Harlequin 128K 2D not showing any video signal

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shadow338
Posts: 12
Joined: Tue Mar 29, 2016 7:56 pm

Harlequin 128K 2D not showing any video signal

Post by shadow338 »

Hello,

I built the 48K version a few years ago and it worked like a charm.
Now it was time to build the 128K version but strange enough I get no video through the composite output. (I have no RGB cable to test).

I checked the voltage of the Z80 and it looks fine (5v) but it seems more related to the video circuit which I have no clue why it's not working.

Any help is very much appreciated.

Thanks in advance!

H.
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1024MAK
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Re: Harlequin 128K 2D not showing any video signal

Post by 1024MAK »

I’ve moved your post to the Sinclair ZX Spectrum Hardware section.

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

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Tiger
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Re: Harlequin 128K 2D not showing any video signal

Post by Tiger »

Meanwhile I've built three Harlequin 128K 2D. There are much soldering points at the pcb and little mistake can result in a problem as you described. First I would check all the soldering connections. Are the jumpers correctly set? Is there absolutely no signal on your Monitor (still as not connected)? Is there a signal when you crap the signal direct from C28? Also there could be a problem with the AD724 (U48) proof the connection of this SMD part. I bought a pcb with a presoldered SMD but one connection of it wasn't good, so I had to resolder it (a very tricky thing because I've no special SMD-equipment) :evil: .
Last edited by Tiger on Sat Sep 18, 2021 10:55 pm, edited 1 time in total.
shadow338
Posts: 12
Joined: Tue Mar 29, 2016 7:56 pm

Re: Harlequin 128K 2D not showing any video signal

Post by shadow338 »

It was a dry pin on U24. After soldering it the computer started working. Thanks!
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Tiger
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Re: Harlequin 128K 2D not showing any video signal

Post by Tiger »

Thank you for the feedback :D
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