Can antone shine a light on this problem ,
got a 48 in for repair ,
found loads of memory chip errors reported on a poor b/w screen .
verified 12 volt , which showed 7.3 v
next test showed this ;
12 volt dropped to 3.6 .
third test only gray screen with vague vertical lines ,
and 12 volt dropped to 1.6 v
i assume internal powersupply , but ztx 213 and 650 do measure correct ( compared to 2 others )
48 with sinking 12 volt
48 with sinking 12 volt
Zx81-16k exp.- Spectrum 48 - Spectrum 128- Interface 1 - DIVide - Zx flashcard- Zx printer - Ram turbo-Velleman interface system-Currah microspeech -Ql - 512k exp.- Ql printer - Cst floppy interf.- Double 3.5 floppy- Minerva - Qimi-and much more .
- 1024MAK
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Re: 48 with sinking 12 volt
Yes, well, definitely something wrong with the DC/DC converter or excessive loading caused by a faulty chip (most likely a 4116 or equivalent DRAM chip).
Which issue board? Does it have the DC/DC modification?
Do any of the 4116 DRAM chips get hotter than normal?
Is the +5V and the -5V in spec.?
Mark
Which issue board? Does it have the DC/DC modification?
Do any of the 4116 DRAM chips get hotter than normal?
Is the +5V and the -5V in spec.?
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: 48 with sinking 12 volt
When i started this issue 2 for the first time ,
All ram chips remain cold-ish but the screen was missing pixels in the trademark text.
tests revealed a 7.x volt 12 line .
after 3 tests , the 12 v line is at around 1,6 volts.
dc-dc modifications have all been done ( and removed ) situation does not change .
now waiting for the transostors to arrive to change tr4 and tr5
All ram chips remain cold-ish but the screen was missing pixels in the trademark text.
tests revealed a 7.x volt 12 line .
after 3 tests , the 12 v line is at around 1,6 volts.
dc-dc modifications have all been done ( and removed ) situation does not change .
now waiting for the transostors to arrive to change tr4 and tr5
Zx81-16k exp.- Spectrum 48 - Spectrum 128- Interface 1 - DIVide - Zx flashcard- Zx printer - Ram turbo-Velleman interface system-Currah microspeech -Ql - 512k exp.- Ql printer - Cst floppy interf.- Double 3.5 floppy- Minerva - Qimi-and much more .