Tc Electronic G Natural repair. Help and advice needed.

[tedsorvino]

Hi all.
I recently found a non functioning TC Electronic G Natural unit, that i don’t know its story. By non- functioning, i mean completelly dead. No lights, no screen. Nothing.

I tried the voltages on the main board pcb and they were very low (2vdc and 3.8vdc instead of 3.3vdc and 5vdc respectively on the digital side and -11vdc and 11vdc instead of -15vdc and +15vdc, respectively, on the analog side).

I disconnected the power supply pcb and the voltages on its connectors were spot on. 3.3 and 5vdc on the digital side and -15 and +15 vdc on the analog. So obviously the problems are after the power supply board.

I have to admit that I also can’t really figure out the exact grounding scheme. 3 different grounds? Digital never goes to the chassis? I guess c ground means chassis ground and not common ground. There is no common ground point. I don’t really know if there is a missing ground cable. There is only one from the main pcb, to the front pcb, connected to the digital ground and also, chassis ground on the audio connectors.

I realized that the large dsp ic 3 (dsp 56362) is getting really really hot very quicly and that the 3.3vdc pad and ground pad are shorted on the mainboard.
So since there is no obvious short (solder, bad pad etc.) around there, I came to the assumption that the large ic maybe shorted and that’s what makes all the board voltages go tripping.
I want my guess to be wrong because it’s a multipin qfp 100 smd ic and even if i can desolder and solder smaller ics, this thing seems gigantic and haven’t got a hot air desoldering tool). I don’t even know if it has software in it and i haven’t got a clue how awhere to find it and write it on the ic. Apparently the G Natural specific software is in ic12, but it may contain other tc electronic programmed functions. Any ideas?

After finding the schematics and pcb layout here:
https://service-tcgroup.tcelectronic.com/g-natural/1/

and here for the power supply:
http://www.dirk-hendrik.com/temp/TC_electronic_SMPS JKS020Q1.pdf

i realized that there were certain parts missing from the main board (c 163, c188, c164, c187 from the power section of the board, c46 and c42 from the dsp section and d27,d28 from around the midi thru on the interface section). Obviously somebody attempted a horribly blind fix. I replaced all missing parts, but the results were more or less the same. Low voltages, hot ic, shorted pads.

Is there a way to isolate the dsp area, in order to check voltages without it in the equation? It would help to figure out if the pads short problem lies elsewhere and i may be lucky and save the dsp ic.
I realized that it takes 3.3vdc from many pins. Should i remove every supply rail?
Thanks in advance

 

[Khron]

Is there a way to isolate the dsp area, in order to check voltages without it in the equation?

See in the schematic if there might be any ferrite beads or inductors on the supply rail(s) to the DSP - removing those would likely be easier than cutting pcb traces.

 

[tedsorvino]

See in the schematic if there might be any ferrite beads or inductors on the supply rail(s) to the DSP - removing those would likely be easier than cutting pcb traces.

Thanks Khron. There are a couple of coils there, but there are also about 25 supply rails. Some of them directly on the ic. It’s a qfp 144. Seems like a quite desperate situation.