com/product-category/digital-multimeter/sdm3055-series/

[bitseeker]

   A quick heads-up... something that just blew me away.

Thanks. I may give these a shot. The 11/11 sale is coming up soon. Have you tried the version with microphone and control button?

Nope. I bought these on a chance, and specifically for my iPod use. I don't care for the audio processing of most phones very much; even the iPwns I've had.

Yeah, I just want it for the remote control so I don't have to take out my phone to change tracks. I found and ordered one on AliExpress for $6.57 and got a $2 coupon since I hadn't ordered anything in a while. So, $4.57 with free shipping. Woot!

[med6753]

In other news....

The Rigol DMM with it's dead LCD display has been fully refunded.

The Siglent SDM3055 has been ordered from Saelig and will be here in a few days. I got the 6% EEVBlog discount however I didn't realize that Saeling was located in New York. And since I'm in New York had to pay sales tax which is 6.25% so it completely wiped out the discount. 

Bugger !
Maybe the USA shop price shipped from Ohio might have worked out better ? 

No, because the company has an office in New York State even if they shipped from Ohio they would have been obligated to charge sales tax. New York is real anal about that stuff. They want their money. They even have been pushing for years that ALL internet sales for NY residents should pay sales tax regardless if the origin has an office/outlet in the state. I say screw them. 

Sorry I wasn't clear; Siglent USA shop.
https://store.siglentamerica.com/product-category/digital-multimeter/sdm3055-series/

Oh OK....got it. Actually not much difference in the final price. Dunno if Siglent USA has free shipping like Saelig does. In the end it figured to about $10 USD more so it wasn't too bad. As long as it works I'm happy. 

[Carl_Smith]

Majorly Elusive Test Equipment Relocation

Misplaced Equipment Temporary Elusiveness Reaction

Missing Equipment Torment Endlessly Recurring

MET. 

No Unit To be Seen, or NUTS.

 

 

OK, the results thus far: one vote for MET, two for NUTS.

Any other votes (or new candidates)?

I did like the idea of fitting something to the word METER, but NUTS seems to flow better so it gets my vote.

[med6753]

Random trick I found on the 8010A. If you short common to mA terminal it will hold the reading until the short is removed thus avoiding paying good money for the touch-hold probe

Neat.

I'll have to try that. Also try it on the 8050A.

[Brumby]

"Oh, NUTS! Now, where'd my frequency counter go?"

You remembered!  I feel honoured.

Still looking for the flipping thing.  I kept it in a cardboard box - one of several I had used to containerise all the smaller stuff.  It should be with the others ... but I haven found it yet.  Still annoyed about that.

PS  A vote for NUTS.  Not sure about MET as yet.

[med6753]

Random trick I found on the 8010A. If you short common to mA terminal it will hold the reading until the short is removed thus avoiding paying good money for the touch-hold probe

Neat.

I'll have to try that. Also try it on the 8050A.

It does work, on both of them. How did you discover that little tidbit? 

[bd139]

A bit of curiosity lead to this revelation followed by some RTFM. I saw a touch hold probe in the service manual for it so I went and downloaded the manual to see how that worked. Couldn't find the manual for it so plan B. This is the probe:



I thought that in this circumstance it wasn't likely that they had put any of the logic inside the probe because if it was a sample and hold probe that would need a full set of range control replicated in the probe which is silly so it must be in the meter and the probe signals the hold.

So I went and looked back in the manual at the theory of operation and found this:



I assumed that ground here was same as common and that the mA terminal was used by the probe so it was a good bet. And it worked.

[med6753]

Very interesting. And I wondered what that hole in the front cover between the volts jack and common jack was for. Now we know.   

[tautech]

A bit of curiosity lead to this revelation followed by some RTFM. I saw a touch hold probe in the service manual for it so I went and downloaded the manual to see how that worked. Couldn't find the manual for it so plan B. This is the probe:



I thought that in this circumstance it wasn't likely that they had put any of the logic inside the probe because if it was a sample and hold probe that would need a full set of range control replicated in the probe which is silly so it must be in the meter and the probe signals the hold.

So I went and looked back in the manual at the theory of operation and found this:



I assumed that ground here was same as common and that the mA terminal was used by the probe so it was a good bet. And it worked.

You should drop this little gem here:
https://www.eevblog.com/forum/testgear/old-fluke-multimeters/

A trick is to Quote your own post and copy then drop it into another post in another thread.

[mnementh]

   A quick heads-up... something that just blew me away.

Thanks. I may give these a shot. The 11/11 sale is coming up soon. Have you tried the version with microphone and control button?

Nope. I bought these on a chance, and specifically for my iPod use. I don't care for the audio processing of most phones very much; even the iPwns I've had.

Yeah, I just want it for the remote control so I don't have to take out my phone to change tracks. I found and ordered one on AliExpress for $6.57 and got a $2 coupon since I hadn't ordered anything in a while. So, $4.57 with free shipping. Woot!

Let us know how you like them; and how you feel about the comfort vs sound quality. I found the firmer mushroom tips to be right on the edge of uncomfortable, but even after several hour-long plus sessions, they never went over that line and seemed to get a little better, or I got used to it. And the tight fit really is necessary to get the sound they're capable of; going to the smaller tips lost all sound quality and noise-cancelling.

Also let us know how the controls work, and on what breeds of phone you've had a chance to try them.

mnem
*Still too much blood in my coffee circulatory system*

[mnementh]

Very interesting. And I wondered what that hole in the front cover between the volts jack and common jack was for. Now we know. 

Pretty sure its just an indexing pin to keep you from plugging the thing in backwards. Sweet & simple. Nowadays that pin would have to have 6 layer micro-sleeve connections and independent internet connectivity...

mnem
*Hunting the Snark since nineteen mumblety-mumble*

[med6753]

After I replaced the reed relays in a Fluke 8600A to fix a gross short term drift I noticed that it still took a good 1.5 hours to completely stabilize. It wasn't a lot of drift but compared to other 4.5 digit DMM's it seemed excessive. Example: with a 9.997V reference it would start out cold at 9.999V and slowly drift down to 9.997V and remain there.

 I determined that the drift wasn't originating in the analog section and the V ref  was rock stable. So it had to be in the A/D conversion somewhere. I nailed it, finally. The 1Mhz crystal that feeds the custom DVM chip at pin 6 was drifting. Replaced the crystal and the drift is gone. I'm a bit surprised by that. Never saw a crystal develop a drift. They typically tend to remain stable with age. Perhaps it was subject to physical shock at one time.   

[med6753]

Very interesting. And I wondered what that hole in the front cover between the volts jack and common jack was for. Now we know. 

Pretty sure its just an indexing pin to keep you from plugging the thing in backwards. Sweet & simple. Nowadays that pin would have to have 6 layer micro-sleeve connections and independent internet connectivity...

mnem
*Hunting the Snark since nineteen mumblety-mumble*

Well...yea, that's what I was implying. It's an index hole for the touch hold probe.

[mnementh]

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. 

mnem
*p00t!*

[med6753]

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. 

mnem
*p00t!*

Go get some coffee. 

[mnementh]

After I replaced the reed relays in a Fluke 8600A to fix a gross short term drift I noticed that it still took a good 1.5 hours to completely stabilize. It wasn't a lot of drift but compared to other 4.5 digit DMM's it seemed excessive. Example: with a 9.997V reference it would start out cold at 9.999V and slowly drift down to 9.997V and remain there.

      I determined that the drift wasn't originating in the analog section and the V ref  was rock stable. So it had to be in the A/D conversion somewhere. I nailed it, finally. The 1Mhz crystal that feeds the custom DVM chip at pin 6 was drifting. Replaced the crystal and the drift is gone. I'm a bit surprised by that. Never saw a crystal develop a drift. They typically tend to remain stable with age. Perhaps it was subject to physical shock at one time.   

Awesome bit of diag there... and those hand-drafted schematics definitely gave me a bit of homesickness. *sigh*

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

[med6753]

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. 

[mnementh]

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*

[bd139]

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. 

mnem
*p00t!*

Go get some coffee. 

Coffee FTW. Cup number 5 here  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. 

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.