Hi.
I have Strange problem with one of mine ZX81
Plane ZX81 with 1K works without problem. i can load and execute programs.
When I connect 16K RamPack (Sinclair 16K RAM) ZX81 most of the time show only white screen without K cursor. Maybe 1 of 10 times starts normally, but very unstable (freezing, crashing, won't work even with 1k programs.
White screen is bright for few seconds then loose intensity and start flickering.
I have 2 Sinclair 16K rampacks. Both of them not working on problematic ZX81.
Ram packs are definitely working because they are working fine on my other two ZX81.
So far I tried:
- Changing ZX Power Supply - its a UK1400, works without problem with other two zx81 with 16K Rampacks
- replace 2 electrolyitic capacitors with fresh new ones
- replace 7805 voltage regulator with switching regulator
- reseated all chips in their sockets multiple times
- change all chips except memory from another full working zx81
- cleaned with eraser and alcohol edge connector on board. (Contacts are shiny )
ZX81 has Pokemon's ZX8-CCB composite mod fitted.
Any suggestions?
ZX81 witk 16K memory pack white screen
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Re: ZX81 witk 16K memory pack white screen
If the RAM pack works with another machine, and works occasionally with this ZX81, the only thing I can think of, is that there is a poor connection that only affects the circuits that go to the edge-connector contacts (I presume that all the edge-connector contacts are in good condition). The poor connection could either be a dry solder joint, or a damaged PCB track.
Mark
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
Re: ZX81 witk 16K memory pack white screen
The edge-connector contacts looks visually OK. I will test with multimeter every corresponded track from edge-connector contacts to destination chips and elements.
Re: ZX81 witk 16K memory pack white screen
I check all traces that leads to edge pins. I didn't see problem. Finally I clean edge pins more radically with sand paper. Now it works OK!!!
Re: ZX81 witk 16K memory pack white screen
With old connectors / pcb's it works sometimes if I pull the device a little bit from the board instead of plugging it as deep as possible.
Re: ZX81 witk 16K memory pack white screen
Yes it's true. That's why I was sure that is only connection problem. So I was little harsh and use sand paper on contacts.
Now it's working perfectly without any issue. And wobble effect is minimum
Now it's working perfectly without any issue. And wobble effect is minimum