HP 33120a Transformer Issue

[opamp2580]

Hello, I recently bought a used HP 33120a for cheap, because it wasn't outputting anything. I knew that that was most likely caused by a blow output fuse, which turned out to be correct. So its working now, but the output waveforms didn't look particularly clean. So I did some probing and discovered considerable ripple on the DC supplies. And it's everywhere- on both the outputs AND inputs to the linear regulators. I went ahead and replaced the electrolytic capacitors for the various supplies, but that had no effect on the ripple. So I checked the output of the transformer and it looks like its saturating. When I unplugged the transformer from the main board, the wave looks more or less normal. So I'm wondering if the transformer is in fact faulty. I've already looked for a replacement, but can't seem to find one, so I was also wondering if anyone knows what voltages the transformer is supposed to supply; the service manual doesn't specify, at least that I've been able to find... I might have to try to find a different transformer (or transformers) that output the correct voltage. I attached pictures of the output of one of the taps on the transformer (the red wire), as well as some examples of the ripple on the output of the regulators. Thanks!

[alm]

Did you check the bridge rectifiers? If one side is open, then it's effectively doing half-wave rectification, which produces more ripple.

[George Edmonds]

Hi

Testing transformers can be a complex matter, but I would suggest that you disconnect the secondary loads and then check for the transformer temperature rise whilst on power over time, if it is saturating it will get very hot.

Do you have the primary mains voltage tapings set correctly?

G Edmonds

[jonpaul]

60 Hz mains frequency not ripple

Check for open return or earth in PSU or wiring

j