Search found 448 matches

by gozzo
Sat Aug 06, 2011 9:18 pm
Forum: Hardware
Topic: ZX81 Video problem
Replies: 10
Views: 3821

Re: ZX81 Video problem

You will need a can of 'freezer spray' - one at a time, squirt the middle of chips inside the zx81 (don't get it on the keyboard membrane tails, though, it will make them brittle and crack)- including the regulator - to see if it makes any difference - when it does, thats the dodgy chip! , if not , ...
by gozzo
Fri Aug 05, 2011 9:06 pm
Forum: Hardware
Topic: ZX81 Power supply specs
Replies: 17
Views: 8835

Re: ZX81 Power supply

Before trying your zx81 out for the first time I would advise carefully opening it up to see if the keyboard membrane 'tails' are ok, and then check if any of the chips are in sockets - if so, carefully remove each chip, squirt the chip pins and the sockets with a good contact cleaner which has a lu...
by gozzo
Fri Aug 05, 2011 8:56 pm
Forum: Hardware
Topic: ZX81 Power supply specs
Replies: 17
Views: 8835

Re: ZX81 Power supply

It should be possible to pick up a genuine zx81 psu eventually as they do turn up on various 'auction' sites now and again - just look for the 1.2 amp version not the older 700mA (0.7amp) version! Unfortunately I cant supply you with one as I only have one 1.2amp type ,and I am keeping it, otherwise...
by gozzo
Fri Aug 05, 2011 8:51 pm
Forum: Hardware
Topic: ZX81 Power supply specs
Replies: 17
Views: 8835

Re: ZX81 Power supply

No, thats just the MAXIMUM amount of current you can draw from this PSU. The zx81 uses quite a bit less than this, just don't use a power supply with a current rating LESS than 1.2amp, especially if using the ZX printer or some other add-ons as it will overheat that PSU.
by gozzo
Fri Aug 05, 2011 8:41 pm
Forum: Hardware
Topic: ZX81 Power supply specs
Replies: 17
Views: 8835

Re: ZX81 Power supply

The lower one - which shows the positive (+) going to the 'dot' in the diagram. Although I said some add-ons need a bit more than 9v, do NOT be tempted to try the 12v setting as it is as this will probably cause the zx81 regulator to overheat, and maybe kill your add-ons, unless you wire in 1 or 2 3...
by gozzo
Fri Aug 05, 2011 7:34 pm
Forum: Hardware
Topic: ZX81 Power supply specs
Replies: 17
Views: 8835

Re: ZX81 Power supply

Set it for 9v with a positive 'pin' /'centre' polarity and it will probably be ok, - but - if using some 16k rampacks(cheetah, viscount, not sure about the sinclair ones, maybe some others), they may need a slightly higher voltage - about 10 to 11v - to work (the zx81 psu actually produces a bit mor...
by gozzo
Sun Jul 31, 2011 5:38 pm
Forum: Sinclair Misc
Topic: No pcb serial Numbers, so any Lists of provenance?
Replies: 5
Views: 2633

Re: No pcb serial Numbers, so any Lists of provenance?

Never seen a 2C158E ULA, but plenty of the other 2 - the 2C184E version seems to fail more than the 2C210E version (have several '81's with duff 2C184E ULA's but never yet some across a duff 2C210E! :) ) As for 'buggy' ROM - there is a software test you can do to find out which it is (although not a...
by gozzo
Mon Jul 11, 2011 10:45 pm
Forum: Hardware
Topic: Dodgy RAM pack
Replies: 9
Views: 2830

Re: Dodgy RAM pack

First thing is to check the three supply lines to the 4116(or equivalent) RAM chips - I've been told they're very touchy about voltages and whatever line powers up before the others! If any chip gets hot enough to make you swear when you touch it, it is definitely duff! I think the most likely probl...