Tek492 blank CRT. Please help

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pjwalczak
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Joined: February 13th, 2017, 5:41 pm
Country: Thailand

Tek492 blank CRT. Please help

Post by pjwalczak » February 13th, 2017, 5:52 pm

I have an old Tek492. Bought it second hand, but was working fine
for a couple of years. Today when I have switched it on, after a long
break (almost a year) - it powered OK, all controls seems to be ok,
but there is nothing shown on the CRT.

Can anybody share some tips what can be done to find the cause
and fix it ?

w2aew
Tektronix Applications
Tektronix Applications
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Joined: December 2nd, 2008, 2:27 pm
Country: United States
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Re: Tek492 blank CRT. Please help

Post by w2aew » February 14th, 2017, 4:52 pm

The first thing to check would be all of the power supply voltages. Common failure modes for this vintage of equipment are failed electrolytic or tantalum caps - of course when they fail, other devices can be victims.

pjwalczak
Posts: 2
Joined: February 13th, 2017, 5:41 pm
Country: Thailand

Re: Tek492 blank CRT. Please help

Post by pjwalczak » February 15th, 2017, 12:12 am

Well, I pulled out the PSU. If to believe markings on caps, almost all are
from 1979! It is plain unbelivable that it was working fine until now.
My props to people who build this marvel. The question is if you can buy
today capacitors that would last for another 38 years of service...

I understand that I would need to look for e-caps low/ ultra low ESR,
rated 105C. For sure all small radials will need to be replaced
220uf/10v x 1
1uF/350V x 1
2.2uF/200V x 6
100uf/25v x 2
22uf/25v x 5
10uf/25v x 1
not sure about big fat caps
750uF/200V 85C x 2
and medium yellowish silver
250uf/20v x 8

Practical question, how can I test PSU removed form the unit ? Also,
where are test points to measure the output voltages from the PSU ?

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