Re: Question on Commodore 720 PSU

From: Christian Dirks <>
Date: Sat, 07 Jan 2012 23:57:06 +0100
Message-ID: <>
Hi Rob,

Am 07.01.2012 22:33, schrieb Rob Clarke:
> Good evening gents,
> Thanks to Ruud and Jens, I have all the missing IC's for my 720. It 
> came with all the cables disconnected and I haven't been brave enough 
> to hook it all up yet but I have connected the PSU to check the 
> voltages and have a couple of questions.
> o Are the PSU's in the 6 & 700 series have any history of being flaky 
> or are they generally OK?
I got my 710 some month ago, and hasn't been used for many years before 
I think.
After about 2 or 3 weeks of occasinally use it once went bang when I 
turned it on.
It blew the 16A fuse for my room.
A bridge rectifier in the PSU had to be replaced to put it back into 
life. Since then, it is OK.
So, 1 out of 1 CBM II PSU was bad here. Thats 100%, but sure not 
> o There is a 4 way, in-line power connector cable tied near PSU with 
> gnd, +5v and +12v and I don't think it connects to anything on the MB 
> - anyone know what it's for?

AFAIR this connector would fit a 8250LP board.
It is not connected to anything in the stock 710 / 720.

> o If I connect the power to the monitor without connecting the video 
> cable from the MB, should I expect to get any sign of life from it? I 
> would of thought I would have at least heard the HV whistle (it's a 
> long time since I had a CRT( but it seems ominously quiet.

When turning my 710 on, I can not hear anything from the CRT. The only 
thing I hear is the fan on the PSU.
With the Mainboard not connected to the PSU, the CRT remains dark an quiet.
> o There are earth straps with a ring connector from the monitor and 
> the PSU. Were these strapped to a screw on the motherboard or to some 
> other part of the case?
On my machine there is a plate with a thread at the metal back metal of 
the case. One lead is attached to it witch a screw and connects to one 
of the 4 screws fitting the PSU in top of the case. The lead from the 
CRT also goes there.

Christian Dirks

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Received on 2012-01-07 23:00:03

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