Sinclair ZX80 / ZX81 / Z88 Forums

Update - I have managed to buy another working issue 3 zx81. I have tested the rampack on this and this also appears to work correctly giving a longer white screen before the cursor appears when it is connected and powered on. So im guessing since the rampack didnt fix my issue the memory is good & ...

So the Ram Pack arrived and is now fitted. The screen now shows more than just a white screen as pictured below, although sometimes it still just shows the white screen. It looks almost like its showing the cursor but its just repeated and scrabled.

Kind of good news then i guess. I did think the A14 & A15 lines looked a bit strange. Ill assume the Z80 is good and wait for the ram pack to test further.

TEST 2 produced same on all other pins apart from the ones bellow

Pin 4 - A14 Pin 5 - A15 Pin 17 - NMI Pin 18 - HALT

Pin 26 - RESET Pin 27 - M1 Pin 28 - RFSH

Pin 19 - MREQ Pin 21 - RD Pin 22 - WR Pin 24 - WAIT Pin 25 - BUSRQ

So Ive already bid on and won an offical zx81 rampack before reading your post :-/ ...lets hope its ok. Ive tested the requested pins now 3 times powering off the zx81 inbetween each test. Test 1 & 3 produced the same readings Test 2 produced diffent on 4 of the pins i think. ZX80 Chip Test 1: Pin 4...

Thanks for the help. I dont have a ram pack but i will look to see if i can get one cheap, so that i can test with this. When using the ram pack im guessing it ignores the internal memory then? When you say control pins do you mean the pins mentioned in that post link? 16 /INT (should be pulsing) 17...

No worries, Happy to take pictures :-) I traced the line where the jumper LK1 links, and it appears to go from pin 18 of the 2nd Ram chip to a dead end, so im guessing its only used when having a different RAM chip configuration. 20190325_072535 - Copy - Copy.jpg 20190325_072535 - Copy - Copy.jpg

Hello, Ive recently been given my dads ZX81, its been stored in the loft for many years and had minimal use. I thought id get it out and have a little play with it, but sadly it isnt working :-(. The ZX81 powers on and produces a white screen on the TV, but i dont get the black cursor. The board is ...