Games that may damage PSG chips

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By ro

Guardian (4188)

ro's picture

10-12-2019, 07:33

If there's a claim, there should be proof. Else it didn't happen. Anyone with a broken MSX cuz of "bad" PSG programming out there?

By Alexey

Guardian (2878)

Alexey's picture

26-09-2020, 20:55

Just wanted to post OpenMSX commands to enable debugger break on illegal PSG command.

proc my_debug_break {} { debug break }
set invalid_psg_directions_callback my_debug_break

By _ThEcRoW

Expert (89)

_ThEcRoW's picture

30-09-2020, 14:47

Maybe a silly question, but does this software(i mean software that has this psg problem) affects ocm(zemmix clones) also?

By ray2day

Hero (549)

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30-09-2020, 15:15

Quote:

Unclear because those who say that may damage PSG chips, they say that is possible only for some MSX.

I saw the 'PSG-may-damage-your-MSX-notification' on OpenMSX in the past and now I am here reading about the problem. Both times the next question rises;
-> Is it known which specific brand/type of MSX computers are involved here?

By pgimeno

Master (238)

pgimeno's picture

30-09-2020, 16:40

ray2day wrote:

-> Is it known which specific brand/type of MSX computers are involved here?

If you look up the specific model in the wiki, and it says it has a Yamaha S3527, it's not affected.

If it says it has an AY-3-8910, it is likely affected.

To mention just one, I've checked the service manual of the Philips VG-8020/00, which has an AY-3-8910 (the VG-8020/19 and later have an S3527). The joystick port is connected to the PSG through two 74LS157, one for the directions and one for the buttons, and the cassette port through a µPC311. All of these are directly connected, no resistors. According to the datasheets:

- The AY-3-8910's output gives 100µA when high, and 1.6mA when low. This seems to imply that it's more likely to damage it when the AY output is low and the other side is high, than vice versa, but I may be wrong here.
- The 157 says it gives -20 to -100mA when shorted, with a footnote that says: "Not more than one output should be shorted at a time, nor for more than 1 second".
- The 311 says it can withstand a short-circuit for 10 seconds.

Whether a reversal of the direction of port A can cause actual damage to any of these chips, I don't know. I guess it might depend on how many simultaneous short-circuits are happening. Eugeny's experiments with GR8NET suggest that under usual conditions, there's no damage. The worst case seems to be: all outputs of port A at 0, all values from joystick and cassette at 1 and held for a while. I don't know the default output of the 311, it may depend on the last input since it's configured with hysteresis. The joysticks are high by default, so this worst case happens with the joystick at rest.

That's if 0's are actually the worst case as I suspect.

Edit: I've found the Canon V20 service manual. It has the exact same surrounding circuitry, so it's likely similarly affected, with the extra problem that bit 6 of the port is connected directly to +5V with no resistor; by comparison, the VG8020/00 schematics did not show this pin, so I assume it was unconnected.

By Manuel

Ascended (16955)

Manuel's picture

30-09-2020, 17:37

I once had this issue on my Sony HB-G900P. The machine wasn't working at all anymore until I powered it off for a while. Reset wasn't even working.

By pgimeno

Master (238)

pgimeno's picture

30-09-2020, 17:59

Manuel wrote:

I once had this issue on my Sony HB-G900P. The machine wasn't working at all anymore until I powered it off for a while. Reset wasn't even working.

I've had that problem with the VG-8020/40, but it's not likely related to the PSG problem. The RAM is very persistent; if the RAM is detected as a ROM, it can take about a minute, if not more, for the RAM to actually lose its contents after it's powered off; a RESET is useless. If the ROM code causes a hang, the symptoms would be the ones that you're reporting.

By ray2day

Hero (549)

ray2day's picture

30-09-2020, 19:09

@pgimeno thank you for you clear explanation

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