I am working on a Peavey Transtube 112 EFX. It came to me with "a loud hum" but no output.
(I am trying to add as attachments a schematic of the power amp for this amp and a drawing of the pinout for the LM3886, but the files simply will not upload. I'll continue working on it and add them when I can.)
I disconnected the speaker, checked for DC on the speaker leads and measured -39vdc with my red voltmeter probe on the wire that connects to the positive speaker terminal and my black probe on the wire that connects to the negative speaker terminal.
I isolated the problem to the power amp by running the a cable out of the effects send to the power amp in of a known good amp and confirming that everything worked as it should.
This amp uses an LM3886 Audio Power Amplifier for its output.
I traced a signal through the power amp to pin 10 of the LM3886. From there, there is no signal out of the LM3886. I measured voltage on the various pins and got the following readings"
Pin 01: 39.3vdc
Pin 02: 0.00
Pin 03: 39.3vdc
Pin 04: -39.5vdc
Pin 05: 39.2vdc
Pin 06: 0.00
Pin 07: 0.00
Pin 08: -1.2vdc
Pin 09: -2.0vdc
Pin 10: 0.00
Looking at the power supply, I measured + and - 15vdc where the schematic shows it, and + and - 39vdc where the schematic shows + and - 35 volts.
I did not find any obvious damage or failed components, although C119 had a cracked solder joint, which I repaired.
I am looking for suggestions as to where to look next. The voltage measurements on Pins 3, 8, and 9 of the LM3886 look fishy. Does it look like the LM3886 may be bad? How would I test that device?
Does anyone have other suggestions as to what might be wrong here?
Thanks.
(I am trying to add as attachments a schematic of the power amp for this amp and a drawing of the pinout for the LM3886, but the files simply will not upload. I'll continue working on it and add them when I can.)
I disconnected the speaker, checked for DC on the speaker leads and measured -39vdc with my red voltmeter probe on the wire that connects to the positive speaker terminal and my black probe on the wire that connects to the negative speaker terminal.
I isolated the problem to the power amp by running the a cable out of the effects send to the power amp in of a known good amp and confirming that everything worked as it should.
This amp uses an LM3886 Audio Power Amplifier for its output.
I traced a signal through the power amp to pin 10 of the LM3886. From there, there is no signal out of the LM3886. I measured voltage on the various pins and got the following readings"
Pin 01: 39.3vdc
Pin 02: 0.00
Pin 03: 39.3vdc
Pin 04: -39.5vdc
Pin 05: 39.2vdc
Pin 06: 0.00
Pin 07: 0.00
Pin 08: -1.2vdc
Pin 09: -2.0vdc
Pin 10: 0.00
Looking at the power supply, I measured + and - 15vdc where the schematic shows it, and + and - 39vdc where the schematic shows + and - 35 volts.
I did not find any obvious damage or failed components, although C119 had a cracked solder joint, which I repaired.
I am looking for suggestions as to where to look next. The voltage measurements on Pins 3, 8, and 9 of the LM3886 look fishy. Does it look like the LM3886 may be bad? How would I test that device?
Does anyone have other suggestions as to what might be wrong here?
Thanks.
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