Sony WM-D6C dc converter

[Goldieoldie]

Same as pin 8 of the motor chip B+

[Walkmann]

Sorry meant the emitter.

[Goldieoldie]

If you have volts on the collector of q601 the motor should run as the motor is connected directly to the collector .what volts do you have on the ebc wrt chassis ?
Have you checked q601 ?

[Walkmann]

Thanks Goldieoldie but if our posts crossed it is the emitter at 6v , C & B at 0v, what is a wrt chassis?

[DMcMahon]

wrt = with respect to, i.e. chassis is the other connection to the meter.

[saxmaniac]

Pin 15 should be at 5.4v according to manual, this feeds base q601. Emitter should be 6v and collector approx 2.4v feeding motor
Did you try what I said earlier, put the machine in play and spin by hand the supply spool to provide pulses to the photo diode. This is just to see whether the fault is connected to the fast wind autostop? As a long shot just to see if anything happens, try with the speed tune switch in both positions. As far as I can tell the stop/start condition is controlled by pin 7 on the servo ic, should read 4.4v when running driven by the collector q704 on the auto stop board, so best check round those things and see if clues appear

[Walkmann]

Hi,

thanks again for suggestions, have tried everything now. No voltage at pin 15 in any condition, Q601 remains at 0,0,6v and spinning the supply spool has not made any difference in any of the motor speed conditions. Only 1.6v at pin 7

I am at a loss and have spent considerable time on this unit having not had a motor issue to begin with, fixing the audio and then no motor.

Might just put down to experience and keep as a spare parts bin for my working D6C

[Mooly]

Go back to basics:

Can you measure +6v at the emitter of Q601.

If you can, and if pin 15 of the IC is at zero then the B-E junction of Q601 is open circuit or you have a break in the print somewhere.

[Goldieoldie]

I have had q601 fail before.I used a ztx 753 .RS stock them part no 295539

[Walkmann]

OK,

thanks will have another look at the traces and if no issues then will have a go at replacing Q601.

[Walkmann]

Ok

continuity & V check around Q601 etc.

Still measuring 6.5v at the emitter and 0v at pin 15 on "play"

Continuity between Base and pin 15, Collector and pin 16 and Ground, Emitter and pin 8 and 6.5v feed from DC DC convertor

Is Q601 therefore "open"?

[Goldieoldie]

Pin 15 should have 5.4v
Have you checked voltages against the service manual ?
Pin 8 should be 6v for example

[Mooly]

Originally Posted by Walkmann

Ok

continuity & V check around Q601 etc.

Still measuring 6.5v at the emitter and 0v at pin 15 on "play"

Continuity between Base and pin 15, Collector and pin 16 and Ground, Emitter and pin 8 and 6.5v feed from DC DC convertor

Is Q601 therefore "open"?

Based on all you have told us in the form of measurements, yes, Q601 is open.

Q601 is a PNP device which means the base emitter junction should drop around 0.6 volts with the emitter the more positive of the two. Your readings are saying you have 6 volts across this junction which is conclusive proof it is open.

With the unit OFF (no power applied) you should also read about '0.6' using the Diode Test range on your meter if you place the red lead on the emitter and the black lead on the base.

It is also often useful to check (to measure) voltage readings across the actual leads of the transistor as well as reading voltages from ground.

The PNP transistor should measure like two back to diodes although if measuring in circuit you may get interaction with other surrounding parts.

The PNP 'diode' equivalent is shown here (top half of image) and should read like two diodes connected as shown.

[saxmaniac]

Q601 should have 6v on the emitter, 2.3 approx on the collector which drives the motor. Pin 15 on ic 601 should be 5.4v feeding the base q601.
Pin 7 ic 601 should have 4.4v for the motor to run. A quick check of the motor is to unsolder the red wire and run the motor from a 1.5 v battery, however if it isn't open circuit, it should do something so the motor is the least likely suspect here

[saxmaniac]

If you have 0v on pin 15 as stated earlier, the ic is being told not to power the motor. It's vital to see what you have on pin 7 as this receives the stop signal from the auto stop board. Check these things first but try to be logical and not just guess at this or that

[Mooly]

Originally Posted by saxmaniac

If you have 0v on pin 15 as stated earlier, the ic is being told not to power the motor. It's vital to see what you have on pin 7 as this receives the stop signal from the auto stop board. Check these things first but try to be logical and not just guess at this or that

Are you sure?

Pulling the base of Q601 toward ground turns the motor on. The transistor base voltage will always be within a small window of around 0.6 volts lower than the emitter.

Pulling it to 0V or conversely seeing 0V on the base is not a valid condition as it implies the transistor junction is open. What determines the motor run voltage is how much current is pulled through the transistor base junction which in turn determines how hard the device conducts.

The difference in base voltage between not running and full on will be very small, in other words you will still see approx 5.4V on the base whether on or off, however the measured 0 volts on the base tells us immediately that the E-B path is open.

[saxmaniac]

Ah yes you're absolutely right, my capacity for being wrong is infinite!

[Walkmann]

OK,

and again thanks for all the assistance with this issue.

I should state again that the motor did not just die instantly as if a component had died it went gradually, i.e. it would spin for a short while then stop and then spin again after the play button was hit, same result with FF and RW. However, the spin time gradually reduced till the motor could not be coaxed to spin at all. Almost as if a component was gradually dying/failing.

Any now I have checked Q601 with the diode facility on my MM and placing the black lead on the base and using the red lead I get 0.6 on the collector and 0 on the emitter, no other combination yields any result.My layout is mainly SMD and am looking at the supplemental board layout so have taken BCE on Q601 reading left to right from above as per this layout.

Mooly take it Q601 is "dead" and should be replaced, that is certainly what the web site Sciencing states; at about £1 to replace is worth a go However also like Saxmaniac's idea that the autostop may be malfunctioning but how to check? Pin 7 on IC601 reads 1.6v in "play"slightly higher than the 1.2v reading suggested on the board layout in the service manual?

[Mooly]

I would have thought you could replace Q601 with a small 'generic' type device like a BC640 but you would have to be sure in your own mind on pinouts before fitting it. In fact any common PNP device of suitable rating should perform OK, at least to test.

BC640

If you momentarily short out collector to emitter then the motor should take off at very rapid speed. Or dab a 15 or 22 ohm across C and E. That would limit current.

We have to ask/wonder whether the transistor has failed because of an overload somewhere (mechanical such that the motor drew to much current)

[Mooly]

Originally Posted by Walkmann

Mooly take it Q601 is "dead" and should be replaced, that is certainly what the web site Sciencing states; at about £1 to replace is worth a go However also like Saxmaniac's idea that the autostop may be malfunctioning but how to check? Pin 7 on IC601 reads 1.6v in "play"slightly higher than the 1.2v reading suggested on the board layout in the service manual?

Just to elaborate on this...

Whether or not there is a fault around the IC or anywhere else at this point doesn't matter. The fact the base of Q601 is at 0V and the emitter at 6 volts is 100% proof it is open circuit or as mentioned, that you have a break in the print.

Your meter readings suggest you may be getting some interaction from other parts around the transistor and so to eliminate that you would need to remove the device to test it more thoroughly... but there is little point beyond the satisfaction of doing so because the 6 volts across B and E shows it to be zapped.

The big question is whether it was pushed or whether it jumped by itself.