Philips N4506 Tape Tension issues

De compact cassette was een schitterende uitvinding van Philips en werd een wereldwijd succes. Ook bandrecorders blijken een tijdloos populair medium.Kun jij ook geen genoeg krijgen van die sfeervol draaiende spoelen? Deel hier je magnetische passie!

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manpackman
Berichten: 14
Lid geworden op: 27 dec 2015, 19:52

Hello,
Just a quick update on my N4506.
The correct belts are fitted and the mechanical brake works after adjusting the spring tension. The reel table heights are now correct and both reels and motors turn smoothly and easily.
However, I have the following problems:

(1) START - when the start button is pressed a tape loop forms beyond the pinch roller. It takes a second or two for the loop to be taken up by the take-up reel. Studying the manual, this could be because the starting current pulse that goes via C44/ R56 and D10 is not reaching motor M2.
(2) WIND - when the wind button is pressed, the reels do not move at all. There is a low frequency hum coming from some part of the circuit or motor.

(3) REWIND - when the rewind button is pressed, the reels are very sluggish and take a few seconds to get going. Rewind seams to be very slow and when 'stop' is pressed a tape loop forms and the tape remains slack.

Any further thoughts from anyone would be most welcome.

Thanks, Colin.
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Will
Donateur
Berichten: 12123
Lid geworden op: 24 mei 2009, 22:56
Locatie: Het uiterste Zuiden
Contacteer:

Test without a tape first. No reels on the recorder and check this:
- PLAY: Left reelholder spins clockwise, counter counts backwards. Right reelholder spins counter clockwise. Capstan roller spins and cannot be stopped easily by holding it with two fingers.
- REW: Left reelholder spins clockwise, counter counts backwards. Right reelholder doesn't spin.
- FF: Left reelholder doesn't spin. Right reelholder spins counter clockwise.

In REW and FF it is hard, but possible to hold the spinning reelholders with your fingers.

If all this works, suspect the tape itself for causing the problem.
Een verzamelaar ziet niet wat hij al heeft, hij ziet alleen wat hij nog mist.

Es ‘t good is moste ‘t good laote.
manpackman
Berichten: 14
Lid geworden op: 27 dec 2015, 19:52

Hi Will,

Thanks for the quick response. I've tried your suggestions and have found the following:

NO TAPE

PLAY - all reel decks move in the directions you have stated. Capstan turns and is hard to stop.
REWIND - left reel table spins clockwise and right hand one stays still. Left reel table is powerful!

FAST FORWARD/ WIND - left reel table does not spin. Right reel table does spin, but drive from motor is VERY, VERY weak and reel table can be stopped easily by applying very little pressure. As mentioned, there IS an audible hum coming from some part of the mechanism.

WITH TAPE - I've tried different tapes, there doesn't seem to be too much difference between an original Philips or a new RTM (Recording the Masters) tape. Both are seven inch (18cm) reels.

Colin.
manpackman
Berichten: 14
Lid geworden op: 27 dec 2015, 19:52

Will,

One thing I have noticed - with no buttons pressed, if I take both belts off, both M1 and M2 motor pulleys revolve slowly but with very little power. Left hand goes clockwise and right hand goes anticlockwise. When I fit the belts, the motors stop.

Colin.
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Will
Donateur
Berichten: 12123
Lid geworden op: 24 mei 2009, 22:56
Locatie: Het uiterste Zuiden
Contacteer:

Next step: clean and check the REW and FF switches.

After this the next suspects are the power connection (+A) to TS503 and 553 and these transistors themselves.
Measure the voltage on the motors (H4, B4 and H6, B5) against ground.
Een verzamelaar ziet niet wat hij al heeft, hij ziet alleen wat hij nog mist.

Es ‘t good is moste ‘t good laote.
manpackman
Berichten: 14
Lid geworden op: 27 dec 2015, 19:52

Hello again Will,

First of all, thanks for looking at this and for your input. However, I've been rather stupid!
When I adjusted the reel table and motor pulley heights, it appears I'd not tightened up the grub screws on the right hand motor pulley. So, yes, the motor shaft was just spinning in the pulley! No wonder there was no power in the take up reel and that I was getting tape loops!
I was just about to try substituting a different motor when I discovered this.
Needless to say, Wind/Fast Forward now works perfectly - and no loops either!
It just goes to show, always suspect the simple things and don't cast doubt on Philips electronic quality. Ah well, you live and learn!

I'll put it back together, check the speeds again and have a play with it for a while.

Many, many thanks again and sorry to waste your time!

Best wishes, Colin.
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Will
Donateur
Berichten: 12123
Lid geworden op: 24 mei 2009, 22:56
Locatie: Het uiterste Zuiden
Contacteer:

Glad you found the cause. :clap:
Een verzamelaar ziet niet wat hij al heeft, hij ziet alleen wat hij nog mist.

Es ‘t good is moste ‘t good laote.
manpackman
Berichten: 14
Lid geworden op: 27 dec 2015, 19:52

Thanks Will,

It HAD to be something simple - after all, Wind/ FF worked fine before I adjusted the reel table heights etc. I should have suspected something stupid sooner, but at least I hadn't started lots of electronics testing!
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