Sony gunk ! - UK Vintage Radio Repair and Restoration Discussion Forum

Goldieoldie · 17th Dec 2015, 4:45 pm

Hi all
Thought this might be useful to others
I had a 1980s Sony Walkman to repair
All the Ali electrolytic caps had gone leaky so replaced
Playback was now working well but on record there was a whistle being recorded.
The freq changed when I switch the iss ( freq shift to min beat on mw recordings )
Thinking the bias Osc freq was low I check with a counter and was ok at 40 kcs
On close inspection the record/ pre amp chip had a feed of the bias osc going to one of the pins.There was what looked like old flux between the chip pins .After cleaning with a mini toothbrush and IPA hey presto all came good.No Whistle !
I am familiar with the brown glue Sony used ,particularly in the 80s which goes conductive but not what looks like flux going the same way !
Hope this info will help others and not what happened to me with a lot of tail chasing !!
Cheers Pete

Refugee · 17th Dec 2015, 5:06 pm

Are you sure it was not electrolyte from the leaking capacitors?
That brown gunge used to be some kind of epoxy foam with a corrosive catalyst. In the days when I did computer repairs we used to call it "Mitac gunge" because Mitac branded CRT screens used to be full of the stuff and it even used to rot through hook-up wire.
I have actually scrapped items due to the amount of time it would have taken to scrape it all out.

Goldieoldie · 17th Dec 2015, 5:18 pm

No. The chips are on the other side of the PCB where the caps are. No caps near the chip.

As I said, it looked like old flux. I think because of the high level/freq going into the preamp chip the prob high resistance of the gunk was sufficient to leak some of the signal to the other pins of the chip. On playback it was not affected .

Refugee · 17th Dec 2015, 5:59 pm

I would consider it unlikely to be flux of the resin variety. If it were plumbers flux that would be a different matter.
Perhaps it was a fleck of dust or grime that has found its way in there at some stage.

Goldieoldie · 17th Dec 2015, 6:08 pm

No it was not grime .
It was between the pins and looked like old flux.
Dissolved with IPA

Studio263 · 22nd Dec 2015, 8:15 am

Another odd thing which one finds in 70s / 80s Sony gear is the red glue that they use to hold the contacts into switches, in particular those with lots of pins. The record / playback switch is a favourite place to find it, it gets conductive with age and causes all sorts of problems.

My cure is to file as much of it away as I can with a small needle file and then chip the last bits out with a craft knife. if you are careful you can then put the switch back in as it is, the solder will hold everything firm.

The layouts of some of the circuits require that there is no leakage in this area at all, e.g. supply lines right next to pins carrying small signals. DC leaking across upsets the bias in the amplifiers, muting the sound or making it distorted. I remember one case with a TC-D5 (original version) that would not record on one channel and an FX-414 TV / radio cassette combination with no sound at all due to the muting being on all the time, both because of the red glue.

McMurdo · 28th Dec 2015, 2:27 pm

The conductive gunk or glue problem occasionally rears its head in more modern stuff that uses SMD. Some high speed assembly machines hold the SMD on the board with tiny blobs of red or brown glue before they're soldered. The glue is then hidden under the chip or capacitor etc. In some types of glue this can, with age, go slightly leaky with similar random symptoms to the white/brown stuff on vintage hifi stuff. But not so easy to find!!

17th Dec 2015, 4:45 pm	#1
Goldieoldie Octode Join Date: Jul 2014 Location: Petersfield, Hampshire, UK. Posts: 1,043	Sony gunk ! Hi all Thought this might be useful to others I had a 1980s Sony Walkman to repair All the Ali electrolytic caps had gone leaky so replaced Playback was now working well but on record there was a whistle being recorded. The freq changed when I switch the iss ( freq shift to min beat on mw recordings ) Thinking the bias Osc freq was low I check with a counter and was ok at 40 kcs On close inspection the record/ pre amp chip had a feed of the bias osc going to one of the pins.There was what looked like old flux between the chip pins .After cleaning with a mini toothbrush and IPA hey presto all came good.No Whistle ! I am familiar with the brown glue Sony used ,particularly in the 80s which goes conductive but not what looks like flux going the same way ! Hope this info will help others and not what happened to me with a lot of tail chasing !! Cheers Pete

17th Dec 2015, 5:06 pm	#2
Refugee Dekatron Join Date: Apr 2012 Location: Worksop, Nottinghamshire, UK. Posts: 5,553	Re: Sony gunk ! Are you sure it was not electrolyte from the leaking capacitors? That brown gunge used to be some kind of epoxy foam with a corrosive catalyst. In the days when I did computer repairs we used to call it "Mitac gunge" because Mitac branded CRT screens used to be full of the stuff and it even used to rot through hook-up wire. I have actually scrapped items due to the amount of time it would have taken to scrape it all out.

17th Dec 2015, 5:18 pm	#3
Goldieoldie Octode Join Date: Jul 2014 Location: Petersfield, Hampshire, UK. Posts: 1,043	Re: Sony gunk ! No. The chips are on the other side of the PCB where the caps are. No caps near the chip. As I said, it looked like old flux. I think because of the high level/freq going into the preamp chip the prob high resistance of the gunk was sufficient to leak some of the signal to the other pins of the chip. On playback it was not affected .

17th Dec 2015, 5:59 pm	#4
Refugee Dekatron Join Date: Apr 2012 Location: Worksop, Nottinghamshire, UK. Posts: 5,553	Re: Sony gunk ! I would consider it unlikely to be flux of the resin variety. If it were plumbers flux that would be a different matter. Perhaps it was a fleck of dust or grime that has found its way in there at some stage.

17th Dec 2015, 6:08 pm	#5
Goldieoldie Octode Join Date: Jul 2014 Location: Petersfield, Hampshire, UK. Posts: 1,043	Re: Sony gunk ! No it was not grime . It was between the pins and looked like old flux. Dissolved with IPA

22nd Dec 2015, 8:15 am	#6
Studio263 Octode Join Date: Apr 2007 Location: Hampshire, UK. Posts: 1,577	Re: Sony gunk ! Another odd thing which one finds in 70s / 80s Sony gear is the red glue that they use to hold the contacts into switches, in particular those with lots of pins. The record / playback switch is a favourite place to find it, it gets conductive with age and causes all sorts of problems. My cure is to file as much of it away as I can with a small needle file and then chip the last bits out with a craft knife. if you are careful you can then put the switch back in as it is, the solder will hold everything firm. The layouts of some of the circuits require that there is no leakage in this area at all, e.g. supply lines right next to pins carrying small signals. DC leaking across upsets the bias in the amplifiers, muting the sound or making it distorted. I remember one case with a TC-D5 (original version) that would not record on one channel and an FX-414 TV / radio cassette combination with no sound at all due to the muting being on all the time, both because of the red glue.

28th Dec 2015, 2:27 pm	#7
McMurdo Dekatron Join Date: Jun 2009 Location: Staffordshire Moorlands, UK. Posts: 5,271	Re: Sony gunk ! The conductive gunk or glue problem occasionally rears its head in more modern stuff that uses SMD. Some high speed assembly machines hold the SMD on the board with tiny blobs of red or brown glue before they're soldered. The glue is then hidden under the chip or capacitor etc. In some types of glue this can, with age, go slightly leaky with similar random symptoms to the white/brown stuff on vintage hifi stuff. But not so easy to find!! __________________ Kevin