Hi all.
I recently found a non functioning TC Electronic G Natural unit, that i don’t know its story.
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 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 the pcb layout here:
and here for the power supply:
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
Comments
From your temperature…
From your temperature observations, I think you are probably correct in surmising that the DSP chip is blown. How that happened (for a previous owner?) would not be easy to say. The power supply design is such that if one rail is brought low, the others will tend to follow.
If I had the board in front of me to investigate, I would carefully remove the DSP chip using solder wick and a chisel-ended bit in a temperature-controlled soldering iron. After cleaning up the board area where the chip was, I would then re-apply power and see if the voltages were now OK. That would at least identify whether it was the DSP that was pulling the rails low. Of course it could mean that, even if you fitted a new DSP chip, the board still might not work, as whatever fault caused the DSP to blow may have damaged other devices..
Fault-finding on surface-mount boards is an interesting exercise.
The DSP chip has EPROM…
The DSP chip has EPROM storage (30K x 24 bit) for the configuration and operation of the device. A replacement part would have to have been pre-progammed w
I don't know what you mean by "The software is definitely on the other chip." The DSP uses three byte-wide 128K SRAM chips for volatile data storage, a 4K x 16 SDRAM for working storage and a 512K x8 flash ROM for program storage..
Ps. By non- functioning, i…
Ps. By non- functioning, i mean completelly dead. No lights, no screen. Nothing. 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 commin ground.