Re: C128 Power Supply repair

From: Gerrit Heitsch <>
Date: Tue, 17 Jul 2012 17:19:32 +0200
Message-ID: <>
On 07/17/2012 02:48 PM, Baltissen, GJPAA (Ruud) wrote:
> Hallo Istvn,
>> I have a broken C128 power supply which has a burnt thyristor.....
> I never opened the PS of a C128 but is it possible it is a 78M05, the 3A variant of the 7805?

The 78M05 is the 0.5A version of the 7805.

If the thyristor is burnt it might mean that the switching regulator is 
shot. The Thyristor is part of the crowbar circuit which is there to 
protect the C128 against overvoltage.

The PSU should work without it.

A good idea might be to just take out the whole regulator circuit and 
just leave rectifier and filter cap. Then grab a small switching 
regulator from ebay like this one:

It's good for up to 3A with some cooling and adjustable. Set it to 5V 
(or 5.2V to compensate for cable loss) before connecting it to the C128 
and you're done.


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Received on 2012-07-17 16:00:05

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