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Hi Everyone,
Not sure if this is the right way to post this but here goes.
After completing the repair on a Kustom Sienna 30 I moved on to a Laney LA65C which appeared to have issues with the output IC.
Before replacing the TDA7294 I thought it might be prudent to check if there were any other obvious faults which could push the repair cost into the "not worth it" column.
Sure enough the voltages emanating from the power supply were incorrect, in fact half of the 25V supply from the transformer was missing. The transformer looked OK, no signs of overheating and the diodes (measured in circuit) also didn't show any issues.
Luckily the secondary wires inside the insulation of the transformer were readily accessible and it was soon found and seen that one half of the secondary winding had a very poor connection. No stress on the wires was apparent so wound a few turns of fine copper wire around each connection, resoldered, checked and re-did the insulation. Transformer now working!
Fitted a new output IC and hoped that would be the end of this repair, but unfortunately there was no audio out into the speaker.
Traced the wiring from the output board back to the control board but could not find any possible issue. Not being familiar with this amplifier I did some further checks and head scratching and found that when a jumper was soldered across from the send to the return jacks sound was once again audible. No amount of pushing, tapping and twisting would bring back the sound when the jumper was removed. Looked for hairline cracks in the tracks of the circuit board but all to no avail, then with the aid of a signal tracer I located a crack in a connection between a resistor and the circuit board track. The resistor was held in position with epoxy glue so it couldn't move and I guess that because of this solid fixture with the glue the connecting wire of the resistor broke away from the circuit board track when stressed by heat or movement.
Anyway with the aid of some fine copper wire a good connection was achieved and the amp roared back into life.
But what caused the IC to go to heaven? Did the poor transformer connection cause sparking and send spikes down the HT lines or did the IC just give up the ghost?
I'll let the amp run on test for a day or two and then return it to the customer.
Not sure if this is the right way to post this but here goes.
After completing the repair on a Kustom Sienna 30 I moved on to a Laney LA65C which appeared to have issues with the output IC.
Before replacing the TDA7294 I thought it might be prudent to check if there were any other obvious faults which could push the repair cost into the "not worth it" column.
Sure enough the voltages emanating from the power supply were incorrect, in fact half of the 25V supply from the transformer was missing. The transformer looked OK, no signs of overheating and the diodes (measured in circuit) also didn't show any issues.
Luckily the secondary wires inside the insulation of the transformer were readily accessible and it was soon found and seen that one half of the secondary winding had a very poor connection. No stress on the wires was apparent so wound a few turns of fine copper wire around each connection, resoldered, checked and re-did the insulation. Transformer now working!
Fitted a new output IC and hoped that would be the end of this repair, but unfortunately there was no audio out into the speaker.
Traced the wiring from the output board back to the control board but could not find any possible issue. Not being familiar with this amplifier I did some further checks and head scratching and found that when a jumper was soldered across from the send to the return jacks sound was once again audible. No amount of pushing, tapping and twisting would bring back the sound when the jumper was removed. Looked for hairline cracks in the tracks of the circuit board but all to no avail, then with the aid of a signal tracer I located a crack in a connection between a resistor and the circuit board track. The resistor was held in position with epoxy glue so it couldn't move and I guess that because of this solid fixture with the glue the connecting wire of the resistor broke away from the circuit board track when stressed by heat or movement.
Anyway with the aid of some fine copper wire a good connection was achieved and the amp roared back into life.
But what caused the IC to go to heaven? Did the poor transformer connection cause sparking and send spikes down the HT lines or did the IC just give up the ghost?
I'll let the amp run on test for a day or two and then return it to the customer.
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