Extremely low volume output with my JVC KD-V6

[hot-diggity]

Recently picked up this deck off eBay with the seller claiming "low volume output." I assumed it might have just been a little difficult to hear, but apparently "low volume" was a bit of an understatement. This is a recording of a random tape with the output volume of the deck set to max.

List of things that I don't think have anything to do with the problem:

• Output ports, the volume is the same whether I use the line out ports or the headphone port.
• Anything controlling overall audio output, monitoring an audio input is in the normal volume.
• Solder connections/wires, visually the wires are all fine and I cleaned most of the solder points.
• On-board equalizers for playback, they seem to function fine but messing with those still doesn't bring the volume anywhere near listenable levels.

Things I can see being possible causes:

• The playback head (right) has some weird crust or something that won't come off with a q-tip and isopropyl alcohol. I don't really think this is an issue as I've spoken to someone that has KD-V6 as well and they also have this on their playback head, and theirs is working just fine. Also, it looks like it's not on the part where the head physically touches the tape.
• There's stains from some sort of liquid in the well the cassette goes in, so I guess there could be water damage to the play head. However, the erase and record heads, which are right next to the play head of course, work completely fine (recorded over a tape on this deck and played it back on another one) and it'd be strange for whatever was spilled here to only affect the play head. This could still be a problem of course, I'm just saying it'd be weird if only the playback was damaged from it.
• The op-amp IC (or some surrounding component like a cap) could have some problem with it. In my mind, this seems like a likely reason because this is the only thing between the play head and those equalizers I was talking about in the other segment.

As I said on the last bullet, that was all from my mind, and my mind isn't exactly a library when it comes to circuitry knowledge, so the issue could very well be something else entirely I just haven't thought of yet (or ignored/overlooked). I do want to test the outputs individually from the op-amp IC and the play head, but I can't wrap my head around the data sheet for the op-amp nor what to look for for raw outputs from the play head, so can't do that at the minute. I've fully exhausted my thinking capabilities on this and have no idea what else to do/look for, so I would highly appreciate it if someone here who knows more than I do can put in their two cents, thank you.

 

[Sam08861]

I'm a beginner still working on a similar issue and muting transistors have been suggested as one item to take a look at. My issue is slightly different as everything is muted, however.

The suggested thing to do was to signal trace and find out where the music stops. I'm new at this, but found several videos on how to do this or make a device to do this. Perhaps worth a google as a another avenue of thought.

 

[hot-diggity]

I'm a beginner still working on a similar issue and muting transistors have been suggested as one item to take a look at. My issue is slightly different as everything is muted, however.

The suggested thing to do was to signal trace and find out where the music stops. I'm new at this, but found several videos on how to do this or make a device to do this. Perhaps worth a google as a another avenue of thought.

Well, looks like to signal trace I need an oscilloscope, which I don't have and costs a fair bit of spending money which I also don't have at the moment. I've checked all the transistors on my board that are in the parts that deal with only the playback volume and they all seem fine, guess I might need to put this project on hold for a bit until I can get an oscilloscope.

 

[WernerO]

• Anything controlling overall audio output, monitoring an audio input is in the normal volume.

Be precise in your decriptions: in source monitoring more, is the output volume normal, yes or no?

• Solder connections/wires, visually the wires are all fine and I cleaned most of the solder points.

What's the point of cleaning solder?

• On-board equalizers for playback, they seem to function fine but messing with those still doesn't bring the volume anywhere near listenable levels.

What do you mean with on-board equaliser? How did you test them?

Things I can see being possible causes:

• The playback head (right) has some weird crust or something that won't come off with a q-tip and isopropyl alcohol. I don't really think this is an issue as

You might try acetone, careful not to touch, or even come near, any plastic parts.

• The op-amp IC (or some surrounding component like a cap) could have some problem with it. In my mind, this seems like a likely reason because this is the only thing between the play head and those equalizers I was talking about in the other segment.

Download the service manual, look at the schematic and follow the signal path from head to output. Often there are arrows indicating the flow.

First check if all stages get the correct supply voltage (DVM in DC mode).

Record a cassette with 300Hz or 400Hz at 0dB on the meters, then play it back. You can use a DVM in AC mode to trace the signal. Maybe not from the head (too faint), but then from the first amplifier stage after the head. You should see tens to hundreds of mV.