Cassette tape delay

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dr pepper said:
Yep it does look diffo.
Do you have the schematic.
Click to expand...
Have a service manual for this model but it does not look like its my pcb in it. I also have a manual for the model 222 that has an xlr on the front panel. Tried to attach the pdfs but not working. Will try again

Edit:
Could not attach pdf or zip but here is two links.
I have a 221 model but I think it is different pcb from whats in this linked manual...

for 221 and 201
**broken link removed**

for 222
**broken link removed**

Dont know if any of thoose are similar to my PCB?
 
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The cassette speed control looks fairly complicated, but I spose the recorder is a higher end one, and motor speed control is a critical part of the system to avoid wow & flutter.

Looks like the board for the tape motor is seperate, 'PM00'. There is a chip that looks like it an amp of some kind QM01, looks like theres a fine tuning pot on this.
Only guessing but I'd say that chip QM08 is the main speed control, probably a phase or frequency locked loop, it gets pulses from QM07 some kind of pulse generator either in the motor itself or on the deck somewhere, the phase locked loop will adjust the sped voltage output to match the frequency of the pulse generator with that of a built in oscillator.
Without actual chip numbers its not possible to go any further, also the chip numbers may well be house coded devices as theres no specific info on the schematic.
You could try adjusting RM04, mark the original position first, and see how much control that has and whether its enough, I suspect it will not have much range, you might be able to increase its range by replacing RM03, the only thing is if you change RM03 for too small a value you might blow the chip.
 
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Is RM04 the pitch control that is there today? Thanks Im trying to understand but think I feel a bit lost
Did not know there where different versions of the board inside the same model.
Did not have the luck on my side this time...

Edit: Found RM04 trimpot
 
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No not like that, but I think you can do it.
You have the 2 blue wires going to where the motor is connected on PM00, this probably wont work, so long as the machine is powered from a voltage that the motor speed controller you want to use is compatible with then theres another way (looks like the machine takes 4 batteries so runs from 6v).
Take the power (blue wires) direct from the DC in socket to the power in on the new speed controller, or from ground and the power switch + if you can suss that out.
Obviously be carefull to get the polarity right going into the new speed controller, if the motor goes the wrong way just switch the wires.
Might also be good to put a 100 ohm 1/2 watt resistor across where the motor was originally connected to try and prevent the original speed control electronics from getting upset, and of course dont try and run the motor at 10x its original speed.
One minor thing, if the new speed controller operates at an audio frequency it might bleed into the audio path, so you'll either need to route cables carefully or mod the controller to run above 20kc.
 
The speed controller can be powered from 1.5v-15v.
Does it work like I did With the original controller powering the new one if its whitin the voltage range?

Is it really going to be possible pitch it up 10x with original voltage from the old speed controller? Only thought it would pitch down and not pitch up as long as I did not increase the input voltage?

This mod feels easier to do because I dont have to desolder components or cut the pcb or taking the unit apart. The old controller is visual through a hole
In the big pcb and it looks like the red an black motor cables are visible

Is it possible to see on the image (components) if it is working above 20kc.


Thanks dr pepper
 
I dont think you'd get 10x speed, I was just making a point that you could put excess load on the motor, you will be able to go quicker, the manufacts wouls have made the motor a little bit quicker than it needs to be, to cope with batteries running out & tight tapes.
I cant be certain however I'd say C2 on the Pwm board sets the running freq, a 555 in astable mode would have a cap/resistor connected to pin 2.
Try it and see, if you can hear the Pwm reduce C2 by half.
 
Thanks, Good to know. Would it be hard to put in a limit that does not make go to fast? Dont want to end up burning it by accident.

And can I power from the old controller if the new controller is in range or is it better from dc directly considering other things?
 
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One thing about powering directly from DC and not through old controller. Would play and start buttons still work?
 
I looked some more at the schematics I have for the different models trying to compare with the first one I found that had the working pitch mod on it.
Here is that one.
(Pmd221, early revision, not same as mine)
The 1K pot is replacing a resistor RM20, 1.2K.
I painted the trace that goes to the motor controller cable socket Pin 4 from right.


Here is the model pmd 222.
Here the 1.2K resistor is named RM52. The trace from this one also goes to the contact to controller socket pin 4 from right.


Here is my board.
I also have RM52, guess it is a 1.2K.
And the trace here is also going to the controller board (pin 4 from right). I dont have the schematic for my revision but it looks like it is the same behaviour. If i replace that RM52 with a 1K I maybe achieve the same result as the mod on the earlier board above?
 

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Oops thats doing things by proxy, I'd not thought you only want the motor running when the deck is playing.
One way to solve that is to put a relay across where the old motor connects and use that to switch power to the speed controller, powering another speed controller from the old motor supply isnt a good idea.
However your reasoning with the speed control mods for other models is sound, give that a try, the resistor inline with the speed calibration pot is a good place to adjust speed, range must be enough to make it worthwhile.
And even if you did blow up the decks speed control you always have the backup solution of using the Pwm speed controller already mentioned, another way of switching power to the motor is to find on the deck where the motor start contacts are, when you press the play button there will be some contacts mechanically pressed to start the motor and electronics.
 
dr pepper said:
Oops thats doing things by proxy, I'd not thought you only want the motor running when the deck is playing.
Click to expand...

It doesn't really matter, some cassette decks switch the motor, others don't - the mechanics of it stop the tape moving anyway, regardless of the motor.

For an echo unit it's even less of a factor, as the tape loop is usually going all the time.
 
Thank you for the great ideas!
I measured voltage from the speedcontroller to the motor and it is 1.7v on play/rewind/forward and 2v when recording. If I use the ”new”’controller I guess I need to use a regulator from about 5v to 2v?

But to begin with I will try and replace the resistor with a 1K pot and see what happens. Just a bit unsure if that will work during recording or only playback...
 
I think you'd be Ok doing the pot mod by the sound of it.
A Pwm regulator is deffo the way to go if you going to replace the original, a constant voltage regulator wouldnt work that well, as the load on the motor changes as the tape runs on, the speed would probably vary, Pwm is less sensitive to torque variations.
Not that it would matter as the torque would be the same at the same part of the tape, therefore speed would be repeatable.
 
I more thought about that the motor seems to be fed from the the original controller with a maximum 2v.
If I connect a new controller that is fed directly from DC source I thought the motor maybe gets to much voltage if the new pwm is fed with 4.5-6v instead.

The pot mod seems nice and the way I want to go but it is confusing. Today the pitch on the front only works in play mode. I dont understand how it will work with the new added pot in rec mode by only changing that 1.2K resistor to a variable one. I thought I hade to make a cut or put in a junper somewhere to get it work while recording aswell.:.
 
Progress
Just replaced the reistor with a pot and now I can pitch until it completely stops. Both during play and recording.
I decided to cut the trace instead of desolder one leg.
Thinking maybe it can be bad to if it is completely turned down to stop? Would it be good with a small resistor in series?

Edit: added 330ohm in series with the pot. Now it does not stop. Strange thing is with pot giving full resistance 1K tape is running faster than before with the fixed resistor that I measured to be 1K (1.2 in schematic)
 

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There may be some difference in resistance to the old setup making the speeds diffo, sounds like you've cracked it anyway.
There would have been some kind of switching involved making the original speed control only work in playback, the resistor inline with the speed calibration pot obviously has effect all the time.
You'd need to oscilloscope the supply to the motor to know whats going on, 2v on your meter may not be what you think, if the motor is driven by a linear voltage that will be correct, however the motor controller might be doing something different making your reading erroneous.
With Pwm as far as most motors are concerned you can apply 6v or more so long as the average voltage taking pulse width into account is around the 2v, this will give the same speed more or less as 2v steady state.
 
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