Tektronix DPO\DSA 70000 series Artesyn AFE 1200 Power Supply repair.

[smaultre]

Hello guys it looks that i acquired the scope from https://www.eevblog.com/forum/testgear/tektronix-dpo70804-oscilloscope-and-acquisition-error-code-321 theme.
And i makes it works OK.
No errors, and SPC is PASS.

But after some hours of powered ON than shutting down witn WINPC, it randomly stops to turn ON.
After some research a found that PSU Artesyn AFE 1200 goes to protective mode (red led).

Now i'm diagnosing the PSU separatelly. Due to high cost of whole scope.

And what i see:
-after connecting to 110V line, its randomly goes into protection\failure mode.
-if so it starts to operate about 0,8-1 sec and goes "red".
- after that, when i quickly (without full cap discharge) re-connect 110V line it's starts, and works well like new.
- when i wait 1 minute for cap discharging sometimes it starts, sometimes goes "red" state.

Whats i'm already try:
- to add capacitance on "hot" and "cold" side, check ESR all looks OK
- ESR check capacitors on power FET's driver side is OK
- ESR check capacitors on cpu/controller side is OK

This PSU is complicated maybe somebody knows the right diagnostic steps, or maybe you know these type of malfunctions?

[squadchannel]

bootstrap caps?

[smaultre]

These are checked, there's no bootstrap caps, looks like a transformer -driven mosfets.

[calibrationfixture]

Hi smaultre,

The 3 Resistors (left from the Big Fat Fuse) don't look good. Color coding vague? Darkened PWB?

Calibrationfixture

[smaultre]

Yes, this resistors are powering stand-by & controller circuits.they looks like a load for the AFC stage they are OK

[smaultre]

Hello, guys this time spent to find an adequate load. And i find a (1400)700W hairdryer..
It starts every-time with this load without  any troubles.
But it not starts so smooth with scope hardware (scope hardware is 100% OK, tested with another PSU), i need to check 12V rail line now.