Trouble with Yamaha MT50 4 Track

A

Andy Rench

New member
I've recently started using my old Yamaha MT50 4 Track again and have been loving it. One weird issue has popped up though:

When recording on the 3rd track, the volume is super low and muffled and slightly warbly sounding. And the volume meter for the track shows it's getting plenty of signal.

Here's what I've tried so far in troubleshooting:

- Tried a brand new high-bias tape (still sounds bad)
- Tried recording the exact same thing on track 4 (sounds great there)
- Tried using the 4th track input and bounce directly to 3rd track (still sounds bad)
- Tried cleaning the heads with rubbing alcohol and cotton swap (still sounds bad)

Is there anything else I should try or should I start looking to buy a new 4-track?
 
Another thing to check is record on track 3, and then flip the tape over and play the recording back. I believe it will now be on track 2, and yes it’ll be playing backwards, but note whether it sounds muffled and otherwise bad there, or if the playback signal is strong and clean.

This will narrow down if your issue is occurring at the point you are recording, or if it is a playback issue.
 
sweetbeats said:
Another thing to check is record on track 3, and then flip the tape over and play the recording back. I believe it will now be on track 2, and yes it’ll be playing backwards, but note whether it sounds muffled and otherwise bad there, or if the playback signal is strong and clean.

This will narrow down if your issue is occurring at the point you are recording, or if it is a playback issue.
Click to expand...

Yes, sounds bad flipped over too.

When I record the signal strength looks great but on playback it's so quiet it doesn't even register in the signal light meter.
 
Was I right that your signal recorded on track 3 played back on track 2 when the tape was flipped?

Now record on track 2 and flip the tape. How does it sound?
 
So, yes. Your playback amps are fine, it is the record amp for track 3 I suspect is the problem. This could be a loose connection, or a failed component. The fact that the meter shows good signal is a clue that would help to narrow down where the issue is. The meter gets its signal from the same place the tape track does. So if the meter works, you know the cause of the problem is something in the signal path between the track 3 head, and wherever the meter taps the signal path. It’s not head wiring because track 3 plays back fine when reproducing material recorded on track 2. I don’t have any schematics for that machine so I can’t be of any more specific help.
 
Okay. Take pictures as you disassemble, put scurries in markets baggies and such. Gently exercise connections...
 
After opening I didn't see any visible loose connections. I'm up for a challenge, but I may be out of my league on troubleshooting this further. 2018-10-25 20.54.31.jpg
 
You’re not look for visibly loose connections. Over time, and depending on the quality of the connector and the environment in which the unit has lived, contacts can oxidize. To mitigate this you “exercise” the connection...(aka unplug, plug, unplug, plug). So gently do that with connections you can see going to/from that main board that’s still in the bottom housing of the unit. That looks like your amp board.

[EDIT]

Of particular interest would be to exercise the connectors on the main board that go to/come from the R/P head...that bundle of gray wires from the headstack. See how it goes to four connectors on he main board each a different color? Gently exercise those, then test again. Be gentle and careful. Careful what you touch. Keep in mind the filter capacitors in the power supply store energy for quite awhile after the unit is powered down and unplugged, so always treat the guts like they are “live” and you could either cause irreparable damage to the unit, or to yourself. Remember: milliamps can KILL YOU.

But...all that aside, I bet it’s not a bad connection. I was looking for relays and it looks like Yamaha handles signal switching using 4000 series logic chips. You see along the left of the main board are those larger chips that say “dbx” on them, well obviously those are for your noise reduction, and then moving to the right you have chips labeled “TC4066...” those ones handle signal switching I betcha, and there’s a trend of those getting dodgy at this age. They are readily available (for now), cheap and not too terrible to replace if you have some experience with a soldering iron.

That’s what I put my money on.
 
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The
famous beagle said:
I would listen to sweetbeats. I know from experience that he KNOWS his stuff.
Click to expand...

Hey, thanks, beagle. I’ve learned a lot. Including there’s more I don’t know than I do. BUT...I DO know those 4000 series logic chips have been the source of switching problems in the Tascam 388, M-300 series, and even my “M-__” prototype console...so why not the Yamy box? ;)
 
Hello

i have also an issue simalar, my Yamaha MT50 seems to work but signal a bit weak thru RCA and a wee bit distorted/muffled also thru outs and phones. also the LED' maters are blinking very faint

i originaley had to do some work inside machine on the tape transport and removed the chsasis. anyway there are tow wires with ring terminals that have to0 be screwed back on to the chassis (4) screws. but i forgot where.
i had a revelation when i tried to screw the longer one of these wire terminal on to top left screw on the chassis that once it connects the sound goes dead and vice versa! anyway i left this wire off, and taped it up. now it plays but again weak signal. does anyone know this fault?
i am no electronic expert so stabbing in the dark for answers. also does anyone have the service manual they could share? i screwed the shorter black wire terminal that seems to come from near the heads to bottom left is this correct? Any help is much appreciated

Thanks in Advance!
 
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