1040 STF Video Problem

[Colleton]

I'm having a couple of problems with the color output of my 1040 STF  Since I've owned it, the color output has had "engraved" looking vertical lines in it.  More recently, it has been turning blue/green, as though the red component was dropping out. This was intermittent at first, but has become constant  FWIW, the monochrome video output is perfect.  No lines and obviously no discoloration.

 

I've tried several different video cables purchased on ebay (one VGA and two SCART cables), an OSSC and a cheap SCART->HDMI converter.  The OSSC will display the blue/green image when using the VGA input, but nothing when using the SCART input.  I get nothing out of the SCART->HDMI converter either.

 

I've re-seated the Shifter chip and after looking through a schematic have ordered some transistors and resistors from Digikey.  I ordered the 74LS373 D-Latch and 74LS244 Buffer chips that feed the Shifter as well.

 

the schematic I found is for a REV C board.  Does anyone have a schematic for a REV D board?

 

I really don't want to tear into this machine.  Does anyone have any advice or ideas?

 

 

[tjlazer]

The first thing you should do is tear into it and reseat all socketted chips.

[ParanoidLittleMan]

Losing RED color most likely happens after shifter chip - on it's way to color encoder/video out connector. Probably dry soldering. Maybe transistor for amplifying it is what breaks.

Revision of board is really not relevant. Video circuit is same in all STs. Just get schematic and look section around RF modulator - there will be 3 transistors for 3 colors, video connector.

Btw. feeding shifter (those LS chips) would not cause error like this. To fix soldering problem need to have access to bottom of mainboard. Same for replacing transistor or something else. And that's ideal to get rid of some dust ?