pm 3055 scope , power supply problem

[frankhertog]

Hi guys,
I encountered a nasty problem with my PM 3055 scope, one time not starting and the next moment perfectly working. the problem: after starting the scope the power supply goes in the protection mode (no display and a high pitched sound). the triac in the 48v circuit is conducting so the 48v + and - are clamped and the output of al the voltages are near to zero. I made a dummy load as described in the service manual. after connecting this to the power supply the problem was sometimes gone and sometimes not. Some of the condensors showed expansion and I suspected short circuit in a condensor that repaired after restarting and applying tension to the power supply. next I exchanged the condensors of the power supply and the problem was gone for about 2 years. Again mounted the dummy load the problem stayed. Clamping the gate of V6112 to -48V to prevent the triac going into conduction so I could test the system without the protection coming in action was not successful. after close inspection of the board I saw that the triac was touching the casing of the nearby transformer 6001. after creating a gap between the triac and the transformer the problem was gone and the system functioned correctly.

[george.b]

Interesting. My PM3055 does that sometimes. I shall take a look.

[Shock]

http://ftb.ko4bb.com/getsimple/index.php?id=manuals&dir=Philips
Philips PM3055 60 MHz Dual Time Base Oscilloscope Service Manual

Page 9-5 on the power board V6101 V6102? look really close to T6001 is that what you are talking about? V6112 looks like quite a gap on this example.