N2205 Running slow and wobbly
 

Hello
I have just dug out a Philips N2205 cassette player from the back of the cupboard, I bought it a couple of years ago at a car boot. I had assumed that it would have belts that had turned to goo, but no, belts looked good! So cleaned it up, using meths on the all drive surfaces, gingerly lubricated sliding surfaces etc., all rotating items seem to run free, switch cleaner in the pots and all seemed reasonably well.
However things are not quite right, it slows down and goes more wobbly the longer it is on, or further through the tape
I have replaced the main drive belt, no change, repeatedly cleaned the pinch roller and capstan
The machine is running on mains supply
Any suggestions?
Many thanks in anticipation Philip

Re: N2205 Running slow and wobbly
 

Motor speed is controlled by a regulator, T10 and T11. Voltage checks around there should lead you to the culprit.

Service manual available here:
https://www.service-data.com/section...5-no-auto-stop
https://www.service-data.com/section...with-auto-stop

Kevin

Re: N2205 Running slow and wobbly
 

Thank you Kevin
I feared such may be the case!
This exposes my lack of knowledge! The voltage going to the board from the power supply (grey wire) seem to be consistent at about 9.99 to 10.01 volts, what I believe to supply to the motor is fluctuating from about 4.29 to 4.37v as if constantly hunting
I have downloaded the schematic and there appears to be some variations of the circuit but mine is the one with two OF162 diodes, and T10 is AC127 and T11 is AC128

I understand that these are germanium transistors,but does that in itself mean that they are likely to need replacing? and if so with what?

However I am pushing the limits of my ability at this point, not exactly sure what I should be checking for...

Hoping for further guidance

Philip

Re: N2205 Running slow and wobbly
 

Well it could be the motor. It's the same motor used in all these basic decks....getting hold of one might be a problem.....
As for the control board....they were never repaired back 'in the day' and just replaced. However they couldn't be simpler and I believe are just a basic comparator circuit. The AC127 and 128 are still available if you feel up to changing them....you only need a small soldering iron and a steady hand. The two diodes can be replaced by 1N4148's....they are nothing more than standard signal diodes. There is very little else to go wrong with those boards.

If the voltage to the motor appears to be hunting it doesn't necessarily mean that the the control board is faulty. It MIGHT be trying to control a faulty motor by varying the voltage to it....if the motor is faulty for instance, the feedback voltage from it to the comparator will vary so the transistors will try to compensate. Then again if either of the transistors are faulty but the motor is good, you'll possibly get a similar effect.

Not trying to put you off but just explaining that changing the transistors and diodes may not cure the problem.

Re: N2205 Running slow and wobbly
 

Thank you for that, to put it into context, the machine is a curiosity, not in good cosmetic state nor any sentimental value, nice to get it going, but not a problem if I don’t!
It would be disappointing to buy some new (ish) transistors and be no further forward.
I had thought about using one of those Far East LM 317 based voltage regulators (which I have) to temporarily drive to motor, to see if this made to motor run smoothly and consistently ...
Assuming that I wire it correctly, would this be a wise diagnostic plan?
Thanks again

Re: N2205 Running slow and wobbly
 

If you want to experiment then go ahead but the motor controller is not a regulator as such and regulators are not used to control motor speed....not accurate enough. If you want to know about controlling DC motors (such as this) Google 'Servo control of DC motor' or something like that......

Re: N2205 Running slow and wobbly
 

I'm confused! There is no feedback from the motor, Its a standard DC motor, unless of course the circuit is measuring the current through the motor and using that to compensate for speed variations.

Perhaps you could enlighten me.

You could i suppose fit a resistor of around 47 ohms across and instead of the motor and see it the voltage across it fluctuates. If it does the regulator is faulty, if not then it could be the motor.

Re: N2205 Running slow and wobbly
 

On reflection, I think I will order the transistors and diodes, if does not give the hoped for results I am sure the transistors will eventually find a home in something else.
I hadn’t really thought about controller versus regulator
Thanks for help so far
Philip
Edit ... just seen the last post from Michael, may just try the resistors as load.....
Philip

Re: N2205 Running slow and wobbly
 

I’d also check that the small preset pot on the regulator PCB isn’t intermittent or out of tolerance.

Re: N2205 Running slow and wobbly
 

Well it hasn’t been a good cassette player day

Initially I tried the 47-ohm resistor instead of the motor to eliminate the motor, but the recorder went into “end of tape mode” and cut the power, so put that back on the do later pile! ( I did use switch cleaner on the little preset pot- no change though)

Then I thought I would look at a Radiola N2225 , this one has gooey belts so I started with the motor pulley, and it was all but seized, I did get it to move, but it really wasn’t well, so another back onto the do later pile…

Next out was a more modern N2215, this was gooey belted as well, so that was duly cleaned up, progress was good, but tape wasn’t been taken up, upon investigation, the “take up cog” was missing about 15% of its teeth!.... another on the pile!

Next Radiola RA 3302 (same as Philips EL3302) this was a gooey one too, cleaned up re-belted, cleaned and lubricated, created a 7.5volt supply, fired it up….sounded like Pinkey and Perkey,. Not until I turned the supply down to about 5 volts did it sound anything like reasonable and even then it has a dent in the pinch roller from being left in play position, so I think it’s another for the “pile” !

I don’t think that cassette players are my strongest point …

Philip

Re: N2205 Running slow and wobbly
 

You need to keep the right-hand take-up spool turning otherwise it will think the tape has stopped. Just turn it with your finger while carrying out any testing and it will prevent 'end-of-tape' from switching off the power.

Re: N2205 Running slow and wobbly
 

Hi!

These simple motor regulator circuits rely on the internal back–emf generated by the motor's armature due to it's rotation in the magnetic field provided by the permanent–magnet pole pieces, and they operate to stabilise the motor current rather than the motor voltage!

The usual cause of failure to stabilise or run correctly is either badly worn brushes or a badly worn/burnt centrifugal switch contact on the speed governor, assuming the motor uses one.

If there is centrifugal switch governor, there will always be a tiny screw for adjusting the motor speed accessible thro' a hole provided in the side of the motor casing, whereas an electronically regulated motor will not have a screw visible.

If you can't get another identical motor, you might be able to get similar tiny brushes from any of the small hobby motors sold for toys (look for one of about the same size and voltage) or it might be possible to get another Philips deck cheap with a similar motor & control board you
can try!

If you've got a steady hand and you're confident at dismantling the motor, try rubbing the commutator with one of those red fibre–pencils sold by RS etc., to remove as much as the black deposits from the brushes as you can, then make sure you wipe the commutator surface with IPA etc., afterwards to get rid of the fibre particles left over!

If the motor runs in the wrong direction after reassembly you've reassembled it 180 degrees out!

Chris Williams

PS!

I think Mr. Michaelis wrote an article on the principles and faults assosciated with battery–operated motor speed control in the later 1966/1967 issues of P.W., have a look on American Radio History for them!

PPS!

Might be worth looking to see if you can get a replacement brushless d.c. motor that's compatible with the N2205 mechanics, altho' you'd need a variable – speed one!

Re: N2205 Running slow and wobbly
 

Philip,

At the end of the day and you decide to put it back in the cupboard, if you have the original mains lead and want to get some "pay back". The "original" mains lead is rarer than rocking horse droppings !!!

I've seen one go for £30 ! But it has to be the original mains lead !