Sony WM-D6 muting module - UK Vintage Radio Repair and Restoration Discussion Forum

Goldieoldie · 6th Jan 2016, 10:10 pm

Hi all
I wonder if someone has some circuit design software that can help me please
The issue is the muting module has failed CP301 .Its on the circuit inside the dotted outline ( causing low level and distortion plus intermittently drawing too much current ) so has to be disconnected !
This is a common fault with these cassette decks
Switch s902 is normally open,closes on play and s903 is normally open closes on record
I think the idea is the cap 22uf discharges through the 150 k to give a slight delay when play is selected.This is to mute the initial tape getting up to speed
It will work ok without this module but it would be nice to get it right !
I will attach second pic showing wider shot of circuit
I hope to use general purpose smd transistors to save on space .
If someone can help with the resistor values that would be great or another simpler circuit maybe ?
Cheers Pete

Goldieoldie · 6th Jan 2016, 10:12 pm

Wider shot of circuit diagram

Goldieoldie · 6th Jan 2016, 10:17 pm

Sorry I should have said voltages on diagram are when the deck is in play

TonyDuell · 6th Jan 2016, 10:27 pm

There are a couple of things I find odd about that circuit just from glancing at it.

The first transistor in the muting module has the emitter grounded and the base connected to ground through a resistor (and no other connection to the base). Surely it is cut off under all conditions?

There seem to be 2 output transistors in the muting module, I assume one for each of the left and right channels. But one has a base resistor the other doesn't. Why?

Do you have the original module? If so, how is it made? A potted module? A ceramic substrate with thick film resistors and SMD transistors on it? If the latter you might be able to measure the resistors and/or replace the transistors.

Goldieoldie · 6th Jan 2016, 10:34 pm

Hi Tony
The module is well sealed !I don't think I can open it up as its set in resin
Yes the two transistors are for the two channels
Why there is only one base resistor ,I guess to give some isolation between the two op transistors ?

TonyDuell · 6th Jan 2016, 10:41 pm

Well, after another glance, I assume the PNP transistor in the module is saturarated during muting. At which point you end up with its c-e path and the b-e junction of one of the output transistors (the one without the base resistor) straight across the supply line. That is normally a good way to blow up a transistor.

I feel the missing base resistor is an error in the diagram.

As for making a replacement, I would be surprised if the transistors couldn't be substituted by 2N3904 and 2N3906 types. They don't look critical. I think we can calculate the input resistor on the first active transistor in the module from the fact that under normal operation (given the voltage values on the circuit) it has about 2V dropped across it (2.6V less the 0.6V across the b-e junction of the transistor) and it's carrying much the same current as the 150k the ends of which are at known voltages. I would then try 10k or 4k7 for all the other resistors in the module.

Goldieoldie · 6th Jan 2016, 10:43 pm

Thanks Tony

TonyDuell · 6th Jan 2016, 11:51 pm

Incidentally, if you do the calculation I suggested you get a value of around 33k for the resistor from pin 2 of the module to the base of the NPN transistor. Since 33k is a common preferred value, I'll guess that's what it should be.

Goldieoldie · 7th Jan 2016, 6:07 pm

Thank again Tony

7th Jan 2016, 6:19 pm

Dunk it in Niromorse for a week, at least you could measure the resistor values.

Goldieoldie · 7th Jan 2016, 6:21 pm

What's niromorse and where would I get it please ?

TonyDuell · 7th Jan 2016, 6:25 pm

I suspect it's 'Nitromors', a well known paint stripper. Whether it will attack the potting compound on this module I do not know.

Goldieoldie · 7th Jan 2016, 7:01 pm

Pic of module attached
It's a hard brittle type of coating
Anybody know of a solvent ?
I've tried petrol and Hammerite thinners

Ambientnoise · 7th Jan 2016, 7:09 pm

The old Nitromors and Polystrippa were effective at softening several types of potting compound including many epoxies but I think it was the Methyl Chloride in the formulations which did the deed. Modern formulations of domestic paint stripper have removed this but you might be able to find some old stock or get the MC online. It took hours to days and, of course, removed paint markings from the exposed components.

Ken

Ambientnoise · 7th Jan 2016, 9:45 pm

Slight correction to the above post - it may well have been Methylene Chloride was the active ingredient.

Ken

TonyDuell · 7th Jan 2016, 9:49 pm

Yes, I believe that's right. It's also known as dichloromethane and is a common solvent used for welding plastics. You can buy it from 4D Model Shop (amongst other places).

Whether that solvent on its on will attack the potting of the module I do not know.

Goldieoldie · 7th Jan 2016, 10:04 pm

Tried some dichloromethane plastic welding stuff,did not work
Is the stuf in the old nitro mors available in any other products sold today ?

6th Jan 2016, 10:10 pm	#1
Goldieoldie Octode Join Date: Jul 2014 Location: Petersfield, Hampshire, UK. Posts: 1,043	Sony WM-D6 muting module Hi all I wonder if someone has some circuit design software that can help me please The issue is the muting module has failed CP301 .Its on the circuit inside the dotted outline ( causing low level and distortion plus intermittently drawing too much current ) so has to be disconnected ! This is a common fault with these cassette decks Switch s902 is normally open,closes on play and s903 is normally open closes on record I think the idea is the cap 22uf discharges through the 150 k to give a slight delay when play is selected.This is to mute the initial tape getting up to speed It will work ok without this module but it would be nice to get it right ! I will attach second pic showing wider shot of circuit I hope to use general purpose smd transistors to save on space . If someone can help with the resistor values that would be great or another simpler circuit maybe ? Cheers Pete Attached Thumbnails

6th Jan 2016, 10:12 pm	#2
Goldieoldie Octode Join Date: Jul 2014 Location: Petersfield, Hampshire, UK. Posts: 1,043	Re: Sony wm d6 muting module Wider shot of circuit diagram Attached Thumbnails

6th Jan 2016, 10:17 pm	#3
Goldieoldie Octode Join Date: Jul 2014 Location: Petersfield, Hampshire, UK. Posts: 1,043	Re: Sony wm d6 muting module Sorry I should have said voltages on diagram are when the deck is in play

6th Jan 2016, 10:27 pm	#4
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,219	Re: Sony wm d6 muting module There are a couple of things I find odd about that circuit just from glancing at it. The first transistor in the muting module has the emitter grounded and the base connected to ground through a resistor (and no other connection to the base). Surely it is cut off under all conditions? There seem to be 2 output transistors in the muting module, I assume one for each of the left and right channels. But one has a base resistor the other doesn't. Why? Do you have the original module? If so, how is it made? A potted module? A ceramic substrate with thick film resistors and SMD transistors on it? If the latter you might be able to measure the resistors and/or replace the transistors.

6th Jan 2016, 10:34 pm	#5
Goldieoldie Octode Join Date: Jul 2014 Location: Petersfield, Hampshire, UK. Posts: 1,043	Re: Sony wm d6 muting module Hi Tony The module is well sealed !I don't think I can open it up as its set in resin Yes the two transistors are for the two channels Why there is only one base resistor ,I guess to give some isolation between the two op transistors ?

6th Jan 2016, 10:41 pm	#6
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,219	Re: Sony wm d6 muting module Well, after another glance, I assume the PNP transistor in the module is saturarated during muting. At which point you end up with its c-e path and the b-e junction of one of the output transistors (the one without the base resistor) straight across the supply line. That is normally a good way to blow up a transistor. I feel the missing base resistor is an error in the diagram. As for making a replacement, I would be surprised if the transistors couldn't be substituted by 2N3904 and 2N3906 types. They don't look critical. I think we can calculate the input resistor on the first active transistor in the module from the fact that under normal operation (given the voltage values on the circuit) it has about 2V dropped across it (2.6V less the 0.6V across the b-e junction of the transistor) and it's carrying much the same current as the 150k the ends of which are at known voltages. I would then try 10k or 4k7 for all the other resistors in the module.

6th Jan 2016, 10:43 pm	#7
Goldieoldie Octode Join Date: Jul 2014 Location: Petersfield, Hampshire, UK. Posts: 1,043	Re: Sony wm d6 muting module Thanks Tony

6th Jan 2016, 11:51 pm	#8
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,219	Re: Sony wm d6 muting module Incidentally, if you do the calculation I suggested you get a value of around 33k for the resistor from pin 2 of the module to the base of the NPN transistor. Since 33k is a common preferred value, I'll guess that's what it should be.

7th Jan 2016, 6:07 pm	#9
Goldieoldie Octode Join Date: Jul 2014 Location: Petersfield, Hampshire, UK. Posts: 1,043	Re: Sony WM-D6 muting module Thank again Tony

7th Jan 2016, 6:19 pm	#10
Guest Guest Posts: n/a	Re: Sony WM-D6 muting module Dunk it in Niromorse for a week, at least you could measure the resistor values.

7th Jan 2016, 6:21 pm	#11
Goldieoldie Octode Join Date: Jul 2014 Location: Petersfield, Hampshire, UK. Posts: 1,043	Re: Sony WM-D6 muting module What's niromorse and where would I get it please ?

7th Jan 2016, 6:25 pm	#12
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,219	Re: Sony WM-D6 muting module I suspect it's 'Nitromors', a well known paint stripper. Whether it will attack the potting compound on this module I do not know.

7th Jan 2016, 7:01 pm	#13
Goldieoldie Octode Join Date: Jul 2014 Location: Petersfield, Hampshire, UK. Posts: 1,043	Re: Sony WM-D6 muting module Pic of module attached It's a hard brittle type of coating Anybody know of a solvent ? I've tried petrol and Hammerite thinners Attached Thumbnails

7th Jan 2016, 7:09 pm	#14
Ambientnoise Heptode Join Date: Feb 2006 Location: Marlborough, Wiltshire, UK. Posts: 917	Re: Sony WM-D6 muting module The old Nitromors and Polystrippa were effective at softening several types of potting compound including many epoxies but I think it was the Methyl Chloride in the formulations which did the deed. Modern formulations of domestic paint stripper have removed this but you might be able to find some old stock or get the MC online. It took hours to days and, of course, removed paint markings from the exposed components. Ken

7th Jan 2016, 9:45 pm	#15
Ambientnoise Heptode Join Date: Feb 2006 Location: Marlborough, Wiltshire, UK. Posts: 917	Re: Sony WM-D6 muting module Slight correction to the above post - it may well have been Methylene Chloride was the active ingredient. Ken

7th Jan 2016, 9:49 pm	#16
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,219	Re: Sony WM-D6 muting module Yes, I believe that's right. It's also known as dichloromethane and is a common solvent used for welding plastics. You can buy it from 4D Model Shop (amongst other places). Whether that solvent on its on will attack the potting of the module I do not know.

7th Jan 2016, 10:04 pm	#17
Goldieoldie Octode Join Date: Jul 2014 Location: Petersfield, Hampshire, UK. Posts: 1,043	Re: Sony WM-D6 muting module Tried some dichloromethane plastic welding stuff,did not work Is the stuf in the old nitro mors available in any other products sold today ?