hifi engine

Tandberg 3300X R.to R. motor issue

Hi All,

I was listening to some tape on my Tandberg 3300X, when suddenly, the speed started to get unstable.
Thought it could be the belt.
Opened it and it appeared that the motor was not spinning properly. In fact, it had stopped working at all.
Took the motor apart and cleaned/relubed it. Surprisingly, the inside was quite clean, so I added some fresh oil and tried making it spin by hand. Keeps spinning for about five seconds. The adjustable bottom bearing was loose, so I tightened the screw a little, leaving a very slight play.
Motor back in the chassis: now I can make it start, but only for about 15 seconds, before it stops. Switching it on again gives the same result: 15 seconds, then stop.
Is there anything I have overlooked? Could it be a transformer problem?
My skills with an electric motor are limited to the mechanical side of it, so if anybody could give me a hint and a way to a solution, he/she would be most welcome!
Thanks very much in advance!

Cheers,

Hugh.



krokkor's picture

Tandberg 3300X R.to R. motor issue

Hi Hugh,

as shown in the service manual's main electric diagram (pag 21 of the manual) the motor's activation was actuated by a relay (see center of the diagram, the switch named as "motor switch" near the Photoelectric End Stop block). Try to short-circuit the contacts of the relay's switch wired to the 509/510 testpoints on the Bias/Photoelectric/end stop PCB (be careful 'cause these testpoints are under main AC power voltage). This operation will force the motor to run continuously. If the motor runs without stop then the problem shall be searched in the End Stop circuitry. After cleaning the power pilot lamp and the photo transistors Q506 that you can find at the left side of the erase head, remove the short circuit and try to insert a dark paper sheet or simply a business card behind the pilot lamp (inside the tape path); this will simulate the tape's presence and if the End Stop circuit is well adjusted, the motor will run after the Play will be engaged (removing the paper sheet will Stop the motor). If your problem occurs again (after 15 seconds) try to readjust the End Stop photoelectric circuit sensitivity with the trimpot R512 that you can find on the Bias/Photoelectric/end stop PCB.

Cheers

Krokkor

Re: Tandberg 3300X R.to R. motor issue

Hi Krokkor,

Thanks a bunch for your quick reply!
Of course, I had overlooked the photoelectric switch!
A credit card in front of the light makes it.
At least, the motor, which hadn't been serviced since 1975 is clean and well lubed now.
Will re-fit the pulley and the belt after a thorough clean of the whole tape path and have a try.
Begging for the permission to come back in case the issue is not completely solved...
Many thanks again!

Cheers,

Hugh.