PM8500 - av video out

[lobust]

My recently acquired 8500 thinks it has a television connected and it's a bit of a nuisance.

1. Is it normal for the av video out to be active with nothing plugged in?
2. If yes, how do I disable it?
3. If no, ideas how to fix it?

 

[bigD]

IIRC, the AV port is controlled by the Monitors control panel. Is the display shown there?

 

[lobust]

IIRC, the AV port is controlled by the Monitors control panel. Is the display shown there?

Yes, it shows as a second monitor like any other.

 

[joevt]

The 8500/8600 can sense when a composite or s-video display is connected.
The DingusPPC emulator does emulate this behaviour.

The bits are in a board register accessed at address F301E000. It's a 16-bit little-endian register.
Read the register in Open Firmware like this:

F301E000 rw@ 4 u.r

Composite video is 0x0080 for not connected. 0 for connected.
S-Video is 0x0040 for not connected. 0 for connected.
Unused bits are pulled high: FF3F.

We should be able to see which is stuck at connected.

I don't know if there's any Power Mac 8500/7500/7600/8600 schematics that can help you find the related components on the motherboard.

 

[lobust]

The 8500/8600 can sense when a composite or s-video display is connected.
The DingusPPC emulator does emulate this behaviour.

The bits are in a board register accessed at address F301E000. It's a 16-bit little-endian register.
Read the register in Open Firmware like this:

F301E000 rw@ 4 u.r

Composite video is 0x0080 for not connected. 0 for connected.
S-Video is 0x0040 for not connected. 0 for connected.
Unused bits are pulled high: FF3F.

We should be able to see which is stuck at connected.

I don't know if there's any Power Mac 8500/7500/7600/8600 schematics that can help you find the related components on the motherboard.

My apologies, I somehow missed your reply after I posted this thread.

So, I got into open firmware (after some messing about - I didn't realise these old world machines defaulted to serial io...) and did as you suggested.

The response is "FF7F"

Additional pertinent information - the a/v breakout board is no longer plugged in to the logic board. I noticed while troubleshooting that most of the ribbon cable conductors were broken at the solder joints (not impressed with the construction/soldering on this little board ), so I have completely removed it for now. The behaviour is unchanged though - it still thinks there is a second monitor connected.