Philips DCC 900 repaired but with REC problems

Good morning everyone!
I just took a Philips DCC 900 to a repair shop.
They recapped the REC/PLAY BOARD and a smaller board attached to it and repaired part of the circuit board.
Now the play with DCC and analog cassettes works perfectly but the recording has a problem.
I attach the video of the recording of a 1KHz signal.
Can anyone help me understand what the problem is and how to fix it?
Thank you all.

It looks like it mostly works, you’re just getting a massive amount of dropouts when you play back the tape.

Check if you can play back other tapes without problems. If playback doesn’t work flawlessly, recording will only work worse.

Put the recorder in service mode to play a known good tape, and make sure you get no errors, or maybe just a few. You should see 000000000 most of the time while playing. An occasional “1” may appear, but you shouldn’t see any tracks stay at 1 all the time. Otherwise, try cleaning the head.

Keep in mind that first-generation tapes with white pads suffer from the sticky-slip syndrome: the pad gets black and sticky and the tape doesn’t go through the mechanism smoothly anymore, which makes it impossible for the electronics to keep up. Scrape the black off the pad with a sharp blade or replace the pad, or use another tape.

If possible, try recording something on a tape that has a previous recording that plays perfectly. Append a new recording to the previous recording. If the previous recording plays fine but your new recording doesn’t, it’s a sign that something is really wrong with the recording circuitry. Again, test by playing the old and new recording in service mode and compare the results. If the old recording shows mostly 00000000 but the new recording has a track that’s stuck on 1, that means one track is not recording. If the old recording shows mostly 00000000 and the occasional 1, but the new recording shows ones all over the place, it may be necessary to adjust the recording current or something.

Unfortunately fixing a DCC recorder is not easy and even the service manual doesn’t help much. One thing to know is that the error correction can deal with about 12.5% signal loss. That means as long as 7 tracks out of 8 (of the main audio tracks) are working, it can reproduce the audio, but as soon as there’s a dropout in another track, it can’t recover the data and mutes the audio. It can also deal with lots of errors scattered across the tracks or even a complete loss of all tracks for a short time, but not for long.

There are of course various degrees of possible problems. Obviously because of their age (your recorder is over 30 years old!), many problems in DCC recorders have mechanical causes. A pinch roller that’s uneven, a belt, a dirty head or dirty mechanism… Most problems can be fixed or worked around. There is of course a chance that there’s a problem with the head, but it sounds like your recorder is mostly working so don’t give up!