Hi Yves
As far as HP/Agilent are concerned power supplies are an unmentionable subject, especially after they started using third party ones.
If as suggested this is a switch mode power supply they usually follow a standard layout and by consulting the IC manufacturers data sheets a grate deal can be deduced regarding the individual design, especially as despite the name on them they are normally of Chinese origin.
A serious word of warning, what appears to be the switching/control circuitry common is NOT at 0V but is frequently at about 170 VDC from a low impedance source. A Mains isolation transformer must be used to work on them live and even then one hand must be in a pocket.
May I suggest that you check the value of all resistors above say 10K prior to the switching transformer, you should find a high valve resistor (200K+) from the main storage capacitor to the switching stage, this frequently goes high and produces exactly the problem that you have.
Above all take extreme care around SMPSU's, there are lethal voltages present where you may not expect them to be.
73 George G6HIG
________________________________________
From: hp_agilent_equipment@... <hp_agilent_equipment@...> on behalf of tardz99@... [hp_agilent_equipment] <hp_agilent_equipment@...>
Sent: 29 October 2017 19:55
To: hp_agilent_equipment@...
Subject: [hp_agilent_equipment] hp8770A. power supply problem ITT PowerSystem, PEC 3959 rev K
Hi,
I have an arbitrary 8770a generator that worked very well, but suddenly it broke down. The problem is the power supply and it is really big. I did some basic tests:
- no fuse blown
- no short circuit on the power lines
- the power supply lines comply with the impedance specifications
- all internal power resistors have good values
- all diodes tested are good
- no transistor short circuit and are tested OK
- no electrolytic capacitors tested were short circuits
- thermistor, varistors and overload protection circuits are OK
- when powering up, DC input voltage was correct
- no damaged components or PCBs
The source of the failure is probably the controller or the monitoring circuit, there are many integrated circuits, but without a schematic, it will be very difficult to find the source of the problem. I have the electrical diagram of the 8770a except that of the power supply. So I'm looking for this schematic without much hope unfortunately, it's from ITT PowerSystem, PEC 3959 rev K ... if anyone ever has a copy available it would be really good.
Thanks !
Regards
Yves
