I have a speed problem on a mk3 revox A77 using the old SCB 1.077.725.04 board. The capstan motor runs faster than 15ips and replaced all the necessary caps trimpot. Tested all transistors. A working SCB was taken out of this machine so i know the problem is isolated to this board, but still problem exists. Any advice would be greatly appreciated. Thank you. Regards Darryl from Banbury UK
Check the tacho sensor. First check the distance from the motor. Then the connection to the board. Then the frequency it registers. I have heard that if the tacho sensor is not registering anything the board goes to max speed. The service manual has certain checkpoints and voltages. Look for the schematic of the old board since most downloadable service manual show the newer IC board. I guess you have the High Speed version since the NS version may go faster when faulty but not more the 15ips. Check if the speed is within limits and can be calibrated from the coil (T201). Check if the coil has a core. Sometimes they are lost or broken from previous attempts.
@dchatz Hi and thanks you very much. You made QUALITY TUTORIAL that help many people in many way…. However….! Little question…. My A77 has smoked the last time i plugged it to 220v and play it . The smoke has gone near the heads and smell bad the dead electronic parts… Would you have an idea of the troubleshooting please ? Inm gonna to open it but if i could know where to search…. I don’t have your « level » in electronics !!! Very thanks 🙏🙏🙏😇 and happy new year…
Thank you. Listen, your question is a bit chaotic, there could be a large number of faults. It's like "my car made a noise and now I turn the key and it doesn't start, what can I do". The answer is always simple but to get to the answer needs work and searching. Anyway, what happened to you happens normally on non-serviced A77's with RIFA caps and the nearby resistors. They often smoke bad if not replaced sometime in the past. If I had to guess this is my guess. There are 3 RIFA caps on the relay board and one on the Speed control board. On the relay board also the resistors nearby go bad after the RIFA caps fail. There are many videos about them, also on my channel. Search for "A77 RIFA" and you will get your answers. I hope that will be the problem and you will save your A77. PDF's are on the description of the video. I hope of course you did put the mains voltage selector to 220 or 240V and you didn't plug the mains to 220V with the selector on 120V.
@@mpmp7609 If the RIFAS are the original ones you will have to replace them even if they look good. They are a time bomb. They may go smoking any time. I'm not a professional technician but all professionals and enthousiasts suggest to do that. If the problem is finally the motor capacitors you are fine. Easy and cheap fix also. 3.5 for capstan motor, 4.5 for reel motors. The original reel motor caps are 4.3 but on ebay they sell 4.5, that is OK. Get all three as a set. First replace the one that smoked, see if everything works and then proceed replacing the other 2.
@@dchatz thanks for your advice… it is what i wanted to do . I eared too the un popalurity of the RIFAS’s time bomb ! However for the capacitors the first ITT is a 4,5 and not 4,3. I was surprised to see this value . If you want i saw a french tutorial wich is amasingly detailed … Thanks
Please do a video on how to do the speed adjustment after recapping for BOTH types od speed control boards. Mine is a MkIII that runs slow after recap/new trimpot...
Everybody on Facebook have fancy workbenches with dozens of meters. You get the job done on the sofa, the kitchen table, the bed, anywhere. This impresses me !
VU meter not working in play mode is the default behaviour for A77. Only the mk4 dolby version has working VU in play mode. So no worries, your machine works fine.
Thank you, a very helpful video... just one thing... I think the loose blue wire is originally shown as being soldered to the corner connection. When re-soldering you say it is the black wire that goes there?
Beware, originally there was the old type board (transistor) and at the end there is the new type (IC) board. It's true, on the old one the blue goes to the edge and on the new one the black goes to the edge. So 2 different boards with 2 different wire soldering positions. See the attached files and you will realize when comparing the 2 boards that positions 12 and 13 are reversed from one to the other.
You have the best A77 videos on TH-cam. Fascinating modifications that you explain very well. It's very refreshing to find someone like yourself doing these interesting modifications. Keep up the great work.
@@vitezmiroslav1389 i dont remember but please download the 2 attachments. All values should be there. Otherwise the service manual also has all the values
@@rickyramirez4080 I don't remember at all, both of them are on the service manuals. Old board, R201, I've seen 1K or 2,5K, I would use a 2,2K and it covers both of them I guess, and also I guess linear, new IC board, R217, 10K linear.
It is not possible to trace the problem exactly. 1. Check if tacho sensor works, 2. Recap the speed control board, 3. Check the speed control board transistor, 4. Check the 555 IC (if there is). If you can't do these then you need a technician. Wish you luck.
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I have a speed problem on a mk3 revox A77 using the old SCB 1.077.725.04 board. The capstan motor runs faster than 15ips and replaced all the necessary caps trimpot. Tested all transistors. A working SCB was taken out of this machine so i know the problem is isolated to this board, but still problem exists. Any advice would be greatly appreciated. Thank you.
Regards Darryl from Banbury UK
£
Check the tacho sensor. First check the distance from the motor. Then the connection to the board. Then the frequency it registers. I have heard that if the tacho sensor is not registering anything the board goes to max speed. The service manual has certain checkpoints and voltages. Look for the schematic of the old board since most downloadable service manual show the newer IC board. I guess you have the High Speed version since the NS version may go faster when faulty but not more the 15ips. Check if the speed is within limits and can be calibrated from the coil (T201). Check if the coil has a core. Sometimes they are lost or broken from previous attempts.
@dchatz
Hi and thanks you very much.
You made QUALITY TUTORIAL that help many people in many way….
However….!
Little question….
My A77 has smoked the last time i plugged it to 220v and play it . The smoke has gone near the heads and smell bad the dead electronic parts…
Would you have an idea of the troubleshooting please ?
Inm gonna to open it but if i could know where to search…. I don’t have your « level » in electronics !!!
Very thanks 🙏🙏🙏😇 and happy new year…
Thank you. Listen, your question is a bit chaotic, there could be a large number of faults. It's like "my car made a noise and now I turn the key and it doesn't start, what can I do". The answer is always simple but to get to the answer needs work and searching. Anyway, what happened to you happens normally on non-serviced A77's with RIFA caps and the nearby resistors. They often smoke bad if not replaced sometime in the past. If I had to guess this is my guess. There are 3 RIFA caps on the relay board and one on the Speed control board. On the relay board also the resistors nearby go bad after the RIFA caps fail. There are many videos about them, also on my channel. Search for "A77 RIFA" and you will get your answers. I hope that will be the problem and you will save your A77.
PDF's are on the description of the video.
I hope of course you did put the mains voltage selector to 220 or 240V and you didn't plug the mains to 220V with the selector on 120V.
@@dchatz it seem that is the motor’s condensators… curiously the rifa are in perfect look / shape !!!
Sorry for my amator’s question
@@mpmp7609 If the RIFAS are the original ones you will have to replace them even if they look good. They are a time bomb. They may go smoking any time. I'm not a professional technician but all professionals and enthousiasts suggest to do that. If the problem is finally the motor capacitors you are fine. Easy and cheap fix also. 3.5 for capstan motor, 4.5 for reel motors. The original reel motor caps are 4.3 but on ebay they sell 4.5, that is OK. Get all three as a set. First replace the one that smoked, see if everything works and then proceed replacing the other 2.
@@dchatz thanks for your advice… it is what i wanted to do . I eared too the un popalurity of the RIFAS’s time bomb !
However for the capacitors the first ITT is a 4,5 and not 4,3. I was surprised to see this value .
If you want i saw a french tutorial wich is amasingly detailed …
Thanks
Thank you for such a great and useful How-To video. Please keep them coming! Best Regards,
Thank you too for appreciating my work
Please do a video on how to do the speed adjustment after recapping for BOTH types od speed control boards. Mine is a MkIII that runs slow after recap/new trimpot...
Everybody on Facebook have fancy workbenches with dozens of meters. You get the job done on the sofa, the kitchen table, the bed, anywhere. This impresses me !
This happens when you are not a professional
Great video my capstan is not working so I may have to replace the SCB and hope that takes care of the problem.Thank you for showing how is done .
Hy i have revox a77mk4 , and I have a problem, vu meter not vorking in play mode, vorking only record mode, why? This is normal?
VU meter not working in play mode is the default behaviour for A77. Only the mk4 dolby version has working VU in play mode. So no worries, your machine works fine.
Thank you, a very helpful video... just one thing... I think the loose blue wire is originally shown as being soldered to the corner connection. When re-soldering you say it is the black wire that goes there?
Beware, originally there was the old type board (transistor) and at the end there is the new type (IC) board. It's true, on the old one the blue goes to the edge and on the new one the black goes to the edge. So 2 different boards with 2 different wire soldering positions. See the attached files and you will realize when comparing the 2 boards that positions 12 and 13 are reversed from one to the other.
@@dchatz Ah... OK I understand. Thank you for explaining that.
All the best.
You have the best A77 videos on TH-cam.
Fascinating modifications that you explain very well. It's very refreshing to find someone like yourself doing these interesting modifications. Keep up the great work.
thank you so much. I feel so nice that you find it useful.
Hi, in this video at 20:50 min there is a potentiometer on the right plate. What is the value? How many kohms is it?
@@vitezmiroslav1389 i dont remember but please download the 2 attachments. All values should be there. Otherwise the service manual also has all the values
@@vitezmiroslav1389 the new speed control board has a 10kohm pot
@@dchatz thank you
recommend replacement of control board or can also be repaired
depends, if you need varispeed the new mk4 board is the best. Otherwise for normal operation both boards do the same job fine.
Thanks great video keep em comin😊
Thank you
@@dchatz do you still remember the value of the trimmer in n the speed control board? Thanks😁
@@rickyramirez4080 I don't remember at all, both of them are on the service manuals. Old board, R201, I've seen 1K or 2,5K, I would use a 2,2K and it covers both of them I guess, and also I guess linear, new IC board, R217, 10K linear.
Pᵣₒmₒˢᵐ 😢
What do you mean ?
heloo man , i have a revox a77 , and was work good , until today , the speed of play , is fast , ,can you help me , thanks mate !
It is not possible to trace the problem exactly. 1. Check if tacho sensor works, 2. Recap the speed control board, 3. Check the speed control board transistor, 4. Check the 555 IC (if there is). If you can't do these then you need a technician. Wish you luck.
When the 1600 or 800 Hz reference is not stable, you must change the nF rated caps along with all electrolytics and the rifa.
thank you, good to know