Troubleshooting Sony TPS-L2 W+F

Hi everyone. I have restored quite a few portable cassette players now, from plastic to D6C professionals. In my growing collection I have one and only one that I have emotional attachment to. Roughly 1980 my eldest brother brought home a new TPS-L2 with a clean recording of Genesis “Seconds Out” and left on a table. I had obviously never heard or seen anything like it. Watershed moment for me both with electronics and music.

Fast forward 40 years, and lo and behold my brother gave it to me. I didn’t want to dive into it as I did not want to take any risks making things worse. It sat on a shelf next to other projects until last week. I have restored a WM-3 including some caps and full mechanical as a note. I decided to get going on it. Initially no motor function. Using ChatGPT quickly zeroed in on a commonly failing transistor (Q603). I found a replacement at work and installed. Motor came to life but unit ran max speed with no servo speed control. No impact from the pot. After some head scratching realized I installed the transistor incorrectly, looking at the schematic “from the wrong side”. Changed leads to correct the EBC locations and now Walkman runs and speed control pot is working however I need to have it all of the way clockwise to get close to correct speed. I used Valentin’s restoration article to fully disassemble, clean, and lubricate the auto stop portion. I did NOT put any grease on any plastic parts yet. I pried up the idler tire as directed. The drag force of the unwind spindle is quite mild. I cleaned all rubber but did not replace anything yet. It all looks in surprisingly good condition. I did take some fine grit abrasive and ran briefly on the capstan spindle. I’ve spent quite a few hours on it. Nothing I do seems to fix the dramatic w+f. My frustration is I don’t know how to troubleshoot whether I am having a mechanical issue, or an electrical one. I made a video of music playing and put on YouTube. Hopefully copywrite issues don’t come into play. The speed control is so bad it seems like it’s not just a minor lubrication problem. Any advice on identifying root cause greatly appreciated. I can replace Q601 andQ602 but I generally don’t like shotgun replacement as a method of troubleshooting. Please let me know if video not watchable. Thx.

 

A couple of other things I forgot to mention. Belts are new from Marian. They seem somewhat loose but assume that’s not my issue. I also cleaned the speed pot trace but it had no impact.

thanks

 

I replaced the pinch roller and put a thin small amount of super lube on the auto stop cam lobe and the other cycling pin / slide plastic part of that assembly. It’s the same if not slightly worse. I’m currently at a loss of what to do next. Here are two more pictures. I didn’t disassemble or do anything with this portion of the auto stop. Is that possibly a source of friction? And embarrassingly, this METAL washer was stuck to the motor. I can’t find in the assembly drawing where there are metal washers other than on the ground connection screw on the main circuit board. The mystery one is on the left. I put the circuit board screw and metal washers other than next to it for scale. It had to have come from this unit but I don’t know where. I’m generally careful and put each screw or set of screw in their own plastic closable containers, labeled.

 

Any thoughts? This is only a hobby for me and I don’t repair for hire, so no great urgency.

is there anything I can monitor on the servo board with a voltmeter or scope to assess health of that portion of the circuitry? I’m not an electrical engineer but have a collection of diagnostic equipment I have learned to use over the years.

thanks!

 

@Dauner Do you have a W&F measurement ? Would be interesting to see a figure.
Also, why are you assuming it's an electronic fault ?
I would also consider replacing the belt (but with one from different supplier), as I've seen many instances of high W&F on this unit caused by the belt itself (despite it was new).
Don't assume just because the belt is new it can't be the problem.

 

Thanks Valentin. Not sure why I didn’t think of this earlier but I have my WM-3 that I restored and is working well. I’m going to swap belts and see if W+F is resolved or improved in TPS-L2 and starts up in WM-3.

a bit embarrassing for how long I have been doing this but I don’t have 3Khz tape and software to do measurements. After I swap belts and do an ear test, I’ll use my D6C to create a 3KHz tone tape. I should have done that long ago. On my next order of parts I’ll purchase a known good test tape.

On the tape front I see people mention 3150 Hz. Looks like a DIN Euro standard. I suppose I’ll actually use that instead. I can’t see how it matters but good to use ISO or published standards.

thanks again to everyone on the forum!

mark

 

Doesn't matter if you use a 3000Hz or 3150Hz tape, both WFGUI and Nak T-100 support both standards.
This was probably more relevant back in the day when actual physical devices were used to measure the W&F. It's possible these not all supported both standards.

As for D6C, that's good enough to record a cassette for measuring belt devices.
Fact it has quartz lock is good since you know the frequency variation will be minimal.
Tapes recorded on a deck without quartz lock add another variable: how the deck itself was adjusted. Which is something to be avoided if possible.

 

Valentin, I forgot to answer your question. Initially speed control was not working at all until I replaced Q603 on the servo board. Knowing I had one failed transistor, I can’t rule out that Q601 and Q602 are also questionable, and therefore can’t dismiss the electronics side of things yet. I don’t want to replace 601 and 602 unless needed. If I continue to have no luck mechanically I’ll go and swap 601 and 602 one at a time to continue to remove variables. Thanks!

Mark

 

I understand. Didn't say electronics should be ruled out, rather not assumed it's the culprit without doing some tests.
In my opinion, you first need to test if the problem is mechanical or electronic to have a direction.

Eliminating one variable at a time is not an efficient strategy. You can end up swapping a lot of parts and still not fix the problem.

Think the best approach would be to make a test tape, measure the W&F, change the belt and measure W&F again.
If you see no difference in the W&F, at that point you can assume the problem is likely to be electronic and get down that route.
EDIT: Regarding electronics testing, what should be observed is voltage at the motor with and without load.
If servo loop is working correctly, the voltage should increase when load is added. If that doesn't happen it means the servo is not working.