Remember that the QL has a power supply. Quite often odd crashes (especially if the QL crashes, may be be due to a faulty supply (often simply loose screws in the mains plug)
QL Troubleshooting
Last updated: October 28, 2003
. If you get a complete screen failure, but power light is on
and you are using Gold Card, replace the 8301. Do NOT
use the qpower switch mode regulator with Gold Card (I do
not recommend the use of this without GC either!!)
Check with Miracle that you have the GC mods up to date.
. Check that there are no shorting pins on the expansion connector
(J1). If there are, take out the pcb, and using thin
screwdriver(s) get the pin roughly straight, and then use long
nose pliers to fully straighten it. BE CAREFUL because the
pins are very brittle - you will ony have one chance.
Then put in expansions with much care. I like putting the QL on
its reset end - that way it is easy to see if expansion is
parallel to the QL.
. Remove all upgrades, ROMs etc and see if fault still there.
. RAM failures - use MINERVA. This will flag the FIRST faulty address in
ram, and the relevant chip can be replaced. In fact the QL std memory
test will NOT pick up ram errors where NUL bits are written. Minerva will
eventually as the memory test write data is varied.
. Check that your Sinclair is to latest build spec. (D14+ or has flying
leads over IC23-XZ8302). If not then `2 will secure a circuit diagram and
list of mods from me (UK price).
. Check and clean all mains connections - especially on QL power supply and
mains plug (including fuse holder and screw terminals). Power socket on
QL often has dry solder joints - especially if QL is used with case OFF!
. Don't route mains cables anywhere near printer and disc drive cables.
. Try using QL in different room/ house with and without any accessories,
and with /without different monitor. If problem still there with and
without cleaner then problem probably not mains interference.
. Remove keyboard ribbon cables and clean cable ends & socket. If cable
ends damaged and is not old type (non straight signal lines) cut off .5 cm
from ends. If QL locks up (but an on-screen clock still runs) or few keys
do not work this may be the cause. (To open QL case remove front 4 and
back 4 screws. Do NOT undo the 2 screws under the microdrives).
. Check 5v line (centre and LH pins of main regulator with large heat sink
viewed from front of QL) Renew main 7805 regulator if voltage lower than
say 4.8v. Smear base with silicon grease, and solder 10n capacitor
direct to RH & centre pins (input) as viewed from front of QL. Make sure
retaining screw is tight and that whole heat sink gets hot.
78S05 2A regulator can be used, but hardly seems worth it, and it makes no
difference to expansions. Qpower switch mode regulator produces RF
interference, and again doesn't help expansions. Don't route 7805
to outside QL - this is incredibly bad practise and can only cause
more problems.
. Take out all socketed ICs, external ROM etc, clean legs and sockets with
spray cleaner and replace, pushing down hard. Take static precautions.
Similarily, clean ROM socket and rom cartridge edge connector (latter
with a rubber on the solder tracks). This is VERY often a cause of crashing
on my machines. Why on earth didn't they use gold plated connector.
. Thorn-EMI suggest replacing all ICs 18/23/24/34!! This is a bit drastic
but if you can lay yours hands on a second working QL it is worth
swapping ALL the socketed IC's and then replacing one by one
(take antistatic precautions).
. Use higher capacity power supply (needs 9v DC and 16v AC unless hardwired to
board. Be SURE you know what you are doing. Best solution is to
put everthing in a twoer case (I can advise or do the job).
. I always switch on all equipment with one switch where possible. Some
monitors (esp Microvitek) can cause troubles if leads are removed, maybe
due to floating earths causing voltage difference and blowing 8301.
. If using expansions, make sure connector pins are straight. Tony Price
also recommends using a SMALL sliver of wood and cleaning expansion socket
with contact cleaner.
. Run thickish wire from 5v line (LH pin of regulator) to ram 5v rail
(Thick circuit track running from just above R68 and under IC7).
. SERIAL PORTS. If -12v and +12v lines OK, then problem usually lack of
outgoing RS232. Try the 2
3k -12v pull up to 19/21 of 8302. Illogical
I know but it DOES cure the problem very often. Similarily open network
sockets (centre pin not making contact when plug removed) have been known
to affect serial ports. These must be some internal effects in the 8302.
Failing this, remove IC25 (1488) and replace in socket.
I remove using specialist hot air gun, but Black & Decker electric paint
stripper used CAREFULLY will work. Direct AWAY from plastic parts and don't
overheat. Lever off IC ONLY when solder is fully melted.
Then try different combinations of 8302/1488. I find some 8302s output less
than 2v to pin 2 of 1488 - should be 2.5 or so I am told.
Note on issue 6 boards the HAL should be socketed and swapped as well. The
incoming data is buffered via this (in place of IC27 on issue 5 boards).
YES - the official circuit diagram IS wrong!
. Try the 'bombproofing' mods listed in QL World in Nov 89 - but I
think this is a bit of an overkill.
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Good Luck
