Revox PR99 mechanical and electronic service & potential rebuild - my 1st Revox adventure

smurfer77

Super Member
Hi everyone, I'm newish to the tape forum. I bought my first r2r deck <1yr ago. The rebuild is over in the Pioneer RT-707 service & rebuild thread. I've been enjoying that machine a lot since then, collecting some prerecorded tapes, as well as making my own mix tapes and recording FLACs to tape. The performance really surprised me. I now have 2 more RT-707 for playing with and donor units, but now I have an appetite to step up to a higher speed and 2 track deck and see what that sounds like.

After reading around a bit I narrowed it down to the Revox B77/PR99 and the Technics RS series. @GPS16, a well known member on the tape forum, is partial towards Revox and his expertise on the Pioneer rebuilt enabled me to get a lot more out of the experience, so that had me leaning towards Revox even though the Technics machines looks like serious kit, have three speeds and motors that are scary in size. I think the final straw was when I saw some pics of inside of the Revox B77/PR99; those plug-in boards get me a bit excited as I'm tired of desoldering boards on amps (which is whats I'm usually doing, rather than tape decks)!

Finally I saw one in nice cosmetic condition, with pics of heads showing little to no wear, at a reasonable price and it arrived some time ago. I would like to share my story of my first revox, first 2-track & first 15IPS adventure in this thread. Since I am new to tape, I will try to share all of my beginner thoughts along the way so be warned. Lots of details and pics likely to follow (but you guys love that right?!).

So the box arrived with a couple of tears...
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And some interesting packaging
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And if you know the size of the PR99 you can get some feeling for the level of mess I've made here. What you can't see is the pine cone and needles and the other garage/garden debris that I had already cleaned up!
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The heads have no visible wear! I checked the voltage setting and hooked it up, but there wasn't much happening so I opened it up. Looking clean inside!
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Well, some mounts have been bent and this board was not plugged in properly (note to self, check everything is straight (other boards might be affected).
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After fixing that up, we have everything working and transport functioning. Immediately I can see that the right spindle was wobbling. It looked not to be the table, but just the spindle bent. So I used a trick I have used for trueing up bike wheels to find the high spots. Then I banged it into shape with a rubber mallet (removed from the machine to avoid bending the reel table etc) - gentle taps, over a few iterations otherwise you end up chasing your own tail and overcorrecting.
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No more wobble visible at all. Here she is sitting in one of the listening nooks next to the beloved RT-707.
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Honestly, I've been enjoying my aligned RT-707 so much I've not had much drive to get stuck into the PR99 so far. I've made a couple of recordings and checked playback and all seems good but I've not listened enough to decide if there are not any mechanical, alignment, or electronic issues yet. But before getting stuck into the electronics and alignment I figure the machine is old enough to warrant a mechanical service to start with. So we will start with basic mechanical servicing, and make sure everything is running smoothly before we waste our time on alignment/electronics.

So I've gone ahead and ordered some bits and pieces to aid in the mechanical servicing from MonyPM in Australia. We have if I recall correctly:
(1) Toothed Counter Belt
(2) Transport Kit - Tape Guide bearings + Pinch Roller
(3) long black Counter Belt
(4) motor kit
Am i forgetting something? Looks like I have more than that in the pics. Anyway, I also grabbed an original PR99 service manual :).
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Any particular order I should do things in?
 
smufer77. That's a nice looking Revox :) I'm sure you will have it up to (or beyond) specifications soon! While I'm not personally familiar with the PR99, I'm sure it will perform reallly well, and the extra track width (2 vs. 4) will give you more headroom. It will be interesting to watch progress and to ultimately see how you feel the two decks compare head to head.
 
Hi Smurfer,

Now you have had a practice on the 707, you can now have a go at a proper machine!!! I am not being snooty here you will see what I mean as you progress. If you concentrate on the motor service first you will be well on the way to dismantling much of the machine. The Take Up Motor is not too bad to get at but the Supply Motor may need the Power Supply removing to get at it. As you will be on an Electrolytic spree this will not be too bad.

Get some plastic bags of assorted sizes. The Brake Bands need to be treated with special care as do the motor hubs. The brakes will be a pig to get right again if there is any oil or grease finds it's way onto them. The chemical suggested in the manual is no longer used. When the brake hubs are removed, there are shims under them. They have to go back where they were as they set up the reel height.

There are 2 caps that I can definitely think of which are well known Revox Bombs. There is one on the capstan PCB and may be another either on the mains in plug or behind the voltage selector. This will be obvious if the PSU is removed.

Have fun.

GPS16
 
To get the supply side motor out, just unscrew the 2 screws that hold in the plate with the AC plug. Then you can also get to the RIFA that's likely hiding there.
I also just take out the top plate that holds all the jacks. 2 screws, and lay it aside with all wires connected.

Yes, replace ANY Rifa you see NOW. I would also, at minimum, replace the 2 big FRAKO caps in the power supply.

These decks are a joy to service, since EVERYTHING comes apart without a fight.
 
This PR-99 has sat aside for a months in the queue of projects but it's just moved the priority list; I fired it up this week and it lit up for a few seconds then the VU meters and motor snuffed out. There was a bit of a funny smell too.

Here she is: what a beauty. @GPS16 so nice to see the build quality and the nice little studer stamps all over the place :). And the easy of access and removal of boards is something I'm not use to!
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Here, if you squint, you can see F2 is blown.
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F2 is on the regulated power supply and feeds the audio boards and capstan speed control. I inspected all of those boards and 2 thinks stood out. (1) the output amplifier board needs to be gone over completely, as someone has been there before and the soldering is sub-par. (2) Check out this Rifa cap, C1, on the Capstan servo board;
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So i've replaced that Rifa with a WIMA film cap (note: there is another Rifa (0.1uF, 250V) behind the mains panel near the supply reel). I can't find anything else obviously bad, but I don't have the appropriate fuse to move forwards. Today I've put in an order for subs for all current electrolytics (which includes 6 Frako caps). Oh, and I've ordered a bunch of the appropriate fuses 5x20mm, 0.8A... because I guess I may still need extras if something unseen is damaged.
 
Hi Smurfer,

glad to see the PR99 getting some attention. If you were impressed by the RT707 you are going to be blown away by this baby!!!

The Rifa cap in question is part of the snubber network across the motor control circuit for the capstan motor. If this went short, the capstan motor would go full bore with no further damage. It still needed to be dealt with as the cracks in the resin encapsulation is the mode of failure. It was well on the way!!! The small version on the PSU now needs to be replaced. This one is across the mains. If it lets go there will be acrid smoke and severe shattering of your composure! I had one let go in my A700 and it was not nice!!! It was days before the smell went away!!!

From a quick look at the diagrams, there seems to be the capstan servo, sync amp, input amp and the output amp which have a cap near to the supply to pull current.

The Servo and Input Amp would see a resistor off at the same time.

Have you already been around it with a vacuum? It looks remarkably clean!!!

If I was you I would be removing all PCBs and going to town on the Mechanical strip clean and relube. When all the boards are out it is pretty much 4 screws to remove the transformer/PSU to get to the other Rifa and then the motors can be dealt with. There will be no restrictions then. You now have some dead time to get on with the mechanicals whilst you are awaiting electrolytics. From previous posts you have the bearings and PDP65 in your hands!!!

From my experience on a B77 and 2 C270 machines, the crank for the Pinch Roller would benefit removal and clean/relube as well. All 3 in my machines were pretty much running dry!!! Following the maint the operation of the deck was remarkably less clunky!!! Of course that is up to you!!!

Keep us posted!!! I am going to enjoy this one much!!!

Cheers.

GPS16
 
Hi smurfer,

just read the PM. Thought I would reply here to benefit others.

Pulling the audio PCBs is fine for diagnostics purposes. The Osc can be left where it is. The Rec switches set to SAFE pretty much isolate this PCB. The logic PCB is out on it's own for the moment as the 5V supply for it is dropped by a series regulator from the solenoid supply to keep the audio supplies free from noise.

As said before, I would be replacing the other Rifa and doing the Reel Motors whilst I was waiting. Get the circlip pliers out!!!

Cheers.

GPS16
 
Hi smurfer,

just read the PM. Thought I would reply here to benefit others.

Pulling the audio PCBs is fine for diagnostics purposes. The Osc can be left where it is. The Rec switches set to SAFE pretty much isolate this PCB. The logic PCB is out on it's own for the moment as the 5V supply for it is dropped by a series regulator from the solenoid supply to keep the audio supplies free from noise.

As said before, I would be replacing the other Rifa and doing the Reel Motors whilst I was waiting. Get the circlip pliers out!!!

Cheers.

GPS16

Thanks GPS. I will proceed with the remaining Rifa cap and mechanical service while I wait for the caps. Well, I can't find my circlip pliers now. Still, I plan to do the lube job on the weekend then, before the rest of the caps come mid next week. Am looking forward to getting stuck into this!

I had vacuumed it when it arrived, but the PCBs were already super clean. Hopefully this is a good sign for state of the mechanical sides of things too. It IS a good looking unit!
 
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Hi Smurfer,

Tsk Tsk!!! Hope you find the Circlip Pliers soon.

If you have the PCBs out, find which pins are the 0v and 21V and put you DMM on in ohms. See if one measures really low. You never know!!!

Looks like you have been Rifa Bombed and Frako-ed in one hit!!! When you are on the other side of this project, you will have a machine with some serious longevity!!!

Cheers.

GPS16
 
If you have the PCBs out, find which pins are the 0v and 21V and put you DMM on in ohms. See if one measures really low. You never know!!!
GPS16

Will do.; I doubt I'm that lucky, but worth a shot! Still waiting on my circlip pliers to turn up but might as well get started on what I can. Here is the old pinch roller:
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Apparently the setup on the pinch rollers for the PR99 varies a little; mine was top-cap/PTFE/roller/PTFE/metal-shim. The metal shims that came with the new roller were twice as thin (0.25mm) as the old one (0.5mm) so I used two new ones. The PTFE that came with the new roller was also (0.05mm) thinner. I actually had to use a combination of old and new shims to get the new pinch roller sitting right (0.1 - 0.3mm end float). The rollers were the same thickness, but the new roller does not spin as smoothly (there is a slight but visible and audible wobble, and it spins <1s when I give a flick compared to 2-3s for the original part)...am hoping it will break in a bit with wear/use but am not hopefuly; any wobble here has got to hurt wow/flutter. I did of course clean the shaft, but for now did not lubricate it.

Old parts in rear, new in foreground.
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Well, it looks good installed.
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When I was in there I noticed my capstan shaft is shiny where the tape passes. Some folk recommend reconditioning such a shaft (I assume by light sandblasting?). I can't feel any wear 'edge' by finger. Here is a pic. Thoughts?
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Hi Smurfer,

as long as the variation on the pinch roller does not affect the flat surface of the roller it should be fine. The pinch roller may need to be "run in" for a while. The last one fitted to the C270 was a tad tight. A couple of remove, clean, relube and replace cycles were required before it settled down.

The B77 I have just has the PTFE spacers. I kept with the originals as they looked fine.

My next port of call would be the Rifa Bomb on the power supply. I have had the smoke and smell before!!! I would not want it again. The room reeked for days!!! As I have said before, to change the electrolytics and the Rifa, I would remove the power supply as a brick. You will then be able to get at the reel motors un hindered. The reel motor wiring may have been removed anyway to get the supply out (may be the Tape Dump PCB will affect this). The electrolytics on the supply can then be dealt with on the bench. These machines are "jig saws puzzles" and come apart quite easily to be worked on. Even the wiring down to the On/Off Switch is on spade connectors!!! Well it was on the B77!!!

From working on a 707, you are in for a treat.

Keep us posted.

GPS16
 
Hi,

that method is what I would have "cooked up" if left long enough. Agree that an old pinch roller would be kept for this function. I would also take precautions to keep abrasive debris away from the capstan motor bearings. There would be a couple of layers of circular paper with a tight fitting hole over the capstan shaft to create a barrier. There would also be the spout of a Vacuum Cleaner close by to catch the bulk of any loose debris which gets liberated. This would most likely be carborundum.

It also has to be stressed that this is a ROLLING operation and must not rub in any way. The object is to "change" the surface of the shaft and not rub it away to reveal metal beneath. This will reduce the speed of the machine and may also add eccentricity which will result in flutter. We only wish to restore "grip".

Could you get a better close up of the condition of the heads??!!

I might also add that this would be very low on my to do list as I have 2 A700 machines where the capstan shaft is polished!!!

Cheers.

GPS16
 
GPS, I'm thinking the machine has seen some use as the posts pictured below have significant wear - not just shiny but I can feel the 'slot'. You can see the heads here have some wear but not too bad. Am I correct in saying that the posts should wear much slower than the heads, so the base unit must have some significant miles on it but not all parts (such as heads) are original?
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So I pulled the power supply, to get easy access to everything.
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Bye bye Rifa cap. [EDIT: you should use a suitable X1/X2 cap here; pictured is a conventional film cap used temporarily, but the failure here could be unsafe in multiple ways. This issue is not a joke, it is a serious safety issue, and the law in many regions]
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On closer inspection it is starting to go. Not as bad as the other one was, but this is the one across the mains.
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Next capstan motor came out. I too a LOT of pics of which wires go were.
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Here are a couple of pics before cleaning up:
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And in we go!
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I cleaned everything up, removing all of the gunk, and then applied a bit of the PDP65 (if you have earlier type motors you may need different lube). I really took my time giving some gentle love and care and lubing up the felts slowly. It was really pleasurably watching them look like new... and feel like new. The original bearing felt good and spun nicely thankfully - I guess that sintered bronze is tough!
 
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The reel motors were next. They come out quite easily so I took them out even though you don't really have to. I figure I can give them a better clean if I get them out.
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Unlike the capstan motor, the bearings in the reel motors were struggling to move freely. I replaced them with new ones (black ones in above pic, same maker as original). Not much to do here except clean up and replace bearings. I applied just a very very light coat of lube to the shaft.

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While I have the front cover off, I replaced the two belts and lubed everything that I could... this took some time to dismantle and put together a few bits.
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i was careful not to get my grubby fingers on the brake band or drum. I cleaned the break band with alcohol while I was there.
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Next step is the tape guide path. (caps are arriving mid-week; and other job is I still need to trouble shoot F2 blowing, but not expecting dramas with that.).

Also, i did inspect motor caps (the 3 big ones mounted to the front panel) which is easier with everything out. They look and measure ok.
 
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Hi Smurfer,

the posts keep the tape off the heads during fast winds. They are bound to get hammered. They see the extremes of tape tension at high speed during fast wind acceleration periods. They are shoved out of the way by the Pinch Roller Crank during the Play/Record modes.

The Capstan Motor needs the end of the bearing, which is revealed after rotor removal, pretty much being wet with PDP65. This is the part of the bearing which sets the capstan end float. There is a special low friction washer which the small polished collar runs against. If the machine is ran on it's back, the washer/collar carries the full weight of the spinning Rotor/Shaft.

The reel motors are pretty much a strip replace bearings assemble refit. Not much to add really.

Coming along nicely.

GPS16
 
Smurfer77 ... as usual you are doing a really nice job of going through a machine. I'm sure you're going to be really happy with this one once you get it all tweaked out. If I recall, this is a 2 Track machine - right? If so, do you have any plans to get any of the Acoustic Sounds (or other) master tape copies to play on this bad boy?
 
The Capstan Motor needs the end of the bearing, which is revealed after rotor removal, pretty much being wet with PDP65. This is the part of the bearing which sets the capstan end float. There is a special low friction washer which the small polished collar runs against. If the machine is ran on it's back, the washer/collar carries the full weight of the spinning Rotor/Shaft.

Great, because that is the felt I soaked most heavily, partly because it was the easiest to see what I was doing. I did enjoy seeing the low friction washer, kind of blue on one side; I'm sure there is lots of little details I missed, but I made sure to pay attention to the way those curved washers were setup etc.

If I recall, this is a 2 Track machine - right? If so, do you have any plans to get any of the Acoustic Sounds (or other) master tape copies to play on this bad boy?

Soundmig, good to hear from you; was mentioning you and your 707 story the other day! Listening to my 707 now as I write this My unit is a 2-track high-speed (7.5 & 15IPS) machine. I have no plans to buy any of those master tape copies unless they release something I really really really want. I think my next thing will be buying new tape stock from ATR/RMGI as I've run out of patience with the hit & miss NOS also worry about incurring additional tape path wear with old oxide going everywhere. For one of those new master tape copies I can buy quite a bit of new blank tape. So for now it will be vinyl and flac copies and mix tapes. It's not just the expense of those master tape copies that throws me off but the elitism reeking from there websites and email correspondence. But who knows, maybe I will cave is something awesome turns up.

Going for an all day hike today, but woke up very early so I pulled the tape guides. Note that on one side (take-up) you have a fixed rub block instead of a bearing.
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That rub block, and the old bearing are being replaced by new bearings. And lets use some alcohol to clean up that mess at the same time.
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I am still amazed how easily everything comes apart, with 99% of stuff unplugging. I did pull the headblock off, which wasn't entirely necessary, but I wanted to get in there and clean things up, and also lubricate the mechanism for the posts that pull the tape from the head during fast fwd etc, which is hidden under the head block. I didn't go nuts on the alignment... that will come later once I have the machine up and running again. Will try to keep an eye on tension stability with the rub block being replaced by a bearing, but hopefully with the new pinch roller and a nice clean capstan (i may resurface but am reluctant unless I have issues) all should be good and there will be slightly less tape wear with the bearing vs rub block.

Once more pic: it looks like I have a 'habit'. Isoflex PDP65 (left), Mobil DTE-EH (middle), mineral oil (right). The later is my general treatment for hardware like screws etc... just be careful to apply lightly so you don't have it running everywhere.
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I am going to play with that new pinch roller a bit again later and see if I can't reduce the wobble and determine if it's the shaft, roller, or shim setup (definitely not gunked up I cleaned thoroughly). Other than that, I'm done with the mechanical side until I have the machine running and do some fine tuning of guide alignment etc.

Caps are coming in a few more days, so I may get back to troubleshooting the blowing fuse in the meantime, but for now, off for a hike.
 
Hi Smurfer,

the heads are in real good knick!!!! Plenty of wear left in them. Did you notice the mounting holes for the capstan motor. They are drilled offset as discussed!!!

If you want one of the tapes from Acoustic Sounds, make sure the equalisation is correct. The one I have seen have been IEC and not NAB. You may need an extra IEC Reproduce Card for them.

This is class gear, is it not???!!!

Cheers.

GPS16
 
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