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Repair attempt TC-Electronic Nova System: DSP Audio (guitar)

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obiwanjacobi:
Hi,

I have bought a TC-Electronic Nova System from someone who accidentally connected (touched) the left output to 230v mains (oops!).

So I thought this would be a nice learning project and perhaps I end up with a working unit.
When the unit is powered up, the LCD display shows the initialization message but hangs after that.
So I figured not all is lost, the processor still seems to work...

I opened the unit up and measured the supply voltages. Seems all ok: +3.3v, +5v (for digital) and +/- 15v (for analog).

Then I tried to find the functions for the chips that are used on the main board. Here's the list:
1x 39VF040                  Flash ROM (Software v1.3)
1x (AMIC) A42L0616S-50F         1M x16 CMOS Dynamic RAM (with EDO Page Mode)
3x (CYPRESS) CG7130 ATT          (More RAM?)
1x (Motorola) DSPB56362 AG120       DPS Audio Processor (used as main processor?)
1x CS8414 CSZ               96kHz Digital Audio Receiver (?)
1x AKM AK4620 BVF            24 BIT 192KHZ AUDIO CODEC (with IPGA) (ADC/DAC)
3x 74LV00               4x 2-input NAND gates.
6x NE5532AP            Dual low-noise op-amp. (Texas Instruments)
1x HCT4052            Dual 4-channel analog multiplexer/demultiplexer
1x 74HC139            Dual 2-to-4 line decoder/demultiplexer
2x DG4410            Quad SPST CMOS Analog Switches

Because the (left) output was hit with 230v (connector is located on the main board) I figured that I would work back from that. It is possible that some of the analog circuits are fried - although no caps are blown or other physical marks/smells- I think I have to focus in on the DAC portion of the circuit. I think the processor hangs because it is waiting for some hardware signal that is not coming (because of a faulty component). My guess would be that either the CS8414 (audio receiver) or the AK4620 (DAC/ADC) chips are likely candidates. But I want to confirm that in some way.

The question is basically:
- Is my reasoning sound?
- How do check if these chips are still operating correctly? (is there some signal I could check?)

I do have a multimeter and an old analog 20MHz scope - but no logic analyzer. (Do I need to get one?)
I know I may be a bit in over my head, but still would like to give this a try.

Digital part of main board:


Analog part of main board:

Zarhi:
Self test menu:

1.Power on while pressing "DELAY" + BOOST".
2.Loop the midi in and midi out.
3.Follow the instructions as shown in the display.
4.Power OFF and ON.

Also there is service note:

If you have a product freezing or rebooting intermittently, especially when performing a drop-test,
you must pay attention to the flatcable.

obiwanjacobi:
The unit does not enter the test mode. The same initialization message is displayed (Nova System / TC Electronic).

I checked connectivity of the flat-cable, and all wires connect fine.
Would be very odd if this would have been the fault...

But thanx for the suggestion.

obiwanjacobi:
I turned the unit on for a while and felt the chips with my finger for hi temps (don't have a fancy IR camera like Dave) and both the DSPB56362 processor and the CS8414-audio receiver are getting warm really fast; after a few seconds they're is almost too hot to touch. The AK4620 is getting a little warm but not hot - but I would think a DAC/ADC should not get warm at all.

Is it normal for a DSP processor chip to get really warm/hot (without heatsink!)? Or is it a sure sign it has faulted. Strange how that LCD display is getting data - I can see no other processors on the main board. (there is (probably) a small processor/MCU on the top board with the buttons and display - would that be responsible for the LCD activity?)

Top left what looks like a small MCU (I have refitted the print and did not look at the part number).


The cheapest DSP is about $15,= and the cheapest CS8414 is about $12,= (havent looked up the ADC/DAC yet). Not too bad - but not cheap either...
Do I have a good chance replacing these chips will fix the problem? What else could I try?

Zarhi:
Check R166 ( between TP153 and TP20 ), and R167, they are 0R0 protection resistors between AGND, DGND and PGND.

Top left cpu is ATmega168, and yes, he is driving the LCD.

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