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Fried digital controller - still worth a try?
Old 2 weeks ago
  #1
Gear Head
 

Fried digital controller - still worth a try?

Hi there,
bad things happen, so my Tannoy TDX1 - manufactured by TC Electronics was fried applying 48V phantom power to its output 3/4. It is a digital controller for PA setups, providing equalizing and crossover function for Sats and Subs, mainly for the Tannoy V series. It did a good job and it is not so cheap to get. AND I really hate having fried this otherwise brand new condition thing.

What it does now is it tries to boot up: display shows the version of the OS chip "TC SMC AVR v1.2", followed by a very short "factory reset", then "Kernel cleared", finally starting again from the beginning. It seems it notices sth. is wrong, performs a factory reset and boots again. "Kernel cleared"? - hmmm.

Just speculating- maybe the OS chip is still OK which is good because it might be hard / expensive to get. On the other hand it would be the most easy part to replace as it sits in a socket.

Please see the fotos. You can get some orientation with the grey flat cable that connects the display and front. The Sub outs were the XLRs on the right. On the PCB You can easily spot
- the Motorola DSP chip: Motorola DSPB56362PV120 ($15)
- the "Main Tannoy Ver 101" OS Chip in the Socket
- several memory chips: Cypress CY7C1019CV33-10VC 0431 (probably discontinued..)
- cs8414-cs Cirrus Logic 96 kHz Dig. audio Receiver ($15)
- 74LVOOD - Nand gates (sold on ebay)
- AK4620BF - 24-bit 192 kHz Audio Codec with IPGA

So - do you have any idea if this is worth trying to fix it? I maybe could get a guy who can solder this kind of stuff. But the tricky part should be trying to figure out which part to replace first. Maybe there are some test procedures I could execute beforehand .. maybe some guy with experience knows what to do.

THANKS!
Attached Thumbnails
Fried digital controller - still worth a try?-20200406_203205_1920x1080.jpg   Fried digital controller - still worth a try?-20200406_203214_1920x1080.jpg   Fried digital controller - still worth a try?-20200406_202956_1920x1080.jpg   Fried digital controller - still worth a try?-20200406_203156_1920x1080.jpg  
Old 2 weeks ago
  #2
Lives for gear
 

Do you have any manual or anything that gives the usual procedure for a factory reset? Maybe whatever input pin or jumper or whatever is used to do a factory reset is stuck in the reset position.

At any rate, it's pretty clear that the DSP chip is operating and the PROM chip would also appear to be okay, since it's rather obviously executing some code. The RAM chips I suspect probably are okay; I'd expect it to give some other sort of error ("memory error") or just kind of crash. The audio codec chip might be bad, and it would also seem the most likely to be affected by phantom power of all the main digital chips. I generally might have expected an analog driver circuit of some sort between that chip and the outputs, but maybe they are connected more or less directly. (Incidentally, Digi-Key has what appear to be equivalent SRAM chips available, and they aren't crazy expensive. Many RAM chips are relatively standardized across manufacturers.)
Old 2 weeks ago
  #3
Gear Head
 

Hey,
thanks for your input!!
- the factory reset you do by pressing "up" on the keypad while powering on. I already tried that. Means, the controller does it by itself which is why I suspected it notices sth. is wrong.
- there are some OP amps and "High-Speed CMOS Logic Analog Multiplexers and Demultiplexers" (HCT 4052M) on the way to the audio codec chip, I think.

So you say, this is the central D/A unit here and as it is the first digital chip in the path it´s the most likely to be burnt and you´d try and replace those?

It seems to be one of the tougher ones to find a supplier for..

Is there anything else one could do to analyze the fault? I guess for devices like these there are no service manuals publically available..

I also thought about going officially via TC electronic official partners but I guess this would be at least as expensive as buying another exemplar..
Old 2 weeks ago
  #4
Trying to trouble shoot digital equipment without the proper test gear and schematics is going to be problematic. Have you contacted Tannoy or t c electronics? That might be a good place to start. One caveat...with the COVID-19 shutting down almost everything it might take a while for them to get back to you. Just sayin...
Old 2 weeks ago
  #5
Gear Head
 

.. well I contacted an official partner repair workshop of TC Electronics, wrote an email with all details. But the usual way it goes is that you have to order a repair offer which itself costs about 35€ if you don´t choose to let them fix it.

My guess was that the standard repair would be too expensive anyways and I´ll then have additional 35€ to pay..
Old 2 weeks ago
  #6
Lives for gear
 

If it were mine, I wouldn't be replacing any chips (particularly ones that are not easy to source) without a lot more troubleshooting to try to prove that they aren't working. At this stage there's a lot of guesswork still. Troubleshooting, without the benefit of design documents or maintenance/repair manuals, would presumably involve a lot of time with datasheets for the chips and oscilloscopes and logic analyzers to watch what is happening in the digital realm. Reverse engineering, or at least disassembling, relevant parts of the firmware to see why it thinks it needs to reset could also be involved. All of this is not exactly easy. About all that can be done by plain observation is to see what is clearly working at least to some extent, which helps rule out some parts.
Old 2 weeks ago
  #7
Lives for gear
 

do not expect to get any valuable support from any of the brands which went under the umbrella of/got bought by evil b.!

their main focus is on prosumer/mi gear for which formerly top-of-the line gear gets cannibalized; all manufacturing went to the far east, the tax domicile of some companies is in offshore tax heavens (and they don't even make any attempts hiding this!); i therefore started selling most of the gear from all those brands except for some for older pieces from the 90's which seem to outlast most of their newer gear...

in a nutshell: i applaude your efforts trying to fix your processor - i'd proably be easier to find a used one for reasonable costs.
Old 2 weeks ago
  #8
Gear Head
 

yeah, it´s a pity they´re heading into this low to mid-level crappy not-worth-a-repair domain. That´s how you make money these days. Same with them new Tannoy Gold Monitors. Bang for the buck at least..

What you write is not really encouraging. The workshop offering the repair service seems trustworthy, though not cheap:
https://www.pms-electronics.de/
I checked again and creating an offer is "35€ at least", invoicing according to effort hours. So that might well go direction 100€ without having anything repaired.

Maybe I´ll check with a local allround electronics shop.

My original idea was to try and learn to repair such a thing but as you wrote - without any documentation and testing equipment at hand this might be rather illusionistic than idealistic.

One more thing- is it normal there´s no protection against accidental phantom power in any way?
Old 2 weeks ago
  #9
Lives for gear
 

Quote:
Originally Posted by mrwolfgang View Post
(...) is it normal there´s no protection against accidental phantom power in any way?
i'm technically not knowledgeable but transformers imo should do the trick?

i liked the tannoy/tc x-over quite a bit: the difference in the quality of d/a converters compared to say those of the yamaha ls-9 desk was remarkable...
Old 2 weeks ago
  #10
Most repair places will charge you a fee for looking at the equipment but then if you tell them to go ahead they will count that as a down payment and deduct that from the total charged. It is designed to prevent them from having to trouble shoot equipment and then having the customer say "no just send it back" which means that the repair place is out the time it took to trouble shoot the problem. With digital it is really vital that the repair place have the necessary test equipment and schematics and flow diagrams to trouble shoot the problem. A "local" shop may have the test equipment but without the schematics and flow diagrams it will be a long costly repair IMHO. Best of luck! see post #6 for more info.
Old 2 weeks ago
  #11
Gear Head
 

Would it help the DIY repair job if you would have one identical (working) unit at hand for comparing and analysis?
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