Revox B77 issues - help please.

leddy

leddy

Well-known member
I always wanted a Revox - found a B77 locally for next to nothing, but condition unkown - seller did not know anything about it.

Heads looked good, thank God. Hub adapters included. I could sell those for more than I paid for the deck, so I'm good even if it's junk. I take it home.

Plug it in...

VU meters start jumping around, pegging into the red just from turning the machine on. Checked the voltage selector, it's set for 110 so it's not that. I quickly turn it off. I load a tape and turn it on again to see if it spins. Nope. Nothing. No FF/RW, nothing. VU's start jumping around so I turn it off.

Choices are: make this my first major rehab (been wanting to give it a shot) - any ideas what causes the meters to do this?. Take it to a repair shop, or sell it for parts.

It's the 7.5 ips 1/4 track, not the 15 ips 1/2 track. Wish it was.

Edit: Actually, I think it is a 2-track. I've never seen Revox heads before, but they don't look like 4-track heads. I'll try to post a pic later.

Thanks for any input.
 
Last edited:
Could be worth a shot to open the machine, give it a good cleaning and check if the belt is alright.
Of course a loose belt shouldn't cause the VU's to jump around but it's a common problem on old machines.
It could be one of the relays gone bad too. I don't know how to tell which one but if you can find some way of knowing what causes it to behave like that spare parts is pretty common.

There should be quite a few people on this forum who's more into Revox than I.
 
Was the capstan turning? It should rotate continuously while the machine is powered on. If not, you have a problem since it's a direct-drive machine.

If the entire transport is dead - and it sounds like it - check the internal fuse, it's either 1A or 2A, I forget which. However, the thing with the VU meters is kind of worrying and I have no idea what can cause that, except maybe some kind of short.

EDIT: It wouldn't surprise me if you get 60Hz or whatever on the audio outputs. Try the headphone jack and have it set to input monitor?

Transport control is handled via a PROM which it basically uses as a lookup table to work out which button does what and when - it doesn't have a CPU as such.
Tape sensing is done via a photoelectric cell and LED pair around the head stack - be aware that it can often see through red leader and may stop unexpectedly for this reason. It does mean that you can stick a piece of card in front of the sensor while testing, though - you don't have to hold down the tension arms like on a TASCAM.

The audio cards are along the bottom - IIRC there's a repro card, a record card and a third one as well, but I forget its function. Each card handles both channels. I'd check those for excess voltages.
The control and capstan boards are somewhere in the middle of the machine, near the capstan motor.
 
More info. After pulling the rear case off, it seems evident this unit has had a significant drop at some point. Frame has a bend in it and I can see one card that has been partially pulled out of its socket. Fuses all pass continuity test. I will re-seat all the cards and see what happens.
 
leddy said:
More info. After pulling the rear case off, it seems evident this unit has had a significant drop at some point. Frame has a bend in it and I can see one card that has been partially pulled out of its socket. Fuses all pass continuity test. I will re-seat all the cards and see what happens.
Click to expand...

Ah, right. Check the capstan and control boards as well. It's been a while but I seem to remember that a huge amount of this machine's electronics consists of cards plugged into each other, so there's a lot of places that could come unplugged.
 
Now we're cooking with gas...

Found the card that was rendering the deck fubar. Meters jumped around for a moment, now they are acting normal. Load tape. Works. All functions seem to do their job.

Getting some speed hicups here and there. Pinch roller seems good though. Needs tension adjustment? Won't run 1 mil tape. Throws the tension way off and tape builds up slack before and after the heads. I've got a pre-recorded roll of RMGI 468 on and that is playing pretty good.

Listening to a jazz concert I recorded with a Crown SASS straight to my Nagra IVs. Sounds wonderful.
 
leddy said:
Now we're cooking with gas...

Getting some speed hicups here and there. Pinch roller seems good though. Needs tension adjustment?
Click to expand...

Does the speed become constant if you push the roller? (By the roller cover, not by the roller itself, of course!)

I'm not sure how you adjust the tension on these. That said, are you running it in large or small reel mode? Have you tried changing it?
 
jpmorris said:
Does the speed become constant if you push the roller? (By the roller cover, not by the roller itself, of course!)

I'm not sure how you adjust the tension on these. That said, are you running it in large or small reel mode? Have you tried changing it?
Click to expand...

I'm running 7" reels and have that selected. Didn't try to push the roller - I'll see though.

On recording, some of the knobs are super funky. I'll need to clean out the pots and such, maybe replace one or two. Other than that and the tension issue, this thing could be ressurected. Recorded on some 3M 996 and it sounded great.

It bugs me that there is a slight bend to the entire frame from the drop, but you won't see it when it's put back together.
 
leddy said:
It bugs me that there is a slight bend to the entire frame from the drop, but you won't see it when it's put back together.
Click to expand...

Yeah, the frame is pretty sturdy. I have no idea how you'd be able to bend it without shattering the wooden casing in the process.

You'll probably want this if you don't have it:
ftp://ftp.studer.ch/Public/Products/Revox/Revox_B77/Revox_B77_MkI-II_Serv.pdf
...the user manual is in the same directory.

Worryingly, I'm not sure it is possible to change the tension in the conventional sense. As I understand it (see the Tape Tension circuit in chapter 7) the tension values are set by fixed resistors and it controls the length of the starting pulse.
 
jpmorris said:
Worryingly, I'm not sure it is possible to change the tension in the conventional sense. As I understand it (see the Tape Tension circuit in chapter 7) the tension values are set by fixed resistors and it controls the length of the starting pulse.
Click to expand...

Tension problem has been isolated to one roll of tape - Maxell UD35B. On thicker tapes it seems to be ok. I'm going to put that issue on the back burner unless its up again.

I'm going to dig into the record issues and see if I can sort those out. Thanks for your help, and huge thanks for the link. I was looking for that this morning and could not find it.

Btw - this one has no wood. It was in a metal case with rack ears. I'm going to make a wood case for it if it's running well.
 
Update -

I think the tension issue may have been related to a brake that slipped out of place, probably when it fell. Got that staightened out I am pretty sure.

I am in love with this deck. The build quality is something to behold. I have all the covers off so I can get a good inspection. The counter belts need to be replaced, those are on order. I need to replace a couple of pots, no big deal. Local supply shop will have those (not Studer/Revox, but they're just pots). Some of the switches were broken off. They still work, but I'd like to replace them with original Studer/Revox ones because they are visible. Having trouble sourcing original parts. The ones on Ebay are stupid expensive - like $69 each.

The heads have very little wear, and the motors and electronics all work. This deck is worth fixing. It's going to be nice. Wish it were the 15 ips model, but 1/2 track 7.5 is just fine with me.
 
Yeah, the switches often get snapped off. Some broadcasting companies do this deliberately. IIRC there was some guy on ebay who could rebuild them if you sent him the originals. UK based, though.

Now, if I only knew why the reel motors and pinch solenoid on mine are not running at full power anymore :(
 
You must log in or register to reply here.
Back
Top