Re: Static PET repair (was Re: VCF PET Alive! - April 24th to May 2nd)

From: Ethan Dicks <>
Date: Tue, 30 Mar 2010 02:00:03 -0400
Message-ID: <>
On 3/30/10, Marko Mäkelä <> wrote:
> On Mon, Mar 29, 2010 at 04:57:54PM -0400, Ethan Dicks wrote:
>> The other board (with 6540 ROMs and 2114 SRAMs and the broken Japanese
>> CHRGEN ROM) passes all RAM tests (and does come up with the BASIC
>> splash message), but still locks up on cassette operations.
> Could it be a broken 6522 (or is the PET tape port also driven by a 6520)?

Both.  VIA #1 (A5) PB4 is motor #2, PB3 is (both) write, and CA1 is
read #2.  PIA #1 (G8) CB2 is motor #1, CA1 is read #1, and the
switches are read by PA4 and PA5.

Given that another symptom is "hangs on IEEE operations", the 6522 is
used by both the cassette ports and the IEEE port, so it's a good
first stop.

Fortunately, I have spares for both on hand.  Thanks for the tip.

> If I remember correctly, the very first defect of my C64 was that it hung
> when trying to write to tape.  Apparently, the 6510 on-chip I/O port had
> been damaged so that when it tried to wiggle the CASS WRITE line, also the
> memory configuration lines were being changed.

Ouch.  That must have been a fun one to diagnose - the machine "runs",
so the CPU "must" be good...


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Received on 2010-03-30 07:00:08

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