The traces for the speaker terminal burnt,not sure what cause the shot.The resistance across the speaker terminal was about 20 ohms.I had to cut the burn part of the board away to get 2.3k across them. Outputs test fine in circuit.I see 6v across the speaker terminal and the LED for service is on.Any suggestions on this one?
Do you read 0 ohms from the positive speaker terminals to at least one leg of the output transistors?
Do you read 0 ohms from the negative speaker terminals to the amp's main ground terminal?
Do you read 0 ohms from the negative speaker terminals to the amp's main ground terminal?
Both test read 0 ohms
The positive terminal is connected to the center leg of one group of output and the third leg of a other group of outputs
The positive terminal is connected to the center leg of one group of output and the third leg of a other group of outputs
Does the amp produce rail-rail oscillation on the legs that are connected to the speaker terminals? You may have to drive signal into the amp to make it oscillate.
Is LED400 lit?
Is LED400 lit?
I see no oscillation,LED 400 not on.
I found FET 192 shot and R147/8 open.I replace them.LED 400 now on but R138/9 is smoking
I found FET 192 shot and R147/8 open.I replace them.LED 400 now on but R138/9 is smoking
If the PS gate resistors are smoking, the FETs that they're connected to have likely failed.
After replacing FET 192, did you confirm that the negative regulated voltage was correct?
After replacing FET 192, did you confirm that the negative regulated voltage was correct?
The negative regulated circuit not working,I see about 47v on pin four of the op-amp closest to the RCA jack.The resistors that smoke is connect to pin four and eight of that same op-amp.I disconnect the pre-amp board at the moment to prevent damage if it has not yet been damage.
What parts make up the negative reg voltage?
What parts make up the negative reg voltage?
In the photos I have, R138 and 139 are power supply gate resistors. Is your amp different?
If the negative regulator is driving 50v to the op-amps, virtually every op-amp on the main board has likely been damaged. On the preamp board, many of the 10 ohm resistors feeding the power supply pins of the op-amps have likely opened.
If you have the full tutorial, look at the MTX7801 page. It shows the regulator circuit.
If the negative regulator is driving 50v to the op-amps, virtually every op-amp on the main board has likely been damaged. On the preamp board, many of the 10 ohm resistors feeding the power supply pins of the op-amps have likely opened.
If you have the full tutorial, look at the MTX7801 page. It shows the regulator circuit.
Regulated negative voltage is now normal.I am replacing op-amp now but the NE5532 i don't have it can i used TL072s ?
I replace the op-amps.Offset is gone and amp is producing good audio.
Is it normal for the output inductors to get to hot to touch within a minute?
Is it normal for the output inductors to get to hot to touch within a minute?
They get hot but I can't give you an exact rate at which they heat. If both are the same, I wouldn't suspect that either is defective.
They are cooled by the fans when the amp is driven hard.
They are cooled by the fans when the amp is driven hard.
They getting so hot i can see them starting to sink in the core.Also i can smell them.
If the inductor ares ok what order fault could cause them to over heat?
Both heat up same temperature.
I just notice there is 7v offset just before LED 400 comes on.After it it on the voltage goes down to 0.00 instantly.
If the inductor ares ok what order fault could cause them to over heat?
Both heat up same temperature.
I just notice there is 7v offset just before LED 400 comes on.After it it on the voltage goes down to 0.00 instantly.
What is the frequency of operation of the output stage of the amp?
Does the amp produce 7v of offset with a load connected?
Does the amp produce 7v of offset with a load connected?
As soon as LED 400 lit the 7v is gone.
If a speaker is already connected i still see the 7v but like pulse
Connect the frequency meter across the output terminals?
If a speaker is already connected i still see the 7v but like pulse
Connect the frequency meter across the output terminals?
No. From any point with rail-rail oscillation to the speaker negative.
If the amp drive 7v into a load, there is a problem with the drive circuit or beyond.
If the amp drive 7v into a load, there is a problem with the drive circuit or beyond.
Its no longer driving the 7v into the load .With a speaker connected it stays at 0v.
one the first leg of the output that connect to the positive speaker terminal i see 24.76khz.
One center leg i see 107.6khz
one the first leg of the output that connect to the positive speaker terminal i see 24.76khz.
One center leg i see 107.6khz
100k+ should be OK (shouldn't cause excessive heating of the inductors). It's unlikely that both inductors would be defective.
Are you sure that the windings are melting into the core? It's likely a coating used to prevent movement or noise.
Do you have a way to measure the actual temperature?
Are you sure that the windings are melting into the core? It's likely a coating used to prevent movement or noise.
Do you have a way to measure the actual temperature?
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