Thanks Gerrit! I am sure that this is not a 78M05 regulator. That regulation is done by the DIP IC inside the PSU. This must be the thyristor for sure because searching the web had some results for TGA8542 which mentioned thyristor. The C128 doesn't turn on with this PSU while it works with other C128 PSU (I have tested it with an other one cause I have 2 machines). As it is physically next to the 4700uF/16V capacitor, it has damaged that capacitor too. I have measured voltages on the connector and got the 5.1V on the proper leg when not connected to the machine. Probably it cannot feed the required current. The C128 hardware manual has some PSU schematics and it seems to be rather complicated for me... Of course I know the rectifier and filter cap part, that is easy. I will investigate your ebay item advise, seems promising. Once I have upgraded my A1200 PSU with small switching PSU circuit using 12V input. That works fine but the C128 needs that 9V AC also... Thanks Istvan -----Original Message----- From: Gerrit Heitsch Sent: Tuesday, July 17, 2012 5:19 PM To: email@example.com Subject: Re: C128 Power Supply repair On 07/17/2012 02:48 PM, Baltissen, GJPAA (Ruud) wrote: > Hallo István, > > >> 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: http://www.ebay.de/itm/290572036224 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. Gerrit Message was sent through the cbm-hackers mailing list Message was sent through the cbm-hackers mailing listReceived on 2012-07-17 21:00:06
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