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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 16th Sep 2020, 5:39 pm   #101
Uncle Bulgaria
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Default Re: Uher CR 240 AV Cassette Recorder

Don't you just love intermittent faults! I wonder if an expert has a thought on where that signal could be coming from. Could it be coupled earths from the PSU and the oscilloscope?

It does sound like the ICs are fried, but if you've got some more on the way then at least you'll be able to confirm or rule out that.

The right VU meter seems to have a mind of its own. When I switch on, mine leaps to full deflection and gently comes back, though it does settle to zero deflection after a second or two. It also tends to leap on the application of certain controls. Perhaps something else to investigate. It's funny it's the right one, as I would have thought the left with its dual role as battery meter would have the greater likelihood of being affected by other controls.
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Old 16th Sep 2020, 9:45 pm   #102
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Default Re: Uher CR 240 AV Cassette Recorder

Intermittent faults are a pain, often they will come back with a vengeance.

Yes both my VU meters at times jump around when controls moved. My 4000 VU meter is particularly bad sometimes jumping around for no reason, others have commented that normal on the 4000, seems bad to me.
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Old 17th Sep 2020, 9:52 am   #103
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Default Re: Uher CR 240 AV Cassette Recorder

Found a 7 pin DIN plug and checked the line output signals on Playback at the Radio DIN connector all OK.

Had another close look under magnifying glass at the soldering around the IC 2/3 area. Found a leg of a component had been cut off quite long and was bent over its soldered hole and resting on top of adjacent soldered track. Even though it appeared to be touching, resistance measurement did not indicate a short. While bending the leg away from the adjacent track could see (under magnifying glass) that it was somewhat loose in its soldered hole. Also another component leg on the adjacent track was somewhat loose. Resoldered these but made no difference to the fault symptoms.

Again did a batch of resistance and voltage measurements around IC 2/3 but nothing obviously indicated any possible capacitor shorts.

Decided to leave the 3 tiny Tantalums (near IC2/3) alone.
C24 (10uF) I have not yet spotted on the schematic, but does not appear to be anything directly to do with IC2/3.
C37 (1uF) is on the +9.5V supply rail, the +9.5V measures fine at the ICs. BTW C37 is incorrectly identified on the component layout drawing as 0.1uF
C26 (10uF) is part of the IC2/3 input circuitry together with 3 transistors. Not very sure of the function of this circuitry, but its function is either enabled or modified by the internal speaker switch. Because have good inputs signals at pins 7 of the ICs with zero outputs, consider at this stage that the input circuitry is not at fault.

For good measure will probably replace the 3 electrolytics per IC, C27 (100uF), C31 (100uF) & C35 (1,000uF) for the left channel.

There are 2 other small/tiny capacitors per IC on the compensation pins, C29 (0.1uF) & C32 (220pF) for the left channel, will leave these alone but will try and measure them when IC removed.

Not looking forward to replacing the ICs, will just do the left channel (IC2) to start with to see the results. Think my soldering work on delicate artwork has diminished with age and think it will be difficult to extract the ICs without track damage. Probably will cut off the IC pins at the IC body and extract 1 pin at a time, this should make it a little easier and hopefully reduce any track damage.

Do not find it easy to actually accurately see the IC artwork connections, because the adjacent pins of the IC are physically staggered on the board and some pins are not soldered (the not connected pins) not easy to see compared to a normal row of DIL IC soldered pins.
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Old 17th Sep 2020, 10:07 am   #104
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Default Re: Uher CR 240 AV Cassette Recorder

You have the original circuit diagrams, don't you? I mention it because the PDF I was using before I got the originals (having told SDS my serial number) had some different values, which could be what you're seeing if it's a slightly different revision. I didn't originally have a circuit for the Hall sensor, for example, as the PDF was for the variant with the reflective strobe tape-end detection. That C37 is a 1F on my circuit diagram, but 0.1F on the layout drawing like yours.

The ICs are a pain (I did replace one, but it wasn't broken in the end). I recommend close attention to the big motherboard drawing with the lands and component layout shown, and get used to how many pins there are between the power board connections at the edge of the motherboard and the ICs. I spent a lot of time repairing tracks in that area so learnt my way around quite quickly. The unsoldered pins are a giveaway too. Some flux and solder wick and they come out without too much trouble.
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Old 17th Sep 2020, 10:09 am   #105
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Default Re: Uher CR 240 AV Cassette Recorder

Have now spotted C24. around transistor T6, something to do with the control of the IC1 Op Amp for the line outputs to the DIN connectors.
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Old 17th Sep 2020, 10:22 am   #106
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Default Re: Uher CR 240 AV Cassette Recorder

Yes have the original circuit diagrams which are great compared to fuzzy PDFs but still hard work at times due to eyesight not being as good as it used to be.

C37 is actually a 1uF so it is just the layout drawing showing it as 0.1uF that is incorrect.

Have never been a big fan of solder wick (I can hear people shouting why not ).

Last edited by AC/HL; 17th Sep 2020 at 2:50 pm. Reason: OT aside edited. Please start a new thread.
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Old 17th Sep 2020, 12:16 pm   #107
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Default Re: Uher CR 240 AV Cassette Recorder

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Originally Posted by DMcMahon View Post
Have now spotted C24. around transistor T6, something to do with the control of the IC1 Op Amp for the line outputs to the DIN connectors.
Not sure if this will help but so far as I can make out T4 and T5 mute the inputs to the line output amplifiers, the mute control voltage comes in at the junction of R49 and R50.

When in Record it's via D1 and switch contacts 47-48.

When in Pause it's via D2 and R83.

When in Rew/FF it's via T6.

Same for the input to the audio output amplifiers (by T8 and T9) except that the mute function is overridden in Record by the action of T7.

Lawrence.
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Old 17th Sep 2020, 5:32 pm   #108
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Default Re: Uher CR 240 AV Cassette Recorder

Thank you Lawrence for the useful inputs and expert analysis as usual.

Because there appears to be useful voltage signals on the inputs to the audio output amps I do not think they are being muted in Play mode but certainly will look more closely at the muting operation to doubly check, later when I return home.

As I said previously it does seem strange if both output amps are actually dead, would be good to find something else common to them that would affect their operation.

David
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Old 17th Sep 2020, 5:44 pm   #109
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Default Re: Uher CR 240 AV Cassette Recorder

It's probably a good idea to revisit your aversion to solder wick - if you can remove them without cutting the pins then if they later turn out not to be the problem you won't have ruined them!

I was also not convinced by it until a fortnight ago when I started dipping it in a tin of flux. Suddenly, it became brilliant and I'm now a complete convert. There are sometimes those places a sucker doesn't reach...
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Old 17th Sep 2020, 6:08 pm   #110
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Default Re: Uher CR 240 AV Cassette Recorder

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Originally Posted by DMcMahon View Post
As I said previously it does seem strange if both output amps are actually dead, would be good to find something else common to them that would affect their operation.
Have you measured Vcc on pin 14 of the IC's WRT their ground pins 8 & 10?

Lawrence.
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Old 17th Sep 2020, 6:14 pm   #111
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Default Re: Uher CR 240 AV Cassette Recorder

Yes 9.5V

David
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Old 17th Sep 2020, 11:18 pm   #112
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Default Re: Uher CR 240 AV Cassette Recorder

Quote:
Originally Posted by Uncle Bulgaria View Post
It's probably a good idea to revisit your aversion to solder wick - if you can remove them without cutting the pins then if they later turn out not to be the problem you won't have ruined them!

I was also not convinced by it until a fortnight ago when I started dipping it in a tin of flux. Suddenly, it became brilliant and I'm now a complete convert. There are sometimes those places a sucker doesn't reach...
Tried a few times over many years with minimal success compared to using a solder sucker (probably just bad technique on my part), maybe I should revisit it. In this case I am not worried about ruining the old chips.

David
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Old Today, 8:50 am   #113
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Default Re: Uher CR 240 AV Cassette Recorder

Cannot find my old solder wick supplies so have just ordered some more.

Probably could have tried some copper braid off a cable with flux but as I have not had a lot of success previously, thought best to get some modern fluxed solder wick to get better chance of success.

Undecided yet whether to wait for the solder wick to arrive before replacing the IC's.

Either way will only replace one of them initially, if this does not fix the problem on that channel, then little point at that stage replacing the other one, as then it would indicate the fault is elsewhere.
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