Repair Technics M255X Cassette Deck (Tape speed is too fast)

[PieterDV]

Hello, 
I bought on the internet for my daughter a beautiful vintage Technics Stereo.  There was some work to do.  So I have fixed the mechanism of the SL-10 turntable.  Fine-tuned the FM tuner (ST-S505L).  Repaired/replaced a connector from the speaker connections of the SU-V303 amplifier.

But I am not able to fix the Cassette Deck.  It is a Technics M255X.  The tape drive is running MUCH TO FAST in play mode. The belts are OK. The pressure wheel (I don’t know the correct word in English) is OK (tested by slowing down the big heavy wheel (sorry, no idea in English) .  The motor is simply running to fast.  I found the “Tape Speed adjustment VR” in the service manual but this is not influencing the speed at all.

Another thing that I see is that when you press EJECT the tape playback is not directly stopped.  Maybe this is related ?

Note also that the tape drive was not used anymore for many years, but was stored in perfect conditions (living room).  The old lady (husband died a few years ago) was not aware of a technical issue with the deck.

Can anyone put me in the right direction to solve this speed issue?

Many thanks in advance,
Pieter (Belgium)

[MacGeek]

Hi Pieter,

Your description suggests the motor capacitors may be out of specification and need to be replaced.  Unless you are electrically inclined, this is usually a job for a technician.

[Sir Thrift-a-Lot]

Motor caps were me first thought as well.

[PieterDV]

Many thanks for your help here!

So I have opened the motor and removed the 2 capacitors.  It is one of 10 uF and one of 3,3 uF.  I have checked them with my Tektronix DMM254 multimeter and have the values :  11.00 uF and 3,46.  So this is OK or not ?    ...I can check  those things but I am not a specialist/Engineer. What do you think ?

[OldiesButGoodies]

Hi Pieter...

As Macgeek and STAL pointed out, that speed issue is often related to the motor caps.   I note that you used the VOM's capacitance function to test them.   Can you also use the VOM's resistance function to do a few more tests on them?  After discharging each cap (just short the leads with a wire),  measure resistance - what value do you see?  does it show any value?  does it start with a low value then go to infinite?

[PieterDV]

Dear,

Many thanks  for the help & suggestions.

Today I went to the shop and I bought those 2 new cap's.  Carefully replaced and reinstalled the small circuitboard in the motor.  Unfortunately, the problem is still the same.  Engine is still running much too fast.  So this was not the issue.  Any other suggestions?

Friendly regards,
Pieter

[OldiesButGoodies]

Hi Pieter -

That has happened to me before - I change the motor caps and the speed problem remains. Makes you mad I am sure. Troubleshooting this can go in so many directions that it may be almost pointless to try to do so over posts here,  without being able to see the deck and play some test signals (but I will not let that stop me!).  If you are so inclined, I would check the playback variable resistor to make sure it is working as advertised.  Those tiny pots can go bad easily, depending on manufacturer (and they also go bad if you apply too much mechanical pressure to them - they are fragile and meant to be adjusted gently with a plastic screwdriver).  If you have a good deck as reference,  record a 3000Hz tone from the web (many web sites offer test signals,  or you may own a CD or LP with test signals - the signal does not need to be 3Khz,  though that is what is typically used - just need a reference, can be anything really,  preferably above 1000 hz) and play it back on your Technics - this will be your "reference speed tape" for calibration purposes. Using you DM254 set to "Hz" and connected to one of the outputs,  see what number you get (based on your description of symptoms it may be running at 3100Hz or 4000 even.  Adjust the playback VR and see if it makes any difference - it is was at 4000 it should go up and down by a few hz as you rotate it. If not, I would check that VR out against specs - or, if you want to be get creative,  figure  out a way to slowly add resistance (use small value resistors or an additional variable resistor) in series to the existing VR until the DM254 reads close to 3000 hz.  Not ideal but could get your deck working again. Remember,  half the fun is fixing the deck!   

Another suggestion:  contact a friendly master tech.  I can get Sam Palermo's  contact info,  or Nakdoc, teh Nakamichi master.   If you are diplomatic enough,  they may have suggestions (these guys have a backlog of repairs measured in months/years,  so they are not shy about avoiding having you send them a deck that can be an easy DIY fix).   

Good luck!

OBG

[Sir Thrift-a-Lot]

If you have a good deck as reference,  record a 3000Hz tone from the web (many web sites offer test signals,  or you may own a CD or LP with test signals - the signal does not need to be 3Khz,  though that is what is typically used - just need a reference, can be anything really,  preferably above 1000 hz) and play it back on your Technics - this will be your "reference speed tape" for calibration purposes.

If you have an Android phone, Emperor Norton put me on to a great free app called PA Tone, which is a sweepable signal generator.   Very handy for these types of situations.

[PieterDV]

Many thanks for all your tips.  Finally I have found the problem!    There is also a Panasonic transistor in the motor (AN6610).  I have ordered this motor transitor in Germany (Ebay) and replaced.  Problem solved. :-)  I can again adjust the speed and tape is running normal.    Many thanks to you all for all the tips and to help me to solve the issue. 

Kind regards,
Pieter

[Sir Thrift-a-Lot]

Tremendous.