Looking for a spare 8502

From: Marko Mäkelä (marko.makela_at_hut.fi)
Date: 2004-11-17 23:03:51

My flat C128 (artwork no. 310381 rev 7) seems to think the play button on
the cassette port is stuck down.  It responds to LOAD by writing SEARCHING
and blanking the screen, instead of writing PRESS PLAY ON TAPE.  The CASS
READ, CASS WRITE and CASS MOTOR lines appear to work, because loading a
program with "c2nload" worked.

According to the service manual (schematic diagram on page 73), CASS SENSE
should be connected via C72 (470 pF) to ground and via RP5-2 (3k3) to +5V.

I measured 3k2 between pin 1 (ground) and pin 6 (CASS SENSE), and 3k06
between CASS SENSE and +5V.  Also the pin 26 of the processor (8502) was
well connected to CASS SENSE.

Can this be anything else than a broken I/O gate on the processor?  If not,
does anyone have a spare 8502 for me?  I could trade it for a 6560-101
(NTSC-M video chip for the VIC-20).


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