2235 AN/USM-488 power supply low voltages


richardallred@...
 

I bought this scope earlier this summer as new old stock, never powered on. Due to covid illness I never opened it until a week ago. The scope powered on ,but the trace only covered about 2/3s of the screen and was jumping all over.

After it was warming up only got worse, I decided to check the voltages on the power supply and all were low.

So I did a full recap (caps are still old even though the scope has zero hours) and also replaced the following:

VR 901
Q935
Q946, 947
Q9070
R888,889,890,891,892
R900
and the ac filter
all 3 rifa x class caps


Same problem still exist

Voltages as follows


+5.2=4.3
+8.6=7.4
-8.6=-7.3
+30=+25.8
+100=+87.8

resistance to ground;

+5.2=188oms
+8.6=129.8 ohms
-8.6=81 oms
+30=552 ohms
+100=16k ohms


also the trigger led blinks when the scope is on. I have been reading all the power supply post here and frankly, I'm stumped

This is my first attempt a troubleshooting a switch mode power supply. any and all suggestions would be greatly appreciated

Thanks in advance
R A

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