Revox B710MKII pressure rollers

[perryinva]

I have a few quick questions mainly for Steerpike and Marc, I guess about the B710MKII: the pressure rollers, the heads, and the capstan motor assembly. After much hair pulling and diagnostics on the pair of B710MKII's I've been working on, one serial number 16xxx, the other 13xxx, which puts them both well below the last revision of the deck, which was around 20xxx, I've got them "working".

The newer deck 16xxx, had been poorly worked on by a previous owner, that replaced all the electrolytics & tantalums with either Nichicon ES, or with what appear to be Wima polypropylenes (up to 4.7uF!). He also replaced any small electrolytic caps with Wima polypropylenes. He used mostly Nichicon ES and FG caps in the "normal" sizes. Nice caps to use, for sure, and many old 4559s were replaced with 2134s, as well. However, he lifted & tore many traces which I have repaired, and it, along with the other deck, which appeared factory untouched, are both now re-capped and socketed.

Both decks have nasty pressure rollers. Both so soft/rotted, that I can easily pull a piece of the rubber off with a finger nail. The 16XXX deck has a like new Sony RPS202-3602A head set, and both pressure rollers are the exact same size, while the 13xxx has a larger take-up roller and smaller supply, and a different looking Sony head set, (some face wear and staining evident, but not bad at all really) but with the exact same model numbers. Everything else on the transports is identical. The larger rollers on both decks are ~9mm in diameter and the smaller is ~8mm. The SM shows two different part numbers for rollers on MKI and 1st Gen MKII for supply (#201) and TU (#202). The last Gen MKII shows the same part number for both two (#203) rollers. Since I have to have all 4 re-rubbered by Terry Witt, I can't think of any reason for not making them all 9mm, can you? Both decks have the exact same symptoms, horrible W&F in the .3-.4% range, with tape speed starting at say 3000Hz, and steadily dropping to around 2930Hz as the take-up spool enlarges. I'm assuming this is a result of the shot rollers. I've rebuilt, cleaned and lubed the one decks capstan motors, applying JUST enough torque to the motor PCB fixing screws, (loctite on the screws) to minimize friction on the capstan shafts. I found out very fast that too much tightening increased the friction on the shafts so much that the motors would not even turn them. It is not obvious to me why, though. Still exhibits the same conditions, which is similar to, though much worse, than the B215s I've worked on, which, once the rollers were re-rubbered, function perfectly and well under spec. Make sense to you? Any hints or tips I need to look out for on the motor rebuilds? Seemed very straightforward to me. All 4 reel motors are strong and quiet, so I just lubed the front bearing on each with PDP-65.

The heads on the newer deck are a bit shorter, about 9mm in height, vs 10mm on the older one, with a different head block mounting design, but such that the gap side is the same distance for stroke when mounted. The newer one had ty-raps at various points on the cables, while the older deck had only one at either connector. Do you think this a normal variation in production changes? Or is it likely that the newer deck had the heads replaced with last gen ones, which requires a few EQ mods? Any ideas? Should I look for a better head set?

Thanks, guys!

 

[perryinva]

Bump...Tinman...Sasi...Steerpike?

 

[dr*audio]

Last I asked, Revox still had the rollers for the newer version. Don't know about the older one.

 

[Tinman]

Ugh...... Well, I know they changed from Sony to Canon heads at some point. I forgot right now from which to which, but it something to do with quality control. The older one should have the split head with the adjustable record azimuth. The newer one is likely a bonded one and may have been replaced once. All the Canon heads were bonded, and are used on all B215's.

The old rollers need to stay the same dimensions because a 9mm roller will rub on the guide next to it on the left capstan. Just have Terry re-do them as is.

As to the capstan motors, the thrust bearings should not be binding when you tighten the screws holding the coil board. Are you sure the shims are all in their correct place on each capstan shaft? There should be a little free play, as the magnetic force of the rotor pushes the capstan into the thrust bearings.

Marc

 

[tapetech]

Both decks have nasty pressure rollers. Both so soft/rotted, that I can easily pull a piece of the rubber off with a finger nail. The 16XXX deck has a like new Sony RPS202-3602A head set, and both pressure rollers are the exact same size, while the 13xxx has a larger take-up roller and smaller supply, and a different looking Sony head set, (some face wear and staining evident, but not bad at all really) but with the exact same model numbers. Everything else on the transports is identical. The larger rollers on both decks are ~9mm in diameter and the smaller is ~8mm. The SM shows two different part numbers for rollers on MKI and 1st Gen MKII for supply (#201) and TU (#202). The last Gen MKII shows the same part number for both two (#203) rollers. Since I have to have all 4 re-rubbered by Terry Witt, I can't think of any reason for not making them all 9mm, can you? Both decks have the exact same symptoms, horrible W&F in the .3-.4% range, with tape speed starting at say 3000Hz, and steadily dropping to around 2930Hz as the take-up spool enlarges. I'm assuming this is a result of the shot rollers. I've rebuilt, cleaned and lubed the one decks capstan motors, applying JUST enough torque to the motor PCB fixing screws, (loctite on the screws) to minimize friction on the capstan shafts. I found out very fast that too much tightening increased the friction on the shafts so much that the motors would not even turn them. It is not obvious to me why, though. Still exhibits the same conditions, which is similar to, though much worse, than the B215s I've worked on, which, once the rollers were re-rubbered, function perfectly and well under spec. Make sense to you? Any hints or tips I need to look out for on the motor rebuilds? Seemed very straightforward to me. All 4 reel motors are strong and quiet, so I just lubed the front bearing on each with PDP-65.

When you took apart the capstan motors, did you see any scoring (wear marks) on the shaft bearing areas? It is a common problem and will cause speed, W&F and inter-capstan tension defects. Polishing the score marks can give one a temporary fix, but it's really new motor time if the shafts are scored. It's always the first thing I check when repairing a Revox/Studer cassette. I wouldn't bother with new rollers (or any repair) if the capstan bearings are scored (worn-out).

The capstan thrust bearing should be adjusted so that you have just a perceptible amount of end-play.

 

[perryinva]

Actually, all the bronze bearing surfaces looked good, as did the chromed parts of the capstan shaft that were in contact with them. New motors is not an option for these decks, as the bearing/capstans are matched sets and the only source (reasonably priced, if even at all available new) is a parts deck. There is adequate clearance between the erase head/tape guide combo for the larger roller onthe MKII, maybe not on a MKI,.. I checked by just slipping the right hand roller over the left hand. The only change from that is now both rollers will contact the capstans at the same time. The other rollers caused the take up first, followed by supply. Terry has them now, so we'll see what the results are when I get them back. The new ones from Revox are the nylon hubbed ones and more expensive than getting the bronze hubbed ones re rubbered by Terry.

I'm assuming the shims (5 stacked brass washers, part number 30) just lay on top of the thrust bearing (#34), on the shaft, witht he flywheel holding them in place. Like I said, I could not figure out why tightening the "U" shaped board holder in place would have any effect at all on the shaft, but it does. Even when I tightened it to what I would call "just tight", there was still fore and aft play, and I could rotate the flywheel, but it was obvious it was binding somewhere as it was stiffer, and when powering up the motor, it wouldn't turn at all. It's pretty hard to put it together wrong. I mean the brass washers are the last thing to just slip over the capstan shaft and presses against the small black (o-ring?) base of the fly wheel. Right? They provide clearance take up between the thrust bearing (the one that goes into the notches) and the flywheel. I checked for fore and aft play (about 0.25 to 0.5mm) before I disassembled, cleaned and relubed it and the clearance is the same, just the binding issue if tightened to much.

Marc is exactly correct on the Sony heads. One set has the record head bonded to the play head, the other has potted azimuth adjustment screws for each head. So this was a normal change in Sony manufacturing, not some PO just swapping heads. Good to know.

 

[Alex Nikitin]

Marc is exactly correct on the Sony heads. One set has the record head bonded to the play head, the other has potted azimuth adjustment screws for each head. So this was a normal change in Sony manufacturing, not some PO just swapping heads. Good to know.

If heads are bonded type it is not Sony, it is Canon sendust heads (unless these are not original but a later replacement). Some of B-710mkII and all B-215 and H-1 use Canon heads.

Alex

 

[perryinva]

They have the same Sony part number on back, I'll send pics when I get a chance!

 

[steerpike2]

The reel motors - when their bronze bush bearings are worn - can also cause extreme back tension that causes W&F even if the the pinch rollers are good.

I never figured out why these decks use quite large back tension anyway - with dual capstans, the back tension ought to be largely irrelevant.

The position of the leaf spring that holds the rotor on the capstan shaft also affects flutter. It can go into the shaft in several angular positions - and there is no obvious advantage to any of them. But it does have a small effect according to the Revox literature.

I should have a new (to me anyway) B710-II tomorrow, so I too will be going through your pain shortly!

 

[Alex Nikitin]

They have the same Sony part number on back, I'll send pics when I get a chance!

Perry, please do send pictures. Most likely the second head (the bonded type) is mislabelled. The part number you've quoted - RPS202-3602A - is a discrete sendust-ferrite type with a separate recording head azimuth adjustment screw, used in the Sony TC-K555, TC-K777, TC-FX1010 and few other decks.

Cheers

Alex

 

[perryinva]

The reel motors - when their bronze bush bearings are worn - can also cause extreme back tension that causes W&F even if the the pinch rollers are good.

I never figured out why these decks use quite large back tension anyway - with dual capstans, the back tension ought to be largely irrelevant.

The position of the leaf spring that holds the rotor on the capstan shaft also affects flutter. It can go into the shaft in several angular positions - and there is no obvious advantage to any of them. But it does have a small effect according to the Revox literature.

I should have a new (to me anyway) B710-II tomorrow, so I too will be going through your pain shortly!

Great news then Steerpike! Pay VERY careful attention to the dis-assembly of the flywheel/shaft/thrust bearing/ spacers and the apparant tension of the motor board clamp. Those spacer washers all stick together and are very very thin. Maybe there is a different way to assemble them that I am missing. I will try rotating the flywheel spring around to the various stop points and measure W&F for each, as that is very easy. I figured there HAD to be a reason for all the spaced indents on the flywheel, so that explains a lot. Let me know what your seral number is..there are a ton of revisions on the MarkII depending on SN.

The reel motors on both of mine are in excellt shape. Fast smooth powerful in both directions, so I'm led to believe there are not too many hours on either deck. There is no disceranble play in any bearing. Both mine have the compression collar that clamps to the reel motor via compression of a spider spring, like the MKI, by the 3 screws in the reel table. Crazy complex way of doing it, but it works, and doesn't require a thin spanner to remove like on the B215 or last rev of the B710.

I should have my rollers back from Terry next week, and I'll let you know what happens on both of them.

Naturally, a total recap was absolutely required, with the blue Philips and many Frakos way way out of spec. If you find any odd behaviour, like no sound, as if mute is in when it shouldn't, there is an SN7406 inverting buffer chip in the logic, and two of the 6 gates on one were non-functional, so the inverse of what was supposed to happen, was happening! I pulled the chip from the other deck (they come socketed) and it was obvious it was a replacement chip as well, as some of the legs on the chip had solder residue on them. So apparantly this is a sensitive or oft failed chip. At $1.60 each I bought 6 of them, just in case.

I didn't notice excessive back tension on the MKIIs, they were about the same as the B215s, 8 gm-cm. But I CAN verify that head alignment has a huge effect on W&F. I recently did a complete overhaul for a friend of a B215, and couldn't understand why the W&F were so much higher than my B215s, yet the speed was 3 Hz higher for a 3000Hz W&F tape, but it sounded fine to me. When I checked the tilt/head height/azimuth alignment, it was not optimal based on my test tapes and gauge, so I tweaked it in, using my M-300 gauge, and my Nak cal tapes, as the channel centers were clearly way off. After about an hour of fiddling back and forth with all 3 screws, I finally dialed in all the positions as best it could get, and was amazed to find that the W&F had dropped .04%, so it was now in the same league as my decks (between .03 and .04% avg wtd), and the speed now matched mine as well.

BTW, I just recapped a late serial number B225, I have a question for you in the CD section.

 

[steerpike2]

I have my second B710 Mark-2 now. It is in very good condition cosmetically - well looked after, cassette cover present, wired remote control box and an untouched ReVox cleaning kit and users manual in plastic too. $110 for it which I think is good value (and he threw in two 10.5" empty reels and 2 NAB hub adapters - I'd probably pay $100 for those alone some places)

I'll have to check the S/N. I haven't opened it up yet.

Strangely it has the erase-head-on-the-left-of-the-left-pinchroller headblock; I though this arrangement was dropped early on and would only be found in Mk-1 versions.
It does have the 'head lift' red button - I'm not sure when that was introduced.

I was rather hoping one of the Rifas or Frakos would blow up when the owner showed me the machine - so I could get a better deal! But it worked well almost immediately - it took a few false starts before the take up reel motor un-gummed itself after decades of storage.

The reel motor shafts have a very little side/side & up/down play - but this I have on all 3 of my ReVoxes so I'm begining to think that is how they always were. Capstan shafts are always rock-solid.

On chips: Studer & ReVox had a habit of using specially selected semiconductors in certain circuits - that exceed the 'normal' tolerances of the chip specifications. Though I'm not aware of any in the cassette decks needing to be 'special', some of their cirrcuits only work reliably with specific brands of chips, or tested ones.

 

[perryinva]

Do you mean the tape guide is closer to the pressure roller than the erase head? On both of mine the guide is to the far left. I wasn't aware that the MKI had a different setup. $110 is an excellent price for a working one! I Paid $220-230 for mine and neither really "worked"..they just basically functioned, sort of.

Where the heck is the head lift button located? On later B215s, the Loop button peforms a head lift, it was a rev to the controller chip. Models with SNs under ~12000 do not have it. Very helpful to have for cleaning. The wired remote was a VERY nice bonus! I keep looking for some B202 modules with no luck.

I'm not surprised about Studer/Revox using special chips. They tended to push for high voltage sources for some reason in every piece I've worked on, like 14VDC for the 4066s, and used the non standard quad 4136s as a primary op amp in the B285. The specs on a 4136 are horrible compared to even a 2134. I may try a 4562 there as well. So if I go back into my B285 and swap out the 4136s, the old 201s, and the 14051s, and 4066s with newer, lower noise/distortion and lower capacitanc and resistance versions, I'll let you know how it goes. There is a drop in upgrade for the 201As (201B) in the B285 that is like 1/2 the resistance and 1/4 the switching time, with better linearity as well. Maxim makes a high voltage (17VDC) version of the 4066 that I'm going to try as well.

 

[steerpike2]

Do you mean the tape guide is closer to the pressure roller than the erase head? On both of mine the guide is to the far left. I wasn't aware that the MKI had a different setup.

This is my B215; my other B710 is the same headblock.
http://www.uploads.co.za/files/f29hu0it265dguvdmfey.jpg
My 'new' 710 has the erase head to the left of the left pinch roller, and that white nylon guide is absent, and the pinch roller is necessarily of smaller diameter. From the literature I believed this was an early design change. But there seems to be so much mixing of the upgrades that you can't
match a change directly to a specific date.

Where the heck is the head lift button located? On later B215s, the Loop button peforms a head lift, it was a rev to the controller chip. Models with SNs under ~12000 do not have it. Very helpful to have for cleaning.

The red location 'clear' button lift the heads on later 710s. It is done by an add-on sub pcb to the cpu board that wasn't present in the early models but can be retro-fitted. On the new 710 the button is also labeled 'lift' so it isn't a retro-fit. I don't think there is an easy mod to add the function to an early B215 besides changing the firmware, though it can certainly be added if you have to have it, by adding some AND/OR gates to the pushbutton wiring.

used the non standard quad 4136s as a primary op amp in the B285. The specs on a 4136 are horrible compared to even a 2134. I may try a 4562 there as well.

I haven't paid much attention to the B285 pre. I was thinking of the B250 which is full of NE5532, as is the PR99 - I just assumed similar circuits.

I've been working on some assembler for a PIC microcontroller to perform the job of the B202. Mostly beause I now have so many devices that the two-turntable + two-tape-deck limit of the B202 is overtaxed!
When it is eventually done I'll make it public. The Nokia/ITT protocol that all ReVox stuff of that time uses is susceptible to random triggering - I'm hoping my software is going to be better at sorting out the background IR noise.

 

[perryinva]

I was not aware that the later MKIIs went with the B215 style rollers and tape guide!. Are you sure that is original? Certainly the part numbers for the rollers are not the same. Like I mentioned, you can use the larger MKII rollers on both sides of both mine, certainly not the large B215 style ones. Now I'm very curious as to the serial number! Yes the amps and switches used in the B285 are not my favorites.

I assume you know about the pricey "B212" on revox.de ...I would be very interested in your project if it is less $ than his. It would be cool to have only one sensor interconnected to the other gear instead of a B202 per. Someday I hope to get a B780 to fix up!

 

[steerpike2]

I was not aware that the later MKIIs went with the B215 style rollers and tape guide!. Are you sure that is original?

Yes, original. And both types are discussed in the (paper) B710 service manual I have.
My 'old' B710 and B215 headblocks are identical - although the other parts of the transport differ.

I assume you know about the pricey "B212" on revox.de ...I would be very interested in your project if it is less $ than his. It would be cool to have only one sensor interconnected to the other gear instead of a B202 per. Someday I hope to get a B780 to fix up!

I have seen the German B212 - which doesn't really do all I want anyway. The main part of the 'work' is decoding the IR protocol. Another hiccup is that modern IR recever ICs ignore the reVox protocol beause it uses a 115kHz carrier and the current fashion is 38khz.

There was also an IR receiver board that was intended to be installed inside the B710 - removing the need for a B202.

There is also the option of one day interpreting the data sent back by products like the B226 & B215 - I.e., requesting things like status and counter info.
I'm not sure I have much use for that kind of data - but it is rather fun to see it come up on the B250 display when you ask for it!

I'll go get my 'new' B710 out the car now & check its serial number!

 

[steerpike2]

Odd. My 'new' 710 has little pinch rollers, yet it's a Mark-2. Serial number is 11744, mechanism (and boards) dated March 1982. It doesn't have the back-tension and headlift piggy-back board - but still performs the headlift function - so it must be a modified processor board that I haven't met before.

I've found it's not difficult to turn pinch rollers down in diameter on a lathe, so if I can't get suitable ones locally I will just re-size ones that I can get. I also mentioned somewhere (don't know which thread) that you can use a slice of Tygon synthetic tubing as a pinch roller IF the bronze bushes are still good.

Various service updates and improvements for the cassette decks are outlined here:
ftp://ftp.studer.ch/Public/Products/Recording_Analog/A710/Technical_Info/SI_106-87_D-E_A710_Mod.pdf

 

[steerpike2]

These pics show exactly how I got it. It's dirty, but no signs of abuse. The switches and pots are all scratchy - but that is to be expected.

(Also got a B795 DD-TT from the same guy for the same price; how I was hoping he'd have a B750, but alas not. Why is the amplifier so rare? )

 

[perryinva]

Both mine have little pinch rollers. Just two different combos. Are your supply and take up the same size (9mm), or is the supply smaller (8mm). See my original post..both my serial numbers are higher than your "new" one. Whats the SN of your "old" one? I'll check heafd lift on mine then, they should have it. I saw the IR board and conections in the SM, and the space for it is obviouse, to the left of the meters. But it has a propriotary chip set in it, so making one is pretty much out. Thanks for the mod pdf..I missed it somehow!

 

[steerpike2]

Whats the SN of your "old" one?

It's a mission to get it out of its cabinet, so that discovery will have to wait a while.
Now that I think about it, I believe it may have come from a studio - yet the heads were in remarkably good condition. So it seems it might have been subjected to all the bells & whistles upgrades as they came along - including a new headblock.

I saw the IR board and conections in the SM, and the space for it is obviouse, to the left of the meters. But it has a propriotary chip set in it, so making one is pretty much out.

It's a mask programmed Philips microcontroller. That chip would have almost identical firmware to that in the B202; so my project will work for both applications. By the way, the real B202 doesn't implement the 'monitor' function from the IR handset.