u/CommutatorWhine

I bought this Tascam 234 for 25 euro at a thrift shop in 2015. At that time i didn't nearly have the stock of parts i have now.
Problem: it has two idler wheels for the reel drive motor. Both had melted into the well known sticky goo. The pinch roller had a deep dent in it from being powered off with the machine still in the 'play' position - and aside from that, the rubber of the pinch roller had also gone soft (not quite liquid yet, but you could easily sink a finger nail into it).

I replaced those idler tires with flat gaskets for plumbing use, and it actually ran completely fine like that for 7 years. But after moving to a different house, it sat with pressure on the idlers for 2 or 3 more years. This warped the gaskets badly, and the whole thing made a lot of noise and ran very wobbly. Can't blame them, they're plumbing parts after all.

If you want to replace all belts, it's adviseable to get the whole mechanism out (or at least separated from the rest) of the deck. Just the idlers can be replaced by only opening up the case and unscrewing the idler motor assembly, it has enough space to be moved out of the mechanism and to replace the idler tires. I didn't notice this at first (also assuming i was gonna have to replace the belts again) so i detached the mechanism and flipped back the board, as you can see in the pics.

Now, with proper round running surfaces, it is running smoothly and quietly again.

I have no real use for this thing currently, but maybe some day i'll get back at recording punk bands in Amsterdam, and having 2 4 track tape machines (also have a Yamaha MT400 portastudio) means i have more tracks to work with, if i bounce from machine to machine and want a stereo end result.

My grandma gave this very basic walkman to me in the mid 90s. At that moment i didn't really know what to do with it. I had no tapes of my own.
It wasn't until the early 2000s when i was around 12 years old, that i actually started using it, until i got an MP3 player just a few years later. Still, i kept the thing around. It would occasionally see use on commutes. And somewhere in the early 2010s i dropped it and one channel didn't work anymore. Since i bought the final model Sony walkman in 2007 i think, i just left it at that.

Today it was time to fix it.
First: put some period correct Ni-Cd batteries in it. Well, almost period correct. These are from 2005ish. Yes they still work. Yes i keep an eye on leakage. Test it. One channel still broken.

Now it's time to pay attention to detail. One thing i notice is that the motor hum (remember, this is really a bargain basement walkman, name brand Tanashin mechanism and all..) is audible through both left and right channel, even though the music is only coming through the right.

Signal tracing. I connect the minus of the battery to mains earth. This way i can poke things in the circuit with a standard multimeter probe to inject a 50Hz buzz into the circuit.
Find the shielded wires that come from the tape head and touch. No buzz on left, good buzz on right.
Find volume potentiometer. Welp, turns out the Mitsumi LAG665 all-in-one portable cassette player IC uses a voltage controlled amplifier system so no standard left/right volume control comparison possible.
Grab datasheet. Check IC pinout. Touching pin 5 or pin 6 did result in a hum, so the IC is at least for the most part working correctly.

Because the problem first appeared when i dropped it, it is most likely mechanical damage. At this point i start randomly flexing, poking and prodding the board with a wooden stick. And after a few crackles, the right channel worked again, and stopped again. More poking and prodding and touching components on the other side of the board showed that the issue was somewhere on the top left side of the board. With a work lamp with magnifier i eventually found a broken solder joint. Very hard to see, but it usually appears like a faint ring in the joint. It is heavily zoomed in on the picture of course. The joint itself is 2mm wide at most, and the little component leg usually 0,7mm thick.

Resoldered it, and it works as good as it ever did. The write up took about as much time as finding and fixing the issue.My very mediocre gift that i wasn't very happy with as a 8ish year old kid, but which is now a memory to my grandma.