Telefunken magnetophon C 2200 hifi Cassette Deck

[DMcMahon]

Tonight have been checking out a recent acquisition, a mid 1970's Telefunken magnetophon C 2200 stereo cassette deck.

It is quite large and heavy, feels really sturdy and looks well engineered. Overall condition looks good with a few minor scuff marks.

Opened it up to remove trapped dust from the faces of the VU meters, all 4 drive belts are good and tape transport all works well.

Got it fairly cheap and it was supposed to be fully working. Playback of existing recordings works well when listening from headphones. Spec'd for headphone impedance of 400 ohms but works well on my 32 ohm headphones.

Microphone recording works well, but there is noticeable hum in the background, will try different microphone to see if different. So far only checked left channel as do not have stereo microphone.

Line recording is not good. The left channel is really strong and results in bad distortion even with a very low record level setting (both on playback of the recording and monitoring the record signal before recording). I was using unattenuated phono to DIN cable, later I will try attenuated cable to see if this helps.

The right channel is the complete opposite, a very weak distorted record signal even at maximum record level setting.

Automatic (ALC) recording fared no better.

So plenty more to do, I was hoping that for once "fully working" actually meant that.

David

[ben]

Interesting looking unit. Solenoid in there too! I'd start with servisol in all those switches and pots. Possibly a bad cap or transistor in the rec preamp. At least you have it narrowed down since PB is OK.

[DMcMahon]

Yes hopefully should not be too difficult. Most difficult part may be locating/accessing specific components if have to go down to component level.

David

[DMcMahon]

Rechecked line recording using attenuated Phono to DIN cable (470kohm in each recording channel). Now get pretty good results on both channels.

Strange that the right channel has now come good because before with unattenuated cable, the right channel was very low/quiet, maybe had a bad connection somewhere.

On peak music getting around 0 on the VU meter at around record level 2.5 (6 being max setting). If record level taken above 2.5 there is a hint of distortion coming in when listening on headphones at the cassette deck.

Need to see what the line output to stereo amp sounds like, wondering if my 32 ohms headphones (400 ohms being the spec for the machine) are starting to overload on playback of stronger record levels. Depending upon results may try another cable with 1 Mohm resistor attenuation.

Not sure if the Stereo/Mono switch is working correctly, need to do more tests.

[DMcMahon]

Playback of recordings into stereo amp did have a little audible distortion so will increase the attenuating resistances in DIN to phono recording cable.

[Cobaltblue]

Opened by request.

Cheers

Mike T

[DMcMahon]

Getting back to this to check it out further before selling it.

While rechecking the DIN inputs/outputs pin outs as shown on the schematic in the Service Manual, got side tracked looking at the various electrical set-ups and am struggling to understand Step 5 "Tape Speed Control".

It shows a 3,150 Hz speed test cassette playing and motor speed adjust potentiometer R913. But I cannot really understand the little drawing showing 3 times of 99.5 sec, 100 sec & 100.5 sec, I assume the target time is 100 sec with a +/- 0.5 sec allowable tolerance, but cannot see how this is measured or what the times actually equate to.

There is no text to expain Step 5.

Probably just me being thick, I am sure somebody will be able to explain it.

David

[frsimen]

Step 5 requires you to measure the time taken to play a section of 3150Hz tone from test tape 339 280 009. The tone should last for 100 seconds (once around the clock face +40 seconds from the graphic) with an allowable tolerance of +/- 0.5 seconds.

If you don't have the test tape, you could record 100s of tone using a known good recorder, perhaps.

Paula

[DMcMahon]

Thankyou Paula, that now makes a lot of sense.

I was not intending to do the test, just was trying to understand the test.

However, I do have a 3kHz cassette speed test tape that runs for 10 minutes, am going to use this for some Wow & Flutter tests, but out of interest will time how long the 3kHz tone lasts and also at the same time measure the actual frequency.

David

[DMcMahon]

Rechecked playback using a pre-recorded music cassette (Black Sabbath - Sabotage) with headphones connected to the deck, sounds good and VU meters show the playback signals.

The headphone socket on the deck is a 5 pin "Domino" DIN so had to use a Domino to 3.5mm adapter for my headphones connection.

While doing some fast winding/rewinding of the cassette the tape would intermittently stop rotating, initially thought it was the cassette itself, but after trying several other cassette tapes also got the same problem.

Was about to open it up to investigate when the tape transport stopped all together in all modes.

After removing the bottom cover found that the main drive belt from motor pulley to flywheel was broken. It is a square section belt, do not think I have anything long enough in square section but should be able to find a suitable round belt.

David

[DMcMahon]

Replaced the broken belt and tape transport now back working.

However on a couple of old music cassettes, fast rewind struggles/stops when the Supply spool is heavily loaded with tape, works fine on most other tapes.

Using little finger to manually rewind the bad cassettes could feel that they are much harder/stiffer to rotate than good cassettes. Even though rewind problem appears to be due to bad old cassettes decided to check out the rewind mechanics.

Cleaned all the associated idlers, pulleys etc.

It was difficult initially to see how the supply reel table was driven in fast rewind. By removing all the parts of the "Eject case assembly" was able to see that the Supply reel table is driven by an idler that in turn is driven by the top idler on the slipping clutch assembly, the bottom end of the slipping clutch assembly being driven by a drive belt that was driven by an idler pulley that is driven off the flywheel.

Wondered if the slipping clutch was slipping when the problem tapes would not rewind but with unit rotated 90 degrees on its side could see that the clutch was not slipping but the little drive belt that drives it was slipping around the drive pulley.

The belt felt a little slack so replaced with tighter belt, this improved the rewind issue (with tight cassettes) but not 100%, but happy now that issue is down to the bad cassettes themselves.

Had noticed it previoulsy, there is a strip of black foam on the inside of the bottom plastic cover, the foam makes contact with the end of the main PCB. The foam was decomposing into dust, so cleaned it off and replaced, although could not see any useful function of the foam strip.

David

[DMcMahon]

Originally Posted by ben

Solenoid in there too!

Yes tape auto stop when no tape motion detected.

David

[DMcMahon]

Originally Posted by DMcMahon

Not sure if the Stereo/Mono switch is working correctly, need to do more tests.

Above was/is in Playback mode playing a tape. The Stereo light illuminates when the switch is switched to Stereo but the playback sound is always in stereo (when a stereo recording is played) irrespective of whether the switch is switched to stereo or mono.

Reading the User manual this is correct, the switch only functions during recording (to be checked by further testing). The description of this in the manual is a little unclear due to poor English translation, Google translating the German text for this makes it much clearer.

David

[DMcMahon]

Checked playback of pre-recorded music cassette out to external Hi-Fi amplifier using the Radio-Phono output DIN pins (BU 1 pins 3 & 5) with headphones connected to the amplifier.

Playback sounded good but noticed during the silent breaks between tracks that there was a noticeable hum present (particularly at the higher volume settings) on both channels, the level of which could be changed by use of the volume control on the amplifier. Maybe would not be so noticeable with speakers connected.

Found that the hum was always present in any mode of the tape deck, i.e. play, record, rewind, fast forward, paused play and standby (powered but no keys pressed), but largely masked when music playing.

Rechecked playback with headphones connected to the tape deck headphones socket and basically got identical hum results.

Surprised that the hum is present in the non Play modes (like fast wind etc) as thought the playback amp would be muted.

Looking at the schematic it looks like the Phono line outputs are switched through to the DIN socket by playback switch S 110, so surprising that the hum signal is being output in the non playback modes.

Will need to dig out scope and try and trace the origin of the hum signal, first checking the power supply DC supplies for any mains ripple etc.

David

[DMcMahon]

Power supply ripple checked out OK, the regulated +18V output at C701 was a clean 500mV 100Hz (10mS) and the unregulated +16V at C704 was <5mV 100Hz.

The 2 channels both at headphones output and DIN outputs with music are very clean, with music switched off there is up to 150mV 50Hz noise present. But the noise does not change at all when the DIN to phono cable is unplugged from the deck (cable still connected to scope) and with cable connected the amplitude of the noise signal increases noticeably with the deck switched off.

So unsure how real this noise signal is, maybe it is just phantom pick-up noise, I wish I had a Spectrum Analyzer to check it out more properly.

While checking things out noticed there was a diode lying flay being squashed down by the cable loom at the amplifier PCB. So partially lifted up the board to examine and reposition the diode. To lift the PCB up a little had to remove 4 connectors and their paper ident labels all fell off so reglued them back on once worked out which was which.

At this stage took the opportunity to spray contact cleaner down the end of the Play/Record switch.

Found that the hum type noise could be varied a lot depending upon the orientation of the deck and found by lifting the deck up off the surface it is sitting on, that the hum could be virtually eliminated (the scope noise did not change at all).

With the deck out of its case the underside of the amplifier PCB makes contact with the surface the deck is on so will refit the plastic case to see if hum then is present.

David

[DMcMahon]

With the deck chassis back in its case the standing hum has reduced quite a bit, only really noticeable at high volume setting when listening on headphones with no music playing.

Connecting speakers to the Hi-Fi amp the playback is very good and hum is not noticeable at all.

Did line recordings using DIN to phono cable (with 470k dropper resistors), get average peak VU meter of 0dB at record levels of around 3, playback of recordings is good.

ALC (Automatic Level Control) Automatic recordings work very well, typically peak VU meter readings are 1-2dB below 0dB, still good quality with plenty of volume.

Still to retest microphone recording.

David

[DMcMahon]

Microphone recording on both channels works fine and playback is good.

David

[DMcMahon]

Did some Wow & Flutter tests, will detail soon in my Wow and Flutter Thread.

https://www.vintage-radio.net/forum/...d.php?t=193107

David

[knobtwiddler]

Do you have a live FFT program? You can get a MOTU M2 soundcard for around £120 (it has THD+N below many pro analysers). There is a shareware program called Audiotester.de (and many other shareware / freeware analysers).

The reason I suggest this is that it's easier to observe ripple and noise on an FFT. You could observe a spike at, say, 100Hz - whilst moving / adjusting parts and seeing if the changes make a difference. Obviously, you can do the same thing with a scope, but it will always be set to look at one part of the spectrum, whereas an FFT can show 20-20KHz at once.

[DMcMahon]

No but I have seen a few analysers for download, will have to check them out some time.

David