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Rohde & Schwarz CMU200

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_Wim_:

--- Quote from: _Wim_ on June 30, 2021, 06:26:20 pm ---According to your symptoms it does indeed seem a short circuit is present somewhere. So first thing to do it find the faulty module.

--- End quote ---

Screenshot from pag 112 of this service manual: http://gotroot.ca/cmu200/RS_CMU200_CMU300_other.pdf

arno:
Wim, thank you very much for your help, I really appreciate that. Today I had no free time to keep on the investigation but will come back asap.

Arno

arno:
Hello everybody,

today I measured all the voltages at the test points next to the LEDs. In the moment the unit powers off, there is a huge peak on the rails of 3.3V and 6V (my multimeter [Keysight U1272A] peaked 28V). Have not yet measured with the scope. Took the whole PSU apart, but there are no visible faults at all.

Arno

_Wim_:

--- Quote from: arno on July 01, 2021, 05:21:23 pm ---Hello everybody,

today I measured all the voltages at the test points next to the LEDs. In the moment the unit powers off, there is a huge peak on the rails of 3.3V and 6V (my multimeter [Keysight U1272A] peaked 28V). Have not yet measured with the scope. Took the whole PSU apart, but there are no visible faults at all.

Arno

--- End quote ---

I would try to remove all plugin modules and see it the motherboard boots. If the rails are ok before it turns off, my guess would be this is only a turn off glitch with no actual power in it. When it boots with no plugin, reinstall one card at a time and check if it still boots with the added card.

Be sure to take pictures before removing cards, so you exactly know were everything goes when reassembling.

Ice-Tea:
Check all flatcables on the motherboard. A half unplugged cable has ruined my day once or twice in these machines.

What I've also seen to result in startup issues: the front (computer) module has a fairly weak fan that goes bad and seizes after time. The elcos on the board dry out, behaviour becomes eratic. Often visible cap damage. Worth checking out.

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