HP 3562A Signal Analyser with broken power supply : need help

[psykok]

Hi,

I got the first replacement part: the big diode:



After replacing the diode, I turned the PSU on and again a failure but an other one.
This time the bias part was broken, I had to replace all +/-12v regulator.

Now everything is again back, I have all output on the right value and the 5v is 5.1v and no more 4.7v.

The strange thing is that the psu is making some little whistling sound ... normal or bad sign?

Alex

[Richard Head]

If it's whistling I would put a scope on the DC output to see if it's a voltage control loop instability or just noise in the control loop.
I presume you used exactly the same output diode?

[psykok]

If it's whistling I would put a scope on the DC output to see if it's a voltage control loop instability or just noise in the control loop.
I presume you used exactly the same output diode?

Yes it's exactly the same diode.

OK will check it with the scope, I had no time yesterday evening to do more investigation.
For me the noise is coming from T3 in the bias power supply section, I have to check it to be sure.



Alex

 

[perlmonkey]

Did you make any progress on this? I have a 3563A which I bought "as is" from eBay; resurrected the CRT but the 7805s keep blowing and it has a ROM issue.
I also have a 3562A which was working fine... then I moved to a new house and now it doesn't work; all LEDs light up but don't turn off, no CRT now. Sigh.

[psykok]

Hi,


I don't made any progress on this 3562A, the power supply is working (I have all right voltage at all outputs) ... only in test mode (without charge)
If I charge the psu the power diode (the one I replaced) is getting very hot until braking.

Unfortunately after many ours investigation I still not found any solution.
The only evidence I have is the strange whistling sound coming from the primary transformer.

I have also fixed the broken crt on this instrument, a transistor was broken on the psu board.

By chance my second 3562A is working pretty good without issue


Did you checked the psu on you 3562a to be sure that the startup signal generated by the psu is present?



Alex

[katzohki]

...
The only evidence I have is the strange whistling sound coming from the primary transformer.
...

Uh oh. Could be arcing internal to the transformer.

[psykok]

...
The only evidence I have is the strange whistling sound coming from the primary transformer.
...

Uh oh. Could be arcing internal to the transformer.

Yes it could be
Honestly the transformer is one of the last component which I have not realy tested in this psu.

Is there any way to check if this transformer has a problem ?

Alex

[katzohki]

...
The only evidence I have is the strange whistling sound coming from the primary transformer.
...

Uh oh. Could be arcing internal to the transformer.

Yes it could be
Honestly the transformer is one of the last component which I have not realy tested in this psu.

Is there any way to check if this transformer has a problem ?

Alex

Well the easiest would be to compare a known working one. See if the output voltages match, winding inductance and resistance etc... Or even better, swap it. If it's arcing through when running it might not look like a short when testing at low voltages. Basically you need a Megger or HiPot tester I think.

The other thing to do I guess would be to take it out of circuit and simulate its output. Or at least simulate the various DC power lines.

If you can find out all the parameters of it from the service manual I guess it could be replaceable.

[almstsobur]

     Hey guys, my first post on the EEvblog, been a browser and YouTube watcher for a while. But I thought I needed to chime in here. I ran across this thread searching for a solution to just about the exact same problem, my 3562a also fails the same 3 scope patterns. I also think I have at the least an issue with the same 2 diodes, at least that is where my troubleshooting has ended until those parts get in. However, if someone else besides myself runs into this thread, like I did, I'm pretty sure you have the wrong diode.

      It looks from the picture that the diode you selected is the 85HFR120, however the original diode is a Schotty, also the forward voltage is 600-800mV on the original with the HFR being 1.2V, most of all I have attached a picture of my original and on the picture you have posted, the anode/cathode are in the wrong direction. Please correct me if I am wrong, but I hope this helps the original poster, or maybe someone who comes along this thread later. I have ordered the MBR7560 by GeneSiC Semiconductor as I think it is almost an exact match.

-RP

[almstsobur]

Just a quick follow up; the MBR7560 Diode's did infact work perfectly and my 3562A is fully functional again.

-RP