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From: jerem@tekgvs.UUCP (Jere Marrs)
Newsgroups: net.micro.cbm
Subject: Re: C64 problem
Message-ID: <1300@tekgvs.UUCP>
Date: Wed, 4-Dec-85 19:29:31 EST
Article-I.D.: tekgvs.1300
Posted: Wed Dec  4 19:29:31 1985
Date-Received: Sat, 7-Dec-85 03:28:05 EST
References: <1624@cbsck.UUCP>
Reply-To: jerem@tekgvs.UUCP (Jere Marrs)
Organization: Tektronix, Beaverton OR
Lines: 32
Keywords: 9VAC

>                                                          In my case,
>        it was the power supply that was causing the trouble.
>
>                                 By the way, I had considered just
>        building a whole new power supply from scratch, but it
>        turns out that the transformer used is somewhat wierd also.
>        It has one winding that supplies the the 9VAC at about one
>        amp and another completely separate 9V winding that is
>        center-tapped and half-wave rectified to feed the 5-volt
>        regulator at about an amp and a half.  I would have needed
>        two separate normal transformers to duplicate this.         
>

	That is a viable route - the two transformers. I had one that
way. Hook one up to the 9VAC pins and the other to a regulator (LM-309?)
that can handle about 4A. The increased current capability is useful if
you add such things as IEEE interfaces and 80-column adaptors.

	A better way - and this is what I ended up doing - is to replace
the +5 supply by one of those small switching power supplies and use a 9V
transformer for the AC requirements. I used a 10V transformer (door bell)
with an (EPD? EDP?) 5VDC, 4.0A switching power supply and it worked 
beautifully for the year-and-a-half until I got my 128. I was using both
the BusCard II IEEE interface and the BI-80 80-column converter which drew
more current than the 64 alone. It's not as cheap as the linear power
supply, but I think the reliability factor is increased orders of
magnitude.

				Jere M. Marrs
				Tektronix, Inc.
				Beaverton, Oregon
				tektronix!tekgvs!jerem