replaced 4 track motor, to fast

C

classicaldeath

New member
The motor went out on my tascam 424mkII, I used the part number off the original motor to get one from an online electronics store. It was almost an exact match, but the original motor was 1600/3200 rpm, and the new one is 1600/3100 rpm. Now it runs high speed when the tape speed is set to normal, and rediculously fast when set to high, and the pitch control does work. Does anyone know what the problem is? Thank you for any help.
 
Motor speed calibration required...

Yep
It seems you have a speed governer problem.

Ok 1st you need to locate the the motor relay board (or follow where the motor wires lead to).

There should be a VARIABLE resistor there (It will have a screw on the top).

next...
You are going to need either a calibration tape or a PRE recorded tape to set the standard running speed. (if this is a 2 speed machine then there will be more than 1 setting - there will be 2 settings ie: 1 for each running speed).
Also it would be better if you had 2 tapes (1 recorded at slow and 1 at high) This would be more accurate in setting both speeds.

Dont worry...

This does tend to happen when changeing motors. Beacuse at the factory you will NEVER get 2 machines with the same setting on motor speed. Each machine has to be independantly set to their own running speed. I used to work for an electrical company. And i did quite a few motor changes on Studer and Otari machines (reel to reel) but unfortunatly never had enough money to purchase my own.

Ok
Once you have located these 1 or 2 settings the rest should be fairly straight forward and you should be up and running.

As for the different RPM motor types. Sometimes companies will bring out a new model and thern after it is released they will then start their replacement parts section specific to the current models in circulation. Although you got the right part. There are most commonly differences between the part that was installed in the machine at the factory and the replacement part you recieve from them. This isn't an error on yours or the companies part. Some companies like to change things every now and again. And i will admit setting a precision running speed on a machine can take several hours if your a perfectionist. And it pays to have a scope for measuring running speed and a calibration tape.

Only thing is on the older reel to reel machines i have worked on. You cannot change the running speed of an induction motor, Why... A because the motor windings are specificlly set and there are no brushes. The shaft running through the motor has no contact with anything other that the reel table on the end and the bearing housings, and obviosly the brake drum mounted on the rear of the motor which is servo controlled. On some multi speed induction motors, you will have TWO sets of windings. 1 for the slow speed and 1 for the high speed, so you could imagine the cost of replacing one of those. And here in Uk IT IS NOT CHEAP. And may not even possible at all as teac ceased production and support for about 90% of the reel to reel machines released by their Uk devision. They have little if any leftover stock (parts etc) (most of their reel to reel support has gone to Tascam machines) for the more recent machines they did release but once those are gone thats it. Pretty sad to see it end like that. But i will give credit reel to reel machines have satisfied people arround the world for over 50 years and possibly many years to come. But there will come a time then they fade away to time. just like the 78rpm record, the thermonic valve (Replaced by transistors) and the Marconi Transmitter.

Hope this info helps

Keith
 
thanks for the help and all the info. Adjustment for me doesn't need to be to acurate, tapes recorded in the tascam will be played only in the tascam to be mixed to something else, I just don't want to be running through tapes in less than ten minutes.
 
ok no probs.

But if you ever need another machine or if you change the machine you use, you may come into difficulty becuase the playback speed may vary on different machines so this may be something to take into account.

Hope this helps

Keith
 
Last edited:
For Classical Death,
I have a feeling the 424 portastudio motor kept running all the time and so didnt take long to wear out. You might confirm this by listening carefully for a motor sound when the unit is switched on but no tape playing.
If it does run all the time it might be an idea to keep the machine switched off unless it's being used. Otherwise you might have the same problem with the new motor before too long.
I seem to recall one that was used mainly as a mixer in a music shop and the motor failed in a short time.
Tim
 
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