Portasound Porta One: track 1 signal too quiet (yet registers OK on meter)?

[EasyToAssemble]

I'm new to 4-track recorders, and have just picked up a Portasound Porta One (1985). I'm now doing a basic test to make sure everything works, but track 1 seems to have an issue.

The track 1 meter seems to be registering the input signal OK. So far, so good. But the track 1 signal coming through headphones is barely audible compared to tracks 2, 3, and 4, and equally quiet when I record / play back. I've tried track 2, and that records just fine.

I've also tried flipping the tape to check. The track-1 recording is still low volume when played through the track 4 head.

Does anyone know what this might be? And is this an easy fix (or perhaps something I've missed - though I can't think what)?.

 

[SkywaveTDR]

I can't say without examination of the deck but tapes often have edge damage or dirt will accumulate on the edge tracks and did you try cleaning the head? Also pinch rollers that ae never cleaned then that causes skew which then damages the tape.

 

[EasyToAssemble]

Thanks for the reply. The issue seems to be not just recording, but also any signal put through channel 1 before recording. The meter is registering levels normally, but I have to max out the sliders to hear it, unlike channels 2,3,4. So, it probably isn't an issue with the ingoing mic connection, but rather the stage(s) between that and the recording stage.

I've just tried recording a track on track 4 with the tape flipped. I then turned the tape over, and played it back (in reverse) on track 1, to see how it played back. The signal is there when in Cue mode, but silent when in Remix mode, so I now have NO idea what's going on.

 

[SkywaveTDR]

Well if you look at the schematic the cue takes the signal off the path at a different place than the remix which is applied to a buss. I would look at the places where these items run different- it is basically a signal tracing job that any beginner with a scope could accomplish. You want to check and compare signals right up to the bias trap as this is the record amplifier before it gets mixed with bias. There can be cracked pots (Trimmers) I replace the carbon or plastic ones with Cermet 6mm types from Mouser. Bourns makes them- they are much more reliable. The makers of these boards are also notorious for weak solder joints. It could even be a combination of things. I suspect it is going to take some work to find it.