Pioneer CT-F850 recording/playback issues

[marini]

Hi,

I hope I'll be luckier with this one than with my previous CT-F750...

I got a CT-F850 that looks in pretty nice shape. Came with original box/packaging, manual, etc.
I replaced all the 6 belts + the idler tire (gotta say, a lot easier than with the CT-F750).
I can't notice anything wrong from the mechanic side of things. Normal speed, fast-forward and rewind working nicely, auto-stop, etc.
Whenever I play a pre-recorded tape (original tape), it sounds just fine. The only odd thing is the left channel on the VU meter which barely hits any bar (ie: right channel on +3 and left channel on -10, although the volume is balanced between the channels).
The main issue is with the recording and further playback of a tape.
I got one tape with previous recording on it (CT-W208R) and if I play it on the CT-F850, it goes fine for a fraction of a second and then the left channel just drops to nearly inaudible.
Then I tried to record something on this same tape, using my turntable as a source. By pressing the monitor button on the deck, if I choose tape I observe the same issue I mentioned with the unbalanced levels on the VU meter. However, if I choose source, the VU meter levels are balanced?
Also, when I try to play this tape again, I can hear a mix of what was there before and what I just recorded. Like a ghost sound, similar to when I try to play a mono open reel on my RT-707 with the amplifier in stereo mode.
Curiously, if I get this same tape and play it on the CT-W208R, I can hear just the previous recording!
I really can't figure out what to check, so any help would be greatly appreciated.

Thank you!

 

[zebulon1]

I sounds like the head needs adjustment.
The playback and record heads are in the same container. It seems like its a little crooked in the transport.
Some may advise different:
Mark the Azimuth screws (left and right) so you can turn them back to the original settings.
Play a known good tape and ever so slightly turn the screws and see if you can get the head to track better. Make sure the mechanicals are good and the tape is not getting distorted as it goes from one reel to the other reel.
Check the erase head for proper adjustment. It could influence the tape mechanically as the tape travels across it.
Read the service manual before you try anything and again, mark the azimuth screws before tweeking them. A little goes a long way.

 

[marini]

I sounds like the head needs adjustment.
The playback and record heads are in the same container. It seems like its a little crooked in the transport.
Some may advise different:
Mark the Azimuth screws (left and right) so you can turn them back to the original settings.
Play a known good tape and ever so slightly turn the screws and see if you can get the head to track better. Make sure the mechanicals are good and the tape is not getting distorted as it goes from one reel to the other reel.
Check the erase head for proper adjustment. It could influence the tape mechanically as the tape travels across it.
Read the service manual before you try anything and again, mark the azimuth screws before tweeking them. A little goes a long way.

Thanks for the reply!
I've heard horror stories about trying to adjust the azimuth without having experience/tools for doing it.
Considering that a pre-recorded (original, purchased) tape sounds pretty much fine and I can notice the issues just when recording and further playing a tape, should I still consider the problem being caused by misalignment (sorry, I just have no experience on this)?
If in fact there's a misalignment issue, by getting it corrected would this also fix the VU meter unbalanced channels?

 

[zebulon1]

Probably
Marking the current position is important.
People make a big deal out of things they don’t understand. If the deck is working good enough then leave it.
I look it as if it s not useable why not try and make it worse? The worst that can happen, is it gets better.
There’s not many places to take these decks for repair without a lot of expense. So you have to figure out how to make things work.
I do think that a lot of the problems are issues other that a out of adjustment heads. But you acquired this without known history so all bets are off.
The service manual is very helpful but some interpretation is needed.

 

[marini]

Probably
Marking the current position is important.
People make a big deal out of things they don’t understand. If the deck is working good enough then leave it.
I look it as if it s not useable why not try and make it worse? The worst that can happen, is it gets better.
There’s not many places to take these decks too without a lot of expense. So you have to figure out how to make things work.
I do think that a lot of the problems are issues other that a out of adjustment heads. But you acquired this without known history so all bets are off.
The service manual is very helpful but some interpretation is needed.

Very valid points. I'm gonna give it a try. Thanks!

 

[marini]

So it's been a very long time, but I finally managed to get back into this.
I got a calibration tape to help me check and possibly fix the heads alignment/azimuth.
I tried to follow the steps in the service manual, but there are some bits I don't understand (sorry, I really have no experience on this, but am very keen on learning):



1. What output terminals mean here? Are there pins on the board I should check with a multimeter?
2. What's the maximum it's referring to here?
3. It doesn't seem to have a screw lock anywhere.

As an attempt to check for any changes, I tweaked a bit the adjustment screw clockwise and counter-clockwise, whilst playing a tape. I noticed a difference in the playback quality and output levels on the fluoroscan meters.

Could someone kindly help me with the above, please? Much appreciated!

 

[cferry1]

Primarily, the procedure listed says "Turn the azimuth adjustment screw until the output from both left / right channels reaches a maximum. "

Dependent on the Cal Tape being used.

The procedure should be suggesting to have the Left / Right Channel Outputs to be uniform, simultaneously. The two channels should be ( as close as possible ) equal in amplitude or output level.

Many deck Calibration Procedures suggest the use of an oscilloscope on the Left / Right Channel simultaneously, with the scope displaying a Lissajous Pattern. I suspect Lissajous method is the most precise. (IMO).

One example, here.
Link :https://audiokarma.org/forums/index.php?media/img_20191101_144008669audio-calibration.21095/

 

[ConchBoy66]

People make a big deal out of things they don’t understand. I look it as if it s not useable why not try and make it worse? The worst that can happen, is it gets better.

I just have to butt into this conversation and say that reading this just made my day..