Test Equipment Anonymous (TEA) group therapy thread

[tggzzz]

Left a few bids on the junk at PP auctions, they won't let me buy a Rotek either, think "skycontrols" is controlling the prices to make sure there are no bargains (it's in the T&Cs as we found some time ago).

David

Under 'factory'? I'll do my best not to outbid you

Also: yes, probably skycontrols this time...

I was going to offer a derisory bid for the CI voltage ratio box, but chose not to bid against you. I imagine it is oil-filled, so I hope you don't knacker your back lifting it

[Ice-Tea]

Left a few bids on the junk at PP auctions, they won't let me buy a Rotek either, think "skycontrols" is controlling the prices to make sure there are no bargains (it's in the T&Cs as we found some time ago).

David

Under 'factory'? I'll do my best not to outbid you

Also: yes, probably skycontrols this time...

I was going to offer a derisory bid for the CI voltage ratio box, but chose not to bid against you. I imagine it is oil-filled, so I hope you don't knacker your back lifting it

Truth be told I kinda forgot what your handle is... I backed off when I noticed David was on the case (unless he was already outbid and/or I forgot to check username  )

[Ice-Tea]

Had some fun with a Solartron 1250 FRA (Frequency Response Analyzer). Doesn't work. Lovely tale of wack-a-mole debugging.

Opening her up:



Guess what:



Actually a Farnell power supply. Truth be told: not too impressed. Seems to be covered with.. something? Doesn't look like it's elco guts, maybe degraded conformal coating?



Replacing RIFAs (actually, I need to replace two more, but my magic box of RIFA-be-gone didn't have 22nF). Machine still doesn't boot, voltages all over the place. Luckily, I can lift all boards and then the PSU is pretty decent. So, inspecting boards.

CPU board: eh, something seems to be growing there?



No surprise: very dead NiMh battery. Some corrosion nearby. Funny though, the growth of the connector was nowhere close to the battery.



Excavated the battery, cleaned up the spill. Inserting the board no longer "hangs" the PSU but I'm still opting to take a board from another machine (sans spill). May revert later. Complete CPU board prior to cleaning:



Next board in line looks fine at first sight:



Closer inspections though:



The PSU seems to have taken out some stuff when it went bananas. Swapping this board also. Next board inline:



Well that's not good... Strangely, on the board I'll be swapping this one with, the one IC that is clearly from another series is 'normal' on the swap board. Also a far amount of patch wire on the back. Maybe weak spot revised later in the production run.



1/n

[Ice-Tea]

(continued)



The following two boards are related to expansions (synchronising or some such) and seem fine:




Generator board:



One of two input channels:



All look fine. Plugging back everything and... EVERYTHING SEEMS FINE. For several seconds. After that, a miniature ball of fire escapes. My smell-o-finder (nose) points me in the right direction:



Right. Starts up stably now. Got more work done, will write up later.

[Robert763]

Left a few bids on the junk at PP auctions, they won't let me buy a Rotek either, think "skycontrols" is controlling the prices to make sure there are no bargains (it's in the T&Cs as we found some time ago).

David

Under 'factory'? I'll do my best not to outbid you

Also: yes, probably skycontrols this time...

I see you are getting a couple of pallet loads of HP heavy metal 
I was surprised by the interest and prices on the 8922x GSM test sets. To me the are only good for parts, Am I missing something?  I snagged a TTi TS3021S PSU and a PM5503 video test generator.

[factory]

That Solartron looks a nightmare  , hope you have a manual.

Left a few bids on the junk at PP auctions, they won't let me buy a Rotek either, think "skycontrols" is controlling the prices to make sure there are no bargains (it's in the T&Cs as we found some time ago).

David

Under 'factory'? I'll do my best not to outbid you

Also: yes, probably skycontrols this time...

I was going to offer a derisory bid for the CI voltage ratio box, but chose not to bid against you. I imagine it is oil-filled, so I hope you don't knacker your back lifting it

Truth be told I kinda forgot what your handle is... I backed off when I noticed David was on the case (unless he was already outbid and/or I forgot to check username  )

Left all my bids last night, couldn't be arsed with bidding on the day and wasting all my phone credit.

Well I won half a dozen PP lots (enough to make the trip worthwhile), the HP 3330B being the most expensive.
Got the Rotek high current adaptor, but this is probably a giant door stop*, without the 5 digit calibrator that sky-out-of-control won. There is of course that one at work I can't have, annoyingly it's the six digit version too, which was sort of working when I last used it (but not calibrated). 

David

Edit: OK almost a doorstop, have at least found the pinout of the J11 connector (in Rotek 3900A pdf) that goes to the 350 doorstop adaptor. 

David

[TheNewLab]

Solution. Changed all the passwords to all my online buying places. gave passwords to my wife so she can hide them from me. Now, every purchase I want to make requires her permission. LOL!

[tautech]

Solution. Changed all the passwords to all my online buying places. gave passwords to my wife so she can hide them from me. Now, every purchase I want to make requires her permission. LOL!

Hmmm, not sure you belong here. 

[Ice-Tea]

Left a few bids on the junk at PP auctions, they won't let me buy a Rotek either, think "skycontrols" is controlling the prices to make sure there are no bargains (it's in the T&Cs as we found some time ago).

David

Under 'factory'? I'll do my best not to outbid you

Also: yes, probably skycontrols this time...

I see you are getting a couple of pallet loads of HP heavy metal 
I was surprised by the interest and prices on the 8922x GSM test sets. To me the are only good for parts, Am I missing something?  I snagged a TTi TS3021S PSU and a PM5503 video test generator.

Like other test sets for cellular standards long dead: has an RF gen, spectrum analyzer and some sort of audio generator/noise analyzer all in one neat package.

[Robert763]

Left a few bids on the junk at PP auctions, they won't let me buy a Rotek either, think "skycontrols" is controlling the prices to make sure there are no bargains (it's in the T&Cs as we found some time ago).

David

Under 'factory'? I'll do my best not to outbid you

Also: yes, probably skycontrols this time...

I see you are getting a couple of pallet loads of HP heavy metal 
I was surprised by the interest and prices on the 8922x GSM test sets. To me the are only good for parts, Am I missing something?  I snagged a TTi TS3021S PSU and a PM5503 video test generator.

Like other test sets for cellular standards long dead: has an RF gen, spectrum analyzer and some sort of audio generator/noise analyzer all in one neat package.

Hmm, Has a CW RF generator (no AM or FM modulation), Might have a crippled SA (it's an option on most and even then has limited span etc), It's a huge heavy box with a poor user interface. Interestingly the SA module will work in a HP 8920x and give full span etc, but causes the unit to throw a configuration error.
The 8924C is more usable as it is basically an 8920B in a big box and retains full analog functionality. It's still a big box though.

[Ice-Tea]

Left a few bids on the junk at PP auctions, they won't let me buy a Rotek either, think "skycontrols" is controlling the prices to make sure there are no bargains (it's in the T&Cs as we found some time ago).

David

Under 'factory'? I'll do my best not to outbid you

Also: yes, probably skycontrols this time...

I was going to offer a derisory bid for the CI voltage ratio box, but chose not to bid against you. I imagine it is oil-filled, so I hope you don't knacker your back lifting it

I'd be perfectly happy to take it out of the sale and let you have it but I'm afraid tax regulations probably won't allow it

[Vince]

PCB's and built unit; Vince, can you handle the 0603's?

Yes I can ! It's a huge pain, it's butchery up close, but it's functional... I think !

00H30 here, just spent 3 hours, 3 solid hours soldering this thing ! 
Such a PITA, my eye sight is crap and my glasses are 15yo, can't see squat anymore, need new glasses...
My tweezers are also too crap to handle tiny SMD stuff. Not sharp enough and soft lie butter, they just keep bending / getting out of shape. They are pure trash.
They are still OK for very large SMD packages or through hole components, but for 0603 or SOT23 or smaller, it's pure hell, so much time wasted and so much frustration and anger using them....

Much time was also spent trying to figure out WHERE to put the components on the board, and IN WHAT orientation... because the silk screen for 90% of the components is too small and the white ink is just a blob of paint... so had to look at al the traces on the board and try to match them with the schematic. Fun.

Then I had problems because I was missing two resistors, R2 and R3, 499 ohms.
Eventually decided I could probably do without them... only to think, too late, to look at Zoli's picture of his populated board.... which was missing these resistors as well, ahem...

Then R4 the gate resistor, was 100ohms but no such thing in the envelope... had 120ohms though, so I went for that. Anything would do I thought...

Then R8 and R9, 330 ohms, closest I had was 200 ohms, so I sued that. These resistors stem from the shunt resistor, so I figured the value once again was not that critical, well I think ?! 


Geez I am exhausted, and tired.

Going to bed. Tomorrow I will worry about wiring it all up to a power supply and fit a MOSFET and radiator, and start testing it. It probably won't work first time, that would be too good to be true, so I anticipate some troubleshooting...

Cant wait....

 

[tggzzz]

Left a few bids on the junk at PP auctions, they won't let me buy a Rotek either, think "skycontrols" is controlling the prices to make sure there are no bargains (it's in the T&Cs as we found some time ago).

David

Under 'factory'? I'll do my best not to outbid you

Also: yes, probably skycontrols this time...

I was going to offer a derisory bid for the CI voltage ratio box, but chose not to bid against you. I imagine it is oil-filled, so I hope you don't knacker your back lifting it

I'd be perfectly happy to take it out of the sale and let you have it but I'm afraid tax regulations probably won't allow it

Phew! That was a narrow escape

I have a Julie Research Labs 7 decade KVD. Obtaining your CI voltage divider would be unjustifiable GAS, and I would have to reinforce my wooden floor joists - and probably find a local osteopath

More seriously, thanks for the offer. I know you mean it because you have been personally helpful in the past.

[Brumby]

Solution. Changed all the passwords to all my online buying places. gave passwords to my wife so she can hide them from me. Now, every purchase I want to make requires her permission. LOL!

Hmmm, not sure you belong here. 

Let's see how long he lasts....   

[Zoli]

PCB's and built unit; Vince, can you handle the 0603's?

Yes I can ! It's a huge pain, it's butchery up close, but it's functional... I think !

00H30 here, just spent 3 hours, 3 solid hours soldering this thing ! 
Such a PITA, my eye sight is crap and my glasses are 15yo, can't see squat anymore, need new glasses...
My tweezers are also too crap to handle tiny SMD stuff. Not sharp enough and soft lie butter, they just keep bending / getting out of shape. They are pure trash.
They are still OK for very large SMD packages or through hole components, but for 0603 or SOT23 or smaller, it's pure hell, so much time wasted and so much frustration and anger using them....

Much time was also spent trying to figure out WHERE to put the components on the board, and IN WHAT orientation... because the silk screen for 90% of the components is too small and the white ink is just a blob of paint... so had to look at al the traces on the board and try to match them with the schematic. Fun.

Then I had problems because I was missing two resistors, R2 and R3, 499 ohms.
Eventually decided I could probably do without them... only to think, too late, to look at Zoli's picture of his populated board.... which was missing these resistors as well, ahem...

Then R4 the gate resistor, was 100ohms but no such thing in the envelope... had 120ohms though, so I went for that. Anything would do I thought...

Then R8 and R9, 330 ohms, closest I had was 200 ohms, so I sued that. These resistors stem from the shunt resistor, so I figured the value once again was not that critical, well I think ?! 


Geez I am exhausted, and tired.

Going to bed. Tomorrow I will worry about wiring it all up to a power supply and fit a MOSFET and radiator, and start testing it. It probably won't work first time, that would be too good to be true, so I anticipate some troubleshooting...

Cant wait....

 

I've e-mailed you the updated schematics(attached here); looks like you've forgot about. One mistake already spotted: remove C2(the board is set-up for both LT1761/LP2985; one has cap to the ground, the other to the out+).
Extra parts were included to please Murphy, and to avoid searching the nooks and crannies.
R8&9 give you the current sense gain; the original 330Ω is good up to 3A, with 200Ω is good up to 5A. The pot value is not critical; anywhere between 1-100k is OK(intended to be full pot, not trimmer).
Troubleshooting: before you go any further, check for 10V and 1.25V(V_REF); then install the FET and heat-sink. Otherwise is a good job (well R10 is upside down; did you installed the caps on the bottom? )
Meantime the next 8060A(teased some time ago) arrived - never had been opened before; two side buttons missing, zebra stripes dirty - looks like it will a boring fix(well, except hunting down the missing buttons...).

[Ice-Tea]

Hernia in the waiting:

[Vince]

PCB's and built unit; Vince, can you handle the 0603's?

Yes I can ! It's a huge pain, it's butchery up close, but it's functional... I think !

00H30 here, just spent 3 hours, 3 solid hours soldering this thing ! 

I've e-mailed you the updated schematics(attached here); looks like you've forgot about.

I did remember about azn updated and simplified schematic, and I did hunt for it 10 times, scrolling back pages on TEA / HERE... somehow my brain had forgotten it was in your e-mails rather than TEA 

One mistake already spotted: remove C2(the board is set-up for both LT1761/LP2985; one has cap to the ground, the other to the out+).

Well in my defense, I was only following the schematic, just the wrong one ! 
Fixed now ! 

Extra parts were included to please Murphy, and to avoid searching the nooks and crannies.

Yes thanks for that !
Somehow I managed not to lose any ! I was very careful but with my big fingers, even trying your best is hardly a guarantee... 

R8&9 give you the current sense gain;

Oh OK ! I see now... it's as complicated as I thought, I can now see it's just a standard non-inverting montage.

the original 330Ω is good up to 3A, with 200Ω is good up to 5A.

Hmm yes, easy to calculate now you point it all to me.
5A will be a tad on the low side since I need 5.1 at least to test the PSU I am trying to "fix" for the old man.
Maybe I could lower these 200R resistor just a tad to make sure I can get up to 5.5a or something.
Nope ! Of course I have no SMD resistors in stock... I will add that to my shopping list.

The pot value is not critical; anywhere between 1-100k is OK(intended to be full pot, not trimmer).

Yes that's what I thought too, when I got mixed up with the 1K and 10K trimmers on my bench, and soldered the 10K one by accident ! 
With the two 499 resistors removed / modulation stuff gone, there is only that 10K resistor in line with the Opamp input. I could have not put it in place, but I put it anyway as it was better looking than putting a blob of solder to bridge the footprint ! Since its presence does not affect the voltage registered by the Opamp, I thought let's just leaved it there, does no harm !

Troubleshooting: before you go any further, check for 10V and 1.25V(V_REF);

OK I just did that. Looking good as far power supplies.  Fluke 11 DMM registers spot on 10.00V and 1.250V, not even kidding !
I guess I can't ask for better than that !

Then before installing the FET / trying the load, I decided to test that the trimmer could indeed vary the voltage between ground and the 1.25V reference supply, if just to make sure it was set to 0A at power up rather than full blast !
That's where things started going strange.... my trimmer does not appear to have any lock : I can turn it for hours either direction, the screw never hits a stop ?!    Maybe that's how they are designed, some kind of "clutch" mechanism to keep you from damaging the delicate worm screw mechanism inside ?
So I didn't worry that much about it, but still wanted to check that it could vary the voltage, and make sure it was outputting 0V rather than 1.25V...
So I hooked the DMM between ground and the wiper... and I see two things :

1) If I wind up the trimmer XXXXXX turns to the left, I can get to ground level, good.
2) Then I start turning it CW to increased the voltage, one turn at a time
3) I notice just how slowly the voltage rises.... bit worried.
4) Once I got to 0.85V or something, voltage stops climbing, it won't go any further.
5) To get to that voltage required me cranking the trimmer at least 20 turns ! 

So... why can't the trimmer reach Vref / 1.25V, and do 20 turn trimmers (or more, I don' t know ! ) exist ?! 

So... glad I checked that. I need to troubleshoot that before going any further.

Otherwise is a good job (well R10 is upside down; did you installed the caps on the bottom? )

Yes I did !  After looking for 2 minutes at the top side and failing to locate them, I decided to flip the board and saw two "suspicious" footprints right under each  opamp package !   

[Vince]

OK I worked on my trimmer problem... looks like the trimmer works just fine...
....IF I measure voltage directly on the wiper, ie on the left side of that R1 10K resistor that's in series with the trimmer wiper, going to the opamp input.
...HOWEVER when I measured on the other side of that resistor, i.e. on the input of the opamp, that's where things go wrong !

Input is supposed to draw negligible current hence the 10K resistor in series should be "transparent", have zero effect.

But it does !

So once I spotted that, I went to test it more precisely. I noticed that for low wiper voltages up to 570mV, the opamp input would receive that exact same voltage, good.

However if I start increasing voltage above 570mV then the input voltage rises but only very slowly and when the trimmer is in full lock, putting out Vref / 1.25V, the opamp input sees only 854mV !

So I measured some data point from 570mV all the way to 1.25V, measuring every full turn of the trimmer.

Yes, we like measuring things here at TEA. So here is the resulting graph, because we also like plotting our measurements, here at TEA.

So looks like basically I am turning on some protection diode inside the opamp or something ?

Maybe I ESD damaged the opamp when I handled / soldered it .... 

One thing is for sure though : there is no way I got the orientation of that tiny opamp package wrong when soldering it to the board, because its pinout is not symmetrical ! It's a SOT23 package with only 5 pins not 6, so you just can"t get it wrong...

I have a one spare opamp (thanks for the spares Zoli ! ), so I will try replacing that opamp and be extra careful ESD wise.... crossing fingers 

[Vince]

UPDATE :  I replaced the opamp... problem still there ! 

I am baffled, the circuit is so simple, the input of the opamp is the only thing that can draw current through that 10K resistor !

Tried removing the resistor, bridged its footprint on the board with a piece of wire.

Problem fixed ?! 

Looks like so anyway, I can sweep up to 1.25V just fine now 

Still, strange....

So that means that the input current of the Opamp is orders of magnitude higher than it should be ?! 

Looking at my data points above, when the wiper is fully cranked, 1.25V on one end of the resistor, there is 0.85V at the other end.
400mV drop across 10K (I measured it, it does read spot on 10K ohms), if I get my math right that a current of...40µA ?
Datasheet says in the low PICO amps range.... we are 6 orders of magnitude higher than that.... counterfeit chips ?! 

I don't know... but at least now maybe I can move on to the next step and wire a MOSFET see if that circuit works ... I am a bit worried / anxious now 

[PA0PBZ]

Are you sure that the opamp is powered correctly (pin 5)? Otherwise it could be powered via pin 3 and a protection diode, which will give you the observed behavior.

[Vince]

Yes I checked voltage at the its power pin, 10V on pin #5.

The package is "keyed" / not symmetrical : 3 pins on one side, only 2 pins of the other side (middle pin is not implemented), so it's impossible to mess up.
Of course one should never underestimate the power of stupidity, so maybe I did something blatantly wrong anyway and will discover it later on.... 

[PA0PBZ]

Do you dare to post a picture of the assembled pcb?

[Ice-Tea]

Just got my PP bill.

Sweet baby Jesus.

[Vince]

Do you dare to post a picture of the assembled pcb?

Well I already have ! Just scroll bacl a few messages on this very page 

Here is some more : I pulled my 2SK2117 MOSFET and secured it to some heat sink. Yes I did put thermal paste.. after I took that picture, don't worry !

So I powered it up and... it seems to work, except for one thing : the trimmer can still go up to 1.25V as it should, however that only gives me 2.45Amps or so, barely half of the 5A that it should be able to produce. Yes, it's an old MOSFET with a fairly high Rdson (by modern standards) -->  a bit over one ohm. But I gave it 12V volts so should still be plenty capable of drawing 5A. Also, I know the Rdson of the MOSFET is not the limiting factor here, because I measured the gate voltage which is about 6V.. the op-amp is powered with 10V ! So the op-map is not even TRYING to up the gate voltage.

So the problem is on the board, not in the MOSFET me think..... OTHO maybe the MOSFET is strange as well, because according to the graphs on the datasheet, even with only 6V at the gate I should be able to get maximum current (rated at 9A sustained) fingers in the nose, and I clearly don't.

Maybe the shunt resistors is reading high, or the current shunt amplifier is amplifying too much hence the other op-amp, that drives the gate, think that it's getting 5A when in fact it's achieving only half that....

More troubleshooting ahead ! Going straight to the bench, stay tuned...

[m k]

Do you need some cable to go with it, needs quite thin stuff?

David

Before I need anything I have to check the trafo.
Original fuse was out so who knows what the reality is, and of course the thing is packed away, not far though.

If trafo is sane I'll accept the new connector, if you think you won't have the rainy day one day.

Trafo tested, seems to be ok.
Found 20mm holder and removed its chassis, bent pins and it's in.
Had only T fuses in hand so smallest, 160mA is in place.

Suitable wired test pins emerged from old hard disk power extension thingy.
Some twist, some tin, cut ends, file corners and it's like a new.
Keep in mind that newer extension may have thicker wires.

Not because of this but low ohms is a bit off, short is around 4.