exxos's Atari, Amiga & retro forum

Have you tried removing the 4116 dram the memory needs all the voltages inculding minus 1e one on the diodes is bad for shorting to ground as well


Tom

Yep, all the RAM, CPU, ROMs and anything else socketed has been removed. Short is still present.

The CR1 diode has been lifted at one end too.

Hmm maybe the ttl around the video circuit it gets fried by the fun din connector problem


Tom

Tomswork wrote: 28 Aug 2022 20:14 Hmm maybe the ttl around the video circuit it gets fried by the fun din connector problem


Tom

Definitely worth a look there I think, cheers.

Looking at the schematic just now and I think it would have to be a pretty specific set of circumstances for you to do any damage by plugging the power into the cassette port.

The video port, as per @Tomswork's suggestion is another matter. It could easily damage the video circuit and cause a number of transistors and a couple of ICs to go to short.

That is definitely my next port of call.

Looking at the video port, I've removed C2 and C7 and I seem to be in a position whereby I no longer have a dead short between 5v & GND :)

I hooked up directly to 5v and powered on with a bench PSU and I am getting approximately 5v at the rest of the ICs.

I also did note when having a cleanup of the board, a solder 'splat' appeared from nowhere, and this may also be related, but not 100% sure.

So, I need to make a new keyboard cable, as the original was badly corroded and has started to fail, so I can see if I'm also getting 5v over there, and hopefully the parts I ordered will have arrived.

As for C2 and C7, I'm pretty sure I have spares enough for those.

Tried powering the 12V section using the bench power supply to see if it's generating the +5V and -5V?

Actually, maybe the short was killing the whole PSU section. Maybe try a normal power-up?

Excellent time for the power brick see if all the voltages show up at the ram socket. Do you have the monitor for is or you going to go into a smart connector or composit

Ton

stephen_usher wrote: 29 Aug 2022 19:14 Tried powering the 12V section using the bench power supply to see if it's generating the +5V and -5V?

Actually, maybe the short was killing the whole PSU section. Maybe try a normal power-up?

No, as I removed both the VRMs as part of the troubleshooting and the power transistor, new parts are due in hopefully tomorrow so I will try then. If I get time I may try hooking up two bench PSUs and the main PSU (for -5v) and see whats going where whilst I have all the RAM removed.

-5v works just fine though, it was the only thing that did, but it is a very simple circuit.

Tomswork wrote: 29 Aug 2022 21:45 Excellent time for the power brick see if all the voltages show up at the ram socket. Do you have the monitor for is or you going to go into a smart connector or composit

Ton

See my reply to Stephen regarding the voltages, as for video output I'll be hooking it up to composite on my bench VDU.