A good idea,
but I don't think this is the case. According to the technical
OK... Not having seen the machine, all the rest of us can do is make
guesses, most of which are likely to be wrong :-)
If my response came across as critical, I apologize, this was not my intent.
I welcome any and all suggestions.
I'll have
to do some measurements. I could try hard-wiring the fan to full
power, however this thing *should* work as it is designed, and the fan supply
True. On the other hand, if making the fan run at maximum speed all the
time keeps the machine running, it's worth doing that mod (IMHO) to save
the problem of replacing the CPU or FPU chips.
Agreed that it wouldn't hurt to have the fan at full power, but the point I
was trying to make is that this thing gets *SO* hot that I'm convinced theres
a fault, which should be found, not masked.
I don't think just running the fan at top speed will be enough - it's got
pretty good airflow as it is, and it is on the other side of the cabinet
(fan is at the back, CPU/FPU is at the front). The only way I've been able
to keep the chips cool enough to run is with a muffin fan positioned right
beside them with airflow directed at the heatsinks - much higher airflow
that would be present in it's natural situation.
It has occured to me that with the color frame buffer removed (which I don't
need in my application), I could mount larger heat sinks, and probably make
it stay cool enough with the natural airflow, but I would not feel comfortable
in doing so, as it does not address the actual fault.
A little more information:
The heat seems to be mostly dynamically generated. Holding the CPU/FPU in reset,
or stopping the clock (there's a jumper on the clock line!) results in them
getting warm, but not "blistering hot" which they do as soon as you start them
running.
Scoping around for signs of contention, odd signals etc. I found that everything
looks good (nice lows, highs and full range transitions) except for two pins on
the FPU - 44 and 60. 44 is not shown on the schematic, nor is it described in the
techncial manual description of FPU pins. 60 is described as "TEST - this pin is
not used and should be grounded" and shown as grounded on the schematic.
Both pins are showing an identical waveform - which is a "square edge" signal
of unknown modulation with approx. 0.5v high level. Normally this smells of
contention, however both signals appear to be no-connects as far as I can tell
from the board.
I tried pulling TEST to ground as shown in the schematic - it pulls down with
no trouble (no signficant load), and has no discernable effect. The waveform
on pin 44 is not affected. I have no idea if this is normal...
Unfortunately there are many pins neither shown on the schematic nor described
in the technical description - there are also a fair number of pin connections
shown on the schematic without names or pin numbers. There are also things like
10-pin SIP resistor modules with 10 numbered pin connections, and unnumbered
11'th and in some cases 12'th connections shown on the schematic.
At this point it's probably going to have to wait until I can find another one
to make comparisons with. I haven't found anything blatently out of the ordinary,
and lacking better technical information I have no way to know if signals are
normal or not.
Regards,
Dave
--
dave06a (at) Dave Dunfield
dunfield (dot) Firmware development services & tools:
www.dunfield.com
com Collector of vintage computing equipment:
http://www.classiccmp.org/dunfield/index.html
