Sinclair ZX80 / ZX81 / Z88 Forums

You can see the actual video output at ULA pin 16 See /RFSH at Z80 should be pulsing no matter what. To test the /reset must see it rising slowly from zero at start. If not just make a warm reset shorting it briefly to gnd (can do it at the electrolytic legs is just beside).. if /RFSH is not pulsing...

I recently had this 64K rampack From Microdigital, intended for the TS1500 Clone TK85. K64_01_0001.jpg (Ad From K64 #1 an Argentinian magazine from that time) IMG-20220821-WA0027.jpg The actual Pack Well its not working, I couldn't find any info on-line beside it's "uncommon" It has 8 NEC 4164 RAM I...

1024MAK wrote: ↑Mon Aug 01, 2022 5:21 pm Note, the post above has been edited

Mark

Thanks !

My partial schematic here: https://www.dropbox.com/s/pp72uif115i9uj1/captura%20de%20pantalla%202022-07-24%2021.39.01.png?dl=0 It's a screen capture.. I'm not an expert with this CAD, or any one... This computer has no ULA so the video circuitry is exposed there. It came with the schematics, It's the...

Some progress (?) I did some reverse ingeniering.. In this case 16kbit ram that uses 5v+ only had pin 2 and pin 14 in different buses. Both are connected to separated IC equivalent to 74LS374. I had to study. Captura de pantalla 2022-07-24 21.39.01.png Those are 8bit latches that output the same bit...

Not long ago I saw this...
I just put it back in the right way and all worked fine...

Regarding the soviet chips, I found these links handy to help me understand my way around: https://ganswijk.home.xs4all.nl/chipdir/soviet/chips.htm https://elcomps.com/en/a76 Nice!!! It's always a joy when the machine finally starts up!!!! Well I guess we can officially start the Argentinian Robik ...

The confusion usually rises on the spectrum barrel plug side.. that is positive in the outside and negative in the inside.

Yes
Just double check polarity

OK, Some more done, I realized that HALT line goes to nowhere but the border connector.. so this is not the problem. I found another RAM bank of 8 IC 20220710_202419.jpg (I think these are 16x1bit) Pin 2 seems to be not connected And Pin 14 shows a bad behavior The first of then pulses like this 202...