Author Topic: Light pen screen alignment is out  (Read 1083 times)

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Offline JohnElliott

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Re: Light pen screen alignment is out
« Reply #20 on: 01:02, 15 May 18 »
My guess would be that the problem is in the hardware of the light pen interface.

I think any diagnostic program would need machine code to get an adequate response time.

Offline Starglider

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Re: Light pen screen alignment is out
« Reply #21 on: 01:40, 15 May 18 »
My guess would be that the problem is in the hardware of the light pen interface.

I think any diagnostic program would need machine code to get an adequate response time.
Thank you. I'm wondering if an aging resistor might be a cause in the serial box.

Thanks!, Starglider aka ԹҽɾíƒɾɑϲԵíϲ's RҽԵɾ๏ RҽϲíԹҽs
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Offline Starglider

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Re: Light pen screen alignment is out
« Reply #22 on: 04:59, 15 May 18 »
OK John, I've opened things up. Photos: https://photos.app.goo.gl/VRwa1uQGMpDOiUWo1 (you can zoom in far)


I think the chip at the top right is the counter. Motorola MC74HC4040.


Where would you start? Replace that chip? Replace the resistors first? Anywhere else?


The other chips are gates, trigger inverters, bus buffers.


(Also in the photos is the USA PCW adapter I have to use for the serial port. It's just a passthrough ribbon cable inside. Any chance this could be the cause of my woes?)
Thanks!
Starglider aka Perifractic
"Recordar es vivir"

Amstrad PCW8256 | Upgraded EME-232 DD Drive B
(Also Amiga, C64, Apple //e, Atari 400)

Formerly of The Blue Ribbon Soundworks – makers of SuperJAM! and Bars & Pipes for Amiga

Offline JohnElliott

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Re: Light pen screen alignment is out
« Reply #23 on: 12:40, 16 May 18 »
That level of diagnosis is way out of my league. I certainly wouldn't go replacing components without first having written the diagnostic program to check my guess about what the interface is doing.

Offline Chinnery

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Re: Light pen screen alignment is out
« Reply #24 on: 15:07, 16 May 18 »
Looking at the board, all the ICs seem to be 74xxx logic chips, which are reasonably common.
I know you've been known to take a hammer to a problem to fix it (literally)... perhaps you could use a proverbial hammer and change these ICs one by one? At least you'll know if it was hardware or software :)
Slightly more sensibly, I know my el-cheapo eprom programmer can check these logic ICs, so perhaps a less aggressive approach would be to take each chip out and test it in a similar programmer? Mine is a TL866CS which is freely available on ebay... and not let me down yet in retro rom programming. I haven't yet used it to test a logic chip yet though.

Offline Starglider

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Re: Light pen screen alignment is out
« Reply #25 on: 20:08, 16 May 18 »
Thanks guys!

Thanks!, Starglider aka ԹҽɾíƒɾɑϲԵíϲ's RҽԵɾ๏ RҽϲíԹҽs
http://youtube.com/perifractic
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Thanks!
Starglider aka Perifractic
"Recordar es vivir"

Amstrad PCW8256 | Upgraded EME-232 DD Drive B
(Also Amiga, C64, Apple //e, Atari 400)

Formerly of The Blue Ribbon Soundworks – makers of SuperJAM! and Bars & Pipes for Amiga