开云体育

Hi Craig :
The Cap for 5V light checked O! the may be some short at Front panel interface board ? from the switch boards shielding !
I may need to disassembly the front panel to clean the switch boards !
RegardTony CheungAPR 27 2018

From: Craig Sawyers <c.sawyers@...>
To: [email protected]
Sent: Wednesday, April 25, 2018 10:14 AM
Subject: Re: [TekScopes] 7904 Mainframe damaged

Tony,
If all you can draw is 100ma on 5v lights, you could have a problem with that power supply's pi
section
filter - I had to change C1318 to get my PSU up. It measured 40uf instead of 100uf. That cap may be
right on the edge of failure at certain loads. There are also 2 other caps in that filter - C1316,
C1317.
Note that 5v lights is not regulated on the LV regulator board - it just goes through the board to
the
connectors - so the problem is localized to the cap rectifier board.

I would first change C1318 with any 100uf cap (doesn't have to be tantalum to just test). And, do
the
same sequentially for the other two - swap out then test. They're pretty easy to change.

OK - I've been on vacation in Australia for nearly 3 weeks, and this thread was running before I left!
So I deleted the zillions of mails on this topic, and my comment might well have been already covered.

The 5V lights is sensed by the Inverter Control chip, U1275. It is added to other signals via R1304.
If resistors around that area have changed value, the 5V lights sensing could be trigger happy.

This was probably identified as a problem area, because two different values are in the parts list -
9k31 for pre B181294 and 8k45 after.

Craig