21 Sep
2011
21 Sep
'11
12:11 a.m.
Folks,
Always nice when you've got a piece of good news ;)
I replaced all the mains filtering capacitors in the original DEC GIGI
power supply when one blew only to find that the power supply lasted
another 10 minutes before losing power completely. At this point I
decided given the relatively standard power outputs (5V 3A, 12V 1A, -12V
0.3A) I would source a replacement power supply.
This arrived and was installed yesterday. It I guess unsurprisingly is
substantially smaller and lighter than the original. The original
cooling fan was removed as it was basically transformed directly from
either the mains directly or one of the windings of the main
transformer. I used the fan out of an external SCSI enclosure as a
replacement, although I look to source a high quality brand new one. To
me it looks like the fan primarily is for cooling the PSU only - given
the fan location and the location of the plate that the PSU is mounted
on it looks unlikely that the main circuit board would benefit much.
The machine now happily powers on and I had an hours playtime last night
with the local BASIC monitor.
The GIGI now only exhibits one minor trait, and I'm yet to determine
whether this is down to the LCD panel it is driving being at limits or
whether there is a slight issue with the video generation circuit. Once
in a while, every couple of minutes or so the LCD looses sync and the
picture is dropped. This only happens for a fraction of a second, then
the picture is restored as was.
If anyone has any ideas I'm all ears. For reference I'm using a Iiyama
AS4637UT, an old but extremely capable 18.1" 1280x1024 native panel. If
anyone is interested I can post the horizontal and vertical frequencies
it is being driven at.
I plan on scanning the GIGI brochures I have for inclusion on bitsavers
shortly.
Regards, Mark
21 Sep
21 Sep
10:52 a.m.
I replaced all the mains filtering capacitors in the
original DEC GIGI
power supply when one blew only to find that the power supply lasted
another 10 minutes before losing power completely. At this point I
decided given the relatively standard power outputs (5V 3A, 12V 1A, -12V
0.3A) I would source a replacement power supply.
And thus end up with something which in not a GIGI. OK, it performs just
like one, but it's not original. Yes, I do regsrd the PSU as being part
of the design.
Amazingly, there's a schemtic of the PSU in the technical manual on
bitsavers (it's the only part that does get a full schematic). It looks
to be a conventional SMPSU, and shouldn't be hard to fix (famous last words).
This arrived and was installed yesterday. It I guess unsurprisingly is
substantially smaller and lighter than the original. The original
cooling fan was removed as it was basically transformed directly from
either the mains directly or one of the windings of the main
The schematic seems ot imply there are 2 identical fans which are
connected in parallel across 120V mains or in series across 240V mains.
transformer. I used the fan out of an external SCSI
enclosure as a
Hang on. Do you have a mains-frequency trasnformer? If so, it's not the
PSU shown in the manual, but one that's probably a lot easier to repair.
-tony
2:10 p.m.
On 21/09/11 18:52, Tony Duell wrote:
I've kept the original PSU, and if/when I sell the box on it will go
with it. I've had to chop the wires between the PSU and the motherboard,
but that is the limit of modifications that can't be reversed.
There is a single socket for the fan connector, but the mains inlet can
be inserted into either the 120V or 240V socket. The fan has its own
transformer, so I presumed it was a mains powered fan.
It must be nice to have the skills to diagnose and repair PSU faults,
and maybe with a schematic (thanks for pointing that out) and some help
I'll give it a go, but in the meantime I get to enjoy the GIGI without
wondering whether something is going to go bang...
Mark.
I replaced all
the mains filtering capacitors in the original DEC GIGI
power supply when one blew only to find that the power supply lasted
another 10 minutes before losing power completely. At this point I
decided given the relatively standard power outputs (5V 3A, 12V 1A, -12V
0.3A) I would source a replacement power supply.
And thus end up with something
which in not a GIGI. OK, it performs just
like one, but it's not original. Yes, I do regsrd the PSU as being part
of the design.
Amazingly, there's a schemtic of the PSU in the technical manual on
bitsavers (it's the only part that does get a full schematic). It looks
to be a conventional SMPSU, and shouldn't be hard to fix (famous last words).
This arrived and was installed yesterday. It I
guess unsurprisingly is
substantially smaller and lighter than the original. The original
cooling fan was removed as it was basically transformed directly from
either the mains directly or one of the windings of the main
The schematic seems
ot imply there are 2 identical fans which are
connected in parallel across 120V mains or in series across 240V mains.
transformer. I used the fan out of an external
SCSI enclosure as a
Hang on. Do you have a mains-frequency trasnformer? If so,
it's not the
PSU shown in the manual, but one that's probably a lot easier to repair.
-tony
22 Sep
22 Sep
12:57 p.m.
There is a single socket for the fan connector, but the mains inlet can
be inserted into either the 120V or 240V socket. The fan has its own
transformer, so I presumed it was a mains powered fan.
Right. The schematic in the tech manual shows 2 connectors (120V and
240V) and a 2-winding thing where the windings are in series for 240V or
parallel for 120V. That's the nromal wiring for a msall mains transformer
primary, of course. I guess there's a little transforemr to run an AC fan
in there..Strange. You could prbably have kludged it ot run the origianl
fan on 240V without needing the rest of the PSU.
It must be nice to have the skills to diagnose and repair PSU faults,
Look, if I can do it, anyone can. Seriously. Remmember I've never been
taught any electronics in my life.
SMPSUs are a bit of a black art, it's true, but they do follow logical
principles and they can be repaired.
and maybe with a schematic (thanks for pointing that
out) and some help
I'll give it a go, but in the meantime I get to enjoy the GIGI without
wondering whether something is going to go bang...
Personally, I'd trust a quality PSU from DEC (or HP, or...) rather than
some modern thing from a PC peripheral.
-tony
4840
days inactive
4841
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ard＠p850ug1.demon.co.uk -
mark＠wickensonline.co.uk