Digital Design M1d

[barber02]

Hey Perry,
Sorry for the delayed response. I had a thunderstorm come through yesterday so I shut my lab down early.

The diode connects to pin 7

 

[barber02]

Pin 8 and pin 5 are connected together via a 5 band resistor R227. Best I can discern is that it should a 12k ohm resistor 5 percent tolerance. In circuit it reads about 16k. I’m going to pull it and check it out of circuit.

Pin 8 connects to the high side FETs through a 7 ohm resistor R281 and then the trace continues on to a couple of at the gates of the high FETs (R237 and R235) at 27 ohms each on the last two high side FETs.

David

 

[barber02]

That resistor reads 83.2k ohm out of circuit.

 

[Perry Babin]

Did that solve the problem (assuming that the 12k resistor was the one that was far out of tolerance)?

I've requested more information on this type of amp from another tech. There is little chance but I have nothing solid to work with.

 

[barber02]

No. Pin voltages are the same.

 

[barber02]

I pulled the J111 transistor that is identitfied as Q282 on the board and tested in my transistor tester and this is the result it gave me. Do you think this may be why my output section has no drive and is dead quite? I have positive and negative rail voltage but no drive.

I don’t have any in stock so I’ll have to order some.

 

[Perry Babin]

I don't know what the tester is telling you. Typically, a jfet will read low resistance between the drain and source with a meter and will read as a diode in one direction between the gate and the other terminals.

 

[barber02]

I know. I was a little confused as to the results myself.

 

[barber02]

I forgot to follow up on this repair.

The faulty component was L5 in front of D34 and D23. It was open. Replaced the ceramic inductor and the amp produced audio again.

David