written by
Bojan Šernek

Telefunken M15 Tape Machine Revival

5 min read

The last few weeks of running mix:analog provided a lot of opportunity to test our resolve and mission. After months of smooth operation, the Telefunken M15 Tape Machine started acting up. It has always been one of the favourite automated items for our users at mix:analog and we really want to do good by our users.

telefunken m15 tape machine mainteanance
The Telefunken M15 prepared for maintenance

To see it break down so much in the recent weeks was a truly gut-wrenching experience. And that in turn was nothing compared to the painful but logical decision to take it down completely.

The reason for that is the tape would work normally, but would lock up after rewinding. Or worse, it would not stop after rewinding. Both cases required manual intervention. Sometimes in the middle of the night, multiple times a day, over a weekend if necessary.

Thus, we had to make the decision to disconnect it for maintenance for an unknown period of time. At least until these issues could be resolved. It could have easily taken weeks if not for the great work of our techs Elvis and Žiga.

What follows are some fun facts on what can go wrong with vintage gear as well as some approaches on maintaining Tape Machines. In particular, I will focus on the Telefunken M15. I will list some common problems that we ran into and a few solutions for them!

Component Deterioration

Gear with lots of mechanical moving parts really exercise their mechanical components a lot. All the screws, motors, springs, bearings, belts, pulleys and fasteners see a lot of action. If the machine you are fixing is a vintage piece, it could have easily seen decades of active use.

There are three things to think about in this situation. How do you prepare for the inevitable breakdown, how to quickly fix the problem once it arises and how to manage the downtime.

You can prepare by stocking up on replacement parts. If that is not an option, get educated about modern replacements. Resources such as the original maintenance manual can be invaluable. Especially if it has exact specs and drawing you can use. eBay can really help out with securing actual replacement parts.

telefunken m15 manual
Žiga poring over the maintenance manual of the Telefunken M15 - what could be wrong?

Be wary of things that have a limit lifetime from the get-go like bulbs, tubes, rollers and sometimes bearings. Stock up on these items and have them handy at all times.

It's also possible to mod gear for better reliability: you can convert the bulbs to LEDs for example.

Sporadic Use of Advanced Features

I find that a lot of people don't think so much about this, but it is important. Studio gear was designed to fit into various different situations. Designers did that by adding a lot of features and you are probably not using them all the time.

What happens is that once you do need that feature, it has not been used or tested in a long time and that just means it's that more likely not to work.

For example, the Telefunken M15 has several sensors for tape presence, but most of the features will work with just one of these sensors working. In our case, a broken bulb of one of the sensors made the machine less reliable, but it still worked.

If we used the end-of-tape detect feature, we would hit the problem much faster because it uses that sensor. Instead, we have our own auto-rewind circuitry and that made the machine appear to work and function normally, but it actually was not completely functional!

telefunken m15 without cover
Telefunken M15 Tape Machine insides under the cover... just wow!!

My recommendation is to make a list of all the features you want to use even if it happens only once a year. Go through that list every month to make sure that everything still works.

Anything suspicious should be written down and everything broken down weighed with the cost of the fixes. I find that not fixing your gear immediately is definitely going to bite you in the long run.

Fix it now!

Regular Maintenance Checklist

Here is a regular maintenance checklist for the Telefunken M15 that we came up with:

  1. Power down the machine; Check the fuses, they should all be intact
  2. Power up the machine. Make sure it does not have a remote connected and tape loaded. Listen to it - it should make no odd noises and powers on correctly
  3. Tape detection lamps must be lit, one is close to the headstack and one under the tension arm left of the headstock 💡
  4. The left tension arm must be able to extend in both ways
  5. The tension arm damping magnet must be strong enough so that the tension arm does not hit the extremes when entering wind mode
  6. Check that the stop light is lit, load a tape with a test signal and push the play button
  7. The sound level must be equal on both channels, if not, adjust on the replay cards
  8. Measure THD+N, it should be the same as previous month
  9. Push Rewind. The rewind light must get lit and the tape detached from the headstack
  10. Use the rewind lever to exercise both directions, check that tape is smoothly rewinding in both directions
  11. Go out of wind mode, press record and play at the same time. The recording light must get lit - record a minute of a test signal
  12. Play back the test signal and make sure that the THD+N and level should be the same as last month
  13. Do steps 6-12 with the remote connected. Everything should be the same as before
telefunken m15 maintenance checklist on manual
The Telefunken M15 Manual with a post-it reminder about the maintenance checklist

So, is the Telefunken M15 Alive now?

We definitely poured our heart out to make it so ❤️. This is our third attempt to find out all the problems hiding inside it. We are quite confident that third time is the charm and that it will work well from now on!

What we needed to do:

  • replace the broken detection lamp
  • update the firmware of our controller to better track the timing behaviour of the original remote
  • adjust the tension of the springs at the tension detector lever. The permanent magnet lost some of its flux density. This is normal in the 30 years since the tape machine was made.

So far the updated circuits and software have been out for a week and the problems with tape rewind are gone. The lockup did not happen a single time yet. HURRAY! 💪💪💪

You can check out the amazingly smooth sound of this beautiful and fully automated tape machine directly from your web browser by visiting mix:analog and booking it. Your first 30 minutes of use will be FREE (as of December 2018).
book telefunken m15 through mixanalog app
You can book the Telefunken M15 for online, real-time use on mix:analog

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mixanalog repair telefunken m15 tape machine