[Info-vax] MIcrovax 3100-98

[Michael Moroney]

kludge at panix.com (Scott Dorsey) writes:

>Michael Moroney <moroney at world.std.spaamtrap.com> wrote:
>>"Michael Kraemer @ home" <M.Kraemer at gsi.de> writes:
>>
>>>Dave Froble wrote:
>>
>>>> Then there was the AlphaStation 200 power supplies.  Dropped like flies.
>>
>>>does a cure exist? except calling DEC service?
>>
>>I replaced the power supply in one with a slightly modified (replaced board
>>connectors) PC power supply. Worked great.

>What fails in the AlphaStation supplies are mostly the output decoupling
>capacitors.  Just shotgun all the capacitors out with Panasonic 105C types
>and they'll work for decades more.

What actually happens when they fail? If I recall correctly the symptom
of a failing supply was it only happened when powering on, it would come on
for a few seconds (and appear to be OK) tben it would shut itself off.
Powercycle and it would repeat (may stay on sometimes initially)

Why do the caps fail, do they dry out? Underrated for the voltage present?

DEC always seemed to overdesign power supplies before then. I know the AS200
supplies came from an outside (PC?) vendor.

Aside: I have a VT220 which seems to have a similar power supply issue.
Symptom is when powered on it seems to be 100% dead as if no power or a fuse
is blown, but sometimes it would power on and be perfectly fine until powered
off.  "Sometimes" became less frequently and now it is "never".  Maybe some day
I'll dig it out and try to replace power supply caps, or maybe not.