Revox B710-Not my year......

Wilburchubs

Well-Known Member
Hi again,
Well,the Revox collection has given me headaches so far this year,Crumbling pots,failed motors,usual frako smoke bombs and plain good old fashioned frustration!
My B710 mk2 is the latest to take the piss out of me

No counter action,it displays 0000,will "run up" using the button,but wont advance on play/rew/ff.When rewinding or fast forwarding,the deck stops after 3-4 seconds,but,when it reaches the leader,it stops as it should,and will reset the counter to 0000 again.all sensors are showing a IR light (checked using digi camera),changed counter itself from another machine,checked supply voltages on the psu,got +5v etc as per manual.Stumped.........could it be a chip on the main board?:dammit::dammit:
 
Hi Wilburchubs, it shouldn't be so hard to locate the problem considering it is a permanent fault. It can be almost anything between the counter sensor and the microcontroller. The best thing you can do is the good old fault hunting technique: trace the signal from end to end with the oscilloscope probe, while playing a tape, and see where it doesn't make sense any more.

What you call "changed counter itself", that you changed the sensor? Or the display PCB?
 
Hi
Replaced counter pcb,also replaced the RH sensor as this wasnt working.All sensors showing IR light.Havent got a scope,think its time i invested in one though!
 
Replaced counter pcb,
I don't see a "counter" PCB" in the B710, just a "counter display PCB". Is it what you have changed? If so, what was the reason to change it? As far as I understand your description there is no display problem, and moreover there is no sensor on that PCB that might prevent the counter from running.

also replaced the RH sensor as this wasnt working.
What is the RH sensor? Right hub?

Havent got a scope,think its time i invested in
one though!
Indeed, I'm afraid you cannot solve this problem without an oscilloscope.
 
Counter display cb changed,just to eliminate easy options first,
The ir sensor on take up motor was changed as wasn't working,the one that detects the reel hub turning. Which chip on main board drives the counter? The clock is working fine by the way...
 
The counter function is implemented by the main microprocessor, so there can be no fault there or you would have no other functions at all.The count function accumulates pulses from both left and right reel sensors, and either one being rotated is enough to advance the counter - so it cannot be a fault in the IR reel sensors either.

However, reel sensor signals are squared-up on the microprocessor board by comparator IC1 (LM339), Q1 and Q4, and divided-by-four by flip-flop IC2 (4013). If either of these ICs fail or transistors, the counter will not run.
 
Just to make sure...
You have replaced all Frako capacitors (psu included and first of all) as well the light blue Philips electrolytics, right?

I had similarly frustrating issues with a B710MkII and it turned out to be the capacitors on the PSU board.
 
Just to make sure...
I had similarly frustrating issues with a B710MkII and it turned out to be the capacitors on the PSU board.
Don't forget the rectifier bridge(s). Experience has shown me that they fail much more often than capacitors, and can cause all sorts of problems and intermittent failures. It happened to me once on a A710 (same machine as the B710 with balanced ins/outs), and caused unexpected microcontroller resets. And regulators often fail too.

In fact, the usual rule to spot the source of a failure is to study the schematic to locate the signals that may be missing, grab an oscilloscope and track those signals until you find the culprit. Changing at random all the parts that have a bad reputation is usually counterproductive. Only a very small proportion of all the failures I've seen are caused by the usual suspects. Solve the problem first, then change all the Frakos that you want, but don't start by risking to add even more mess.
 
While I agree that replacing components at random is a bad repair practice, in the case of the Revox machines the FRAKO capacitors are confirmed to be causing all sorts of issues, some showing symptoms that can't readily be attibuted to capacitors failing.

OK, the case where the capacitor goes up in white smoke or flames (!) is an obvious tell and hopefully when this happens there's no collateral damage (although there may be).

In my adventure with a B710 I had a seemingly perfectly working deck. All functions worked ok, mechanically and electronically. I could play a blank tape, FF and REW it and even playback. In some cases, seemingly at random, the deck would shut-off momentarily (all lights out and motors stopped) and then it would come up again. Like a quick reboot.

Eventually I recognized that the random instances were not random but moments where the playback level was close to 0dB in the bar graphs. I theorized that this was a moment of higher current consumption (more leds were lit) and something marginal in the psu was causing it.

I replaced the few FRAKO cap on the PSU but nothing changed. I replaced one or two blue Philips capacitors that were left there on the first pass and voila! All symptoms gone.

In that particular case, it's likely that the culprit were the Philips caps. But the FRAKO ones are also known to cause issues, so even if redundant, I feel it's a good practice to eliminate them as a first step, especially when the symptoms don't appear to make sense.

From the description offered by the OP, and my rusty experience in digital electronics, I would suspect filtering capacitors close to the CPU. But, having the experience with the other B710, I would first eliminate the PSU as a cause.
 
Thanks for the help and advice folks,spotted a couple of the dreaded gold's in there,so going to replace,should have tried that first I know.....:yes:
 
Generally the first thing I do is scream RE-CAP!!

But I'm not going to do that any longer and will curb my activities in threads like this.

This is by now general knowledge. Since the device really should be re-capped anyway, regardless of if it's working or not at the time, I'll always suggest starting there.

Almost always this fixes the problem, but on the occasion when it doesn't, then you can troubleshoot with the knowledge that it's NOT caused by something flakey.

Mind you, this to me only applies to devices with frako and philips caps. Anything else, I'll take a measure of the cap health and go from there.
 
In my adventure with a B710 I had a seemingly perfectly working deck. All functions worked ok, mechanically and electronically. I could play a blank tape, FF and REW it and even playback. In some cases, seemingly at random, the deck would shut-off momentarily (all lights out and motors stopped) and then it would come up again. Like a quick reboot.

Eventually I recognized that the random instances were not random but moments where the playback level was close to 0dB in the bar graphs. I theorized that this was a moment of higher current consumption (more leds were lit) and something marginal in the psu was causing it.

I replaced the few FRAKO cap on the PSU but nothing changed. I replaced one or two blue Philips capacitors that were left there on the first pass and voila! All symptoms gone.

That happened to the one I had, too! Boy, was that freaky to troubleshoot!
 
Almost always this fixes the problem, but on the occasion when it doesn't, then you can troubleshoot with the knowledge that it's NOT caused by something flakey.

I've allways preferred to repair the fault first - then recap if need be.....

My house is litterarely filled with decks waiting to be repaired after having being re-capped :)

And the list keep's growing :D
 
Sometimes, recap is the repair needed. Case 1 my B710 mentioned above. Case 2, a "dead-kaputt" (as advertised) B795. Cause: Blown capacitor across the power switch, took with it fuse and faulty PSU capacitors, perhaps causing the shunt capacitor to go.

I have repaired, adjusted and been using dozens of vintage equipment and don't consider recaping them, not just yet. But if it's a Revox and doesn't function properly, it saves time - and perhaps the unit - to replace 5-10 capacitors and go from there. We are not talking about every single electrolytic or tantalum capacitor; just the FRAKO and (based on own experience) large-ish blue Philips ones as well.
 
Sometimes, recap is the repair needed. Case 1 my B710 mentioned above. Case 2, a "dead-kaputt" (as advertised) B795. Cause: Blown capacitor across the power switch, took with it fuse and faulty PSU capacitors, perhaps causing the shunt capacitor to go.

I have repaired, adjusted and been using dozens of vintage equipment and don't consider recaping them, not just yet. But if it's a Revox and doesn't function properly, it saves time - and perhaps the unit - to replace 5-10 capacitors and go from there. We are not talking about every single electrolytic or tantalum capacitor; just the FRAKO and (based on own experience) large-ish blue Philips ones as well.
When I had a problem similar to what you described in your Case 1, it turned out to be completely unrelated to the capacitors, it was caused by a rectifier that had developed intermittent high impedance with time. When I had a problem of non-functioning B790 the culprits were the regulators. In fact I saw a cap-related fault exactly once, it was not on a Revox and the defective cap was neither a Philips nor a Frako. I repaired dozens of decks too, so the sample is comparable to yours in size, but our experiences differ a lot. Of course, if like Tinman says you have decided to change the caps anyway you can always give it a shot. The upside is that you may change the culprit in the process - but that's relying on luck and the chances are scarse. The problem is that it may cause more issues that will only make problem identification even more difficult: solving one problem, then changing the caps and solving one other problem should it happen is vastly easier, that's the rationale of doing things in this order. Not saying that recapping can never solve a problem but it is seldom successful. Recapping as a first attempt to solve an unknown problem only makes sense if you are desperate or don't have the equipment, service manual or training to locate the problem.

As you may have guessed, I don't advise trying to fix a deck if you don't have minimal equipment. An oscilloscope is a bare minimum, otherwise you won't be able to know what happens in your circuit, and then fixing it gets very, very difficult.
 
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Sometimes, recap is the repair needed.

Yep - but after having spend most of my adult life repairing all sorts of electronics, i do prefer to locate the fault first, and then get a view on what may be the best options to make the repaired item last.

Maybe a total recap, maybe not.

Shotgun recapping is not a repair job in my optic.

I prefer to know i actually did the repair needed for making a piece of electronic usable again.

Am i too oldfashioned - maybe - i'm used to bringing things back to factory standard again - not on a wish to basis, but has to ....
(It could be medical or avionics ..... those darned things better be 112%)
 
Shotgun recapping is not a repair job in my optic.
That is very nicely put :thmbsp: I'll just add that in the case of an intermittent fault, it is very common to fool oneself into believing that the problem is solved by replacing the usual suspect, just because it doesn't immediately fail, and send back a machine that is still defective. We've all seen it at least a few times in professional repair shops that strive to do it right, so imagine what a sloppy "just replace all the caps and it will be fine" policy can do.
 
I've allways preferred to repair the fault first - then recap if need be.....

My house is litterarely filled with decks waiting to be repaired after having being re-capped :)

And the list keep's growing :D

You guys make me sound like I just recap EVERYTHING on sight, but that's not at all the case.

I have just learned by experience that FRAKO and often the blue philips caps ARE the problem. So I put a meter across a few and look for shorts, but ultimately I just go ahead and swap them. I ONLY do a full recap after then fixing the original fault if the caps I replaced didn't..... But I would have replaced them ANYWAY.

Only then do I decide if I want to change more caps.

On a lot of old gear I don't change any caps at all, because they just didn't need it.

Revox just seems the most plauged, at least I have yet to come across one that didn't need ANY caps changed.

Geez, guys... :D
 
You guys make me sound like I just recap EVERYTHING on sight, but that's not at all the case.

I have just learned by experience that FRAKO and often the blue philips caps ARE the problem. So I put a meter across a few and look for shorts, but ultimately I just go ahead and swap them. I ONLY do a full recap after then fixing the original fault if the caps I replaced didn't..... But I would have replaced them ANYWAY.

Only then do I decide if I want to change more caps.

On a lot of old gear I don't change any caps at all, because they just didn't need it.

Revox just seems the most plauged, at least I have yet to come across one that didn't need ANY caps changed.

Geez, guys... :D
This is exactly the procedure I use, Mark.:yes:
 
You guys make me sound like I just recap EVERYTHING on sight, but that's not at all the case.

No Marc ! - Not by a longshot are anyone trying to imply you're shotgunning anything !

I have just learned by experience that FRAKO and often the blue philips caps ARE the problem. So I put a meter across a few and look for shorts........

And THAT is the correct way to do things - If a supply rail in - let's say a Revox thingie - is shorted ... Your Ohmmeter says so , you can grab the wire cutter an locate which cap is shorted.

(On old computer memory boards you can use the term "American fault finding : Sit down and wait for maximum smoke ! How? Grab the 5Volt 30Amp supply .... We knew the cupper traces could handle 10 Amps each, but the ceramic packages would act like popcorn - Hehe.. )

Then replace it and your powersupply is up and running again .

Then the magic thoughts appear, like when there is something wrong with the left front bearing on your car : Well - Am i wrong in thinking the Right bearing has done the same mileage ? Yeahh, and i'd be the worlds biggest dirtbag if i don't change that too :D

....., but ultimately I just go ahead and swap them. I ONLY do a full recap after then fixing the original fault if the caps I replaced didn't..... But I would have replaced them ANYWAY.

Well - can't we just agree on this ? I'm the kind of guy who likes to know which one caused the defect :)

Revox just seems the most plauged, at least I have yet to come across one that didn't need ANY caps changed.

It can happen - this one was found to be perfect, had been repaired once back in 1976 - heads changed, capstan shaft changed, minor adjustments done - and then was packed away untill i found it three years ago.

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It is still running fine, i haven't done a thing yet except cleaning heads occasionally.

But as they say at the Ford Garage ..... Ford is a poor car, needs a lot of service, We do see a lot of need for service, funny enough - VolksWagen people has the same impression about WV cars

:D
 

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