mbSID crashes, won't boot

[tangram]

My mbSID has been up and running and working well for some time. I've used it for tens of hours without any problems. Now suddenly I have crashes, (sound locks up, panel locks up after a few seconds, but works well until then) and reboots, but most of the time it won't even start up (top row of display is shaded, no MIOS message comes up, sometimes all LEDs light up, sometimes none, sometimes a selection).

I need some help identifying the problem. What parts can cause these issues? Since it has been working for some time, i know there are no shorts on the board themselves, the undersides are sealed off with glue on all sides, and I have checked all topside connections. Power supply delivers good and stable voltage (4.97V and 13.90V). From troubleshooting when building, i haven't experienced faulty serial registers from the DIN and DOUT modules causing issues like this. Also, the SID would not be the problem as communication is one-way. Can anyone help identify likely candidates causing these symptoms? Unstable PIC? Any tests I can perform?

[pay_c]

The first you can do is checking your 78xx´s. Just let the SID run for some time and then touch them. Do they get hot (especially the 7805 on the main core)? It sounds like a prob with the 78xx, because the probs start after a while and not from the beginning.

[tangram]

Thanks for the tip, but no, doesn't seem to be them, they are fairly cool. I'm using the optimized C64 PSU design, and the power is stable and voltage high enough (also over IC socket).

And actually, it doesn't start at all now. A selection of leds light up, top line of display is shaded (but not black).

I have tried disconnecting DINs and DOUTs, uploading the application without control surface enabled, so it's not the serial registers. When uploading, confirm messages were returned via midi, so the PIC is alive, so is the optocoupler, even tried replacing with a new PIC. Today i'll try replacing the EEPROM.

Thorsten, what elements are actually initialized, ie. where the PIC relies on a response, at startup?

[TK.]

where the PIC relies on a response, at startup?

there is only one thing  which can cause such an effect, and thats the "brown out reset" unit, which restarts the chip (or holds it in reset state) so long Vdd is less than the selected voltage level. The Bvdd level was ca. 2V before MIOS V1.8, and it is ca. 4.45..4.83V with MIOS V1.8

So, if your PIC is running with MIOS V1.8, there is a high chance that if the PSU is not strong enough, a short voltage drop will cause the reset, and that then the circuit remains in this state due to higher power consumption.

I activated this protection mechanism for a good reason, because once the voltage drops below 4.5V, there is a high propability that the BankSticks will be formated unintendionally - therefore a PSU problem cannot be fixed by releasing the protection, but it must be fixed by improving the power connections (or by using a better PSU)

A simple way to check if this assumption is the reason for the failure: disable the backlight of your LCD. If this doesn't help, remove also the DOUT module. Is the MBSID running stable under these conditions?

Best Regards, Thorsten.