Tandberg 12-21 reel to reel does not record. - UK Vintage Radio Repair and Restoration Discussion Forum

jmcilkley · 20th Nov 2021, 9:38 pm

Playback is fine but when recording the "magic eye" shows that the signal is getting that far but there is nothing recorded on the tape. When recording over another recording the erase head clearly works as it just records blank.
My first thought was the complex multi-way switch so I sprayed the tracks with contact cleaner but no change. Since neither track records it looks like the same problem on both channels. Any suggestions?

ben · 21st Nov 2021, 12:23 am

Likely dud caps in the preamp. I had a similar problem on my series 12. Can't recall if it was rec or PB, but will check. I think they were 4.7uF ones that had gone s/c.

jmcilkley · 21st Nov 2021, 2:39 pm

The switching arrangements are quite complex as most of the circuits are used for both record and playback. I have a circuit diagram and as far as I can tell, the playback does go through a 4.7u cap into the pre-amp but the record comes from the output of the pre-amp and through a 2.5u cap. That would mean that maybe these caps have failed in both channels. I will check and see.
Thanks for the suggestion.

jmcilkley · 25th Nov 2021, 10:56 am

I changed most of the electrolytic caps but still no recording. Most of the caps tested ok, a few being slightly out of spec but still working. Does anyone have any other suggestions?
Attached is the circuit diagram for one channel so maybe that will help.

jmcilkley · 25th Nov 2021, 2:13 pm

Well, to save any head scratching - I fixed it. I cleaned the head and pinch roller before I even tried the tape recorder. Then I went through testing it and found that it didn't record but played back existing tapes. After checking everything in the record line and finding nothing amiss I recleaned the record/playback head using acetone this time (alcohol used before) and so much gunge came off and now it all works! Surprising that it played back ut wouldn't record - both using the same head.

DMcMahon · 26th Nov 2021, 10:39 am

A little surprising that nothing recorded after first clean but not that surprising that more dirt deposits comes off on subsequent more thorough cleaning on what looks like clean heads.

David

TIMTAPE · 26th Nov 2021, 11:51 am

If there was that much dirt on the head to result in no audible recording then it must have played back all tapes poorly as well. Perhaps you're not familiar with what good, normal playback on these machines sounds like.

I get to see many tape machines. Over the phone some owners insist they have already thoroughly cleaned the heads but when I inspect for myself I find the heads are often (by my standards) filthy.

It's important to actually look at the head face before and after cleaning. Best viewed in a strong light with a magnifier.

Acetone isnt recommended. IPA is normally fine, and much safer.

jmcilkley · 1st Dec 2021, 12:54 pm

Thanks to everyone for those posts. I hear what you say about acetone but I had cleaned the heads with IPA already until nothing more came off and then the acetone had a tremendous effect. The same with the pinch wheel - I cleaned it with IPA but it didn't shift the brown oxide. I guess the tape deck hadn't been used for a long time and the oxide had sort of fused with the pinch wheel and heads.
The recording quality is now excellent.

20th Nov 2021, 9:38 pm	#1
jmcilkley Tetrode Join Date: Jan 2020 Location: Ilkley, West Yorkshire, UK. Posts: 92	Tandberg 12-21 reel to reel does not record. Playback is fine but when recording the "magic eye" shows that the signal is getting that far but there is nothing recorded on the tape. When recording over another recording the erase head clearly works as it just records blank. My first thought was the complex multi-way switch so I sprayed the tracks with contact cleaner but no change. Since neither track records it looks like the same problem on both channels. Any suggestions?

21st Nov 2021, 12:23 am	#2
ben Dekatron Join Date: Aug 2006 Location: Madrid, Spain / Wirral, UK Posts: 7,498	Re: Tandberg 12-21 reel to reel does not record. Likely dud caps in the preamp. I had a similar problem on my series 12. Can't recall if it was rec or PB, but will check. I think they were 4.7uF ones that had gone s/c. __________________ Regards, Ben.

21st Nov 2021, 2:39 pm	#3
jmcilkley Tetrode Join Date: Jan 2020 Location: Ilkley, West Yorkshire, UK. Posts: 92	Re: Tandberg 12-21 reel to reel does not record. The switching arrangements are quite complex as most of the circuits are used for both record and playback. I have a circuit diagram and as far as I can tell, the playback does go through a 4.7u cap into the pre-amp but the record comes from the output of the pre-amp and through a 2.5u cap. That would mean that maybe these caps have failed in both channels. I will check and see. Thanks for the suggestion.

25th Nov 2021, 10:56 am	#4
jmcilkley Tetrode Join Date: Jan 2020 Location: Ilkley, West Yorkshire, UK. Posts: 92	Re: Tandberg 12-21 reel to reel does not record. I changed most of the electrolytic caps but still no recording. Most of the caps tested ok, a few being slightly out of spec but still working. Does anyone have any other suggestions? Attached is the circuit diagram for one channel so maybe that will help. Attached Thumbnails

25th Nov 2021, 2:13 pm	#5
jmcilkley Tetrode Join Date: Jan 2020 Location: Ilkley, West Yorkshire, UK. Posts: 92	Re: Tandberg 12-21 reel to reel does not record. Well, to save any head scratching - I fixed it. I cleaned the head and pinch roller before I even tried the tape recorder. Then I went through testing it and found that it didn't record but played back existing tapes. After checking everything in the record line and finding nothing amiss I recleaned the record/playback head using acetone this time (alcohol used before) and so much gunge came off and now it all works! Surprising that it played back ut wouldn't record - both using the same head.

26th Nov 2021, 10:39 am	#6
DMcMahon Dekatron Join Date: Apr 2019 Location: Worthing, West Sussex, UK. Posts: 6,604	Re: Tandberg 12-21 reel to reel does not record. A little surprising that nothing recorded after first clean but not that surprising that more dirt deposits comes off on subsequent more thorough cleaning on what looks like clean heads. David

26th Nov 2021, 11:51 am	#7
TIMTAPE Octode Join Date: Jul 2006 Location: Perth, Western Australia Posts: 1,969	Re: Tandberg 12-21 reel to reel does not record. If there was that much dirt on the head to result in no audible recording then it must have played back all tapes poorly as well. Perhaps you're not familiar with what good, normal playback on these machines sounds like. I get to see many tape machines. Over the phone some owners insist they have already thoroughly cleaned the heads but when I inspect for myself I find the heads are often (by my standards) filthy. It's important to actually look at the head face before and after cleaning. Best viewed in a strong light with a magnifier. Acetone isnt recommended. IPA is normally fine, and much safer.

1st Dec 2021, 12:54 pm	#8
jmcilkley Tetrode Join Date: Jan 2020 Location: Ilkley, West Yorkshire, UK. Posts: 92	Re: Tandberg 12-21 reel to reel does not record. Thanks to everyone for those posts. I hear what you say about acetone but I had cleaned the heads with IPA already until nothing more came off and then the acetone had a tremendous effect. The same with the pinch wheel - I cleaned it with IPA but it didn't shift the brown oxide. I guess the tape deck hadn't been used for a long time and the oxide had sort of fused with the pinch wheel and heads. The recording quality is now excellent.