[Info-vax] MIcrovax 3100-98

[Bill Gunshannon]

On 11/2/19 11:08 AM, Michael Moroney wrote:
> 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.
> 


As long as we are talking power supplies, does anyone know anything
about the power supply in the VXT 2000+?  Mine has died and I was
wondering what the chances were I could replace it with a PC power
supply.

bill