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Tektronix 465m - bad LV power supply?

I just got a used Tek 465m. It worked perfectly when I tested it, and then a couple more times after that. It would then intermittently not turn on (although the screen illum would still work). Now, it consistently won't turn on (still screen illum, tho).

I have opened it up and tested the +5/-5/+32 leads in a couple places on the board, and none show what they should:

+5 = -0.11 V

-5 = -0.05 V

+32 = -0.04 V

there is some, but very little, variance in the above numbers over time/tests.

i'm a beginner repairing electronics, but i have the feeling this is a simple repair -- the thing worked perfectly until a couple days ago... could it be something as simple as a busted cap? i have the owners/ maintenance manual with lots of diagrams in it (although, it seems, none of the power supply circuits). could anyone point me in the right direction to solve this problem? any help would be appreciated! thanks,

gabe schine

Reply to
gabeschine
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gabeschine wrote in news: snipped-for-privacy@i13g2000prf.googlegroups.com:

well,first check to see if any internal fuses are open,the 32 unreg has a fuse. it could be bad electrolytics;they dry out with age or their ESR rises and the raw,unregulated supplies are not high enough for the regulators to work.

TEK PS supplies all reference to one supply,and use pullups so if one supply dies,they all go out.

HV multipliers are prone to fail,too;that's the black box with a heavy red lead that goes to the front of the CRT.

Google for BAMA and download a service manual for the scope so you will have schematics to work from.

--
Jim Yanik
jyanik
at
kua.net
Reply to
Jim Yanik

innews: snipped-for-privacy@i13g2000prf.googlegroups.com:

Thanks - got the schematics. Tested all the fuses I could find (4 of them) and they all check out.

Your ref to the PS - does this mean that if the PS dies, I would see anything from the Scale Illum. feature? That's the only part of the scope that still works when power is on.

Now I need to go and learn what everything you said means :). Thanks again

Reply to
gabeschine

gabeschine wrote in news: snipped-for-privacy@l22g2000prc.googlegroups.com:

I hope you got the circuit descriptions,its VERY handy in learning about how your scope's circuits work.A great aid in troubleshooting. TEK used to write very good circuit descriptions for their instruments.Not anymore.

One more thing,TEK regulated power supplies often use "foldback" current limiting;where when one supply gets overloaded,it *shuts down* that supply instead of simply limiting it's current output. Since that supply may be used in some of the other regulated supplies,they ALL drop in voltage.

--
Jim Yanik
jyanik
at
kua.net
Reply to
Jim Yanik

innews: snipped-for-privacy@l22g2000prc.googlegroups.com:

...

The manual can be downloaded from this site:

formatting link

Circuit Descriptions should be in this file, AFAIR.

hth, Andreas

Reply to
Andreas Tekman

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