I’ve been asked by someone to have a go at repairing his Grids (it’s a real, factory-built grids, not a DIY job). Here is the back story:
Do you have anything to suggest on resurrecting a Grids that I suspect has had a high power spike down the 5volt rail? I’m not 100% sure that is what happened as I got it the way it is. But it’s doing my head in having such a good module sitting here which i suspect doesn’t need much done to get it up and running.
Olivier didn’t want to suggest too much to fix it and sent me another at wholesale price which was nice of him and I didn’t push him for suggestions etc as he’s already good enough to freely open source his stuff and provide schematics etc.
I’ve replaced D1 and P1 and have checked when powered things look good. I’m getting the -5 ref off the LM4040 and also the expected 5 volts elsewhere like the midi expansion and at R3 connected to pin 29 of the atmega.
Olivier suggested (and i think he’s right) that a high voltage down the 5 volt rail has killed the op amps, shift register and the processor. He coudln’t send me a new processor as he programs them all in circuit.
I was wondering would you consider having a look at it and replacing those chips if need be and pop a new processor on and flash it? I’d give it a go myself but as you know i’m a through-hole dinosaur and even though I do the odd bit of smd i’m not really tooled up for something like the processor swap or then flashing it.
I’ve had a crack at it, and have floated off the Atmega with hot air and put a new chip in its place. Applying power seems to result in 5V in the right places, as the owner suggests. However, all attempts to flash the chip fail - the AVR programmer doesn’t get a valid signature from the chip (It’s a genuine AVR ISP mk2 programmer, and it definitely works, and the cable was connected the right way round).
Any suggestions on how to proceed? Is it worth replacing the crystal or the crystal timing caps? Or proceed to replacing the op amps and 74HC595 switch? Or just set it aside? It’s owner doesn’t have any great expectations. Any advice appreciated.