DEC TU81 - "Logic Off" permanently illuminated-

Ulrich Tagge u.tagge at
Sun Mar 6 13:39:36 CST 2016

Hi All,

maybe someone can help me to bring my TU81 back to life again.

I have checked the following, before turning on:

- All capacitors on the Mail Power Supply and the one below the vacuum 
pump are fine
 > OK
- Voltages check
 > OK
- Fuses
 > The Fuse for the diagnostics power connector was burned: changed

Problem is, that the "Logic Off" is constantly illuminated, after 
turning on.

I had a look into the Tx81 Pathfinder documentation, and checked the 

- Check if Blower is running
 > OK
- Disconnecting all DC connectors
 > Same result

Pathfinder tells me changing the power supply.

I hear only an relay clicking when turning on the Power Supply, also, 
when nothing is connected, in this time the "Logic Off" light blinks one 

I think, that the power supply checks itself that the voltages are OK, 
and that this fails.

Any hints or tips?

Many Greetings

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