29 May
2008
29 May
'08
12:07 p.m.
You could try one of the CBM clubs, there should be someone who has some
spares..
The other option is rewinding the transformer, not the most thrilling
option..
Hang on a second...
Why do yuo think the transformer is the problem?
This sounds like a switch-mode PSU. And while transformers can and do
fail in those, it's not at all easy to diagnose the fact. They normally
have windings witha very low DC resistance and will test as a dead short
on any nornaml multimeter.
Most of the time, when a SMPSU blows its fuse violently, one of the power
semiconductors, often on the mains side, has gone dead shoirt. If you're
lucky, a rectifier diode. If you're unlucky, the chopper transistor,
which has possibly been damaged by a failure in some other component
(that's why I said 'unlucky -- if you just replace the transistor, the
new one will most likely fail again at switch-on).
In this case, a replacement fuse held, which makes me suspect that some
other component in the mains circuit has filead open-circuit. Maybe a
current sense resistor or a surge-limiter thermistor, or...
The last i had, was suffering of a bad 9vac
transformer that one I replaced
and the PSU was up again.
-RIk
-----Oorspronkelijk bericht-----
Van: cctalk-bounces at classiccmp.org [mailto:cctalk-bounces at classiccmp.org]
Namens Ade Vickers
Verzonden: woensdag 28 mei 2008 21:20
Aan: 'General Discussion: On-Topic and Off-Topic Posts'
Onderwerp: RE: Transformer repairs
Rik wrote:
Maybe this is some help.
http://www.zimmers.net/commie/docs/sx64.txt
http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/c6
4/sx-64/index.
html
I do have a 22MB pdf file with the schematics, if you got a ftp I'll
upload it.
Hi Rik,
Thanks - I found the schematics via Wikipedia (of all places); and the text
file too (can't remember where that was linked from).
From the description, I think it's the
"+12 volt switcher (2.8 Amps)"
that's
blown; the question is, where the heck would I get one of those from??
Here's the pin-out (from the solder side, heatsink towards you):
240v o o 0v
240v o o 0v
n/c o o 0v o 0v
n/c o o 12v o 12v
0v o o 12v
0v o o 12v
Yes, there are two additional pins stuck out of the side; it looks like the
taps have been taken out separately. The 6 0v/12v connections are a guess,
based on the fact there are pins, and they're soldered into the same pads as
the outboard 0v and 12v. They may, of cours, all be n/c
Also, 0v is not *really* 0v, given that there's AC going in; except that
it's already been through a rectifier, which seems odd to me. Is this
something to do with it being a switching PSU?
From what I can tell, this board is designed to
produce 9vac, +12v and +5v.
I could fabricate an entirely new PSU, or even hacksaw
up a PC supply (an
old AT type with a physical on/off switch) to go in this one's place; but
it'd be nice to keep it reasonably authentic.
Cheers,
Ade.