AOIP PJ6301 schematic

[masterx81]

Hi!
I have bought at a cheap price this nice piece of test equipment. The input section works perfectly, and agree with great accuracy with my 34401a. The output section have seen better days. Traces burnt, an some components replaced.
Would be easier repair it with some schematics, or at least, know the value of the original components used (and replaced).
I not see any custom component, so the repair seem quite possible. I've already sent a mail to AOIP without any answer.
Thanks!

[2N3055]

There is no schematic in public that I know of. AOIP won't give it to you, probably.
It's a shame it is output because output is quite more complicated.

Take detailed photos of boards and post them here. We'll give it a try.
As you said, apart from special A/D module for the meter (that works well for you), most of the components are off the shelf, at least active part. There are quite a lot egzotic resistors and relays though..

[masterx81]

Here some pictures.
In the next days i'll do some reverse engineering of the traces, as usual with missing schematics. The board seem a 4 layer, but the internal layers not seem used a lot for routing, mostly used for power supply/ground plane.
I see replaced diodes and seem also the capacitor. I suspect that also the TO220 was replaced (now an irf9610). I not know what is the purpose of the diode placed across the capacitor under the board. Another strange thing is a single component replaced with 2 in what seem anti-series connection. They are marked CM 3AGUB (can't find anything about them, i can't neither recognize the logo of the maker).
I hate when i find boards with a repair attempt,  i never know if the component replaced are compatible with the original parts.
Thanks for the help!

[masterx81]

So, anyone have a photo of this device, please?
I've started removing the relays for made easier the repair. I've noticed 2 relays, one 5v and the other 6v (connected to the same uln driver ic), i suspect that one of them was replaced with wrong voltage rating.

[masterx81]

Hi!
Today i've put my hands for the second time on this device...
I'm fixing some burnt traces, but i'm sure that some components were replaced by someone before me, and i not know what there was before...
In the meantime, maybe someone have worked on this nice thing, and have some photos of the pcb?
Thanks!

[masterx81]

I've found an uln driver (used for driving the relays) shorted on one channel.
But now i'm trying to understand what components have replaced who have tried to repair it before me.
He had replaced an Sma component with 2 of this things in series:

I can't find what component is, and i not know neither the manifacteur. Seem a CM 3AGUB.
I'tried to identify it, without success. When low current (2ma)/"high" voltage is applied, it stops at around 38v.
Seem to not have polarity, i think that is a mov...
Someone know exactly what component can be? Thanks!

[masterx81]

And, it's working! The damaged uln was making a mess.
The backlight seem a bit low, and there is a 0.19mv offset to deal with, but seem ok.

[masterx81]

I have one last thing to fix, the binding posts of the device are in really bad shape and needs to be replaced, but i can't find anything  that can be adapted
[ Specified attachment is not available ]
The back thread is 4mm, quite long, and they allow a wire to be clipped. Thay allow to use safety plugs.
Anyone have seen something similar?
Thanks!

[masterx81]

Little update. I was not able to source similar binding posts, or with the safety shroudings, or the screw  type, but nothing with both the features. So, i've used cyanacrilate and sodium bicarbonate to rebuild them, and the result is quite good.

The only problem is that after the repair the device is a bit off calibration (most of it on the current output mode, almost 2ma, as a fixed offset on all the scale).
Someone know how to calibrate it? On the output section it has 3 multiturn pots, but i've a bit of fear touching them.... and i hope/think that the calibration is stored on the nvram....

[2N3055]

Little update. I was not able to source similar binding posts, or with the safety shroudings, or the screw  type, but nothing with both the features. So, i've used cyanacrilate and sodium bicarbonate to rebuild them, and the result is quite good.

The only problem is that after the repair the device is a bit off calibration (most of it on the current output mode, almost 2ma, as a fixed offset on all the scale).
Someone know how to calibrate it? On the output section it has 3 multiturn pots, but i've a bit of fear touching them.... and i hope/think that the calibration is stored on the nvram....

DON'T you touch a thing!!

Calibration is fully in software. CFG->ADJ menu  (9456)

Get docs here.. I will remove it in few days..

https://drive.google.com/drive/folders/1KSJduUsf-sB5nqVKtSFHcdqdH_yZwq2j?usp=sharing

[masterx81]

I've seen that menu before, but i not knew the password, thanks!
With the adj menu i've managed to match the voltage with my 34401 on both 60mv and 0.6v range, but on 60v range it goes very well up to 56v, when i try to go above that voltage seem that something is clipping it.
In current output, i can't made adjustments as seem that the error is too much, and give me an error. An output of 0ma give -2.5ma, and 50ma give 47.5ma. An offset of -2.5ma. So i think that i need to understand why the current output is so much out of specs.. The repair job isn't ended 😅
Really thanks!!

[2N3055]

I've seen that menu before, but i not knew the password, thanks!
With the adj menu i've managed to match the voltage with my 34401 on both 60mv and 0.6v range, but on 60v range it goes very well up to 56v, when i try to go above that voltage seem that something is clipping it.
In current output, i can't made adjustments as seem that the error is too much, and give me an error. An output of 0ma give -2.5ma, and 50ma give 47.5ma. An offset of -2.5ma. So i think that i need to understand why the current output is so much out of specs.. The repair job isn't ended 😅
Really thanks!!

No problem.

On mine display was really bad and I managed to find a replacement that was not backlit. It is old bitmap display not easy to find. I had to reverse engineer the protocol before I figured out which one...
But on mine analog worked fine.

It is really useful instrument.
I hope you manage to fix it.

[masterx81]

Whoa! That's an insane time consuming job reverse engineering the protocol to replace the display!
For that occasion, i've managed to find an AOIP SA 32 broken on ebay, that shares the same frontend, so thag i have some spare parts...

I think that the first thing that i need to check is the psu rail voltage used to generate the current and voltage. Maybe is a bit too low and clip the voltage output, and moved a bit low the 0 point of the current output.
Maybe are the multiturn pots? Need to check better the circuit, but i can't exclude that someone before me have moved the pots....

[2N3055]

Whoa! That's an insane time consuming job reverse engineering the protocol to replace the display!
For that occasion, i've managed to find an AOIP SA 32 broken on ebay, that shares the same frontend, so thag i have some spare parts...

I think that the first thing that i need to check is the psu rail voltage used to generate the current and voltage. Maybe is a bit too low and clip the voltage output, and moved a bit low the 0 point of the current output.
Maybe are the multiturn pots? Need to check better the circuit, but i can't exclude that someone before me have moved the pots....

Not so much. When I say people MSO scopes are very useful, they don't listen. It was enough to see what kind of traffic goes over the bus to realize it was bitmap, and then a little research on old displays came up with possible candidates. Bit more verifying and that was it. It was standard display at the time, but fell out of fashion, I guess.

Yes, verify power buses. Multiturn pots are not going to move 10%. Something is wrong.
Or someone before you was in and they screwed up by tampering with pots.

Verify semiconductors  in output stage... you know, the usual...
LT precision opamps used inside are sensitive. One slip of meter probe, you touch something wrong and pufff.. If someone was in there before, check them.

As long as ADC module and reference is good and stable, all other parts are repairable.

[masterx81]

You still have to know how decode the various formats, so you have found a compatible display with the same protocol?
In any case i've measured the voltages, and there are 66v, seem to me a bit low. The output range is -10 to +60, but i get only 56v, and i not think that is a coincidence..
First i try to remove the mov that had been replaced by who have tried to repair it before me, then i've seen a strange diode across the supply line, i think a zener, soldered on the bottom layer. If without this i still get  low voltage, i'll start the search...

--- Edit ---
Without mov and diode i still get 66v on the main line, and i can confim that i can output from to -10v to +56v...

[2N3055]

You still have to know how decode the various formats, so you have found a compatible display with the same protocol?
In any case i've measured the voltages, and there are 66v, seem to me a bit low. The output range is -10 to +60, but i get only 56v, and i not think that is a coincidence..
First i try to remove the mov that had been replaced by who have tried to repair it before me, then i've seen a strange diode across the supply line, i think a zener, soldered on the bottom layer. If without this i still get  low voltage, i'll start the search...

--- Edit ---
Without mov and diode i still get 66v on the main line, and i can confim that i can output from to -10v to +56v...

Display protocols are connected with display chips and are quite standard. It was older "dumb" bitmap protocol. I do have " a bit of experience", that is true..

Trace a schematic a bit, before just soldering in and out components.

Voltage reference uses PWM to create 0-Max voltage signal.
It is always the same -1V to +10V on my other calibrator from AOIP.
There is attenuation and amplification in output.

Try to isolate part that creates variable reference input to power amp.
Measure voltage there. Than you know how much is amplification in 60V range.

Try to trace part of circuit that switches amplification. If you find one of trimmers is in that circuit, than it might be that it needs to be adjusted.
But my experience is that with these calibrators, these parts of circuit are using fixed parts (for stability) and with such tolerances so it is sufficiently close to be pulled in perfect cal just by software.

Make good hires photos, so you can make notes on them. That way you can also post them here so we can maybe be able to discuss it better.

[masterx81]

The real problem is that i not know how the output voltage is generated, and i'm having difficulties finding also how the 66v voltage is generated. Near the transformers i have only 63v, 50v and 25v capacitors, but near the output section i have this 66v line (with 100v cap), and i not see buck transformers around. I think that they use a center tap. As is a 4 layer pcb, it's quite difficult to trace the inner lines. Can be seen a little with a strong light and watching "through".
First of all i'm trying to understand what is the purpouse of the 3 multiturn trimmers, and trying to understand how the voltage goes from the isolation transforers to the 100v capacitor... I think that the capacitor was replaced by who have made the first repair attempt, as it's different from the others. Also the replaced mov were in parallel to this capacitor, so the damage was for sure here (and the uln that i've replaced was in the same zone).
Here an high res photo...

On the top leftnsection there is the input signal conditioning, bottom left the the voltage input of the board, with isolation transformers, top right there is the output section, there were a lot of burnt traces, i've replaced the uln (tssop 18 package near the heat sink), and a relay (who have made the repair before have used a compatible but a wrong voltage relay), who have tryied to repair before me seem that have replaced the fet attached to the heat sink, some diodes around it,  the blue electrolytic, the mov (that now are 2 mov in series) and the relay.

[masterx81]

And this is a thermal view. The hottest components are some 78l05 and 78l15, nothing strange

[2N3055]

From memory my board is slightly different.

Two trimmers in up right are part of PWM DAC I think .

[masterx81]

Quite strange, the voltage output from the transformer seem to decrease over time. The 66v is generated by 2 secondaries in series. One at 31v and the other at 36v, and both decrease.
There is one transformer for acquisition and one for output, there are 2 smps driven by two si9112dy, input voltage steady at 20vdc. Quite strange, i not see a voltage feedback section. Need to trace a bit.
On the output sections goes a +5, a +/- 15, and this 2 31/35v generated by the smps.
Quite cool, communication between digital board and analog board seem to be via optical coupling.

Edit

Actually the voltage decrease, then is pumped up, and so on, so there must be a sort of feedback

[masterx81]

I still think that the problem is on the voltage supply section. I think the the ouput voltage of the 2 windings must be 35v and 35, but one of them is only at 31v. I'm tempted to interrupt the line to the circuits and see if without load the voltage is the same. And... i can't really tell how the si94112 chip get a feedback, as there isn't anything that can send back.
I have fear that the problem is the transformer itself, that output a lower voltage. That would be a great problem, as it's a custom made....

[2N3055]

I still think that the problem is on the voltage supply section. I think the the ouput voltage of the 2 windings must be 35v and 35, but one of them is only at 31v. I'm tempted to interrupt the line to the circuits and see if without load the voltage is the same. And... i can't really tell how the si94112 chip get a feedback, as there isn't anything that can send back.
I have fear that the problem is the transformer itself, that output a lower voltage. That would be a great problem, as it's a custom made....
(Attachment Link)

All is possible.
With power off, can you measure secondary coils resistance?
And try to wiggle transformer a bit while measuring voltage when it is on.

You might have a problem with winding end not connecting pin (not soldered or broken)  correctly.
I had that exact problem with one of the windings on my calibrator (other one).

I had to perform delicate surgery in epoxy around terminal to get to wire and connect it.
Worked well.
It is perfect now.

[masterx81]

I've made some measurements and discovered some interesting things. I think that the smps controller work only with the feedback of the primary current.
Once rectified both secondaries of the transformer go directly to a relay, that choose the range. When set in 60v output it select the 35+35v output, else it choose only the first "tap" at 35v. When in 60v range i measure around 35 volt on the first tap and around 31v on the second tap (the 66 volts of the prvious tests).
When in 6v range i get aroud 33v on the first tap, and aroud 36v on the second tap (70v total)
Measuring the ac voltage with the 34401, directly at the output of the transformer (before rectifier diode), i get in 60v range 22.7vac on the first tap and 21.8vac on the second tap, while in 6v range 22.3vac on first tap and 22vac on second tap. I know that is an high frequency signal, but can be quite indicative.
After the relay, there are 2 current limiting resistors in series (total 13.6ohm) that allow me to measure the voltage drop, and i get 90.7mv on both ranges (6.6ma) at 0v output and 113.3mv at 50v output (8.3ma).
6/8ma can be too much current without load? This thing in output current mode must source at least 60ma....
I've checked diodes, capacitors and inductances after the widing, and all is good.
In current mode it choose the first tap with aroud 33.9v with 0ma output. With the output at 60ma it go at 32v.
The voltages in current output mode are quite good, so i can't explain the 2.3ma offset.
The dc voltages of the +/- 15 and 5v windings are similar to the voltages of the other transformer (+/-18.9vdc vs +/-18.4, 7.4vdc identical).
Measuring the voltage drop across the current sensing resistors on the primary side, i get (on 2x 1r resistors in parallel) 256mvac with 60ma output current set, and 179mvac with output set at 60v...

The current on the primary side not seem too bad in 50v dc output vs 60ma current output, the ac voltages out of the transformer seem quite good, it's the dc voltage of the second tap that seem to drop too much. The diode measured with the tester seem good.

I think that the current offset and the clipping of the output voltage are 2 different unrelated problems.

But by now i'm more confused than before doing all the tests...
I'm starting to think that the problem it's really the transformer, at best it output 70vdc, that not leave any room on a -10+60v output. I think that the correct rectified voltage must be something something around 80vdc.

[2N3055]

The switcher that feeds output stage is basically tracking pre regulators for output stages.
That keeps dropout on output transistors getting too high and keeps dispation low.

[masterx81]

I've removed the transformer, and the feedback is given by a second primary, it's a type of feedback that i not see very often, most of the times i see a feedback from the secondary via an optocoupler.
According to the de5000, the resistance/inductance of those 2 windings are :
From gnd to first tap: 285mohm / 154uH
From first tap to last tap: 265mohm/ 142,5uH
From gnd to last tap: 0.536mohm/ 588uH

Why both windings in series have an inductance that ins't the sum of both single inductances?
In general, not seem too bad

I've also found that the 2 6.8ohm resistors in series are out of spec, both at 7.4ohm. Not change much, this are here only to allow a soft discharge of the capacitor after them.