Test Equipment Anonymous (TEA) group therapy thread

[mnementh]

Yeah looking at this one it's definitely a possibility. The main divider network is ok which is the difficult one and the second one is just a bunch of close tolerance standard values. I reckon I can knock something up on JLCPCB and use 0.1% or better SMD resistors.

The issues will be thermal tracking and any residual stresses in the resistors either after soldering or due to differential expansion when the temperature changes. Thermal tracking can be minimised by hillbilly engineering. I don't know the significance of the the stresses, but through hole will be better. For an extreme example, I refer you to

It seems to me that anything made from phenolic resin PCB & SMDs would be no more thermally co-reactive (most likely less so) than the original, which was made of thin-film resistors & silver traces printed on a thermally conductive ceramic substrate. Am I missing something here?

mnem
 

[Specmaster]

EEEEEEEEEEK!!! OUT OF COFFFEEE!!!   

None to brew... no instant left... not even the cheap mexican shit.

mnem
*chewing on a used coffee filter*

Time to start drinking TEA then 

In this house that would be worse than contacting the bubonic plague. 

Naaahhh... I just shambled about zombie-like until we made it to my son's Pokemon League meet, whereupon I downed a couple NineBucks Mocha Frappucinos. They're alright as long as you don't expect them to taste like coffee.     

Picked up a big can of Chock-Full-o-Nuts when we headed back, which my wife brewed while I heated up the bacon & eggs & biscuits "breakfast for dinner" she'd made while we were out. Which was, in fact, exactly what I was thinking of making for myself all the way home. 

mnem
I used up a lifetime's worth of luck finding her... *sigh*

 bacon & eggs & biscuits "breakfast for dinner"  That sure sounds like a red neck dinner 

[0culus]

Gee....I wish all fixes were this easy. 7A26 plug-in acting out on channel 1. Of course 20mV and .2V ranges the worst (always seems to be the case).

Opened it up. Pulled the attenuator blocks. Careful application of Deoxit Gold G5 on visible leaf switches with a cotton swab. Short sprays on the back side. Insert and test. Perfect. 

How do you get them out without damaging those tiny wires with a ferrite bead that seems to connect the attenuator board(s) with the amplifier?

I suspect my 7A26 needs some deoxit as well.

[edit] I think you mean the metal covers on the top side? That say "caution delicate board".

Yep, the 7A26 has those VERY DELICATE wires on that ferrite bead connecting the attenuator board to the main board. Luckily I didn't have to mess with that. I pulled the metal cover off the channel 1 switch assembly then I removed the 4 attenuator blocks. The used a cotton swab soaked with Deoxit Gold G5 on the exposed leaf contacts and attenuator board. Then I removed the rear cover on the plug-in and several quick shots of Deoxit down into the switch assembly where the rear contacts reside.

Got lucky. It worked. Will it stay that way? Time will tell. But I was prepared to pull the attenuator board if required and do that "brute force" polishing method I used (and documented) on the 7A24 plug-in. Which BTW still works fine despite the nay sayers who said I would ruin the assembly.       

OK, cool. I haven't been able to find anything online about deoxit G5 being unsafe for the special PCB material (polyphenylene oxide). How do the attenuator blocks come out? I'm afraid of breaking something. 

Pull straight up (carefully) with a pair of duck bill or wide needle nose pliers. They simply plug onto the attenuator board with 6 pins. And don't mix them up. Plug into the same location they came out from.

So this fixed channel 2, which had issues on the same two attenuator settings that your channel 1 was having. Did not affect channel 1's issues. I think channel 1 may need a full adjustment.

[mnementh]

...Picked up a big can of Chock-Full-o-Nuts when we headed back, which my wife brewed while I heated up the bacon & eggs & biscuits "breakfast for dinner" she'd made while we were out. Which was, in fact, exactly what I was thinking of making for myself all the way home. 

mnem
I used up a lifetime's worth of luck finding her... *sigh*

bacon & eggs & biscuits "breakfast for dinner"  That sure sounds like a red neck dinner 

  right back atcha, buddy. Ain't nuthin' wrong with fresh-made bacon & eggs any time of day or night. Comfort food; it don't give a flying fuck what anybody else thinks, and a plateful with one biscuit is actually still on my diet. Plus, I get to come home to someone who'll make 'em for me "just because" so "neener-neener-neener!" atcha too, while I'm thinkin' of it.  

mnem
Yum.

[tggzzz]

Yeah looking at this one it's definitely a possibility. The main divider network is ok which is the difficult one and the second one is just a bunch of close tolerance standard values. I reckon I can knock something up on JLCPCB and use 0.1% or better SMD resistors.

The issues will be thermal tracking and any residual stresses in the resistors either after soldering or due to differential expansion when the temperature changes. Thermal tracking can be minimised by hillbilly engineering. I don't know the significance of the the stresses, but through hole will be better. For an extreme example, I refer you to

It seems to me that anything made from phenolic resin PCB & SMDs would be no more thermally co-reactive (most likely less so) than the original, which was made of thin-film resistors & silver traces printed on a thermally conductive ceramic substrate. Am I missing something here?

Ceramic and silver traces are much more stable and predictable than FR4 + ceramic(?) SMDs.

The original would have been professionally designed, including consideration of coefficients of expansion.

The original would have been professionally manufactured, with known components and temperature profiles.

How much that matters in this specific case is left as an exercise for the student.

[mnementh]

Yeah looking at this one it's definitely a possibility. The main divider network is ok which is the difficult one and the second one is just a bunch of close tolerance standard values. I reckon I can knock something up on JLCPCB and use 0.1% or better SMD resistors.

The issues will be thermal tracking and any residual stresses in the resistors either after soldering or due to differential expansion when the temperature changes. Thermal tracking can be minimised by hillbilly engineering. I don't know the significance of the the stresses, but through hole will be better. For an extreme example, I refer you to

It seems to me that anything made from phenolic resin PCB & SMDs would be no more thermally co-reactive (most likely less so) than the original, which was made of thin-film resistors & silver traces printed on a thermally conductive ceramic substrate. Am I missing something here?

Ceramic and silver traces are much more stable and predictable than FR4 + ceramic(?) SMDs.

The original would have been professionally designed, including consideration of coefficients of expansion.

The original would have been professionally manufactured, with known components and temperature profiles.

How much that matters in this specific case is left as an exercise for the student.

Wasn't saying you're wrong, just saying that obviously there's considerable thermal co-reactance in the original design, which may or may not have been accounted for. Remember too that the obverse is true; thin-film printed resistors of this sort were a new technology and the precision & stability we take for granted in modern thin-film ceramic substrate SMDs was exotic tech back then.

Which was precisely why I suggested  a couple pages back that it might be "an interesting exercise" to try and build one from SMDs. 

But until YOU mentioned it, bd couldn't be arsed, so whatever... unless it was my goading that prompted him to actually consider it. 

mnem
*toddles off to warm bed and warm wife*

[med6753]

Gee....I wish all fixes were this easy. 7A26 plug-in acting out on channel 1. Of course 20mV and .2V ranges the worst (always seems to be the case).

Opened it up. Pulled the attenuator blocks. Careful application of Deoxit Gold G5 on visible leaf switches with a cotton swab. Short sprays on the back side. Insert and test. Perfect. 

How do you get them out without damaging those tiny wires with a ferrite bead that seems to connect the attenuator board(s) with the amplifier?

I suspect my 7A26 needs some deoxit as well.

[edit] I think you mean the metal covers on the top side? That say "caution delicate board".

Yep, the 7A26 has those VERY DELICATE wires on that ferrite bead connecting the attenuator board to the main board. Luckily I didn't have to mess with that. I pulled the metal cover off the channel 1 switch assembly then I removed the 4 attenuator blocks. The used a cotton swab soaked with Deoxit Gold G5 on the exposed leaf contacts and attenuator board. Then I removed the rear cover on the plug-in and several quick shots of Deoxit down into the switch assembly where the rear contacts reside.

Got lucky. It worked. Will it stay that way? Time will tell. But I was prepared to pull the attenuator board if required and do that "brute force" polishing method I used (and documented) on the 7A24 plug-in. Which BTW still works fine despite the nay sayers who said I would ruin the assembly.       

OK, cool. I haven't been able to find anything online about deoxit G5 being unsafe for the special PCB material (polyphenylene oxide). How do the attenuator blocks come out? I'm afraid of breaking something. 

Pull straight up (carefully) with a pair of duck bill or wide needle nose pliers. They simply plug onto the attenuator board with 6 pins. And don't mix them up. Plug into the same location they came out from.

So this fixed channel 2, which had issues on the same two attenuator settings that your channel 1 was having. Did not affect channel 1's issues. I think channel 1 may need a full adjustment.

I would try one more time with channel 1 before considering tearing it down. But if you need to here is the procedure for reference:

https://www.eevblog.com/forum/testgear/restoring-tektronix-attenuator-switch-deck-assemblies/msg2413092/#msg2413092

Since that 7A26 attenuator board also includes part of the vertical pre-amp I would not immerse those components in the IPA solution when cleaning any grit off the contacts. Just spray those contacts areas down to get rid of it.

[BU508A]

bacon & eggs & biscuits "breakfast for dinner"  That sure sounds like a red neck dinner 

And how do you call this?



I am missing the porridge anyway ...   

[Specmaster]

Now that is what I call a full English breakfast, Porridge is a Scotsman's breakfast. 

[bd139]

That’s what I’m having for lunch now that is 

[Specmaster]

...Picked up a big can of Chock-Full-o-Nuts when we headed back, which my wife brewed while I heated up the bacon & eggs & biscuits "breakfast for dinner" she'd made while we were out. Which was, in fact, exactly what I was thinking of making for myself all the way home. 

mnem
I used up a lifetime's worth of luck finding her... *sigh*

bacon & eggs & biscuits "breakfast for dinner"  That sure sounds like a red neck dinner 

  right back atcha, buddy. Ain't nuthin' wrong with fresh-made bacon & eggs any time of day or night. Comfort food; it don't give a flying fuck what anybody else thinks, and a plateful with one biscuit is actually still on my diet. Plus, I get to come home to someone who'll make 'em for me "just because" so "neener-neener-neener!" atcha too, while I'm thinkin' of it.  

mnem
Yum.

Absolutely naff all wrong with fresh made bacon and eggs but bacon and eggs and biscuit that's a no no, but I suspect that you Merikins possibly call fried bread, biscuits, to us Brits, biscuits conjuror up something to be eaten with cheese or sweet biscuits to eaten with coffee or Tea, so are you going to spill the beans as to just what it is that you call "biscuits"??     

[BU508A]

for comparison: typical German breakfast:



Argh, wrong link. 

I'll leave it. This is what I wanted to post:

[Specmaster]

Thanks, but I couldn't possibly eat all of that for breakfast 

[Specmaster]

I usually have a dish with some fresh grapes in the bottom, sprinkled with an inch of fruit and flakes cereal and ice cold milk poured on the top for my breakfast, very healthy 

[BU508A]

The idea behind is: eat what you like, not all of them.     

[Specmaster]

The idea behind is: eat what you like, not all of them.     

And chuck the rest of it in the bin, what a wasteful lot you Germans are 

[BU508A]

The idea behind is: eat what you like, not all of them.     

And chuck the rest of it in the bin, what a wasteful lot you Germans are 

 

We have refrigerators, too. Lot of what's leftover will come the next day on the table 

[Black Phoenix]

 

We have refrigerators, too. Lot of what's leftover will come the next day on the table 

And sometimes even taste better that the day before when It was done!

[bd139]

Yes I had reheated lasagne for breakfast today 

[BU508A]

And sometimes even taste better that the day before when It was done!

When I'm doing for example sauce Bolognese for spaghetti, I'll prepare it one day before.
When it is reheated, it tastes much better. It is a nice trick. 

[BU508A]

Yes I had reheated lasagne for breakfast today 

Well, I think, you my friend are afraid of nothing. 

[beanflying]

Evening all. Dinner for One shack style tonight on the new bench 

[tautech]

Solvent fumes are a good hunger suppressant ! 
No way I could survive on that little in mid winter. 

[med6753]

Never been much of a breakfast eater. Just give me my coffee...which I am drinking right now. 

Typical American breakfast. Mostly starch and carbs. No wonder we're fat. 

[beanflying]

Solvent fumes are a good hunger suppressant ! 
No way I could survive on that little in mid winter. 

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