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

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Old 7th Sep 2020, 10:43 am   #81
DMcMahon
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Default Re: Uher CR 240 AV Cassette Recorder

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Originally Posted by DMcMahon View Post
My trap door spring is missing also, when I got the unit I thought the trap door was also missing but it popped out when I removed the cassette lift.
This maybe a total red herring but the other day while looking through a component storage box for something I found the CR240 trap door and in the same little compartment was a little spring. I was sure that the trap door spring was missing when the unit arrived and if it was not missing I definitely do not remember storing the spring away.

The only similar spring I remember fairly recently was one that appeared to fall out of one of my R2Rs (TK 141 maybe) that I could not easily find a home for. Will have to try the spring in the CR240 to see if it fits/works.

David
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Old 12th Sep 2020, 5:55 pm   #82
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Default Re: Uher CR 240 AV Cassette Recorder

21 posts split to a new thread: https://www.vintage-radio.net/forum/...d.php?t=170971
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Old 13th Sep 2020, 11:20 am   #83
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Default Re: Uher CR 240 AV Cassette Recorder

Uncle Bulgaria, can you remember if the Record LED operates normally (goes on/off) with the Record switch, when all the plug in boards are removed ?

I think it should.

David
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Old 13th Sep 2020, 12:46 pm   #84
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Default Re: Uher CR 240 AV Cassette Recorder

Removed the record switch contact arm locking pin (and disengaged locking latch) and tried moving the arm to see if record led would go out, it would not go out at any position of the arm (this is with all plug in boards removed).

Rotated the contact arm 180 degrees and now have correct operation of the Record LED, (by manually moving the contact arm to Play and Record positions) also checked continuity of the numerous record/play switch contacts (using Uncle Bulgaria's very useful Record/Play switch contact sketch), all are good.

In this position the first contact of the contact arm (as looking from the front left hand side) is uppermost, which agrees with Uncles Bulgaria's previous inputs.

But now the contact arm metal latch mechanism is on the left side of the contact arm and will not latch and from previous discussions know that it should be on the right hand side.

So the only logical conclusion is that when I superglued the 2 broken halves of the contact arm together I got them 180 degrees out. At the time was sure they fitted that way due by the broken line marks on the 2 halves appearing to match up.

So looks like I need to break the superglue joint without wrecking the contact arm pieces and re-glue them the other way around, which will be a challenge.

First I will refit the boards and see if Record/Playback actually work with the contact arm in the correct way and manually operate the record switch to the Record and Play positions (with no latch).

David
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Old 13th Sep 2020, 3:43 pm   #85
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Default Re: Uher CR 240 AV Cassette Recorder

That is a real pain, David! Perhaps it's like calligraphy, when great concentration on letter form means that it's only when one steps back that one realises the word is spelled wrong.

In answer to your original question, yes, all the lights function as normal with no boards in place.
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Old 14th Sep 2020, 10:48 am   #86
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Default Re: Uher CR 240 AV Cassette Recorder

No sound at all on Playback.

Using internal microphone get record signals on the VU meters but no sound while monitoring the recording or when playing it back.
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Old 14th Sep 2020, 2:53 pm   #87
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Default Re: Uher CR 240 AV Cassette Recorder

Most obvious question first - did you have the internal speaker engaged? I've got personal experience of failing to remember to press the button down and wondered why there was no sound!

I found it quite awkward to trace the signal because the board connections aren't accessible when the boards are on. The circuit diagram is quite clear about the pin connections though, so I made up some thin wires with some tulip connectors (?) - the pieces from a D-sub socket - on one end and Veroboard pins on the other. This enabled me to have the relevant board out on the desk with the crucial pins connected, but accessible to probing. It's quite straightforward to trace the signal from numbered 'out' pin to numbered 'in' pin.

If it's on the VU meters then board 300 must be all right. Have you monitored the signal at MP3 and MP4 (the loops next to the volume control)? From my reading of the diagram, and racking my brains for what I did when I was fixing motherboard cracks, there must be an output on 515 and 501 for the signal to be getting to the Preamplifier board 300 and thence to the meters.

The output to the power amplifier is 528 and 514 which is MP3 and MP4, so between those you should be able to see where the signal's getting lost. If you make up some jumpers to get the Dolby board out of the case, you can probe around the individual components if the signal's getting lost somewhere on the board.
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Old 14th Sep 2020, 4:23 pm   #88
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Default Re: Uher CR 240 AV Cassette Recorder

Thank you for the inputs, yes did have the internal loudspeaker switch pressed in (switched it several times to be sure), still to check if the actual switch is working of course, no reason why it should not be.

Soon will start some monitoring investigations.

David
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Old 14th Sep 2020, 5:28 pm   #89
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Default Re: Uher CR 240 AV Cassette Recorder

Tried another tape to be sure and made sure that both tapes played OK on another player, which they do. Did a mic recording and played back on another player, it played back, but at low volume, so even though it looks like recording is working, the playback of it is not good.

Internal Loudspeaker is good and the internal loudspeaker switch checks out good continuity wise. No playback signals at MP3/MP4.

As you say difficult to monitor many of the signals. I do not really want to or have the time to make up extension cables for the boards but may have to later.
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Old 14th Sep 2020, 5:59 pm   #90
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Default Re: Uher CR 240 AV Cassette Recorder

You can do it from the bottom of the motherboard with the boards plugged in, just remember which way you're looking at it, and there's no way of clipping leads on so you have to probe with a point and a steady hand.

It might be worth checking the Dolby switch - I still have an intermittent problem on one channel when Dolby's engaged, which goes away when I press a point on the motherboard under the board connector, so there's a niggling bad connection there.
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Old 14th Sep 2020, 9:40 pm   #91
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Default Re: Uher CR 240 AV Cassette Recorder

Same lack of playback with Dolby switched in or out.
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Old 14th Sep 2020, 10:42 pm   #92
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Default Re: Uher CR 240 AV Cassette Recorder

Uncle Bulgaria, in Playback do your VU meters show the Playback signal ? I thought they were like the 4000 Remote Monitor meter which only displays the Record signal.

After much probing around I am now seeing an intermittent Playback left channel signal at MP3 (and also on the VU meter) and some other intermittent signals, I think I might possibly have some of your motherboard cracked tracks.

David
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Old 14th Sep 2020, 11:12 pm   #93
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Default Re: Uher CR 240 AV Cassette Recorder

My meters work in playback if this helps.
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Old 15th Sep 2020, 8:12 am   #94
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Default Re: Uher CR 240 AV Cassette Recorder

Thank you Pine Martin, that does help. I had thought that the VU meters may only display the record signal like my Uher 4000 Remote Monitor.

When I see the good music signal on the Left Channel at MP3 on the scope (basically the output of the Dolby board) I also see a good music signal at the left channel VU meter and by checking the schematic had almost convinced myself that is correct. So good to get your confirmation so as not to waste time trying to prove it one way or the other.
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Old 15th Sep 2020, 8:40 am   #95
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Default Re: Uher CR 240 AV Cassette Recorder

Still getting quite an intermittent playback signal on the left channel at MP3, not yet able to prove if due to the signal being intermittent at the output of the playback amp or intermittent at the Dolby board, every time I monitor those places the signal comes good before I can monitor.

Plugged stereo headphones into the 1/4" headphones jack to make sure there is no output signal present (when scope shows good signal at MP3), there is no audible signal there at all.

Scoped the intermittent good left channel signal to the input of the IC2 amplifier chip (pin 7), this is good and controllable by the volume control. But there is zero output at the output pin 12. IC 2 drives the loudspeaker and headphones, IC 3 does the right channel.

IC 2 & IC 3 are TBA 820P which are a 14 pin DIL package, these are long superseded by 8 pin version TBA 820M. Can still purchase the 14 pin TBA 820 as NOS but some of them are silly premium prices.

Have got a somewhat intermittent signal at MP4 on the right channel but not the music playback signal, but a 50Hz (20mS) sinewave, maybe a mains hum signal, have not yet traced its origin. Like the left channel the 50Hz signal arrives at the input of the amplifier (IC 3) and is controllable by the volume control, but there is zero signal at the output of the amplifier.

Possibly looks like the two TBA 820 amplifiers are dead but before I fully condemn them, need to check the various capacitors (including Electrolytics and Tantalums) around them in case their outputs are being pulled down.

Trying to find a 7 or 8 pin DIN plug so can check the line outputs at the Radio and Autoradio DIN sockets (the 7 pin plug will probably also fit the 8 pin socket actually).
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Old 15th Sep 2020, 12:17 pm   #96
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Default Re: Uher CR 240 AV Cassette Recorder

My lack of signal was caused by a duff capacitor, so I'd be tempted by that route. Also problems caused by the board-board connectors as they can be very intermittent unless cleaned and tightened. I had mused on the possibility of a more significant modification involving replacing the TBA 820Ps with a lower noise modern equivalent, but thought getting it going was my priority!

Perhaps there's a power supply problem to both ICs? What are the DC conditions like? I hope they haven't both died as the rest of the unit has signal through it. It would be most annoying if just the final output stage had had some kind of trauma. Don't forget the possibility of dry joints, as well.

If you need another TBA820P I may have one you can have for the postage.
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Old 15th Sep 2020, 2:51 pm   #97
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Default Re: Uher CR 240 AV Cassette Recorder

Power supply rails to both amplifier IC's had thoroughly checked OK.

Used a large magnifying glass to inspect the main board (motherboard) artwork and soldering connections, nothing obvious untoward found. Tried tapping all over the place to see if I could make the left channel signal when good (at MP3) go bad and also to see if could make the right channel 50Hz signal disappear/make the music signal appear at MP4 but nothing changed.

With a few more tests convinced myself that there is a good chance that the left channel and also probably the right channel TBA820 are actually dead, so have ordered a couple of new 14 pin TBA820's. They were quite cheap so if not used no hardship. Does seem strange though if both are dead.

In the meantime while waiting for the parts will check out the various capacitors around those ICs. For the very small Electrolytics and the tiny Tantalums may be best to replace them regardless of how they test. Unsoldering/removing and resoldering/refitting will physically stress them and worst case a good measured capacitor may turn bad after test & refitting. Hopefully I will find suitable values and small sized capacitors as not a lot of space in that general area.

Thank you Uncle Bulgaria for the IC offer, I had already ordered them before I read your post.

Need to further chase the intermittent good signal on the left channel and the lack of a good signal/but a 50Hz signal on the right channel.

David

Last edited by DMcMahon; 15th Sep 2020 at 2:57 pm.
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Old 15th Sep 2020, 3:39 pm   #98
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Default Re: Uher CR 240 AV Cassette Recorder

I have retained the capacitors I changed - mainly on the motherboard that were not decoupling properly - as I'd like to put them through the capacitor tester when I've built it to see if they are actually duff. I'm not a fan of the bodging 'recap' and, like you, want to know what's wrong!

I used Wurth Elektronik for the electrolytics as I thought aesthetically they were suitably Germanic, and it was a shame to remove the hard-cased distinctive Elkos. But that's just me being silly about something no-one will ever see!

I did add some extra filtering to the TBA820Ps and have attenuated the headphone out a bit to reduce the noise on minimum volume.

If you've got a 50Hz hum, how are you powering it? Through AutoRadio with a PSU, or with the Z131 mains adaptor? I did replace the large capacitor in the Z131 (reservoir?), and had to do some work on the 600 Power Supply board too. Doesn't this suggest (and I'm grasping at half-understood technicalities here) a filter or decoupling failure between the power rail and the signal?
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Old 15th Sep 2020, 5:01 pm   #99
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Default Re: Uher CR 240 AV Cassette Recorder

I am still using an external PSU connected directly to the battery compartment connector (as from Post 24/26) which has a clean output, the last time I checked (need to double check it).

I do need to try it back on the Z131 to see if same 50 Hz symptom exists.

If it is a real 50Hz signal (seems to be) then hard to understand where it is coming from, more tests should help, possibly could be a capacitor related issue.

I wish I had some noise on headphones minimum volume to attenuate, it is dead

David
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Old 16th Sep 2020, 1:52 pm   #100
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Default Re: Uher CR 240 AV Cassette Recorder

Scoped the output of the PSU with no connection to the CR 240, no sign of any 50Hz signal. Connecting the PSU to the 240 gives a large 50Hz signal with the 240 powered or unpowered ?

After disconnecting and reconnecting the connections several times the large 50Hz signal reduced down to around 5mV. Now there is no 50Hz signal on the right channel at MP4 and even better now have a good playback signal at MP4, the same amplitude as the left channel MP3. Like the left channel the signal gets through to pin 7 of the right channel TBA 820 (IC 2)and is controllable by the volume control but once again there is zero output at pin 12 of the TBA 820.

Also now the signals are no longer intermittent ?

A symptom I did not report before is that the right channel VU meter all ways displays a signal around -3dB (sometimes larger), the only time this disappears is when Record is selected.

Last edited by DMcMahon; 16th Sep 2020 at 2:06 pm.
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