Hi,
I'm looking for a bit of help with a faulty spectrum.
I've been given an Issue 2 48K Spectrum with a PSU fault. If I connect it briefly to a bench PSU it hits a current limit of around 800ma. I've not kept it on for more than a few seconds as I don't want to inadvertently damage anything more. I suspect the problem is likely to be a faulty chip and/or an issue with the +12/-5V generator.
Before I wade in, is there a good way to diagnose the likely issue ? I would usually apply the power for a while and see what chip(s) heat up but it would be good to get a steer if there is something more systematic I can do - and avoid damaging anything more if possible.
Thanks,
Andy.
Issue 2 - PSU fault
Re: Issue 2 - PSU fault
Are any of the major components in sockets? Popping out any that are would be an obvious first step.
Derek Fountain, author of the ZX Spectrum C Programmer's Getting Started Guide and various open source games, hardware and other projects, including an IF1 and ZX Microdrive emulator.
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Re: Issue 2 - PSU fault
Yes there are things you can do.
But first, what (if any) chips are in sockets?
I'm presuming you can solder and desolder, and have a digital multimeter? Apart from the bench PSU, do you have any other test gear?
Fault finding may involve either track cutting or cutting chip pins, are you okay with this?
Mark
But first, what (if any) chips are in sockets?
I'm presuming you can solder and desolder, and have a digital multimeter? Apart from the bench PSU, do you have any other test gear?
Fault finding may involve either track cutting or cutting chip pins, are you okay with this?
Mark
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Re: Issue 2 - PSU fault
Hi Both,
Thanks for your couple of replies. Pulled the ROM and ULA, earlier today, which were in sockets. Overcurrent limit stopped tripping and, long story short, the ULA 5C112 appears to be faulty.
I've now replaced on a temporary basis with a 6C version from another spectrum. The machine now powers up and get to the (c) message; however, there appears to be another fault. As soon as I press a key, the keyword token is displayed and them the spectrum tries to reset. It get part way through the reset and the screen displays a largely black paper with a single vertical white line in each character cell.
I suspect this is a lower memory fault and I'll try to get the retroleum ROM loaded for a more complete memory test. But if there are other potential faults then it would be good to know!
@mark - my electronic skills are reasonably good and I'm fine cutting tracks and desoldering chips etc. I've also got a bench scope etc.
Andy.
Thanks for your couple of replies. Pulled the ROM and ULA, earlier today, which were in sockets. Overcurrent limit stopped tripping and, long story short, the ULA 5C112 appears to be faulty.
I've now replaced on a temporary basis with a 6C version from another spectrum. The machine now powers up and get to the (c) message; however, there appears to be another fault. As soon as I press a key, the keyword token is displayed and them the spectrum tries to reset. It get part way through the reset and the screen displays a largely black paper with a single vertical white line in each character cell.
I suspect this is a lower memory fault and I'll try to get the retroleum ROM loaded for a more complete memory test. But if there are other potential faults then it would be good to know!
@mark - my electronic skills are reasonably good and I'm fine cutting tracks and desoldering chips etc. I've also got a bench scope etc.
Andy.