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jay_oldstuff · 6th Aug 2017, 5:11 pm

You should see 3.5mhz at the cpu pin 6. Also do you have a logic probe? if not very easy to make its just a couple of led's and transistors, have a look at example 3 hear for a simple one to make http://www.eleccircuit.com/many-logi...circuit-ideas/ with this you can have a look see what is running on the ULA CPU RAM and ROM. Im hopeing its somthing other than the ULA. least all your IC's appear to be socketed.

Jay

6th Aug 2017, 5:11 pm	#57
jay_oldstuff Octode Join Date: Jan 2005 Location: Hyde, Greater Manchester, UK. Posts: 1,074	Re: Sinclair ZX81 You should see 3.5mhz at the cpu pin 6. Also do you have a logic probe? if not very easy to make its just a couple of led's and transistors, have a look at example 3 hear for a simple one to make http://www.eleccircuit.com/many-logi...circuit-ideas/ with this you can have a look see what is running on the ULA CPU RAM and ROM. Im hopeing its somthing other than the ULA. least all your IC's appear to be socketed. Jay __________________ The light at the end of the tunnel is probably the headlight of an oncoming train