Another Tandberg puzzle. - UK Vintage Radio Repair and Restoration Discussion Forum

Tractorfan · 27th Jan 2015, 12:07 pm

Hi,
After replacing all the lockfit transistors in my noisy Tandberg series15 (thanks everyone for your help, btw), I was playing a tape which had been recorded too quietly. On turning the volume control right up to hear the recording, the machine broke into a low frequency oscillation which could be heard as a 'pulsing' sound with the lamp illuminating the counter 'pulsing' in sympathy. So, serious enough to drag the supply down. Reducing the volume stopped it immediately, but advancing it again did not invoke the oscillation again.
I replaced the BC147 & BC149 transistors with BC107 & BC109s (some of which were recycled from my junk box) and I wonder if I've inadvertently put a duffer in somewhere?
Otherwise, it works well but can't be made to oscillate every time.
Cheers, Pete.

Restoration73 · 27th Jan 2015, 1:16 pm

See if you can invoke the instability by wiggling the knob of the record/playback/amplifier
switch on the left. If so, it may be the contacts. I'm assuming you have checked any
dc decoupling capacitors.

Tractorfan · 29th Jan 2015, 6:58 pm

Hi,
Finally managed to have another play with the Tandberg. The low frequency oscillation appears to be temperature related. I tried to invoke the instability, nothing would start it. The machine worked impeccably for about three quarters of an hour and then the ocillation started. Now nothing would stop it, even switching the machine off for a few minutes and then back on did nothing. It needs to be left to go stone cold, then it's OK for another period.
I changed all the lockfit transistors as per my earlier post, plus four that were also BC149 types, but in a grey rectangular package. I must have inadvertently put a bad 'un in. Just got to find out which one!

Cheers, Pete.

Nicklyons2 · 29th Jan 2015, 8:55 pm

Tin of freezer required I think. Suspect any large electrolytics as well as transistors.

Tractorfan · 29th Jan 2015, 9:55 pm

Hi,
That thought crossed my mind too. I'll have to see if I can source some around here. That's the down side of living out in the sticks, no local equivalent of Maplin's. I'll get it back on the bench and rip the b

r apart once more!
Cheers, Pete.

Nicklyons2 · 29th Jan 2015, 10:33 pm

Pete, expensive it may be, but try a pharmacy and see if they have any freezing spray for the first aid of burns if there's no Maplins equiv nearby.

Tractorfan · 29th Jan 2015, 11:37 pm

Hi,
Ooh, now why didn't I think of that!

The pharmacies here seem to have a wider range of stuff than in the UK, so it's well worth an ask.
Thanks!
Cheers, Pete.

Tractorfan · 1st Feb 2015, 9:21 pm

Hi,
I think I've finally sorted it. Turned out to be Q110 in the DC voltage regulator. Replaced it with another BC149 and all seems well (so far).
In the absence of a proper freezer spray, I improvised with an aerosol spray meant for freezing pet waste in order to make it easier to pick up. Fortunately I'm a non smoker and it is a transistorised tape recorder as I later spotted that the spray is highly flammable!

However, it is scented and the Tandberg gets quite fragrant after a period of use!
Mind you, it took three goes, as spraying other suspect transistors stopped the oscillation temporarily. All three replaced anyway,
Cheers and thanks again, Pete.

Nicklyons2 · 5th Feb 2015, 2:02 pm

Pete, glad you got it sorted - more 'dodgy' lockfit trouble,
Nick

Tractorfan · 5th Feb 2015, 3:09 pm

Hi,
Er, not directly, Nick. I replaced all the lockfits, as advised, with metal cased BC107 or BC109s. It was a dodgy BC107 that was causing me grief! So, I replaced that with a spare BC149 which had a grey rectangular encapsulation. So far, so good!
Thanks for the freezer idea.
Cheers, Pete.

27th Jan 2015, 12:07 pm	#1
Tractorfan Dekatron Join Date: Mar 2008 Location: St. Frajou, l'Isle en Dodon, Haute Garonne, France.(Previously: Ellesmere Port, Cheshire, UK.) Posts: 3,183	Another Tandberg puzzle. Hi, After replacing all the lockfit transistors in my noisy Tandberg series15 (thanks everyone for your help, btw), I was playing a tape which had been recorded too quietly. On turning the volume control right up to hear the recording, the machine broke into a low frequency oscillation which could be heard as a 'pulsing' sound with the lamp illuminating the counter 'pulsing' in sympathy. So, serious enough to drag the supply down. Reducing the volume stopped it immediately, but advancing it again did not invoke the oscillation again. I replaced the BC147 & BC149 transistors with BC107 & BC109s (some of which were recycled from my junk box) and I wonder if I've inadvertently put a duffer in somewhere? Otherwise, it works well but can't be made to oscillate every time. Cheers, Pete. __________________ "Hello?, Yes, I'm on the train, I might lose the signal soon as we're just going into a tunn..."

27th Jan 2015, 1:16 pm	#2
Restoration73 Nonode Join Date: Jun 2013 Location: Surbiton, SW London, UK. Posts: 2,801	Re: Another Tandberg puzzle. See if you can invoke the instability by wiggling the knob of the record/playback/amplifier switch on the left. If so, it may be the contacts. I'm assuming you have checked any dc decoupling capacitors.

29th Jan 2015, 6:58 pm	#3
Tractorfan Dekatron Join Date: Mar 2008 Location: St. Frajou, l'Isle en Dodon, Haute Garonne, France.(Previously: Ellesmere Port, Cheshire, UK.) Posts: 3,183	Re: Another Tandberg puzzle. Hi, Finally managed to have another play with the Tandberg. The low frequency oscillation appears to be temperature related. I tried to invoke the instability, nothing would start it. The machine worked impeccably for about three quarters of an hour and then the ocillation started. Now nothing would stop it, even switching the machine off for a few minutes and then back on did nothing. It needs to be left to go stone cold, then it's OK for another period. I changed all the lockfit transistors as per my earlier post, plus four that were also BC149 types, but in a grey rectangular package. I must have inadvertently put a bad 'un in. Just got to find out which one! Cheers, Pete. __________________ "Hello?, Yes, I'm on the train, I might lose the signal soon as we're just going into a tunn..." Last edited by Tractorfan; 29th Jan 2015 at 7:03 pm. Reason: Rearranging the worms.

29th Jan 2015, 8:55 pm	#4
Nicklyons2 Octode Join Date: Jan 2013 Location: Barnsley, South Yorkshire, UK. Posts: 1,517	Re: Another Tandberg puzzle. Tin of freezer required I think. Suspect any large electrolytics as well as transistors.

29th Jan 2015, 9:55 pm	#5
Tractorfan Dekatron Join Date: Mar 2008 Location: St. Frajou, l'Isle en Dodon, Haute Garonne, France.(Previously: Ellesmere Port, Cheshire, UK.) Posts: 3,183	Re: Another Tandberg puzzle. Hi, That thought crossed my mind too. I'll have to see if I can source some around here. That's the down side of living out in the sticks, no local equivalent of Maplin's. I'll get it back on the bench and rip the br apart once more! Cheers, Pete. __________________ "Hello?, Yes, I'm on the train, I might lose the signal soon as we're just going into a tunn..."

29th Jan 2015, 10:33 pm	#6
Nicklyons2 Octode Join Date: Jan 2013 Location: Barnsley, South Yorkshire, UK. Posts: 1,517	Re: Another Tandberg puzzle. Pete, expensive it may be, but try a pharmacy and see if they have any freezing spray for the first aid of burns if there's no Maplins equiv nearby.

29th Jan 2015, 11:37 pm	#7
Tractorfan Dekatron Join Date: Mar 2008 Location: St. Frajou, l'Isle en Dodon, Haute Garonne, France.(Previously: Ellesmere Port, Cheshire, UK.) Posts: 3,183	Re: Another Tandberg puzzle. Hi, Ooh, now why didn't I think of that! The pharmacies here seem to have a wider range of stuff than in the UK, so it's well worth an ask. Thanks! Cheers, Pete. __________________ "Hello?, Yes, I'm on the train, I might lose the signal soon as we're just going into a tunn..."

1st Feb 2015, 9:21 pm	#8
Tractorfan Dekatron Join Date: Mar 2008 Location: St. Frajou, l'Isle en Dodon, Haute Garonne, France.(Previously: Ellesmere Port, Cheshire, UK.) Posts: 3,183	Re: Another Tandberg puzzle. Hi, I think I've finally sorted it. Turned out to be Q110 in the DC voltage regulator. Replaced it with another BC149 and all seems well (so far). In the absence of a proper freezer spray, I improvised with an aerosol spray meant for freezing pet waste in order to make it easier to pick up. Fortunately I'm a non smoker and it is a transistorised tape recorder as I later spotted that the spray is highly flammable! However, it is scented and the Tandberg gets quite fragrant after a period of use! Mind you, it took three goes, as spraying other suspect transistors stopped the oscillation temporarily. All three replaced anyway, Cheers and thanks again, Pete. __________________ "Hello?, Yes, I'm on the train, I might lose the signal soon as we're just going into a tunn..."

5th Feb 2015, 2:02 pm	#9
Nicklyons2 Octode Join Date: Jan 2013 Location: Barnsley, South Yorkshire, UK. Posts: 1,517	Re: Another Tandberg puzzle. Pete, glad you got it sorted - more 'dodgy' lockfit trouble, Nick

5th Feb 2015, 3:09 pm	#10
Tractorfan Dekatron Join Date: Mar 2008 Location: St. Frajou, l'Isle en Dodon, Haute Garonne, France.(Previously: Ellesmere Port, Cheshire, UK.) Posts: 3,183	Re: Another Tandberg puzzle. Hi, Er, not directly, Nick. I replaced all the lockfits, as advised, with metal cased BC107 or BC109s. It was a dodgy BC107 that was causing me grief! So, I replaced that with a spare BC149 which had a grey rectangular encapsulation. So far, so good! Thanks for the freezer idea. Cheers, Pete. __________________ "Hello?, Yes, I'm on the train, I might lose the signal soon as we're just going into a tunn..."