16 Dec
2015
16 Dec
'15
9:26 a.m.
Robert Jarratt wrote:
...sounds very similar to my experience with that PSU. The cure seems to be
simple run that machine then mine has stopped powering off now it seems.
I don't even know if the power off is because of an detected overload at
all, I had problems to even power on the machine the first time before
changing the caps. It would start only the approx 5 time if I switched it
on and I think that those problems are related.
I've installed VMS 7.3 and some additional packages and played for some
days with that machine and it is running stable now if I power it on.
The only thing that I still have to complain about is that the NiCad Pack
is empty again a little to fast for my taste, the Battery was a new one..
Regards,
Holm
--
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Tonight I
replaced the leaking capacitors on the +12V/-12V board, and also
replaced the two similar ones that looked and measured fine. I put the PSU
back together, put in a couple of less important boards and drives, and
the
machine now seems to power on OK. I measured the
ripple using the power
connector for the front panel and that looks OK too. Unfortunately though,
that connector only sends out +12V, +5V and -12V. It does not have output
for +3.3V, so I have not, so far, been able to check the ripple for this.
It is a
bit
awkward to test on the bench with a dummy load.
As I did not replace the capacitors on the +5V/3.3V board, because the
underside is very hard to access, and I am reluctant to pull them off and
solder from above, I would like to be sure there is no ripple on the 3.3V
supply. So, I was wondering if anyone has any neat tricks for probing the
+3.3V supply with the PSU installed in the machine?
Next job is to replace the capacitors on the little DSSI terminator, they
are
easy to change.
I spoke too soon :-(
The machine stayed on for a couple of minutes and then powered off. I
suspect there is a problem with it detecting an overload that may not
actually be there. Looks like I will need to get a dummy load and put it on
the bench to see if it still happens there.
I do recall that when it first failed it would stay on for shorter and
shorter periods each time I tried it. So perhaps there is some component
warming up and then causing a failure?
Regards
Rob