I have got an AV-3650 in very good state and want to use it to digitize some videotapes from the early 80s. The machine is even clean on the inside. I lubricated it and tested the mechanism. Everything OK.

The heads are in good order, and surprisingly, the belts and capstan are in perfect condition. They don´t make rubber parts like that any more. I have a good enough RF level coming into the demodulator. The input signal is passed all right to the output in EE mode.

But in play and record the capstan is turning too fast. This model has a separate DC motor for the capstan, as it was an "editing deck" of the era. The tape runs at about twice the normal speed. I measured the voltage at the capstan motor, at about 13 V. I remember many years ago, when I used to repair other Sony VTRs, it was supposed to be from 5 to 7 V.

The power transistor is not shorted, and its base voltage is about 0,7 V higher than the emitter voltage where the motor is connected, so the trouble comes from somewhere in the servo circuit.

The trouble is, I do not have the service manual. I could try to trace back the circuit visually, but not knowing the correct voltages nor waveforms, it will be very difficult to find the cause of the problem.

There are one or two places on the Web where the AV-3650 service manual can be downloaded for a very reasonable fee, but you know, I live in Cuba, and not having an account in a US bank, must limit myself to free downloads.

Maybe somebody can tell me where can the service manual be downloaded from?

Thank you very much.

Hi!
I do my best for you to find one!:yes:
Best regards,
TV-collector:stupid:

Hi!
I do my best for you to find one!:yes:
Best regards,
TV-collector:stupid:
Thank you very much!! Meanwhile I am fighting the machine, tracing the servo circuits and testing any suspicious component.

Hi my friend on Cuba!:smoke:
I placed a request in 3 forums and placed a request for you
on this site:
https://elektrotanya.com/list_wanted

Please check it in the next weeks if something happens there.:ntwrthy:
Good luck.:scratch2:

Regards,
TV-collector:stupid:

Good morning to Cuba!

Does this help?
https://www.manualslib.com/manual/1189598/Sony-Av-3600.html#manual

Best regards,
TV-collector:stupid:

WOW that brings back some memories! I'd say replace all the electrolytics on the boards, they're 50 years old now and ready for retirement, you might have a few bad semiconductors in there as well, early generation plastic body transistors had some moisture wicking issues. Good EIAJ machine to really appreciate.

What is 4/3 AM radio in Germany? 4:3 aspect PAL television? Never quite understood why PAL used an FM video carrier.

What is 4/3 AM radio in Germany? 4:3 aspect PAL television? Never quite understood why PAL used an FM video carrier.

Never heard the term "4/3 AM radio," can't help there.

No color TV system used FM for a video (broadcast) carrier.

SECAM used an FM chroma subcarrier.

Analog video tapes use FM modulation for the video signal. In professional formats, the complete composite luma/chroma is carried by the FM. In home formats, the FM carries luma only, while the chroma subcarrier is carried in its native format, heterodyned to a lower frequency, so the luma FM carrier acts as "tape bias." This is called 'chroma under."

Hi my friend on Cuba!:smoke:
I placed a request in 3 forums and placed a request for you
on this site:
https://elektrotanya.com/list_wanted

Please check it in the next weeks if something happens there.:ntwrthy:
Good luck.:scratch2:

Regards,
TV-collector:stupid:
Thank you very much, but the manual they have is for the AV-3600, another model. It is a simpler machine, with the AC motor moving everything (the heads, the capstan and the reels), and it has only a drum servo.

The AV-3650 has a separate DC capstan motor, and one additional capstan servo board. The drum servo works like in the 3600, sending variable DC to a brake coil that acts upon a squirrel cage rotor mounted in the drum shaft. The pulley ratio is such that the free-running drum speed is over the correct value, so the brake coil is always retarding it.

The capstan servo board sends a variable voltage to the DC motor, so the speed is controlled to keep the off-tape signal synced to the input video. So, when one presses Record, there is less disturbance at the edit point.

This was optimistic thinking, because the 3650 has no vertical blanking switcher (can go into Record in the middle of one field) nor rotary erase heads (present in the later color model, AV-8650). So the edits were never perfect, but good enough for industrial-educational use.

Anyway, my machine is not going to edit/record anything, just play back. But now is triyng to break some Guinnes records, running an entire 1-hour tape in 35 minutes flat.

WOW that brings back some memories! I'd say replace all the electrolytics on the boards, they're 50 years old now and ready for retirement, you might have a few bad semiconductors in there as well, early generation plastic body transistors had some moisture wicking issues. Good EIAJ machine to really appreciate.
Thank you very much.

I agree with you, but recapping an entire 3650 is an enormous task. I´d rather check the waveforms and replace just what has failed. It is not going to be very reliable machine after that, I know some other component may fail afterwards, but she is not going on-air, just will work sporadically when some EIAJ tape surfaces.

I am afraid that the vast majority ot these tapes in Cuba were thrown in the garbage years ago. But I kept have some that I want to play back. They may have recordings of important construction works in the mid-70s and early 80s.

Agreed a re-cap would be a daunting task but do keep in mind that if only the "bad" caps were replaced now the other 50+ year old caps are not far behind in failure and that could take out a few semiconductors along the way. I guess the biggest question is just how valuable the 3650 is and now much effort you want to put into it.

I have the service manual for the AV3670CE, which is the CCIR version of the AV3650. Let me know if it could help you.

I have the service manual for the AV3670CE, which is the CCIR version of the AV3650. Let me know if it could help you.

Thank you very much, jib2. It sure will be helpful. Surely some parameters will be different (frequencies, time constants) but the overall schematic will be pretty the same.

Do you have it in a digital form? So it can be sent electronically.

It is in PDF. If you leave me a PM with your email address, I'll send it to you.

Thank you very much for your kind help, jlb2. I received the service manual, and am sure it will be very useful.

I think the 3670 was the succesor to the 3650, adapted to record and replay the (then) newer high density V-7x tapes. (The 3650 can play back those tapes if the heads are in good condition, and maybe tweaking a little the preamplifier frequency response, but it can not erase nor record on them.)

And of course the CE is the European (CCIR) model.

Having in mind the different field frequencies, the circuit must be very similar.

The next thing to do is to check the differences between the manual and my machine. I hope Sony did not made significant changes in the servo circuit from the 3650, because in the 70s it was a big deal to redesign a production line.

I will keep you posted on my work on the 3650.

After jlb2 let me have the European model (AV-3670CE) service manual, which I studied very carefully, I got the full AV-3650 service manual, including all the supplements. When you look at all the changes Sony made to this product in the course of several years (sometimes the supplements were separated by just a few months) you may think this was a very popular VTR at the time. Otherwise, they would not have bothered at all with so many updates.

In this model, the capstan is powered by a DC motor that has a frequency generator (FG) inside. The output of this generator is used by the servo circuits to control the speed and the phase of the tape in relation to the incoming video signal, so when you press Record to start editing, the transition is smooth. (Not having rotary erase heads, "smooth" is a little too benevolent term.)

Well, I tried measuring the output frequency of the FG, and got only silence. There must be an open in the coils. That's why the capstan overspeeds, because the servo doesn't get any reference signal.

I trust I may get another motor from a similar machine that belongs to a friend of mine. He has it only as a showpiece, and is not interested at all in restoring it. I hope his machine is a late model, like mine, because among the changes Sony did to the 3650s, there was a new capstan motor in the post-1974 machines.

203780

This is the AV-3650 capstan motor. The connections to the motor itself are in the V-shaped plate at the right. The two purple wires are from the PG, and they measure infinity.

The brown thing in the upper part of the motor (left in the picture) is not made of metal, but instead is a thin rubber-like cilyndrical cover that goes over half the thing.

If my friend's machine has a different kind of motor, I may have to repair this one. Nothing really difficult, I think, except that the tiny Allen wrench to open it may be hard to find. (I live in an embargoed country, you know, and can't have all the tools I would like.) But if 20 years ago any technician here could replace individual VHS or Beta heads in their home workshops, and adjust the penetration too, this can't be too difficult. (No, we can't splice damaged filaments in vacuum tubes, yet :):):))

Thank you very much for your kind attention. I will keep you posted, and maybe in January this 3650 will be in working order again.