Hey all. Found a mint looking A-77 mkIV at a garage sale this morning for 7 bucks :banana: , I couldn't believe it when the lady told me how much. I didn't even bother asking if it worked, just gave her the money and said thanks.
Came with 2 steel 10 inch revox reels (one full), the adapters and a mint acrylic reel cover (without a single scratch). This beast is a pleasure to look at, even though she don't play :tears:

I opened her up looking for anything obvious and found a burnt 630ma fuse, but after a quick drive to the source, she still wont play. FF and RW work fine. Just no capstan spin. When i spin it by hand it does coast for a bit...So I assume it aint all seized up or something?
Any tips you guys can give me on where to start looking for the problem. I don't have a service manual either (anyone have a pdf of one??). I would love to get this beauty singing again.

Thanks for any help in advance.

Rick

Wow, now that is a score! :thmbsp:

There are two types of A77 dust covers. One is rectangular and just coers the upper half of the machine. The other is oval-shaped and fully covers 10.5" reels. Which one did you get? If it was the latter, count yourself exceptionally lucky, as these are very rare, and highly desirable.

The possibilities that come to mind with the A77 capstan motor are:
1) A bad motor-run capacitor
2) A bad motorl controller board
3) Power supply problems
4) A shorted motor.

BTW: If you get this up and running, you will discover that this is a realy terrific machine. :thmbsp:

great score slabi!

bluebook says,

REVOX REEL, A-77 IV DOLBY
Manufacture Years: 1977 - 1981
MSRP: $1,170.00
USED: $306.00

Great score!!
Measure voltage at the capstan motor. Post results.
Ron

Thanks guys. Looks like this is a definate keeper for me, and more of a score than I originaly thought.
Goldear...Can I test the things you say are possible faults with just my dvom (fluke 88)?

Gonna attempt a pic with my crappy camera phone...

Wow, you did get the good dust cover! Oh, I'm jelous now!!! :D

I'm not sure if you can diagnose this with a VOM or not. You really need to get yourself a cheap scope.

You can get copies of the service manuals that will help to walk you through the process. But they're likely to cost you much more than that machine did. The A77 service manual is probably one of the best, and most comprehensive service manuals that I have ever seen. They are like an inch thick! So you picked a good deck to work on. :yes:

Damn boy, you did good! :yes:

I snagged a filthy one about 3 weeks ago for $10, but no reels, hubs or dustcover. It does work and sounds fine. I'm going to break her in by letting my father-in-law play/copy all his mono 60's tapes, and after that I'm not sure where she'll wind up as I already have a very nice Akai GX-635D in my main system.

Helluva score for $7.00!!!!!!

Thanks guys. I managed to find a pdf of the manual, now to see if I can actually do anything with it. I know the 2 fuses on the power supply board are holding up. Next I'll see if anything on the capstan motor board jumps out at me.

Correction on the Power supply board fuses. The 630 ma one has indeed blown again. And so it begins... :dammit:

Nice find. Found my suitcase model at an estate sale also. Came with original box but no manual.

Thanks guys. I managed to find a pdf of the manual, now to see if I can actually do anything with it. I know the 2 fuses on the power supply board are holding up. Next I'll see if anything on the capstan motor board jumps out at me.

Correction on the Power supply board fuses. The 630 ma one has indeed blown again. And so it begins... :dammit:
Actually, this is good news from a diagnostic stanpoint: It tells you that something following these fuses has shorted-out. This should make the trouble-shooting process easier, not harder. :thmbsp:

But PDFs that size (a couplehundred pages) can be pretty hard to work with; unless it happens to support effective text searching. Even so, I find it much easier to thumb through a hard copy. But, perhaps if you don't mind burning a ream of paper, you could printout your own copy...

Rick,
Is the blown fuse black inside the glass? If so, you have a dead short to trace. You'll need to check components for the fault.

Ron

you can also contact Revox and supply the unit's serial number. they keep track of every deck they've serviced. they might have previously fixed that particular deck and any information can be helpful. at least you can get the unit's history.

The fuse has no discoloring. I actually watched as I powered up the unit and pressed play and never saw it blow. I'm a mechanic and am used to actually seeing the fuse blow...this one blew without even a hint of light flash?

One of the hints the manual gives is to check the capstan motor capacitor #c151, but I seem to be missing (or can't find), the diagram with that circut? So I can't locate that cap.
I wanna check the motor for shorts, but of coarse ya gotta take half the damm thing apart just to get to the point where the wires enter the motor :thumbsdn:

The capacitor is far more likely to have shorted. That is a common mode of failure for a 30 year old capacitor. Don't waste your time testing the motor until you have located this cap.

Hey:
Send this unit to me and you will never have to worry about it again ever.
I will send you my address for shipping when you let me know.


Seriously you got a GREAT deal on the A77, as well as the plastic cover , which sells on ebay for upwards of $200 . Great find.
Good luck
Ed

I spent many years of my life and career behind the controls of an A77. They are all but indestructable.

On the A77 the dominant failure mode is the .47uF capacitors associated with the control relays toward the left rear of the machine. These caps are in rectangular packages with clear plastic cases. You can actually see the internal short!

Mouser has good replacements, p/n 5989-250v.47

* * * * *

Also, check the pinch roller pressure. This tends to decline with age. There is an adjustment for this right next to the roller.

Good luck with your machine.

Fred Longworth
http://www.repairaudio.com
StereoTech Classic Audio Repair

Thanks for all the replies so far guys. I sent it into a tech nearby that told me it needed the capstan motor replaced. They say it was shorted? I checked all 3 wires against each other (90-98 ohm) and also checked to case chassis and found no short.
I'm no electrician (just a mechanic), but I expected to find a short to chassis when the tech said the motor was shorted. Looks like I'm gonna need outside help.
Found a dude with a capstan motor out of a markI that looks identical. Can any of the RTR techs online verify this will work. I wish there was someone that lived on my street that could fix her for a few beers....but that seems highly unlikely.

Oh well....I'm gonna put on some beach boys and chill for the night. This damm deck has me all upitty.

apreciate any advice any and all have to offer, and thanks again.

Thanks for all the replies so far guys. I sent it into a tech nearby that told me it needed the capstan motor replaced. They say it was shorted? I checked all 3 wires against each other (90-98 ohm) and also checked to case chassis and found no short.
I'm no electrician (just a mechanic), but I expected to find a short to chassis when the tech said the motor was shorted. Looks like I'm gonna need outside help.
Found a dude with a capstan motor out of a markI that looks identical. Can any of the RTR techs online verify this will work. I wish there was someone that lived on my street that could fix her for a few beers....but that seems highly unlikely.

Oh well....I'm gonna put on some beach boys and chill for the night. This damm deck has me all upitty.

apreciate any advice any and all have to offer, and thanks again.
I think that the Mark 1 mortors are probably electrically compatible. The issue is that the bearings changed over time on these units. Mark ones used a sintered bronze bearing, if memory serves. And I think that either the Mk 3s or 4s might have used a sealed bearing of some sort. So I'm not sure how easy this swap will be. :scratch2:

Thanks guys. Looks like this is a definate keeper for me, and more of a score than I originaly thought.
Goldear...Can I test the things you say are possible faults with just my dvom (fluke 88)?

Gonna attempt a pic with my crappy camera phone...

good god - 7$ including the large acrylic cover....? i payd 40 solo for the small one :)

btw - a great tape. 2 track or 4 track, which speeds (there were several different combinations).
looks nice even with the crappy quality pic.

we could bring them together to let them mate and make little MKIVs :banana:

my is an 2track version...

Helge

Hey guys. Just decided to open the A-77 back up and check out those caps you mentioned by the control relays. As I said before I only have a DVOM and not sure how to properly check a cap with it, so I went ahead and de-soldered them for a closer look. They do appear to look pretty shabby to me...But if you would not mind taking a look yourselves and give me your more professional opinion.

Sorry about the big pics, I'm not the most digital savvy. Amazed I even got the macro to work :D

pics to A-77 caps are here....clicky clicky (http://www.streamlineauto.net/myaudiopics/)

If what I see is indeed blown caps, can I get replacements from the local radio scrap (AKA Source)? If the salesman is as much of an idiot as I am when it comes to electronics can you guys give me any info that will help me describe what I need, or any suitable replacement.

Thanks again for all your advice. I hope the electrician was wrong about the shorted capstan motor (as I think he may be).


Rick

Re the capstan motor: Most likely, what's gone bad are capacitors on the capstan motor's FG servo circuit board. Like most caps this old, these are crapped out with age, and due to this, it won't run on speed. Replace the caps on this board, and then see if the capstan motor doesn't run quite nicely!

(As for me, I have a Mk 1 A77 made in 1969 that right now is a total mess, needing the above recap, a new recording head, one VU meter and the bottom feet replaced, and the ability to rewind restored. [This is the second A77 I've known that wouldn't rewind. Where does this problem originate?] Sports aluminum trim around the reel turntables....a cosmetic special-order I understand. I've never seen another like it. :-))

Hey, Mr Slabi: Any change you could send a copy of the manual to us helpless people who have a problem, mine lost playback and I am trying to figure it out, would be alot easier with the manual

Thanks
Reel to Reel

Two things:

First, Under the flip-down dress panel that covers the heads, there are two switches. The one on the left turns the reel motors on and off. That might be a good place to start to look. I guess that it is there so that you could manually cue a tape, otherwise I have no idea what that switch would be used for. It's a very nice tape deck by the way. I bought mine at a garage sale for about $25 if I recall correctly and it works and sounds great.

Second, I have an owners manual and a service manual in PDF format. I can upload it to www.sendspace.com and post a link where any AK member with the link will be able to download it. I will need any one person to send me their email address via PM in order to start the process. The manuals will stay on sendspace for only a few days then they get automatically removed. The file sizes are huge at 18 MB and 78MB so be patient. If you are on dial up, oh boy! Send me PM, we can find a way to get it to you. After I have an email address it will take about 30 ~ 45 minutes to upload them Via my DSL connection. After the upload is complete I will post the link in this thread.