A&H GS3000 mpu problem

Discussion in 'Tech Talk - Electronic Repair Modifications DIY' started by Kevin Porter, Mar 16, 2017.

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    The New AT5047 Premier Studio Microphone Purity Transformed

  1. Nanner Puddin

    Nanner Puddin Active Member

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    Knoxville, TN
    Update: Well I got my GS3000 back from my local Genius type tech guy. It turned out that there was a cold solder joint on the MPU that was causing the problem. He fixed that up and now it works fine. There was also a cold solder joint in one of the group meters, so this very well could be an issue endemic to the time period and/or factory where A&H produced it. Anyway, I do plan to get an extra MPU from A&H if I can, as a real failure on that could really screw me over in the future, as I plan on keeping this for a long time. Thanks to everyone for the help and good luck Kevin!!!!!

    Doug
     
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  2. Boswell

    Boswell Moderator Well-Known Member

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    Glad you got it fixed!
     
  3. Kevin Porter

    Kevin Porter Active Member

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    I just ordered the part from Jam Industries located here in Canada. They are the national distributor for A&H. Its a 3-4 week wait for them to get the part. It about 120 bucks all told.
    I have since bent and broke pins off the last eprom trying to get er going again. Not this time. LOL
    If i had more money i would have ordered a few of them. Jam part number is
    002-347JIT GS3000 MPU PCB
    Web page https://jamindustries.com/contact/
     
  4. Kevin Porter

    Kevin Porter Active Member

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    OK Bad news. I just got an email back from Jam industries and they said there is no more MPU's available so they have cancelled my order.. I am going to try and see if they can service the card locally. If not i will be shipping it to Boswell for repair.. Boswell, could you message me your shipping info??
     
  5. Nanner Puddin

    Nanner Puddin Active Member

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    Well crap, mine just died again. One thing is wierd, every mute is on except the two Mutes for the AUX busses just above the master section. I have some jobs coming into the studio so I have to get this fixed quickly. I called Full compass here in the states and the said they can get a replacement but it will take 4-8 weeks on backorder. I went ahead and ordered even though I expect to be disappointed the same way as Kevin was. I also ordered an EPROM programmer and some blank EPROMS and sockets from EBAY. Hopefully I can get this fixed up as I really love this console!

    Doug
     
  6. Boswell

    Boswell Moderator Well-Known Member

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    Most likely to be bad contact between the EEPROM pins and the socket. If you have the official download of the EEPROM contents, it's worth programming one of your new ones and simply swapping it over to see if that makes any difference. If it works after doing that, use it for your immediate studio jobs and then consider swapping out the socket when you are under less time pressure.
     
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  7. Kevin Porter

    Kevin Porter Active Member

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    I managed to fix mine. I burned a eeprom and that didn`t work but hey i learned to burn eeproms!! Turned out the 5 volt regulator was blanking out in the power supply so i would check that out. Simple one dollar fix. Solder in a new regulator. Its been good ever since. I had broken legs off the original eeprom popping it in and out several times so the one i burned came in handy after all. There is no choice but to fix the MPU you have seeing as there is no supply for MPU`s anymore.
     
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  8. Kevin Porter

    Kevin Porter Active Member

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    The hardest part about the repair was decabling the console and staring at it forever once i had it standing up with the back off it. LOL I too love this console. Its been great and im quite happy i didn`t have to send it out anywhere to get it fixed. I actually bought all the parts in the power supply and was going to replace them all but once i changed out the regulator and it started working i just put it back together and will save the other caps and resistors for another day..Dont lose hope. Its a great console and can be brought back. If i could do it so can you. Bozwell has been a great inspiration in this endeavor and i have learned a lot as a result of his guidance on this and other repairs i have made to other gear i have.
     
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  9. Nanner Puddin

    Nanner Puddin Active Member

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    Well how about that! I stood the console up and started checking the voltages on the MPU starting with the 15.6v input. I went backwards then from the 5V side and there was no voltage until after the 1 Diode. I poked around some more with the DMM and the all of the sudden it came on. In effect, the old circuit disturbance test. I pulled the board and reflowed the solder joints on the regulator and the diode. She is back in place and running as of now. I am now on a mission to aquire all of the spare parts I can that are on that board, and still available.

    On the plus side, I now have an EPROM programmer, a bunch of sockets and some blank EPROMS. I also have not heard back from Full Compass on whether they can get a spare board from A&H. I expect that to be a bust, but I will keep you guys posted.

    Thanks for all the help Kevin and Boswell!

    Doug
     
  10. Kevin Porter

    Kevin Porter Active Member

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    Awesome! I had a feeling you would ace it one way or the other. The parts on that MPU are pretty common and you should be able to get them just about anywhere that sells electronic stuff. All in all its a pretty bullet proof console aside from the MPU. I have never had any other issues with mine other than the only "digital" pcb in the console. I expect its a happy day in Knoxville
     
  11. ByronDonald

    ByronDonald Active Member

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    Hi..i am looking through the schematic it appears there are 3 supplies that branch off from the main outboard PS. VA VB VC. They all appear to be fed from the 16v+ and 16v- plus ground from the external power supply I think my problem may lay in the VA part of the supply. Looks like the filtering and IC regulation is inside the mixer so the next step is to de wire the mixer and get it into an upside down position to work on.
    Probably a 50 cent cap causing all this grief.
     
  12. Boswell

    Boswell Moderator Well-Known Member

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    If your mixer is a GS3000, then the power supply should be the RPS11. I don't have access to the schematics of that PSU. What are the nominal voltages of the three power supply outputs? What do they actually measure when switched on but not powering and then when powering the mixer?
     
  13. Kevin Porter

    Kevin Porter Active Member

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    So Byron, what are the symptoms you are having with the console?
     
  14. Andy Halliday

    Andy Halliday Active Member

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    Southampton, UK
    Hello everyone :)

    Guess what! I too have a GS3000 with all the MIDI lights on and no signal anywhere!

    Actually, it's not my board, it was in the studio I just started working at in Southampton, UK. The studio has been a bit neglected and the board belongs to someone else who used to record here.
    I decided to plug it in and see how it compared to direct in recording to the Focusrite Scarlett 18i20... I'm sure it's going to be magic if we can get it working again... I'd love to be using the board and the tube pres...

    So - I need to open this beast up and resit the EPROM, right? OK - here goes!
     
  15. Nanner Puddin

    Nanner Puddin Active Member

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    Hey Andy, so when you say the MIDI lights are on, do you mean the Mute buttons are all red? Do you see a Green number in the LED diplay in the center section(probably a 1)? If the mutes are on AND there is no number, it could be the EPROM, but it might be that there is no power to the internal MPU board. That was the case with mine and the culprit turned out to be a bad diode in the onboard power supply right before the Voltage regulator. It would be well worth your time to trace the voltage from the supply wire( i think 24v from memory) all the way to the 5v that the eprom uses.

    Once I figured out the problem, it was an easy fix. Before that it had bedeviled me for quite some time, as it had worked intermittently. I love my console and I think if you can get it running you will too.

    I hope this helps!

    Doug
     
  16. Andy Halliday

    Andy Halliday Active Member

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    Hey Doug,
    Forgive me - yes - that's what I mean.
    Mute lights are all on. No green numbers... I look forward to this beaut working properly!
    I have no intermittent fault - it does the same thing every time I power it up.
    You mention "It would be well worth your time to trace the voltage from the supply wire( i think 24v from memory) all the way to the 5v that the eprom uses."
    What would I do to achieve this? I can't see even where to unscrew to get inside the board at present and am not massively experienced with electronics. That said, I have a GCSE in Electronics, made a Monome controller once, to apart an SSL at work once to update it or something like that, and am confident I can achieve the required result if I have a guide or some such...
    Any help appreciated in where to start!
    I also have a fairly cheap but prob not too bad multimeter and soldering iron!
    Peace thank you
     
  17. Boswell

    Boswell Moderator Well-Known Member

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    There are several likely causes for this problem:

    1) Low or absent power to the MPU board (the fault that Doug described)

    2) A poor contact on either the MPU board connections or the EPROM pins

    3) A hard fault on one of the MPU board components

    4) An EPROM image corruption

    Of these, faults 1 and 2 are the more likely. Identifying which one would require access to and maybe removal of the MPU board.

    The GS3000 schematics are downloadable here. Since I have never had to get inside a GS3000, I'm not the best one to guide you on that task. GS3000 owners Doug or Kevin here may be able to offer help on that.
     
  18. Nanner Puddin

    Nanner Puddin Active Member

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    Knoxville, TN
    Andy,
    So first, make sure do download the schematics in the link Boswell included. In fact, you should download every document that is related to the GS3000. Next, you will need to stand the board on its back on a sturdy table(hopefully yours has the meter bridge). Elevate it with a couple of 2x4s so you will be able to test it while powered up, but don't attach the power yet. There are a series of screws around the edge that hold the bottom cover on. Take those out and you will see the MPU board just off center and attached with screws and one red wire and one green wire. The top quarter of this board is the power supply. This will match the schematic on page 16 of the schematics file. Start by checking the voltage on the red and green wires. The red is positive. I should read ~16v. If that is fine then leave the ground probe on the green and check the voltage on the third leg of the voltage regulator(the right leg). That should be 5v. If not, the problem is somewhere between those two points so you will have check each component along the way.

    I would very seriously consider having someone around as a helping hand for this, as you will want to place your probe then turn on the console to check the voltage, then immediately turn off. If the probe accidentally touches two points at once it could cause a lot of damage to the circuit, so use that process for each component. I hope the picture helps, that is the MPU from my console. If you have any questions please let me know.

    Oh, and if one of the components is bad, you will have to remove the board to replace.

    MPU Pic.JPG
     
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  19. Boswell

    Boswell Moderator Well-Known Member

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    That's a great set of instructions and an amazingly clear photo from Doug. On his unit at least, the microprocessor is soldered in, but the V1.02 EPROM is in one of those terrible side-force sockets. My guess is that one of the EPROM pins is no longer making good contact with its socket. That type of socket causes a perennial headache, and it's why I had constant battles with the bean-counters in various companies' design departments to use the more expensive turned-pin ones. How do you put a cost on a reputation for reliability?

    For your unit, try the EPROM re-seating technique I detailed in post #5 of this thread, taking GREAT care that your screwdriver blade that does the twisting slots in between the EPROM and its socket and not between the socket and the circuit board. It looks as though you should have sufficient access to use a small plastic-handled screwdriver for this task without having to remove the board from the mixer. Be sure the mixer mains lead is unplugged from the mains while doing the re-seating. If you follow Doug's positioning suggestions, you can re-power and check before moving the mixer or putting the bottom cover back on.

    Let us know the result of re-seating, so we can advise you on what to do next.
     
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  20. Andy Halliday

    Andy Halliday Active Member

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    Southampton, UK
    Hey - sorry, I missed this last week - AMAZING thank you so much. I'm gonna get someone in to help me do this, and report back ASAP.
    Again - thanks so much.
     
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  • AT5047

    The New AT5047 Premier Studio Microphone Purity Transformed

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