Tektronix PWS 4000 series Schematic/Service manual request

[candrian]

Hello,

Does anyone have a schematic or a service manual of Tektronix PWS 4000 series? I'm troubleshooting one of these and I'm looking for any documents that may save me time.
I would also appreciate any available info on how to calibrate it as I may need it once I replace any faulty components.

[RomDump]

Hello,

Does anyone have a schematic or a service manual of Tektronix PWS 4000 series? I'm troubleshooting one of these and I'm looking for any documents that may save me time.
I would also appreciate any available info on how to calibrate it as I may need it once I replace any faulty components.

There is no schematic or service manual for the PWS4000. Itech Electronics is the ODM for this.

You didn't say what exact model or problem you are having.

To get an idea how the circuit works, check out the schematic for the BK Precision 1785B on this thread.

Also:

Tektronix Calibration Software

Tektronix Calibration Procedure

There is a few YouTube videos on troubleshooting.

I would check if the transformer is not burnt because of the wrong input voltage. Check if the protection diodes on the output isn't damaged.

[candrian]

Hi RomDump,

I really appreciate your will to help! Your info is very helpful.
It is a PWS4323 and while it was working fine one day I realized that it couldn't provide any current.

Here are some tests I performed:
PWS4323 set to 2V 1A, DC Load set to CC 2A the output of the PWS is 0.11V 0.436A (lower than the limit) !!
PWS4323 set to 27V 1A, DC Load set to CC 2A the output of the PWS is 1.83V 1.62A (higher than the limit) !!

I then probed the output using a scope



I opened the enclosure, I cleaned the dust (not much) and I started looking for a faulty part on the front end. The diode looks to be fine. While I measured the two capacitors on the binding posts, I didn't notice any strange numbers on ESR or capacitance values but I replaced both capacitors just in case. I reconnected everything and I run a few tests using my load and it seems now that it can give current but there are still some cases which is failing. For example if I set it to 30V 2A or 1A and I switch it on I get a saw tooth output. If I first set it to 10 or 20V and then while it's on go to 30V its working fine. It seems the issue is focused to voltages higher than 20V or something close to 20V. I'm not sure if the capacitor replacement did the difference or it was just random or it is correlated to something else I did without noticing maybe while cleaning? I used a soft brush and compressed air. 

Here is another probing I did once I replaced the capacitors and I set the output directly to 30V


Another strange thing that I'm not sure if it's caused due to the replaced capacitors is that while I have set the output for example to 20V and PWS measures it as 20V when I measure it with the DC load and cross check it with a DMM it's a bit higher eg 20.3V if I set it to 30V the difference will be even higher eg 30.7V. When I go to low voltages the difference is close to 100mV or less.

[RomDump]

Candrian,

Unfortunately I have limited experience working with the PWS4000 series. It look like a stability issue on the feedback path causing oscillation.  Sorry I can't help further.

[candrian]

While troubleshooting the PSU I'm probing here and there trying to understand how it operates and what may have broken. Removing the capacitors on the binding posts the output with no load is an AC voltage of around 4Khz with a DC offset so the waveform is all positive. I'm not sure if this is how the psu tends to regulate the voltage because when I place back the front capacitors this waveform is totaly cleaned out to a DC voltage. So it looks this could be a normal operation but if not, I may get a step closer to find what is broken.

Anyone with previous experience, could you please tell me if this is expected? Is the output of the main regulating transistors a clear DC voltage?