Yamaha MT4X Problem

[fourtracker]

Recently my Yamaha MT4X started changing pitch randomly while I was listening to a song I’d been messing around with. I hadn’t dropped it or damaged it in any way, and the tape speed was set to where I had kept it to record the song (9.5 cm/sec, with the tape speed control knob at the stop point in the middle).

I had cleaned the heads, the capstan and the pinchroller a day or so before, using an alcohol-based cleaner for the heads and capstan, and a non-alcohol-based cleaner for the pinchroller as the manual suggests. I played the tape I recorded the song on right after cleaning and it worked fine. I figured something had happened to the tape, but after trying other tapes I’d recorded on the problem persisted.

Finally I opened it up to have a better look at the guts while I played the original tape to see if I could get any closer to the root of it, but everything looked normal. The belts for the tape mechanism moved along at what looked like a regular speed.

I thought about taking the tape mechanism assembly apart for an even better look at the belts (looks like there’s two of them) to see if they had in fact stretched/worn. But I’m hesitant to do it because I don’t want to mess it up worse, and also because the changes in pitch I heard weren’t happening at regular time intervals. If that were the case, it would imply to me that there’s wear and tear at specific spots on one or both of the belts, and therefore I should replace them.

I’m probably overlooking something embarrassingly simple here, but if anyone has any idea what’s going on here I’d really appreciate it. Sorry this post is long-winded – just trying to be as specific as I can for anyone who has advice.

Thanks.

[The Ghost of FM]

The problem may not be a mechanical one and thus doing visual inspections may be of little value.

The play speed is also regulated by a pitch control circuit which may have a faulty electronic part that a technician will have to test and look for by doing electrical measurements with meters and sprays that check for thermally defective parts.

Find a decent service center and get an estimate.

Cheers!

[A Reel Person]

That's typical of belt driven units, when the belt's stretching & wearing out.

[fourtracker]

I think I'll have someone give it a once-over before I do anything if it's reasonable - barring that, I'll proceed with extreme caution.

I just e-mailed Yamaha about new belts - I think I can replace them as long as I do it very carefully, with some help from my father, who tinkers with electronics pretty often and always works smart (working hard with this type of thing almost seems counterproductive).

Seems like there's a lot of tinkerers on this forum. Any pointers on how to proceed if I choose to do this myself?