Unstable TS2068.
3 messages · 2005-08-16 → 2005-08-16 · Yahoo Group era · View archive on archive.org
Participants: Jarek Adamski, Jeff
Preserved from the Timex/Sinclair 2068 Yahoo Group (2001–2019), which is no longer online. Text reproduced from the archive.org archive; email addresses masked.
Messages
1. Unstable TS2068.
Jarek Adamski · Tue, 16 Aug 2005 08:55
Hello!
I got a TS2068 that was powered with reversed voltage.
Sometimes after power on it runs OK (30%), sometimes
wakes up with black screen and white border (70%).
No element gets hot (except th 74LS245 that usually
are warmer than others). I've also cleared the pins
of ROMS. The coil produces normal sound. No extra
hadware is connected. Pressing on the boar gives no
effect. All: /RESET, /BUSRQ, /INT, /NMI, /HALT, /WAIT
are in high state, when it hangs.
What can be wrong?
Jarek Adamski
2. Re: Unstable TS2068.
Jeff · Tue, 16 Aug 2005 17:38
Jarek;
I think that one of the chips (most likely the SCLD) was damaged by
the reverse voltage. I've seen this before where components become
unstable but not outright failed after being hit with reverse voltage.
3. Re: [ts2068] Unstable TS2068.
Jarek Adamski · Tue, 16 Aug 2005 23:59
After connecting YABUS.ZX (well, it doesn't work with
TS slot, so I removed its decoders to avoid bus
conflict), the computer starts correctly in 98% tries.
In 2% it hangs as before.
The hang is between DRAM test (red disapperaing
vertical bars) and EXROM access. What doest the ROM
do in that time or what is waiting for?
EXROM paging-in is not the problem, as similar
hangs were with ZX48 PROM inserted in HOME ROM
socket.
However, no hangs when I inserted EPROM in HOME
ROM socket (it was 27512, programmed with unknown
contents, but the ZX Spectrum copyright appears,
so at least one page is ZXROM).
--
Jarek Adamski