6 Jun
2010
6 Jun
'10
10:05 p.m.
On Sunday (06/06/2010 at 06:54PM +0100), Tony Duell wrote:
Yes... this is a fuse but it has not blown... ever. The machine got
pretty extensive use from early 1976 until 1984 or so and even with the
low 8V rail, it did heroic efforts for me.
I completely agree... although, I am now prepared to replace the transformer
so once I have desoldered the original I suspect I'll be putting back the
new ones.
I agree with this too absolutely.
I have another homebrew S100 machine from the same era and it too has
a marginal power supply... but I won't think twice about rebuilding
that one with a set of switchers. It has no pedigree or authentity to
be preserved... other than it is built in a wooden box with a bright
orange Formica front panel... a piece that was left over from my mom's
new kitchen in 1979 ;-)
Chris
--
Chris Elmquist
That sounds
very low indeed. I wouldn't expect a transformer secondary
to drop below rated voltage with only half load on it! Are you sure you
haven't got a shorted turn somewhere?
My experience is that a single shorted turn in a mains transformer will
cause enough primary-side current to be drawn to blow the fuse. Of course
that's assuming there is a primary-side fuse -- but if there isn't there
darn well should be :-) Still, it can't hurt to measure the primary
current with no load on the
secondaaries. If you have a wattmeter, masure the power consumed by the
trransformer with no secodnary load (note that this is _not_ the product
of the primary corrent and the mains voltage, they will not be in phase).
If there is significant power drawn on no-load, then suyspect a shorted turn.
Yup. Have a wattmeter and can make this measurement... however only
after desoldering all the connections from the transformer to the
chassis mounted bridge and the bridge mounted on a PCB since none of
this is connectorized.
I agree with
Tony that you should do some more tests to see if there's
something wrong with the transformer or rectifier. For a start, look at
the secondary voltages and current drawn from the supply with all the
secondaries open circuit. Excessive no-load current is a reasonable
indicator of a shorted turn.
I should have read on before writing the above :-) If you
eventually do need to upgrade the power supply, could you fit
just one switcher in the cabinet with that transformer? Use it for the
8V line, and keep the old PSU for the rest?
My personal view (if I had such a machine) is that as the originial PSU
wasn't a switcher, you shouldn't use a switcher to do any form of upgrade
or repair. But it's really up to you.