Jon Hughes
Member
Hi everyone who's interested,
A while ago there was a thread running on an MK2 soundboard repair by action76. There seemed to be quite a lot of interest in the thread but sadly it just seemed to fade out.
I had 3 soundboards in need of repair (had) and decided to give them a run at repair. From the original thread I noted that the DAC (AD1851N-U16) could have been a problem source - so that would be my starting point.
Board 1 - dead, logic probe on pin 9 (voltage out) of the DAC was dead, inputs on pins 5, 6 & 7 showing logic. Pulled the DAC (U16) and replaced with a 16 dip dual in line socket and replaced the AD1851N. Powered up, one bong and then the music - nice one, one down two to go.
Board 2 - dead, logic probe on pin 9 & 10 of the DAC both dead, inputs on pins 5, 6 & 7 showing logic. Pulled the DAC (U16) and replaced with 16 dip dual in line socket and replaced the AD1851N. Powered up, no bong but now the diode light is on. Logic probed the whole circuit, all inputs and outputs good leading to U16. The logic stops past U16 into pin 9 so it's difficult to trouble shoot past there with the probe. Noticed U37 (TL084) was warming up and was getting nothing from inputs on pins 2 & 3 of the chip also R42 was negative on one side and no output on the other (but had voltage output of around 2.5V). R43 was exactly 6.19K ohms as expected so that wasn't the problem. Decided to pull U37 and replaced with 14 dip dual in line socket and placed in new TL084 chip. Powered up, bong and then music - nice one, two down one to go.
Board 3 - also dead, exactly the same problems as board 2 except U37 was super hot.
I've had to order two DAC chips from Hong Kong to complete the boards - which are currently missing in the photos. I just kept swapping the good one from board to board.
The logic in the circuit is reasonably ok to follow, if you are an intermediate and have some skills in repair working, you just need a fair amount of spare time and patience to trouble shoot. From what I've seen the common problem has been U16, followed by a few others. I hope this helps for anyone with a dodgy sound board that they want to repair. Sheet 3 of 5 of the manual covers all the problem chips I encountered - maybe this part of the circuit is vulnerable (possibly from a voltage surge or something).
I'll help anyone, in need, if I can but it's difficult when the board is not in front of you.
A while ago there was a thread running on an MK2 soundboard repair by action76. There seemed to be quite a lot of interest in the thread but sadly it just seemed to fade out.
I had 3 soundboards in need of repair (had) and decided to give them a run at repair. From the original thread I noted that the DAC (AD1851N-U16) could have been a problem source - so that would be my starting point.
Board 1 - dead, logic probe on pin 9 (voltage out) of the DAC was dead, inputs on pins 5, 6 & 7 showing logic. Pulled the DAC (U16) and replaced with a 16 dip dual in line socket and replaced the AD1851N. Powered up, one bong and then the music - nice one, one down two to go.
Board 2 - dead, logic probe on pin 9 & 10 of the DAC both dead, inputs on pins 5, 6 & 7 showing logic. Pulled the DAC (U16) and replaced with 16 dip dual in line socket and replaced the AD1851N. Powered up, no bong but now the diode light is on. Logic probed the whole circuit, all inputs and outputs good leading to U16. The logic stops past U16 into pin 9 so it's difficult to trouble shoot past there with the probe. Noticed U37 (TL084) was warming up and was getting nothing from inputs on pins 2 & 3 of the chip also R42 was negative on one side and no output on the other (but had voltage output of around 2.5V). R43 was exactly 6.19K ohms as expected so that wasn't the problem. Decided to pull U37 and replaced with 14 dip dual in line socket and placed in new TL084 chip. Powered up, bong and then music - nice one, two down one to go.
Board 3 - also dead, exactly the same problems as board 2 except U37 was super hot.
I've had to order two DAC chips from Hong Kong to complete the boards - which are currently missing in the photos. I just kept swapping the good one from board to board.
The logic in the circuit is reasonably ok to follow, if you are an intermediate and have some skills in repair working, you just need a fair amount of spare time and patience to trouble shoot. From what I've seen the common problem has been U16, followed by a few others. I hope this helps for anyone with a dodgy sound board that they want to repair. Sheet 3 of 5 of the manual covers all the problem chips I encountered - maybe this part of the circuit is vulnerable (possibly from a voltage surge or something).
I'll help anyone, in need, if I can but it's difficult when the board is not in front of you.
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