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 31st Aug 2022, 12:59 pm   #1
untune87
Pentode
 
Join Date: Oct 2010
Location: Greater Manchester, UK.
Posts: 161
Default Uher SG 561 Royal

Hi all,

My partner's grandad passed away earlier in the year, and the house clearance unearthed an old reel-to-reel recorder in the loft. It was offered to me, but I had no info about it whatsoever until it arrived in my hands—I was expecting a little Grundig portable or similar, so I was pleasantly surprised to see this tidy-looking Uher machine. A sticker on the side suggests that he acquired it from the hospital he worked at, and it was still threaded up with a recording of Mike Oldfield's Tubular Bells II—so last use would have been sometime after 1992. It was in dire need of a clean, but it had been stored with the lid on and the speed selector off (as I understand it, the prolonged pressure on the flywheel from being left in position can form a flat spot that can be a problem on these machines.)

I cleaned it as best I could; the heads are in fair condition, it's mechanically noisy in 9.5 and 19 cm/s but other than that it works quite well! FF and RW are solid and smooth. The counter belt had snapped and the main drive belt will surely benefit from a replacement. Rubber parts have seen better days too but that's expected.

I really like the fact that you can just pull and swap out the head block, and would love to get the dual half-track option as that would be very useful for recording projects. All in/out connections are on DIN sockets, and luckily I had some DIN/phono breakout cables from another machine. Behaviour is a bit odd though—at first I thought I might be missing something, or there were issues with bad cables, but after a bit of thorough testing I'm fairly confident the problem is a fault in the electronics.

The unit has a number of settings for various combinations of record and playback utilising the two channels. I will focus on the main three: MONO I, MONO II and STEREO.

Playback:
I managed to dig out a tape with two channels of recording on it. If I run the line out, headphone out or projector out (in effect another stereo line output) to another device then then everything functions exactly as it should: Both MONO I and MONO II function independently and push their own channel to both phono outputs (essentially doubling them) and STEREO sends channel 1 left and channel 2 right. No playback issues at all. The line output level is fixed and is not influenced by volume/tone controls, although the headphone out is.

If I try to play the tape back using the internal amplifer and speakers then I hear one recording on the MONO I setting, another on MONO II, but switching to STEREO I hear the contents of the MONO I channel only (although the VU meter for channel 2 appears to be displaying correct levels for the inaudible channel.) The volume control pot for the R channel does nothing.
I also tested the loudspeaker outputs, left works properly but right is dead. It's my presumption that the right channel is not functioning and I am just hearing everything through the left speaker in all modes.

Monitoring from an external source (not recording):
I connected a keyboard to the left and right line inputs. Note that there are two different phono ins, one dedicated to higher levels and another for lower signals/radio etc that I believe also goes through the mic preamp circuit. The issues here are present regardless of which input is used.

Signal into the left line input, MONO I and II: both register on the VU, speaker playback audible, STEREO: channel 1 only.
Signal into right line input, MONO I & II: both register on the VU, speaker playback audible, STEREO: channel 2 only and it is very thin, quiet and noisy despite the meter showing a decent level.
I tested this process with headphones and both channels work correctly. I think that what is happening is that the monitoring is working properly but, as with the playback above, I am not hearing a right channel because the amplifier is not pushing anything to the right speaker.

Recording:
Using the MONO II setting I can listen back, record, monitor off-tape and even use the echo feature and everything is ok.
MONO I and STEREO however, monitoring off the tape during recording is silent. This goes for both the internal amp/speakers, and via the line out. We know the playback head functions on the left channel correctly in all modes due to the first test, So I can only assume that the issue here lies in the recording circuitry?

Summary:
Playback and input monitoring works correctly as long as it is routed out via the line outs or headphone out. The right channel of the internal amp/speaker (including loudspeaker output) doesn't function properly. Something to do with the amp driving the right loudspeaker seems to be at fault.
Recording only works for MONO II (the right channel). Having the machine set to STEREO when recording will record to channel 2/R, but not to channel 1/L. Given that the inputs and source monitoring work all the way through, could this be a fault with the left channel of the record head/record circuit?

Apart from having it open and a brief glance round I've not done much yet other than testing every possible situation to narrow down the behaviour. Does anyone with experience know what is likely to be the issue? Bad transistors perhaps? Or could the right speaker be broken and affecting the output too?

I found a schematic here: https://audio-circuit.dk/downloads/u...l-tape-sch.pdf

With the recording side I'm not sure where to start so any advice is greatly appreciated. Thanks!
untune87 is offline  
Old 31st Aug 2022, 2:25 pm   #2
DMcMahon
Dekatron
 
DMcMahon's Avatar
 
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 6,587
Default Re: Uher SG 561 Royal

I also think that the SG 561 and similar other Uhers are attractive looking recorders.

I have one but have not looked at it for a quite a while, when I original had a quick look it was not functional but I cannot remember now what specifically was non functional, I must locate it and have a fresh look.

I find the extensive Playback & Record options can be confusing especially when trying to fault find.

Have not fully digested your extensive Post but from a quick read it does sound like at least 2 separate problems, a bad right channel on the playback amplifier output or drive stage and a bad channel record amplifier maybe at the head stage.

Some of the early Uhers used Bogen heads which have a bad reputation for failing (I have had 2 go open circuit) later machines used Miniflux/Woelke heads which generally do not fail.

Using a digital meter (as opposed to analogue to reduce risk of magnetizing the head) I would check that the head is not open circuit, can additionally use a series resistor to provide some current limit protection during measurement.

No easy way I know apart from going in with a scope and monitor the signals to work out what is failing, with a working good channel you can do comparisons which can help.

As always worthwhile using switch contact cleaner on the relevant switches including the Record/Playback switch. After that also worthwhile next checking the transistor voltages to see if any obvious bad transistors.

David

Last edited by DMcMahon; 31st Aug 2022 at 2:42 pm. Reason: Typo correction
DMcMahon is offline  
Old 31st Aug 2022, 2:47 pm   #3
DMcMahon
Dekatron
 
DMcMahon's Avatar
 
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 6,587
Default Re: Uher SG 561 Royal

A photo of mine in post # 25 :-

https://www.vintage-radio.net/forum/...d.php?t=163477


David
DMcMahon is offline  
Old 1st Sep 2022, 9:30 am   #4
untune87
Pentode
 
Join Date: Oct 2010
Location: Greater Manchester, UK.
Posts: 161
Default Re: Uher SG 561 Royal

Morning David, thanks for the reply;

Indeed they are very nice looking machines! I hadn't seen one until now. I see from your pic that you have the handle on the bottom which mine was missing, and also your speed/transport selector knobs look like they might have been replaced at some point? (though they look very nice!)

I spent near a week on-and-off testing, making cables to see how everything functioned and making notes which I tried to condense down—but still it ended up being quite an extensive post!

But yes you're right, to re-iterate the summary, playback is fine apart from through the in-built amp/speaker (right channel). I found this odd because the outputs all work. The line outs are tapped off before most of the power amp circuit which makes sense, but the headphone on the other hand appears to go through most of the same and yet it behaves properly.

I wondered if perhaps the speaker is dead and that's affecting the 'loudspeaker' part of the circuit. The external plug can be flipped 180 degrees to cut the internal speaker out but testing both ways yielded the same result. It's all up in the top-right corner of the attached schematic.

As for recording, if not the heads then maybe dead transistors. There's an interesting video of an SG 560 repair but it's unfortunately all in German and I don't speak any! But it seems that they identify and replace a couple of duff transistors, T24 & T29 if I worked out correctly. It's more of a profile of the workshop than a repair, but it did demonstrate how to get the case open and supported properly: https://www.youtube.com/watch?v=waKLb-GXc_U

Input monitoring and meter indication all seems ok though, so perhaps it does point at the heads. I might see if I can pick up an alternative head block to test it out.

Contact cleaning is usually the first thing I do (alongside all the other cleaning) but it looks like I'd have to dismantle the whole thing to get to the backs so it's on my 'to-do' list for now Thanks for the suggestions!

Cheers
untune87 is offline  
Old 1st Sep 2022, 8:14 pm   #5
DMcMahon
Dekatron
 
DMcMahon's Avatar
 
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 6,587
Default Re: Uher SG 561 Royal

Quote:
Originally Posted by untune87 View Post

I see from your pic that you have the handle on the bottom which mine was missing, and also your speed/transport selector knobs look like they might have been replaced at some point? (though they look very nice!)

From looking at the one that is currently on eBay can see what you mean about the selector knobs, this is how it arrived when I purchased it, so do not know how it came to have these different knobs.

Yet to find where my one is hiding.

David
DMcMahon is offline  
Old 1st Sep 2022, 10:47 pm   #6
DMcMahon
Dekatron
 
DMcMahon's Avatar
 
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 6,587
Default Re: Uher SG 561 Royal

Quote:
Originally Posted by untune87 View Post
But yes you're right, to re-iterate the summary, playback is fine apart from through the in-built amp/speaker (right channel). I found this odd because the outputs all work. The line outs are tapped off before most of the power amp circuit which makes sense, but the headphone on the other hand appears to go through most of the same and yet it behaves properly.

Cheers
Yes the headphones working does sound confusing, have not yet looked at the circuit.

David
DMcMahon is offline  
Old 2nd Sep 2022, 10:26 am   #7
untune87
Pentode
 
Join Date: Oct 2010
Location: Greater Manchester, UK.
Posts: 161
Default Re: Uher SG 561 Royal

Hi David,

I *think* those knobs come from the Uher Royal De Luxe C, very similar looking at least, they have that silver trim. Perhaps the originals had cracked, either way I think they suit it!

If I get time this weekend I will open it up and have another look around. I'm tempted to test the rec head but I'm very wary of causing further damage, usually I try to stay away from the heads
untune87 is offline  
Old 2nd Sep 2022, 11:30 am   #8
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
Default Re: Uher SG 561 Royal

Are the headphone socket switch contacts and the loudspeaker socket switch contacts making ok for the RH channel ?

Lawrence.
ms660 is offline  
Old 2nd Sep 2022, 1:48 pm   #9
untune87
Pentode
 
Join Date: Oct 2010
Location: Greater Manchester, UK.
Posts: 161
Default Re: Uher SG 561 Royal

Hi Lawrence

Good question; looking at the schematic, the switches that cut the channels via the headphone could potentially be the problem. I don't see any issues with the loudspeaker ones at a glance, if the headphone (R) switch was stuck open it might explain why the headphones work but the speaker doesn't. From what I can tell (a tippex mark and a typewritten sticker that says 'to audiometer') this was the output that was used frequently for whatever purpose the machine originally served, so it would make sense that it could have been damaged through use.

Problem is I'm not particularly familiar with these 'domino' DIN sockets, or how it triggers the switches. Is it something with the barrel of the connector maybe?

When I get a chance I will open it up and inspect it more closely, see if anything stands out

Cheers!
untune87 is offline  
Old 2nd Sep 2022, 1:58 pm   #10
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
Default Re: Uher SG 561 Royal

Quote:
Originally Posted by untune87 View Post
Problem is I'm not particularly familiar with these 'domino' DIN sockets, or how it triggers the switches. Is it something with the barrel of the connector maybe?
Yes, it's the shell/barrel of the din plug that operates the switch in the socket, see the "Socketry" section in the down load link below:

https://www.vintageshifi.com/reperto...ers-Manual.pdf

Lawrence.
ms660 is offline  
Old 2nd Sep 2022, 3:04 pm   #11
untune87
Pentode
 
Join Date: Oct 2010
Location: Greater Manchester, UK.
Posts: 161
Default Re: Uher SG 561 Royal

Thanks Lawrence!

I couldn't leave it alone and quickly opened it up while I had ten minutes, cleaned the contacts, but noticed that there's a very very suspicious (cold) looking joint on one side of the switch on the headphone connector. Continuity is spotty, there for some but not making it all the way around... I have a feeling the culprit has been found (fingers crossed)

I'll reflow it when I get a chance and report back
untune87 is offline  
Old 2nd Sep 2022, 3:54 pm   #12
untune87
Pentode
 
Join Date: Oct 2010
Location: Greater Manchester, UK.
Posts: 161
Default Re: Uher SG 561 Royal

Yep, that was it... literally a two minute fix. Right speaker now works perfectly!

If anyone encounters similar I've attached a diagram with the switch contacts circled; mine was the outside of the two but if that connection between 506 and 507 is broken then the loudspeaker doesn't work; 506 is wired directly to the headphone out so continues to work.

One problem down, it's just the recording to figure out now!
Attached Thumbnails
Click image for larger version

Name:	sg_561_headphone.jpg
Views:	55
Size:	144.3 KB
ID:	264121  
untune87 is offline  
Old 2nd Sep 2022, 4:00 pm   #13
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
Default Re: Uher SG 561 Royal

Excellent, good result so far

Lawrence.
ms660 is offline  
Old 3rd Sep 2022, 4:24 pm   #14
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
Default Re: Uher SG 561 Royal

Quote:
Originally Posted by untune87 View Post
Using the MONO II setting I can listen back, record, monitor off-tape and even use the echo feature and everything is ok.
MONO I and STEREO however, monitoring off the tape during recording is silent. This goes for both the internal amp/speakers, and via the line out. We know the playback head functions on the left channel correctly in all modes due to the first test, So I can only assume that the issue here lies in the recording circuitry?
Yes, from what you describe.

T23 and T24 and their associated components form the record amplifier in question for the left channel, the input to the amplifier is taken from the same point that the source is monitored, connection I on the main board which connects to the +ve side of C37 is the input to the amplifier, the output from the amplifier (C46) connects to the record head via R192, R194, contacts m & g on the function selector switch (Section X) plug/socket connector 79 and finally R211.

It might be something simple like dirt on the record head, switch contacts or plug/socket connection not making, a broken connection somewhere or a short, failing that it's likely to be a component failure.

If the left channel level meter responds properly when in record then the problem should be between the VU meter driver input (-ve side of C71) and the record head, if it doesn't then the problem should be between that same point and the input to the record amplifier if the meter driver is working properly.

If that's any help.

Lawrence.

Last edited by ms660; 3rd Sep 2022 at 4:34 pm. Reason: extra info
ms660 is offline  
Old 4th Sep 2022, 2:28 pm   #15
DMcMahon
Dekatron
 
DMcMahon's Avatar
 
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 6,587
Default Re: Uher SG 561 Royal

Quote:
Originally Posted by untune87 View Post
Yep, that was it... literally a two minute fix. Right speaker now works perfectly!

If anyone encounters similar I've attached a diagram with the switch contacts circled; mine was the outside of the two but if that connection between 506 and 507 is broken then the loudspeaker doesn't work; 506 is wired directly to the headphone out so continues to work.

One problem down, it's just the recording to figure out now!
You are doing very well, hopefully you can home into the recording problem area, especially with Lawrence's useful inputs.

David
DMcMahon is offline  
Old 5th Sep 2022, 12:16 pm   #16
untune87
Pentode
 
Join Date: Oct 2010
Location: Greater Manchester, UK.
Posts: 161
Default Re: Uher SG 561 Royal

Thanks both for your input! Over the weekend I had it open again, inspected the board for anything that stood out, but nothing obvious.

I tried an experiment; points U and V (on the schematic, beside function selector switch sections X and XI) are the last points on the board (bottom right on the illustration) that go off to the switch then subsequently to the record head. I tested continuity between these points and the pins that connect to the head block. Everything is good there (or at least from the board, through the switch and up to the male head block pins.)

I desoldered and swapped those two wires on the board around, so that U and V now went to opposite channels. Essentially just flipping the rec head so that the channels are inverted whilst recording. Left channel record circuit now goes to rec head right, right channel record circuit goes to rec head left. Obviously the playback channels and outputs remain the same.

Since both speakers are working now, it's much easier to work out what's going on with playback. I tried recording and monitoring off-tape as I did so.

With original wiring, STEREO: Right channel works, left is silent. MONO I, meter works but there is no sound. Mono II, meter works and I hear sound. The ECHO(2) setting works correctly.

With the wiring inverted, STEREO: Right channel works, left is silent. MONO I, meter works but there is no sound. MONO II, meter works but the sound is quieter/thinner. ECHO settings don't work.

Unless I've oversimplified and this experiment is flawed, I believe this points to a duff rec head. If the left channel electronics were compromised then I would expect that the right channel (playback) would stop working, given that they were routed to the right channel of the rec head. But the right channel electronics (which work fine per original wiring) going to the left side of the rec head results in silence of MONO I and STEREO. It could well be that the head is broken AND there are issues with the left channel record circuit, but I'll likely need a replacement heads before I can work out the issue there!
untune87 is offline  
Old 5th Sep 2022, 1:25 pm   #17
DMcMahon
Dekatron
 
DMcMahon's Avatar
 
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 6,587
Default Re: Uher SG 561 Royal

It does sound like the record head is defective, I would be brave and measure it, although not easy to work out the correct pins at the head connector, the wiring is very tight (and fragile) there.

After much searching I have just found my SG 561 (and my SG 560 which I had forgotten I also have).

On my 561 the playback head is Bogen and the record head looks the same.

I will start a new Thread soon for my 561 when I start looking at it properly.

David
DMcMahon is offline  
Old 5th Sep 2022, 2:03 pm   #18
untune87
Pentode
 
Join Date: Oct 2010
Location: Greater Manchester, UK.
Posts: 161
Default Re: Uher SG 561 Royal

Quote:
Originally Posted by DMcMahon View Post
It does sound like the record head is defective, I would be brave and measure it, although not easy to work out the correct pins at the head connector, the wiring is very tight (and fragile) there.

After much searching I have just found my SG 561 (and my SG 560 which I had forgotten I also have).

On my 561 the playback head is Bogen and the record head looks the same.

I will start a new Thread soon for my 561 when I start looking at it properly.

David
Hi David,

It's certainly pointing that way isn't it! Going off the schematic and diagrams (there are pinout diagrams at the very bottom right corner for the head block connectors) the pin for the L/CH.1 is (79), R/CH.2 is (80), and common is (84). If I remember correctly, left is a red/white twisted pair and right is yellow/green. It's hard to say exactly because there's a resistor squahsed in there for each one, blocking the view of the actual solder joints. Easy enough to get a DMM probe into those pin sockets though.

If you could tell me the best method to test the rec head, I'll give it a go later.

Glad to hear you found yours! I look forward to seeing the thread. I was very curious about the 560/561/562 differences. I assumed the numbers referred to mono/stereo options, but with the changeable head block that isn't the case. The 560 has mic sockets on the left side and a different VU comapred to this one, but like I said, most of the info I found was in German so I didn't get far with it.
untune87 is offline  
Old 5th Sep 2022, 4:04 pm   #19
DMcMahon
Dekatron
 
DMcMahon's Avatar
 
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 6,587
Default Re: Uher SG 561 Royal

Was forgetting about the useful head pinout drawing and the series resistors.

On mine yellow and white are the common connections to pin 84 for the record head.

Using a digital ohmmeter both my record heads measure 3.45kOhms (84 to 79 and 84 to 80). My 4 track head block assembly is Z 348 (think yours will be the same) so the series resistors are 3.3kOhms (as per schematic info), so this means that the DC resistance of the heads is around 150 Ohms.

If your head is defective would expect it to be open circuit on the problem channel.

I also measured my record heads using my Chinese component tester expecting it to show an inductance reading in addition to the resistance. But after flashing up a picture of a resistor in series with an inductor (with no values displayed) it then changes to only showing a resistor, 3,481 Ohms for left and 3,499 Ohms for right. For a head without a series resistance connected it does display the resistance and inductance of the head itself, so looks like the extra series resistor confuses the meter measurement.

David

Last edited by DMcMahon; 5th Sep 2022 at 4:10 pm.
DMcMahon is offline  
Old 5th Sep 2022, 4:47 pm   #20
DMcMahon
Dekatron
 
DMcMahon's Avatar
 
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 6,587
Default Re: Uher SG 561 Royal

I misread the head block number, it is Z 346.

David
DMcMahon is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 8:07 pm.


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.