Thread: Zx81
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Old 22nd Apr 2020, 10:58 pm   #280
SiriusHardware
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Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,482
Default Re: Zx81

Yes, fantastic job if that was your first time doing a major desoldering job, and with a manual solder sucker as well. I confess I thought you had bought an 'electric' one.

As always, try the simple stuff first. Carefully remove the new ULA from the socket and make sure none of the pins went heading off in the wrong direction, ie, got folded over, when the device was inserted. It's very easily done, still happens to me occasionally even after 40+ years of doing this kind of thing. Is the IC socket you fitted an 'ordinary' socket, or a turned-pin type? Turned-pin sockets are great but the IC pins all have to be arrow straight otherwise it can be very difficult to get the IC in.

If all looks OK we'll come up with a list of things to measure from and to to see if there are any missing connections from the ULA socket to anywhere else.

Sorry to have to ask: But you did solder that apparently unsoldered pin that I pointed out? Something like that would definitely cause a problem like this.

Also - I'm assuming you have already tried this - does it behave any differently when the RAM pack is not plugged in, so it's just the bare 1K machine?
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