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Reel To Reel All discussions pertaining to reel to reel decks. These include general usage, recording, playback, and service questions. For subjects related to tape itself, see the Open Reel subforum under this one. Obscure service subjects that don't quite fit go in the Help and Do It Yourself subforum.

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  #1  
Old 03-20-2017, 10:55 AM
Jim Valenti Jim Valenti is offline
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Revox a77 record problem

Channel one went dead on record. Channel two is perfect. Playback and source work fine. Went from no problem to no response in an instant. Can someone tell me where to start trouble shooting? Recapped from a nagra kit about 1 month ago and everything was working fine. Thanks
  #2  
Old 03-20-2017, 11:06 AM
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You didn't tell us if the left VU meter in record had indication or not. That info is needed.

First look at the record head with a dental mirror and look for oxide deposits. It is difficult to see the left track without the mirror.

If head is good, your record relay may have bad contacts. Rap on the bias board or on the relays during record with a tool handle to see if audio comes back.

And you replaced all cal pots when you replaced caps?
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  #3  
Old 03-20-2017, 04:35 PM
Perryed Perryed is offline
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Swap the pcb cards and see if the problem switches channels too.
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  #4  
Old 03-21-2017, 01:07 PM
Jim Valenti Jim Valenti is offline
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Thanks for the response The meters do work in record. I cleaned the relays but no change. I switched the pc boards and the problem moved to channel 2. All the pots on the record boards have been replaced except one ( my dog actually ate the correct one). I didn't have the right resistance and don't know if I can change the value or by how much. Also what do you put in the switch so the machine will run without the back cover? Where should I go from here?
  #5  
Old 03-21-2017, 07:26 PM
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Reevocks Reevocks is offline
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Quote:
Originally Posted by Jim Valenti View Post
Thanks for the response The meters do work in record. I cleaned the relays but no change. I switched the pc boards and the problem moved to channel 2. All the pots on the record boards have been replaced except one ( my dog actually ate the correct one). I didn't have the right resistance and don't know if I can change the value or by how much. Also what do you put in the switch so the machine will run without the back cover? Where should I go from here?
Hello Jim.

Since the problem moved with the board swap, the problem is on one of the boards. Also, since it happened so fast, that would reduce the probability of P503 opening. However4, since the VU meter works, the signal is coming into the board. However, if either C510 and/or C511 open, the signal will not get to the record head, yet the meters will work. If you didn't replace the tantalum capacitors on those boards or any other board, I strongly recommend you obtain some and do so. Tantalum capacitors can internally short or open with less notice than an incandescent lamp burning out. Hoping you have a service manual. If not, a schematic and board layout is included.

As for the interlock cheaters, (interlock bypass tools) a photo is also included. These are nails and work quite well. A few notes of caution.
Please don't insert or remove the nails with the power cord plugged into the mains.
Shrink tubing or electrical tape will insulate the nails.
The two inch length isn't mandatory, just convenient. The 1/8th inch diameter is close to the diameter of the interlock device in the rear cover. Any smaller diameter may not provide good contact and may fall out.

Robert
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  #6  
Old 03-21-2017, 07:38 PM
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The Nagra kit you installed replaces all record board electrolytic caps, so you may have a bad or broken circuit trace or solder joint (due to you replacing the caps). Also may be the pot you did not replace. If all good, then a bad transistor. Remove and test them with a DMM.
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  #7  
Old 03-22-2017, 09:06 AM
Perryed Perryed is offline
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There are multiple sources for replacement boards out there. They are relatively inexpensive, just be sure it`s guaranteed to work. Good luck!
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  #8  
Old 04-17-2017, 09:04 AM
napovo napovo is offline
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A77 Record relay not close

Hi,
I have a A77 and got the same problem. I found that because the Record relay is not close properly. You can check yours as well. When I use a stick to force the relay to close, recording become good.
Anybody can tell me how to have the record relay close tightly pls? The contact cleaner spray doesnt work. I measure the DC at pin 9 of the record relay card at 20.9v when it is power on. The C602 has been recapped 500uF 3V to 470uF, 50V.

Thank you very much
  #9  
Old 04-17-2017, 03:17 PM
napovo napovo is offline
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Record relay voltage

Hi, I check on the record relay input voltage, between pin 4 and pin 5. The voltage is 15V instead of 24V which cannot close the relay completely.
How can I increase the voltage at the pin4 to 24V pls?

Thank you
  #10  
Old 04-17-2017, 06:56 PM
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tubenirvana tubenirvana is online now
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Quote:
Originally Posted by napovo View Post
Hi, I check on the record relay input voltage, between pin 4 and pin 5. The voltage is 15V instead of 24V which cannot close the relay completely.
How can I increase the voltage at the pin4 to 24V pls?

Thank you
it is not a matter of increasing the voltage, it looks as though something is 'pulling' the 24V, ie, an overload or near short somewhere. So you will need to figure out what is pulling the 24V down to 15V!
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  #11  
Old 04-17-2017, 08:33 PM
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See if the 27 volt power supply is correct when in record mode. Close is good because that supply is unregulated.

If good, then check for bad contacts in relay B on board 307.
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