Commodore VIC-20 Troubleshooting Guide: Difference between revisions

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This page concentrates on '''hardware faults''' that affect every VIC-20—NTSC models built around the MOS 6560 and PAL models that use the MOS 6561. Step-by-step diagnosis is given for the two major board families (ASSY 324003 and the cost-reduced ASSY 250403/VIC-20CR), together with tables of the most frequent symptoms, IC failure modes and electrical test points. Follow anti-static precautions at all times and remember that the early two-prong machines contain a live 9 VAC / linear-regulated 5 V supply.

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CPU, VIC and often one VIA remain socketed, ROMs still grouped together (UA14-UA16). SRAM count drops to three larger 6116-type ICs. Transistors '''Q3 & Q4''' with zener '''CR1''' sit next to the cassette/user-port edge and control motor +6 V.

~~== Reference documentation ==~~

[[Category:Commodore Systems]]

* ''The Friendly Computer – Technical Manual, Model VIC-20'' (full schematics, parts lists).

* ''VIC-20 Programmer’s Reference Guide'' – memory map & I/O register summary.

* Ray Carlsen’s VIC-20 repair notes – chip-by-chip symptom tables.

* Community forums: ~~Denial (sleepingelephant.com) and Vintage-Computer for real-world repair logs.~~

~~With the tables above, a multimeter, and (ideally) a spare set of socketed chips, most VIC-20s can be revived in an afternoon. Happy troubleshooting!~~

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 This page concentrates on '''hardware faults''' that affect every VIC-20—NTSC models built around the MOS 6560 and PAL models that use the MOS 6561.  Step-by-step diagnosis is given for the two major board families (ASSY 324003 and the cost-reduced ASSY 250403/VIC-20CR), together with tables of the most frequent symptoms, IC failure modes and electrical test points.  Follow anti-static precautions at all times and remember that the early two-prong machines contain a live 9 VAC / linear-regulated 5 V supply.
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 CPU, VIC and often one VIA remain socketed, ROMs still grouped together (UA14-UA16).  SRAM count drops to three larger 6116-type ICs.  Transistors '''Q3 & Q4''' with zener '''CR1''' sit next to the cassette/user-port edge and control motor +6 V.
-== Reference documentation ==
+[[Category:Commodore Systems]]
-* ''The Friendly Computer – Technical Manual, Model VIC-20'' (full schematics, parts lists).
-* ''VIC-20 Programmer’s Reference Guide'' – memory map & I/O register summary.
-* Ray Carlsen’s VIC-20 repair notes – chip-by-chip symptom tables.
-* Community forums: Denial (sleepingelephant.com) and Vintage-Computer for real-world repair logs.
-With the tables above, a multimeter, and (ideally) a spare set of socketed chips, most VIC-20s can be revived in an afternoon.  Happy troubleshooting!