Beloved Tandberg Series 15 - UK Vintage Radio Repair and Restoration Discussion Forum

Paulus.d · 12th Jun 2009, 2:29 pm

I very recently got one of these and settled down to a nice day of refubishment. Apart from the usual fixes - crackly pots,recording switch, track changing switch, it looks sweet - even the belt is working - wow

After cleaning I tested it - I'd had it playing before hand at low volume before it was cleaned because the volume control was stuck, almost glued. Now, on turning up the volume, and not too much, the amplifier goes into, what I could describe as motorboating - it goes b-b-b-b-b and the pilot light on the tape counter dims.

Any idea what this is

? I've been waiting sooooooooo long for one of these to become available as I had one in the past.

Please HELP

Paul

Steve_P · 12th Jun 2009, 2:32 pm

At a guess, capacitors. Coupling caps as a further guess.

Cheers,

Steve P.

Paulus.d · 12th Jun 2009, 2:33 pm

Such a quick reply, steve

Power supply PCB? Yes

Steve_P · 12th Jun 2009, 2:38 pm

Maybe, or Amplifier section.

Is there a circuit anywhere that I can refer to. I'm going out now getting a car, will be back later on.

Cheers,

Steve P.

DOFFERY · 12th Jun 2009, 5:49 pm

Paul are you talking about volume when replaying a tape? If so check it in the amplifier &/or record position, let us know. To me it sounds like switch trouble but your results will confirm or deny my thoughts.

Colin.

Paulus.d · 12th Jun 2009, 6:22 pm

The machine is in playback with a known good tape, recorded on my Elizabethan LZ34. In record, there's a pop noise as the lever is moved, the VU meter needle jumps then it settles down into silence.

In AMP mode again there's a pop then silence - even if you turn the volume full.

The 'fault' only seems to appear on playback, as it's a 15-41 on tracks 1-4 and 2-3. Reducing the 'BASS' level seems to decrease the effect. If you turn it up full on bass and volume the noise goes B-B-B-B the counter lamp almost goes off! When I got this unit the record lamp was out - the bulbs blown - could this have anything to do with it

?

I had one of these in the past, and I kind of remember it did the same thing, leading to an inexperienced teenager stripping the thing, re soldering all the joints, directly soldering wires to the circuit boards and mucking it up completely!!!!

I have looked at the CAP values on the power amp pcb> All of the big ones are 1000uF but different voltages. The one on the transformer is 0.1uF @1000v (smoothing cap?)

It's been a long time since I've played with standard mount components - my last job was in charge of a Surface Mount line making PCBS all Day.........

Best wishes Paul

DOFFERY · 12th Jun 2009, 7:02 pm

Apart from the head pre amp, all would appear to be OK so that rules out problems with the power or output sections .

I would still check the switches, track /function.

Colin.

Paulus.d · 12th Jun 2009, 7:15 pm

Can you please explain the reasoning behind the diagnosis? - sorry to be a pain but I've cleaned the switches a couple of times now....

Paul

Nickthedentist · 12th Jun 2009, 9:17 pm

I've certainly had several cassette decks that have motorboated horribly because the record/play switch was intermittent.

A dose of Servisol and operating it rapidly a few dozen times almost always sorts it.

Good luck,
Nick.

DOFFERY · 12th Jun 2009, 9:33 pm

As above Paul.

I don't know how you have cleaned the switches but they also need lubrication, failing that solution you need some expert attention.

Colin.

Steve_P · 12th Jun 2009, 9:42 pm

The lights in the meters go off and it is affected by the tone controls. I'd still suspect the power supply.

Cheers,

Steve P.

Paulus.d · 13th Jun 2009, 2:10 pm

Have rechecked the rec/play/amp switch again, this involved pulling a couple of plugs and unclipping the contacts off. Cleaned with slightly abrasive paper and polished up the contacts - guess what? found 1 top hat contact missing! I thought thats it!! FIXED!! however found it in the bottom of the case, replaced it plugged it all back, switch on.......still B-B-B-B dimming lights!
Tried unplugging speaker, changing speaker, switching to external - still the same.

Paul

Steve_P · 13th Jun 2009, 2:15 pm

Right. Do a capacitor change. This is some sort of feedback and my guess is Coupling or Decoupling caps. Do a resolder and check the PSU.

Cheers,

Steve P.

DOFFERY · 13th Jun 2009, 4:46 pm

You may well be right Steve but before he starts on that "journey" might I ask if it is the same on all three speeds? Have you cleaned, lubricated the speed change switch ?

Colin.

Paulus.d · 13th Jun 2009, 9:16 pm

Yep - it's the same on all 3 speeds, no change as far as the motorboating

But some more information for you - as the volume is increased, it first begins to hum then the hum subsides into the B-B-B sound. If you play the tape as you do this, it plays normally up to about 4 on the volume scale then humming starts, as you approach 5-6 then B-B-B and heavy distortion is present on the music. If the bass control is then turned down the B-B-B subsides slightly and the volume increases.

I might have a way out of this though - a mate of my son's, on visting today recognised it immediately and on questioning has 2 busted tandbergs at home - he says the're indentical. He also has some proper switch cleaner ( all I had was some very old CPC stuff I nicked from work about 2 years ago and some methylated spirit!)

So hopefully I can swap parts and get 1-2 working....

Best wishes Paul
PS thanks for your input guys, it's good to have people who know stuff about this!!!

Paulus.d · 13th Jun 2009, 9:17 pm

sorry quick question - lubricate with what

??

Steve_P · 13th Jun 2009, 9:49 pm

Servisol will do.

Go on, do some soldering, you never know. If you've got a 'new' supply of parts, why not try. You never know...

Cheers,

Steve P.

DOFFERY · 13th Jun 2009, 10:36 pm

Hi Paul,
Just looking at your earlier post, you say it is OK on record/amp , did you try a recording & monitor the input using the volume control at a similar level or did you just switch to rec/amp The same with the amplifer position, an input & volume level as you describe for play, see if your problem arises on these tests

Colin.

julie_m · 14th Jun 2009, 8:36 am

If it hums at low volume settings and becomes unstable at high volume settings, that sounds very much like a power supply issue. Something's asking for more current than the power supply can provide; and the supply is first losing smoothing, then collapsing altogether. If you've a 'scope, look at the power rail. Check the smoothing capacitor(s), the rectifier diodes and the mains transformer. A diode going O/C means the supply will be reduced to half-wave; a S/C means the supply will be half-wave and the transformer will get hot.

Hunts smoothing bomb · 14th Jun 2009, 9:29 am

Could be stabbing in the wrong direction here because I don't know this machine or have a cct for it, but by what you are saying I have to say it sounds like the machine is solid state and that it sounds like (as Steve P has said) leaky coupling caps or something very similar.

By increasing the volume it sounds like that somehow the bias to the output stage is being upset and the more you increase volume the more current is flowing through the stage continuously, this is putting undue load on the power supply (from which the pilot lamp is fed) causing it to cut in/out giving your dimming lamp symptoms and B B B B B B noise through the speaker!

Of course I could be completely wrong but I think I would start with cap testing.

Cheers

12th Jun 2009, 2:29 pm	#1
Paulus.d Hexode Join Date: Mar 2008 Location: Margate, Kent, UK. Posts: 355	Beloved Tandberg Series 15 I very recently got one of these and settled down to a nice day of refubishment. Apart from the usual fixes - crackly pots,recording switch, track changing switch, it looks sweet - even the belt is working - wow After cleaning I tested it - I'd had it playing before hand at low volume before it was cleaned because the volume control was stuck, almost glued. Now, on turning up the volume, and not too much, the amplifier goes into, what I could describe as motorboating - it goes b-b-b-b-b and the pilot light on the tape counter dims. Any idea what this is? I've been waiting sooooooooo long for one of these to become available as I had one in the past. Please HELP Paul Last edited by Station X; 14th Jun 2009 at 8:20 am. Reason: Disguised eBay reference removed.

12th Jun 2009, 2:32 pm	#2
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Beloved Tandberg Series 15 At a guess, capacitors. Coupling caps as a further guess. Cheers, Steve P. __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

12th Jun 2009, 2:33 pm	#3
Paulus.d Hexode Join Date: Mar 2008 Location: Margate, Kent, UK. Posts: 355	Re: Beloved Tandberg Series 15 Such a quick reply, steve Power supply PCB? Yes

12th Jun 2009, 2:38 pm	#4
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Beloved Tandberg Series 15 Maybe, or Amplifier section. Is there a circuit anywhere that I can refer to. I'm going out now getting a car, will be back later on. Cheers, Steve P. __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

12th Jun 2009, 5:49 pm	#5
DOFFERY Retired Dormant Member Join Date: Aug 2004 Location: Blackpool, Lancashire, UK. Posts: 1,488	Re: Beloved Tandberg Series 15 Paul are you talking about volume when replaying a tape? If so check it in the amplifier &/or record position, let us know. To me it sounds like switch trouble but your results will confirm or deny my thoughts. Colin.

12th Jun 2009, 6:22 pm	#6
Paulus.d Hexode Join Date: Mar 2008 Location: Margate, Kent, UK. Posts: 355	Re: Beloved Tandberg Series 15 The machine is in playback with a known good tape, recorded on my Elizabethan LZ34. In record, there's a pop noise as the lever is moved, the VU meter needle jumps then it settles down into silence. In AMP mode again there's a pop then silence - even if you turn the volume full. The 'fault' only seems to appear on playback, as it's a 15-41 on tracks 1-4 and 2-3. Reducing the 'BASS' level seems to decrease the effect. If you turn it up full on bass and volume the noise goes B-B-B-B the counter lamp almost goes off! When I got this unit the record lamp was out - the bulbs blown - could this have anything to do with it? I had one of these in the past, and I kind of remember it did the same thing, leading to an inexperienced teenager stripping the thing, re soldering all the joints, directly soldering wires to the circuit boards and mucking it up completely!!!! I have looked at the CAP values on the power amp pcb> All of the big ones are 1000uF but different voltages. The one on the transformer is 0.1uF @1000v (smoothing cap?) It's been a long time since I've played with standard mount components - my last job was in charge of a Surface Mount line making PCBS all Day......... Best wishes Paul

12th Jun 2009, 7:02 pm	#7
DOFFERY Retired Dormant Member Join Date: Aug 2004 Location: Blackpool, Lancashire, UK. Posts: 1,488	Re: Beloved Tandberg Series 15 Apart from the head pre amp, all would appear to be OK so that rules out problems with the power or output sections . I would still check the switches, track /function. Colin.

12th Jun 2009, 7:15 pm	#8
Paulus.d Hexode Join Date: Mar 2008 Location: Margate, Kent, UK. Posts: 355	Re: Beloved Tandberg Series 15 Can you please explain the reasoning behind the diagnosis? - sorry to be a pain but I've cleaned the switches a couple of times now.... Paul

12th Jun 2009, 9:17 pm	#9
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,844	Re: Beloved Tandberg Series 15 I've certainly had several cassette decks that have motorboated horribly because the record/play switch was intermittent. A dose of Servisol and operating it rapidly a few dozen times almost always sorts it. Good luck, Nick.

12th Jun 2009, 9:33 pm	#10
DOFFERY Retired Dormant Member Join Date: Aug 2004 Location: Blackpool, Lancashire, UK. Posts: 1,488	Re: Beloved Tandberg Series 15 As above Paul. I don't know how you have cleaned the switches but they also need lubrication, failing that solution you need some expert attention. Colin.

12th Jun 2009, 9:42 pm	#11
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Beloved Tandberg Series 15 The lights in the meters go off and it is affected by the tone controls. I'd still suspect the power supply. Cheers, Steve P. __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

13th Jun 2009, 2:10 pm	#12
Paulus.d Hexode Join Date: Mar 2008 Location: Margate, Kent, UK. Posts: 355	Re: Beloved Tandberg Series 15 Have rechecked the rec/play/amp switch again, this involved pulling a couple of plugs and unclipping the contacts off. Cleaned with slightly abrasive paper and polished up the contacts - guess what? found 1 top hat contact missing! I thought thats it!! FIXED!! however found it in the bottom of the case, replaced it plugged it all back, switch on.......still B-B-B-B dimming lights! Tried unplugging speaker, changing speaker, switching to external - still the same. Paul

13th Jun 2009, 2:15 pm	#13
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Beloved Tandberg Series 15 Right. Do a capacitor change. This is some sort of feedback and my guess is Coupling or Decoupling caps. Do a resolder and check the PSU. Cheers, Steve P. __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

13th Jun 2009, 4:46 pm	#14
DOFFERY Retired Dormant Member Join Date: Aug 2004 Location: Blackpool, Lancashire, UK. Posts: 1,488	Re: Beloved Tandberg Series 15 You may well be right Steve but before he starts on that "journey" might I ask if it is the same on all three speeds? Have you cleaned, lubricated the speed change switch ? Colin.

13th Jun 2009, 9:16 pm	#15
Paulus.d Hexode Join Date: Mar 2008 Location: Margate, Kent, UK. Posts: 355	Re: Beloved Tandberg Series 15 Yep - it's the same on all 3 speeds, no change as far as the motorboating But some more information for you - as the volume is increased, it first begins to hum then the hum subsides into the B-B-B sound. If you play the tape as you do this, it plays normally up to about 4 on the volume scale then humming starts, as you approach 5-6 then B-B-B and heavy distortion is present on the music. If the bass control is then turned down the B-B-B subsides slightly and the volume increases. I might have a way out of this though - a mate of my son's, on visting today recognised it immediately and on questioning has 2 busted tandbergs at home - he says the're indentical. He also has some proper switch cleaner ( all I had was some very old CPC stuff I nicked from work about 2 years ago and some methylated spirit!) So hopefully I can swap parts and get 1-2 working.... Best wishes Paul PS thanks for your input guys, it's good to have people who know stuff about this!!!

13th Jun 2009, 9:17 pm	#16
Paulus.d Hexode Join Date: Mar 2008 Location: Margate, Kent, UK. Posts: 355	Re: Beloved Tandberg Series 15 sorry quick question - lubricate with what??

13th Jun 2009, 9:49 pm	#17
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Beloved Tandberg Series 15 Servisol will do. Go on, do some soldering, you never know. If you've got a 'new' supply of parts, why not try. You never know... Cheers, Steve P. __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

13th Jun 2009, 10:36 pm	#18
DOFFERY Retired Dormant Member Join Date: Aug 2004 Location: Blackpool, Lancashire, UK. Posts: 1,488	Re: Beloved Tandberg Series 15 Hi Paul, Just looking at your earlier post, you say it is OK on record/amp , did you try a recording & monitor the input using the volume control at a similar level or did you just switch to rec/amp The same with the amplifer position, an input & volume level as you describe for play, see if your problem arises on these tests Colin.

14th Jun 2009, 8:36 am	#19
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: Beloved Tandberg Series 15 If it hums at low volume settings and becomes unstable at high volume settings, that sounds very much like a power supply issue. Something's asking for more current than the power supply can provide; and the supply is first losing smoothing, then collapsing altogether. If you've a 'scope, look at the power rail. Check the smoothing capacitor(s), the rectifier diodes and the mains transformer. A diode going O/C means the supply will be reduced to half-wave; a S/C means the supply will be half-wave and the transformer will get hot. __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

14th Jun 2009, 9:29 am	#20
Hunts smoothing bomb Octode Join Date: Oct 2005 Location: Wimborne, Dorset, UK. Posts: 1,407	Re: Beloved Tandberg Series 15 Could be stabbing in the wrong direction here because I don't know this machine or have a cct for it, but by what you are saying I have to say it sounds like the machine is solid state and that it sounds like (as Steve P has said) leaky coupling caps or something very similar. By increasing the volume it sounds like that somehow the bias to the output stage is being upset and the more you increase volume the more current is flowing through the stage continuously, this is putting undue load on the power supply (from which the pilot lamp is fed) causing it to cut in/out giving your dimming lamp symptoms and B B B B B B noise through the speaker! Of course I could be completely wrong but I think I would start with cap testing. Cheers __________________ Lee