exxos's Atari, Amiga & retro forum

@jacolover
what about yours TT dip switches?
Dip 8 is responsible for DMA sound:
This is mine:

Thats the one I was thinking of DMA sound..

Cyprian wrote: 12 Dec 2020 23:38 what about yours TT dip switches?
Dip 8 is responsible for DMA sound:

I see this popping up once in a while. But is there evidence at all that DIP switch 8 has any effect? In my TT switch no. 8 is off. It has always been off. Still, it has both working DMA sound and PSG sound. (BTW: The keyclick is generated by the PSG and is not related to DMA sound.)

czietz wrote: 13 Dec 2020 12:47 But is there evidence at all that DIP switch 8 has any effect? In my TT switch no. 8 is off. It has always been off. Still, it has both working DMA sound and PSG sound.

Maybe when you have time, look in TOS see if there is any mention of this switch in there ?

exxos wrote: 13 Dec 2020 12:51 Maybe when you have time, look in TOS see if there is any mention of this switch in there ?

Good idea! I just did -- for TOS 3.06.

The DIP switch 8 does not enable/disable any hardware. It merely influences the bit for DMA sound in the _SND cookie. The logic is inverted -- as noted in Cyprians post (should have read it more carefully :( ). So, when the switch #8 is on, the bit indicating DMA sound capability in the _SND cookie is off and vice-versa.

Like I said, this does not directly influence any hardware. But software that takes into account the _SND cookie might refuse to do DMA sound when the switch is on (like in Cyprian's machine).

But let's get on-topic again. If there no sound at all (not even PSG sound, like keyclicks) in the TT there's something else amiss. @jacolover, do you have a scope? In that case for troubleshooting I suggest getting the schematic from dev-docs.org and tracing the sound from the PSG (in case of keyclicks) to the output. In that way, you should be able to see where it's faulty.

Cyprian wrote: 12 Dec 2020 23:38 @jacolover
what about yours TT dip switches?
Dip 8 is responsible for DMA sound:

That's not in the Atari official dev kit documentation.

Thanks guys, been checking a few things tonight, here is what I have found. The 1992 chip has it's 8.2 v present, the two LF147 that drive the on-board speaker have +- 5 on one, but +8, -4 on the other, so that one chip may have gone bad. Also, the on-board speaker reads 58 ohms, that can't be right, I would think either 4 or 8 ohms but I see no marking on the speaker, so don't know what the correct value is. Either way, there should be output on the RCAs I am making an assumption that the lack of sound may have been caused by the earlier owner putting UK roms in upside-down, that has been rectified by me, the TT comes on and runs except for the sound (and a flaky HD floppy). Need to investigate further, and any suggestions welcomed!

Yes, should be an 8 ohm speaker. Basically it's a standard PC speaker.

OK so a couple of questions here as I still have no sound from the TT. Looking the board closely over, I note on U210 a bodge wire connecting to pin 17 to a resistor, the board trace on the top surface is totally blow off and looks carbonized, not sure where that trace originally went as the resistor connection does not show continuity to the resistor (10 ohm) that is bodged onto pin 17. Are there bodge wires as a feature of the TT to U210? Not sure that U210 has anything to do with the sound so this is probably a dead end.

exxos, does your diagnostic cartridge, which can select the TT, generate sound signals I can trace chip-to-chip on the TT? Perhaps I can use that to at least track down where I am loosing or not getting audio from. Thanks!

@jacolover, @czietz was trying to help earlier and provided some good suggestions for you, you may have missed his post?