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ReVox B215 will stop unless "pause" was key-in after "play"?

Y

yjwu

New Member
Hello:

Recently my friend sent me his ReVox B215 for diagnosis. The problem was full bars of VU meter at start up. The audio function and control was O.K. Sound quality is good.

So far I had not found any clue to this problem but new trouble developed.
Now the machine can play, FF, Fast backward, record only when I hit the corresponding key then PAUSE, otherwise the machine will stop within 4 seconds. The tape counter either got stuck on displaying type of tape, i.e. C 60, C90 etc, or 00:00:00. Now the the machine was degraded to full bars in VU meter, no counter reading, immediate stop unless "pause" was followed after normal key-in.

The only thing I had done on this machine was de-soldered audio control microprocessor (IC 5 on control board) and put it in my STUDER A 721. It function normally. When I replace this IC to ReVox B215, trouble surfaced!

Anyone can give me a hint on what was wrong on this B215?

Many thanks!

Yeun-Jung Wu
 
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Yeah, same thing that's wrong with all of them. I have 5. Re-cap it! Just do it and get it over with.

As to your actual problem.... maybe you lifted a trace and didn't notice. Also, these IC's are very static sensitive. Hopefully you didn't damage it while
moving it about. Take a magnifier and check your solder work!

I've fixed 3 decks with full VU just by recapping them. Between out of spec one's and the occasional shorted blue philips, you may as well.

Marc
 
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+1, I've 2 of them and have recapped 2 others plus 2 B710s. Total waste of time trying to troubleshoot anything on those decks until after a total professional recap of all the electrolytics. I guarantee while replacing the caps you will come across a few lifted traces. I thought the b215 had problem traces, but compared to the b710 they are wonderful.
 
Thank you all for your suggestion. Re-cap B215 seems to be mandatory to keep it healthy. Mine STUDER A712 might follow the same step of gradually mal-function.
As for the immediate stop, I do worry about the static problem. Hopefully it could be broken trace when I socket this IC.

I had re-cap 220uF, 22uF capacitors on control board. Today I will re-cap I/O board first.

Thank you again!
 
Oddly enough: when I re-cap all the electrolytic capacitors on control board and I/O board, VU meters are still in full scale. Tape counter still does not work.
B215 can play without record board, so I remove that board but problem stayed.
As for the Dolby board, I swapped in my Dolby board from my healthy STUDER A721. No luck.
As for the immediate stop problem, all traces from IC 5 are good. （negligible resistance measurement from the pins of IC to next component) Maybe the wired program code had been altered/damaged during the swap?
Then re-cap the reel motor board?

Yeun-Jung Wu
 
You may have killed one of the Micro processors. I had to get a new one for one of mine too. I think it WAS the one that runs the display. And you DID plug each one back in the right place, right? They are all different software.
 
I only swapped IC5 between STUDER A721 and ReVox B215. The VU meter display is controlled by this chip. In STUDER A721, both VU meter display and counter functioned normally. But when I replaced IC5 back to ReVox B215, the "stop after play" sympton developed. Play, FF, Rewind can function only when "pause" followed immediately.

The operation of STUDER is different from that of B215. But it is hard to comprehend that placing IC5 in A721 once would change its characteristics. It maybe what the warning of "sensitive to static discharge" is meant to.

There are two other microprocessors which for A721 and B215 are not interchangeable.
One of them responsible for keyboard scanning should be fine since all the keystrokes are interpreted correctly. I don't know how to check the third microprocessor.

I had ordered a microprocessor for ReVox B285 before. Yes, they do have them in stock but is quite expensive. The shipping and handling almost double the total expense.

Thank you for your input!
 
Hello,
I have the similar issues but with my Studer A721. After 5 seconds stop play unless I press pause key. Also the counter is stuck on showing C60. How did you solve the problem? Appreciate your support!
 
Not a common problem and now 2 in a row! The digital comm bus is pretty difficult (impossible?) to troubleshoot . Not sure who can diagnose past chip replacement. I have a B215 with one bad bus chip, but luckily the other ones work .

How did you readjust the tach signal?
 
Hi, my Studer A721 that came from a broadcasting station and had been in storage for years is coming back to life after having fully recapped it and LCD display replaced. I’m having an issue however with the auto cal as it’s not completing its cycle. I believe one of the bleeping tones could be missing. I had the opportunity to try out other audio boards however these are not recapped and that didn’t help matters. I have replaced IC7/IC8 on the I/O board and all voltages seem to be there. Playback is great but recording is poor compared to source. I have built the calibration tool but so far I had no success in aligning the recording part of the deck! I can’t imagine that the recording section of the head is failing as the playback is perfect. Any help greatly appreciated please. Thanks.
 
Hi Jascha.

Yikes, I've not yet come across that problem!

I'll only touch (and investigate) my B215 if and when a fault occurs, but a thought crosses my mind (without looking at the service manual)
at some kind of internal backup to store the previous tape's record/playback EQ settings. I wonder if the deck has defaulted to a first-time-switch-on state?

Recording bias will be incorrect, so the treble will be dull or excessive, playback EQ (de-emphasis) will also be incorrect.

Treble: Too dull = over bias and/or too much de-empasis, too bright = under bias and/or too little de-empasis.
  • Does the deck fully erase a previously well recorded/modulated tape?
One drawback to this machine, is that there isn't any apparent manual overide - your machine is stuck
in a particular bias, and de-emphasis setting I can only assume? And also will not 'update'?

In the meantime, I'll need to search my service manual for my B215, I assume it is near identical to your A721?
 
B James said:
Hi Jascha.

Yikes, I've not yet come across that problem!

I'll only touch (and investigate) my B215 if and when a fault occurs, but a thought crosses my mind (without looking at the service manual)
at some kind of internal backup to store the previous tape's record/playback EQ settings. I wonder if the deck has defaulted to a first-time-switch-on state?

Recording bias will be incorrect, so the treble will be dull or excessive, playback EQ (de-emphasis) will also be incorrect.

Treble: Too dull = over bias and/or too much de-empasis, too bright = under bias and/or too little de-empasis.
  • Does the deck fully erase a previously well recorded/modulated tape?
One drawback to this machine, is that there isn't any apparent manual overide - your machine is stuck
in a particular bias, and de-emphasis setting I can only assume? And also will not 'update'?

In the meantime, I'll need to search my service manual for my B215, I assume it is near identical to your A721?
Click to expand...

Hi James,

Thanks for sharing your thoughts on my A721. Much appreciated. The A721 has lots of similarities to the B215 although some ICs are given a different IC number such as IC8 on one will be IC7 on the other. The A721 has its right keyboard plugged into the remote interface as opposed to the B215 which connects directly to the system board and of course one has balanced connections vs photo sockets and the buttons on the front are not in the same location on both machines. That’s all I know about their differences.

Your thoughts on this fault point to the EEPROM on the system board in this case? The machine does erase a tape fully I believe and playback is not an issue at all. No matter what overbias setting I set using the home built bias tool, I can’t seem to get a flat frequency response as the HF are about 6db higher than the 500Hz reference. I doubt that it’s the head at this point and although I do have a brand new head in my possession I don’t happen to have the special jig to align the head if I replace it. I would have to invent something so I can set the alignment as close as possible to the old head. In the other hand I would not be 100% if the current head was set up properly by the radio station engineers if they ever replace it.
Any further help would be very much appreciated please when time permits.

kind regards
 
Hi Jascha

With spending so much time on restoring other dead 'inferior' decks, and recently on my Revox A77, I'm a little 'out of synch' with the B215. ;o)

Ahh yes, the EEPROM! I had forgotten ... I'll need to look into this.

Also, somewhere in the service manual it talks about removing/adding a capacitor to tame the Rec/Replay head's characteristics - I think some batches of
heads needed some extra compensation?

I'm busy at the moment with other things, but I'll take a peek into the service manual at some point, in the mean time download
the service manual for the A721 from www.hifiengine.com. I can't as I've exhaused my download limit from that site at least for a day or two. ;o)

regards.
 
B James said:
Hi Jascha

With spending so much time on restoring other dead 'inferior' decks, and recently on my Revox A77, I'm a little 'out of synch' with the B215. ;o)

Ahh yes, the EEPROM! I had forgotten ... I'll need to look into this.

Also, somewhere in the service manual it talks about removing/adding a capacitor to tame the Rec/Replay head's characteristics - I think some batches of
heads needed some extra compensation?

I'm busy at the moment with other things, but I'll take a peek into the service manual at some point, in the mean time download
the service manual for the A721 from www.hifiengine.com. I can't as I've exhaused my download limit from that site at least for a day or two. ;o)

regards.
Click to expand...
Hi James,
Thanks for your time to help me out. If you wish you can always use elektrotanya to download your manuals too. They’re quite useful too and here’s a link for you:
https://elektrotanya.com/studer_a721_sm.pdf/download.html

I have not come across yet any reference to the capacitor for the replay/rec head and will have a look. I have to say that the B215 is more informative than the A721 manual even though they are mostly similar,
Good luck with your A77…. I got stuck on one recently and still kind find a fault with it. It belongs to a friend of mine and there’s an issue with it that no voltage is getting to the take up motor. I checked everything on the replay board and my suspicions are the relays, most likely the sockets themselves or bad solder joints. There also an issue with the capstan motor or the board itself but this machine resides abroad so I can only help out when I visit the country it resides I’m afraid.

Best regards
 
Last night I looked at the SM for the B215, and the procedure for bias/EQ set up is similar to the 'over bias' technique for their reel to reel machines.

For Type I tapes ...

(1) It is important to understand that - Increasing the bias = increasing the amplitude of the 105Khz bias 'carrier'. The SM doesn't say this, but that is what is happening.

Inject 10Khz input at approx -20dB, then proceed and turn the potentiometer on your calibration circuit so that the high frequency bias 'carrier' (as I call it) increases from its low value to high - then note the peak value (Vpeak of the 10Khz audio) and continue until you reach approx -6dB below that peak.

Now, -6dB is 1/2 the peak value, so if your peak 10Khz trace is (say) 100mV, then stop at 50mV.

The maths ... -6dB = 20Log(V/Vpeak), or V = Vpeak*10^(-6/20)

I think for TDK AD-x, the desired peak drop is -6.5dB, so (in theory) V = Vpeak*10^(-6.5/20)

(2) The second part of the EQ set up relates to playback EQ - according to the SM, set up an input at 500Hz at -20dB and note its output Vout.
Then inject 10Khz and 18Khz at -20dB and turn the playback EQ potentiometers so that the output at 500Hz = output at 10Khz and 18Khz.

I'm guessing, but when the self calibration electronics of the B215/A721 run through their routine, they probably can 'tweak' the bias/EQ to ±20% of the value that
was set in the (1)+(2) procedure above.

Of course, this may not be the solution - a fault elsewhere could prevent the machine from remembering the auto calibration.

I'm out today, so tonight or tomorrow I'll read the manual again, just to check that I too have understood this correctly. ;o)

Patience is everything in this game! ;o)

James.
 
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