[PPRAANet] Opinion on failed power supply

[Dennis N0ABC]

My 2¢:

Sounds like you've done enough testing/troubleshooting. What my 
attention is drawn to is the copyright date of that schematic being 45 
years ago. Since you obviously wish to bring it back to life, and expect 
the CRT to still be viable, I would suggest the replacement of the those 
caps you mentioned, plus any other electrolytics especially, and any 
other components that you could even remotely suspect of being 
age-deteriorated.

I'm thinking I may need to replace a lot of capacitors and other 
components in this old human chassis of mine. Trouble is, I can't find 
my schematic. And, I don't want to divulge the copyright date!

Good luck!

Dennis

On 2/27/2021 10:50 PM, GEORGE W SHAIFFER wrote:
> Attempting to fix problem with an old heath kit 'scope.  Beam is not visible, verified crt filament is good, 1375V HV is good.
> Mid-voltage supplies are about 40 V low.  Circuit is a FW two diode rectifier with R C filters.  Voltage from Rectifier is rated 250 VDC
> with 100 uF 300 WVDC capacitor  feeds a series 500 ohm 10W resistor that becomes the 160 VDC source with another 100 uF 300 WVDC
> capacitor forming a Pi filter.  Supply has a 10 K ohm 10 W bleeder resistor across the second cap.  From the 160 V DC supply a 533 ohm
> resistor and a 300 uF 175 WVDC capacitor forms the 135 VDC source.  160 V source measures around 120 t0 125 V DC and the 135 V
> source is around 105 V DC.  Schematic shows copyright date of 1975 and my thought is that the 3 section electrolytic capacitor has dried out
> from age and is not capable of charging to required voltages.  No sign of leakage or excessive current anywhere and I am considering replacing the 3 section 100uf, 100 uf, 300 uf caps with individual caps at rated value and at least equal or greater than rated WVDC.
> 'sope did work for several hours before the loss of trace problem happened.  I have all manuals and diagrams.
> Finally the question:  Does my diagnosis and decision to replace the caps seem reasonable or should more testing be done.  I do have an
> old (similar vintage) capacitor checker that seems operational so I can check the filter cap values but lots of de-soldering will be required.
>
> Thoughts?  Suggestions? Other ideas?
>
> George W Shaiffer
> KE0QCC
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-- 
73

Dennis Major, N0ABC
Laurel ARC VEC, Regional Coordinator #10 / Ø
(CO, IA, KS, MN, MO, ND, NE, SD)
Pikes Peak Radio Amateur Association VE Team Leader