Tandberg 15 putrid smell! - UK Vintage Radio Repair and Restoration Discussion Forum

Chris55000 · 12th Mar 2019, 4:44 pm

Hi!

I tested my Tandberg 15 I won in September last year – the level meter lights up in record and there was an assortment of ghastly noises from the amplifier on playback, followed by a nasty smell of cremating!!!

Will that only be the dreaded Rifa type supressor cap/resistor or do other items have incendiary tendencies in these?

I bought an Original Factory S.M. with the orange cover so hopefully identification of remains won't be an issue!

Chris Williams

G6Tanuki · 12th Mar 2019, 5:31 pm

It could be a Rifa that's let-out the magic smoke; alternatively it could be an electrolytic that's done likewise.

I'm not familiar with the particular recorder's circuit but many 1950s/1960s electronics included Selenium rectifiers in place of the traditional valve - these were often in the form of a flat aluminium-cased package that's bolted to the chassis to aid heat-dissipation, and they make a truly unforgettable smell when they fail!

paulsherwin · 12th Mar 2019, 6:13 pm

Yes, if the smell was like terrible flatulence or a stink bomb then it was the selenium rectifier dying. Be careful if that's the case, as the gas is actually poisonous as well as smelling disgusting.

Chris55000 · 12th Mar 2019, 6:46 pm

Hi!

It didn't smell like selenium going off – I've come across hundreds of L.T. selenium bridge reccys in all sorts of record–players, table radios, 'grams and industrials over the years and I've never had a stinky one!

(There's always a first time tho', and I have had windings in continental motors and transformers go off like I was smelling!)

I'm hoping it's not the early versions that had a h.t. winding for brakes & solenoids – if that's gone I'll have to cross Ed's palm with (quite a lot of!!) silver!

Chris Williams

PS!

The rectified L.T. line has got "+40V" marked on the circuit drawing, so a 15–0–15V @ 2A transformer ought to do if I do need a new one!

ben · 13th Mar 2019, 10:52 am

I have worked on plenty of this model and the only cause of burning has been the Rifa cap across the motor stop /tape end sense switch (on top of the transformer) and on another occasion a bias oscillator transistor.

Open it up, clean the rec-pb switch contacts gently with some contact spray on a q tip, work switch 30 times. That should sort the noises. Then plug in again and observe, being ready to yank the plug if things get hairy!

These are transistorized units from circa 1970 and I don't recall seeing a selenium rectifier in them. If you post your serial number I can check. Production continued as late as the 80s!

EDIT> The rectifier does appear to be a selenium type, at least in the early models - see attached schematic. You should change it if there is the foul smell! Then check with a series limiter resistor or lamp. It may of course have died of old age, but there could be a fault downstream in the regulator or amp. I attach the relevant section from the manual.

ricard · 13th Mar 2019, 1:54 pm

I had a model 15 where the motor was wired for 110V even though the machine itself was wired for 230V. Oddly enough, the motor behaved as expected, except for the fact that the windings got very hot so it emitted a burning smell without getting so hot that the enamel on the coil wires would char.

After rewiring the motor for 230V, it worked fine. Strange. It didn't look like the motor had been replaced either, so I'm assuming it was a manufacturing error at the factory.

I'd say otherwise the most likely cause of a bad smell is the Rifa cap (or actually, it's a capacitor and resistor combo, see Ben's schematic excerpt above) across the motor switch.

ben · 7th Jul 2019, 12:36 am

Bumping this. Got another one of these myself on the bench with suspected leaky silicon rectifier, to be confirmed tomorrow. I wonder would this circuit, especially c125, take kindly to a drop-in silicon bridge, or would a series resistor be prudent? There also seems to be an NTC, which would suggest the designers were cautious about inrush current.

TrevorG3VLF · 7th Jul 2019, 11:55 am

I would think that a little silicon bridge would be all right. The silicon bridge may give a very little increased voltage but there is resistance in the transformer to limit the inrush current.

12th Mar 2019, 4:44 pm	#1
Chris55000 Nonode Join Date: Aug 2007 Location: Walsall Wood, Aldridge, Walsall, UK. Posts: 2,870	Tandberg 15 putrid smell! Hi! I tested my Tandberg 15 I won in September last year – the level meter lights up in record and there was an assortment of ghastly noises from the amplifier on playback, followed by a nasty smell of cremating!!! Will that only be the dreaded Rifa type supressor cap/resistor or do other items have incendiary tendencies in these? I bought an Original Factory S.M. with the orange cover so hopefully identification of remains won't be an issue! Chris Williams __________________ It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed!

12th Mar 2019, 5:31 pm	#2
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,998	Re: Tandberg 15 putrid smell! It could be a Rifa that's let-out the magic smoke; alternatively it could be an electrolytic that's done likewise. I'm not familiar with the particular recorder's circuit but many 1950s/1960s electronics included Selenium rectifiers in place of the traditional valve - these were often in the form of a flat aluminium-cased package that's bolted to the chassis to aid heat-dissipation, and they make a truly unforgettable smell when they fail!

12th Mar 2019, 6:13 pm	#3
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,947	Re: Tandberg 15 putrid smell! Yes, if the smell was like terrible flatulence or a stink bomb then it was the selenium rectifier dying. Be careful if that's the case, as the gas is actually poisonous as well as smelling disgusting.

12th Mar 2019, 6:46 pm	#4
Chris55000 Nonode Join Date: Aug 2007 Location: Walsall Wood, Aldridge, Walsall, UK. Posts: 2,870	Re: Tandberg 15 putrid smell! Hi! It didn't smell like selenium going off – I've come across hundreds of L.T. selenium bridge reccys in all sorts of record–players, table radios, 'grams and industrials over the years and I've never had a stinky one! (There's always a first time tho', and I have had windings in continental motors and transformers go off like I was smelling!) I'm hoping it's not the early versions that had a h.t. winding for brakes & solenoids – if that's gone I'll have to cross Ed's palm with (quite a lot of!!) silver! Chris Williams PS! The rectified L.T. line has got "+40V" marked on the circuit drawing, so a 15–0–15V @ 2A transformer ought to do if I do need a new one! __________________ It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed! Last edited by Chris55000; 12th Mar 2019 at 6:52 pm.

13th Mar 2019, 10:52 am	#5
ben Dekatron Join Date: Aug 2006 Location: Madrid, Spain / Wirral, UK Posts: 7,498	Re: Tandberg 15 putrid smell! I have worked on plenty of this model and the only cause of burning has been the Rifa cap across the motor stop /tape end sense switch (on top of the transformer) and on another occasion a bias oscillator transistor. Open it up, clean the rec-pb switch contacts gently with some contact spray on a q tip, work switch 30 times. That should sort the noises. Then plug in again and observe, being ready to yank the plug if things get hairy! These are transistorized units from circa 1970 and I don't recall seeing a selenium rectifier in them. If you post your serial number I can check. Production continued as late as the 80s! EDIT> The rectifier does appear to be a selenium type, at least in the early models - see attached schematic. You should change it if there is the foul smell! Then check with a series limiter resistor or lamp. It may of course have died of old age, but there could be a fault downstream in the regulator or amp. I attach the relevant section from the manual. Attached Thumbnails __________________ Regards, Ben. Last edited by ben; 13th Mar 2019 at 11:01 am.

13th Mar 2019, 1:54 pm	#6
ricard Octode Join Date: Mar 2006 Location: Lund, Sweden Posts: 1,632	Re: Tandberg 15 putrid smell! I had a model 15 where the motor was wired for 110V even though the machine itself was wired for 230V. Oddly enough, the motor behaved as expected, except for the fact that the windings got very hot so it emitted a burning smell without getting so hot that the enamel on the coil wires would char. After rewiring the motor for 230V, it worked fine. Strange. It didn't look like the motor had been replaced either, so I'm assuming it was a manufacturing error at the factory. I'd say otherwise the most likely cause of a bad smell is the Rifa cap (or actually, it's a capacitor and resistor combo, see Ben's schematic excerpt above) across the motor switch.

7th Jul 2019, 12:36 am	#7
ben Dekatron Join Date: Aug 2006 Location: Madrid, Spain / Wirral, UK Posts: 7,498	Re: Tandberg 15 putrid smell! Bumping this. Got another one of these myself on the bench with suspected leaky silicon rectifier, to be confirmed tomorrow. I wonder would this circuit, especially c125, take kindly to a drop-in silicon bridge, or would a series resistor be prudent? There also seems to be an NTC, which would suggest the designers were cautious about inrush current. __________________ Regards, Ben.

7th Jul 2019, 11:55 am	#8
TrevorG3VLF Rest in Peace Join Date: Apr 2011 Location: Matlock, Derbyshire, UK. Posts: 1,378	Re: Tandberg 15 putrid smell! I would think that a little silicon bridge would be all right. The silicon bridge may give a very little increased voltage but there is resistance in the transformer to limit the inrush current.