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Williams boards colour issues

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Rasputin View Drop Down
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    Posted: 02 Aug 2020 at 8:20am
Morning gents, I've been testing some spare cpu boards since the early hours and need help!

A defender cpu board boots and runs but the screen is just displaying everything in red only.

On a Joust cpu board it boots and runs but seems to be missing the blue.

I know it's not monitor related so my question is are the colours driven on the cpu boards by specific transistors? All red on Defender meaning blue and green have failed and the lack of blue on Joust means the blue transistor has failed?

Any help would be appreciated as ive been awake way to long now!

Thank you..
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DanP Quote  Post ReplyReply Direct Link To This Post Posted: 02 Aug 2020 at 10:47am
Get hold of the schematics.  R, G, and B all have a transistor in the latter stages (I think it's a 3904 or 3906).  IIRC they are labelled Q1, Q2, and Q3.   Can't look at the moment to confirm which is which.  If these are broken you will lose a colour.

HTH

Dan
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rasputin Quote  Post ReplyReply Direct Link To This Post Posted: 02 Aug 2020 at 11:42am
I can't find the schematics for this early board revision 5770 09471-X4
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Post Options Post Options   Thanks (0) Thanks(0)   Quote chadsarcade Quote  Post ReplyReply Direct Link To This Post Posted: 02 Aug 2020 at 1:25pm
Check the obvious as well, the connectors on Wms boards often suffer from cracked joints, and tarnish which can lead to bad connections. Also the pins in the molex plug may need a scrape with a blade and check they still have some spring.

Other than that, as above I'd start with the output transistors and work back from there.

There are certainly schematics for both sets out there, try searching for Theory of Operation manual for both "early" and "late" revisions. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rasputin Quote  Post ReplyReply Direct Link To This Post Posted: 02 Aug 2020 at 1:48pm
So I've been checking the transistors and there are 11 ive checked so far.
3xrows of three and 2 lower down on their own.
I noticed the middle one on the second row is different 9016 not 8938 like the two either side of it. Could this be causing the all red output only?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote chadsarcade Quote  Post ReplyReply Direct Link To This Post Posted: 02 Aug 2020 at 3:28pm
It's probably an equivalent, easiest way to check would be to swap it for the corresponding transistor in the circuit for another colour and see if the problem moves.
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