HP54720D debug, potential power supply issue

[sirloin]

Hi, about 7-8 years ago I bought a used HP 54720D. It has been working great with very light use.

A couple months ago I went to turn it on and just got a blank screen colour background appeared but no controls. I didn't have time to deal with it then so I left it for another few weeks.

Now there is no power when I try to turn it on, nothing comes on. I took it apart to look at the power supply and noticed that there are two thermal fuses(?) that were open. I bought a set of replacements and installed them, plugged in the power supply and it instantly blew them again.

So the fuses are not the problem, merely the result of some other failure. Has anyone had any experience with one of these power supplies?  These seem to be on a standby power rail of some kind, as they blow as soon as I turn the master switch on. I also have the power supply completely removed from the system while testing.

I have attached some images of the power supply, it is a Yokogawa PS495-0101. I saw one on e-bay, but it costs about $200USD with shipping so I wanted to try some other things first.

I did try measuring some caps, none seemed to be bulging, but it seems impossible to measure them in circuit.

I was hoping for some suggestions or that someone else had some experience with these power supplies before.

Thanks!

[gomezj]

Hi,
I have the same problem, Did you repaired finally?
What is the source for the resistors/thermal fuses?
Thanks in advance!
Thanks!

[weakbit]

Hello,
I've the same HP54720D Oscilloscope - interest with the same issue the 2pcs 22Ohm Resistors are interrupted. And I found out that the Transistor part 50 (2SC3866) is also defect. The Location is near by part 54 - maybe are the Resistors around are also defect. I've no service manual maybe you have one so I can search again.
Update 23.10.2021: A defect Z-Diode was found part 57 but I don't know what this voltage will be? Do anyone know what is the voltage of this 57 Z-Diode?
Please tell me more about your repair - I would like to repair my HP54720D again because for such a money (USD1300,- at eBay + USD300,- Postal Service + Import TAX all in all I've paid €1800,-) I never get a Oscilloscope like this.
Best Regards
weakbit