UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players

Notices

Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

Closed Thread
 
Thread Tools
Old 11th Sep 2009, 12:33 pm   #121
Paulus.d
Hexode
 
Join Date: Mar 2008
Location: Margate, Kent, UK.
Posts: 355
Default Re: Beloved Tandberg Series 15

Hiya Guys, back now again after some treatment and ready to go again.
Just to let you know, the pre-amp and power amp boards are safely screwed back in and wiring is all tidy. The track switch is completely out, including the head wiring and the bias adjustment pcb behind the heads. I've already had a go at re-wiring the damaged track switching and got it working in 1-4, 2-3 and duo mode, but it's not pretty and I seem to have lost the free head ability because of the damage to the contacts.

I am still at a loss as to why the volume goes down and gets distorted when the erase head wiring is connected - I am now thinking I've muddled the pairs of wires up in my haste on the play and erase so that the bias is feeding into the play ciruitry - hence the removal of the head / track wiring and boards so that I can re wire again, playing more attention.

Thanks to all with staying with this topic - at MUST be near the end now...
Paulus.d is offline  
Old 22nd Sep 2009, 9:24 pm   #122
Paulus.d
Hexode
 
Join Date: Mar 2008
Location: Margate, Kent, UK.
Posts: 355
Default Re: Beloved Tandberg Series 15

It's Fixed

Finally

There now follows a brief run down of the faults:

1. Damaged Track switch
2. Faulty Power Amp Board
3. Damaged Speaker
4. Lamp behind record meter blown

And here's how it was done!

Power Amp Board caused the B-B-B-B motor boating fault - Board replaced.
Damaged track switch caused loss of track 2-3 - rewired 100% to use undamaged area's contacts.
Speaker damaged by pounding with B-B-B - will need replacing, but don't have one yet.
Weird fault where volume goes down when turned up thought to be very high frequency - disappeared when rec meter lamp replaced

The machine has been almost totally rewired and tidied up. Even the head wiring was replaced right up to the bias pcb. I don't know how the record lamp features in the other fault but, looking at the diagram, it's a part of the 85.5mhz erase / bias Oscillator so I suppose it's possible it has to be there

Anyway, this has been a long rocky road - 4 months of thinking, drawing, soldering and trying to stop myself just getting another one!
thanks for all who stopped by the thread and help with their specialised know-how

Best regards Paul
Paulus.d is offline  
Old 22nd Sep 2009, 11:09 pm   #123
Steve_P
Dekatron
 
Steve_P's Avatar
 
Join Date: Sep 2003
Location: Bolton, Greater Manchester, UK.
Posts: 6,644
Default Re: Beloved Tandberg Series 15

Well done and thank heaven for that.

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...?
Steve_P is offline  
Old 23rd Sep 2009, 7:58 am   #124
Paulus.d
Hexode
 
Join Date: Mar 2008
Location: Margate, Kent, UK.
Posts: 355
Default Re: Beloved Tandberg Series 15

Thanks Steve - I still don't know how it lasted soooooo long!!! I have some spares left but the power amp board IS faulty


Anyway, perhaps the mods might want to close this thread now before I waffle onto page 8!!!!!!

Best wishes Paul
Paulus.d is offline  
Old 23rd Sep 2009, 7:33 pm   #125
af024
Octode
 
Join Date: Jan 2003
Location: Ashby-de-la-Zouch (it's not by the sea)
Posts: 1,254
Default Re: Beloved Tandberg Series 15

Well done that man!

I wonder if the spools will now need some new slipping clutch felts? Perhaps I shouldnt have mentioned that - sorry. I never spoke.

All the best,

Andy
__________________
Now where on earth did I remove that from?
af024 is online now  
Old 24th Sep 2009, 8:47 am   #126
Paulus.d
Hexode
 
Join Date: Mar 2008
Location: Margate, Kent, UK.
Posts: 355
Default Re: Beloved Tandberg Series 15

Probably! AND a new belt - wind is very sluggish.

But I can cope with these, the last 4 months has been a trial. It proves really that you shouldn't buy anything without truly knowing what you're getting yourself into. It was a bit much to presume a 30 years+ machine would work first time without any intervention!

Will still keep this thread up to date, at least until it's operational.

Best wishes Paul
Paulus.d is offline  
Old 25th Sep 2009, 2:57 pm   #127
ricard
Octode
 
ricard's Avatar
 
Join Date: Mar 2006
Location: Lund, Sweden
Posts: 1,631
Default Re: Beloved Tandberg Series 15

Quote:
Originally Posted by Paulus.d View Post
Weird fault where volume goes down when turned up thought to be very high frequency - disappeared when rec meter lamp replaced
Don't have the schematics for the 15 close, but I know that some oscillator circuits use a lamp to stabilize the output voltage. Novel idea to use the recording level meter bulb for that, but hey, you need the lamp for that anyway so it saves a component.

(I've also seen battery operated transistorized recorders with indicator tubes derive the HT for the indicator tube from an extra winding on the bias oscillator. Or mains operated recorders with an extra winding on the motor so that it functions as a transformer as well. Whatever works I guess.)

/Ricard
ricard is offline  
Old 25th Sep 2009, 3:20 pm   #128
Paulus.d
Hexode
 
Join Date: Mar 2008
Location: Margate, Kent, UK.
Posts: 355
Default Re: Beloved Tandberg Series 15

It does make sense to use the lamp if it has to be there anyway. The circuit diagram should be on this thread somewhere around page 3? if you find it, have a look!
Paulus.d is offline  
Old 28th Sep 2009, 12:00 pm   #129
ricard
Octode
 
ricard's Avatar
 
Join Date: Mar 2006
Location: Lund, Sweden
Posts: 1,631
Default Re: Beloved Tandberg Series 15

Took a quick look at radiomuseum.org where they have the schematics. Well, doesn't look like the lamp is part of the oscillator circuit though, it's just that they have a slightly unusual way of disabling the oscillator and record meter driver and lamp when the unit is not in record mode: they disconnect the ground (0V) instead of the positive supply (+24V). Perhaps done like that because the oscilllator coil is referenced to +24V, so that when turning it off it dies out nicely instead of being cut off abruptly.

The lamp does have one extra function though; because of its internal resistance it is responsible for causing the oscillator 0V line to pull up to +24V, so if the lamp is missing or broken, could be the oscillator doesn't shut off as it should.

/Ricard

Last edited by ricard; 28th Sep 2009 at 12:05 pm.
ricard is offline  
Old 29th Sep 2009, 1:50 pm   #130
Paulus.d
Hexode
 
Join Date: Mar 2008
Location: Margate, Kent, UK.
Posts: 355
Default Re: Beloved Tandberg Series 15

That sounds logical to me - what I was getting was the bias frequency 'switched on' during playback, which had the effect of freaking the power amp out and causing the volume to decrease as you turned up the volume control unless you backed off the treble, filtering the high frequency out!

Anyway all is done now - the unit is re-built and is fault -free, at least in electronics. The winding / rewinding is sloppy because the belt needs replacing - I did boil it which helped for a few hours, winding really well, but it soon went back to being crap! , and the speaker is a bit duff, it sounds ok at loud volume with minimal bass ,but as you decrease it distorts, burps and farts! the external speaker i'm using sounds sweet.

Basically the machine is living up to it's believed reputation and I've waited 15-20 years to get my hands on another one of these beasts. Once the little problems are sorted out (just money being the BIG problem) I'll be more than happy with it - it's playing, recording, all systems go (touch wood!) I know it's age - I've basically brought it back but it's still possible it will go again at some point, just hope it's not too soon!

Best Wishes to all

Paul.D Margate (Paulus)
Paulus.d is offline  
Old 29th Sep 2009, 5:45 pm   #131
ben
Dekatron
 
ben's Avatar
 
Join Date: Aug 2006
Location: Madrid, Spain / Wirral, UK
Posts: 7,484
Default Re: Beloved Tandberg Series 15

great news!
Now I you mention the bulb, I vaguely recall being told by the local Tandberg language lab enginer back in the day, that the bulb was significant. Now I know why!

I recently cleaned up the mechanics of a series 15 I got from a forum member. With a new belt (acually a NOS one I had saved up for ages) the difference was colossal. I don't know where you'd get a belt these days, ebay being the obvious starting place....
__________________
Regards,
Ben.
ben is offline  
Old 29th Sep 2009, 6:03 pm   #132
DOFFERY
Retired Dormant Member
 
Join Date: Aug 2004
Location: Blackpool, Lancashire, UK.
Posts: 1,488
Default Re: Beloved Tandberg Series 15

Should you be interested I have the belts.

Colin
DOFFERY is offline  
Old 1st Oct 2009, 3:24 pm   #133
ricard
Octode
 
ricard's Avatar
 
Join Date: Mar 2006
Location: Lund, Sweden
Posts: 1,631
Default Re: Beloved Tandberg Series 15

Another alternative is to use a large diameter o-ring for a belt, which should be available from a supplier of hydraulic equipment such as hoses and seals. I think what you need for the Tandberg something around a diameter of about 180-190mm; the thickness should be 3mm. It's a bit different for different machines owing to differing pulley sizes.

The main drawback of o-rings is that they are not as elastic as the original belts. Still, it's nice to know that it will always be possible to get some sort of replacement. (Note that o-rings are specified in terms of diameter, not in belt length as is customary for drive belts).

/Ricard
ricard is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 10:49 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.