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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 18th Nov 2018, 5:21 pm   #61
ms660
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Default Re: Revox A77 Stops Playing (Transport Fault)

Just looking at table 5.9-46 in the service manual, it gives the voltages for the rewind and winding motors, why are two voltages given in each column for the rewind motor when in the Play/Rec mode?

Lawrence.
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Old 18th Nov 2018, 6:21 pm   #62
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Default Re: Revox A77 Stops Playing (Transport Fault)

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why are two voltages given in each column for the rewind motor when in the Play/Rec mode?

Lawrence.
Look at the power switch. You can turn the machine on for either large or small spool hubs. The difference is the amount of oomph fed to the reel motors in play/rec in order to have some rough matching of the torque to the required tape tension.

The posher A700 had tension sensing arms to servo control the tape tension.

David
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Old 18th Nov 2018, 6:49 pm   #63
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Default Re: Revox A77 Stops Playing (Transport Fault)

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why are two voltages given in each column for the rewind motor when in the Play/Rec mode?

Lawrence.
Look at the power switch. You can turn the machine on for either large or small spool hubs. The difference is the amount of oomph fed to the reel motors in play/rec in order to have some rough matching of the torque to the required tape tension.

The posher A700 had tension sensing arms to servo control the tape tension.

David
I know that, that's not in question, look at Table 5.9-46 for the rewind motor, in Play/Rec. mode it shows 55.6 = 49 (large hub) 42.6 = 36 (small hub) that's two voltage figures for each hub selection.

Further down the table for the same motor in rewind mode it gives 99 which is just one voltage figure.

So far as I can make out the voltages for the rewind motor in play and record should be the same unless there's an error in the schematic or I've missed something that's relevant.

I suspect the first of the two voltages given is the voltage with reference to the 0 volts connection on the mains transformer and the latter being the voltage referenced to the 6 volt tap, if that's the case why not do the same regime for the same motor in rewind mode eg: 105 = 99.

Lawrence.

Last edited by ms660; 18th Nov 2018 at 6:59 pm.
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Old 18th Nov 2018, 8:49 pm   #64
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Default Re: Revox A77 Stops Playing (Transport Fault)

I'll get my original paper A77 manual out when I get home.

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Old 18th Nov 2018, 9:08 pm   #65
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Default Re: Revox A77 Stops Playing (Transport Fault)

Cheers, I've only got a web download copy in English but I checked a German version and that showed the same voltage table with the same contents as well, there's a brief mention of that voltage table in section 4.2. (Tape Tension) following the expected results table of the tension test using a "pullometer"

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Old 18th Nov 2018, 9:45 pm   #66
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Default Re: Revox A77 Stops Playing (Transport Fault)

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... look at Table 5.9-46 for the rewind motor, in Play/Rec. mode it shows 55.6 = 49 (large hub) 42.6 = 36 (small hub) that's two voltage figures for each hub selection.
I think that table actually reads: 55 - 6 = 49 , and 42 - 6 = 36

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Old 18th Nov 2018, 10:16 pm   #67
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Default Re: Revox A77 Stops Playing (Transport Fault)

It doesn't show up too well on my PC, even worse in the German version of the manual where the symbol between the figures looks like a triangle, I came to the conclusion in an earlier post that the voltage to the right was referenced to the 6 volt tap on the transformer but why just in play or record mode does it also give the voltage referenced from the 0 volts connection, why not that in rewind mode as well, it would complete the picture so to speak.

Lawrence.

Last edited by ms660; 18th Nov 2018 at 10:23 pm. Reason: Clarification
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Old 19th Nov 2018, 12:00 am   #68
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Default Re: Revox A77 Stops Playing (Transport Fault)

Just got home. Been doing horsey things this weekend.

Table 5.9-46 is quite clear.

Rewind motor big spools 55-6=49 Vac
Rewind motor small spools 42-6=36
Winding motor big spools 55
Winding motor small spools 42

Rewind motor in >> 21
Rewind motor in << 99
Winding motor in >>105
Winding motor in << 15

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Old 19th Nov 2018, 12:25 am   #69
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Default Re: Revox A77 Stops Playing (Transport Fault)

I had a conversation with the O/P yesterday. The problem appears to be on the transport board or the supply to it. The motors are unlikely to be part of the problem.

I told him that a method of measuring the 24V supply would be across the pilot lamp which is above the power switch.

We need to find out what’s happening to the 24V supply. What concerns me is that that it appears that in the fault condition the relay(s) start chattering.

This is unlikely to be caused by the stop circuit. until we know exactly what’s going on with that 24V supply, we can't progress any further.
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Old 19th Nov 2018, 12:43 am   #70
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Default Re: Revox A77 Stops Playing (Transport Fault)

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I had a conversation with the O/P yesterday. The problem appears to be on the transport board or the supply to it. The motors are unlikely to be part of the problem.

I told him that a method of measuring the 24V supply would be across the pilot lamp which is above the power switch.

We need to find out what’s happening to the 24V supply. What concerns me is that that it appears that in the fault condition the relay(s) start chattering.

This is unlikely to be caused by the stop circuit. until we know exactly what’s going on with that 24V supply, we can't progress any further.
Will try to investigate the 24v supply later this week. Time isn't on my side til then. Many thanks for all your comments.
Not sure if I misread your comments but the relays only chatter when wind or play is pressed after the fault occurs.

Last edited by Raving Loony; 19th Nov 2018 at 12:50 am.
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Old 19th Nov 2018, 1:15 am   #71
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Default Re: Revox A77 Stops Playing (Transport Fault)

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Not sure if I misread your comments but the relays only chatter when wind or play is pressed after the fault occurs.

I take that includes REW as well as FF & PLAY
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Old 19th Nov 2018, 1:22 am   #72
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Default Re: Revox A77 Stops Playing (Transport Fault)

I think the motor voltage was a question from Lawrence, and may not be a matter of the OP's problem.

If the 24v supply isn't right on a Revox, all the mechanism control relays will be acting silly and anything can happen, also the forces from the brake and pinch-wheel solenoids will be low.

There's no point in thinking about anything else until this supply is fixed and running properly. It'll cure quite a number of odd behaviours all at once. It may be the only fault on the machine.

David
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Old 19th Nov 2018, 1:29 am   #73
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Default Re: Revox A77 Stops Playing (Transport Fault)

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Not sure if I misread your comments but the relays only chatter when wind or play is pressed after the fault occurs.

I take that includes REW as well as FF & PLAY
Yes it does include rewind. I made a video of it but it's 5 meg and wont zip up any smaller
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Old 19th Nov 2018, 10:21 am   #74
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Default Re: Revox A77 Stops Playing (Transport Fault)

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I think the motor voltage was a question from Lawrence, and may not be a matter of the OP's problem.

If the 24v supply isn't right on a Revox, all the mechanism control relays will be acting silly and anything can happen, also the forces from the brake and pinch-wheel solenoids will be low.

There's no point in thinking about anything else until this supply is fixed and running properly. It'll cure quite a number of odd behaviours all at once. It may be the only fault on the machine.

David
Correct , the problem with this machine is the 27v supply rail . Once thats put right it`ll come back to life.
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Old 19th Nov 2018, 11:10 am   #75
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Default Re: Revox A77 Stops Playing (Transport Fault)

Just a thought ... I had similar transport problems on one of my machines. It turned out to be a failing back emf protection diode across one of the relay coils. The diode was intermittently going short preventing the relay from operating.
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Old 19th Nov 2018, 11:10 am   #76
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Default Re: Revox A77 Stops Playing (Transport Fault)

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Just got home. Been doing horsey things this weekend.

Table 5.9-46 is quite clear.

Rewind motor big spools 55-6=49 Vac
Rewind motor small spools 42-6=36
Winding motor big spools 55
Winding motor small spools 42

Rewind motor in >> 21
Rewind motor in << 99
Winding motor in >>105
Winding motor in << 15

David
Cheers, and sorry folks for any thread diversion, the workings out by Revox of the rewind motor voltages in Play/Rec mode I understand, what I don't understand is why they didn't show the same for the same motor in Rewind mode

Lawrence.
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Old 19th Nov 2018, 11:13 am   #77
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Default Re: Revox A77 Stops Playing (Transport Fault)

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Quote:
Originally Posted by Radio Wrangler View Post
I think the motor voltage was a question from Lawrence, and may not be a matter of the OP's problem.

If the 24v supply isn't right on a Revox, all the mechanism control relays will be acting silly and anything can happen, also the forces from the brake and pinch-wheel solenoids will be low.

There's no point in thinking about anything else until this supply is fixed and running properly. It'll cure quite a number of odd behaviours all at once. It may be the only fault on the machine.

David
Correct , the problem with this machine is the 27v supply rail . Once thats put right it`ll come back to life.
Hi Guys.
I do intend to try and recap the power supply board (probably the end of next week) as it seems to be the issue amongst all of you. If I could have a list of components I need to buy that would be a start as I can't remember if there is already a list on here.
I managed to play two reels yesterday without error (not one after the other but a couple of hours apart) which it has never done before. The only change I made (good or bad i'm not sure) was to adjust the regulated voltage down to 21v as it was on 24v. The unregulated section read 18.5v but I have not had the error since. This is probably just coincidence and now I've said it the fault will happen again.
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Old 19th Nov 2018, 11:47 am   #78
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Default Re: Revox A77 Stops Playing (Transport Fault)

You need a 2500uF cap (3300uF 35v) is what I`m using as the 2500`s are not available any more , you will need to get creative fitting it , I glue it to the board. .) https://uk.rs-online.com/web/p/alumi...itors/8752588/

You will need a 1000uF 35v cap : https://uk.rs-online.com/web/p/alumi...itors/8073416/

and a 3.3uf 35v cap : https://uk.rs-online.com/web/p/alumi...itors/1727927/

All of those will work fine for you . Make sure you get the polarity right and you `ll be good to go .

These are just examples of what you need , if you just put the uF rating in the search box you`ll get lots that will match and are in stock you can use 35v OR ABOVE NOT BELOW and you can use up to double the uF rating but stick as close as you can if you can get them .

THE BLACK/ WHITE / DOTTED LINE ON THE CAP SIGNIFIES NEGATIVE .. something I have never under stood , why not mark the positive leg ? I guess it doesnt really matter , just messes with my OCD ..hehe

Last edited by NorfolkDaveUK; 19th Nov 2018 at 11:55 am.
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Old 19th Nov 2018, 11:54 am   #79
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Default Re: Revox A77 Stops Playing (Transport Fault)

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You need a 2500uF cap (3300uF 35v) is what I`m using as the 2500`s are not available any more , you will need to get creative fitting it , I glue it to the board. .) https://uk.rs-online.com/web/p/alumi...itors/8752588/

You will need a 1000uF 35v cap : https://uk.rs-online.com/web/p/alumi...itors/8073416/

and a 3.3uf 35v cap : https://uk.rs-online.com/web/p/alumi...itors/1727927/

All of those will work fine for you . Make sure you get the polarity right and you `ll be good to go .

These are just examples of what you need , if you just put the uF rating in the search box you`ll get lots that will match and are in stock you can use 35v OR ABOVE NOT BELOW and you can use up to double the uF rating but stick as close as you can if you can get them .
Many thanks Dave.
Only problem is they only do two of them in packs over £100. Will have to see what other options there are.
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Old 19th Nov 2018, 12:01 pm   #80
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Default Re: Revox A77 Stops Playing (Transport Fault)

https://uk.rs-online.com/web/p/alumi...itors/2244303/

https://uk.rs-online.com/web/p/alumi...itors/3150754/

Packs of five.
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