Revox B790, help needed!

[henkuk]

Right, I had the table home and been looking at what I want and needs to be done.

From previous posts and some PM messaging, here is where I am. Please tell me what I do wrong, what you would do first and what you would not worry about!

1/ Channel imbalance - Initially with eh AKG cart fitted by the seller, I had a strong right and weaker left channel. Swapping this around for an AT this turned around, but all cartridge leads are correct and fitted to the same contact pins as on the AKG. Connections are solid on the tonearm. The difference on either setup are not so that you fall off your chair but definately noticeable.

What can this be? From a PM from Grainger, he reckons it's not cart allignemt, ie twisted in relation to the groove.

If so, what can it be if all connections are correct?

How do I go about finding out what is causing the issue.

2/ The AT sits slight further forward, by about 1 or 2 mm compared to the AKG. How do I adjust this so that the stylus hits the groove in a line from the spindle that is indeed stil linear tracking?

Nothing on the cart mount seems to allow for this. The manual appears to suggest the arm but I can not find the adjust to move that arm completely back or forth in relation to the table spindle centre.

I am really stuck and try to make various adjustments at the time.
I think I might have bitten a little more off then I can chew here in trying to get it right. Please help me on the way with some clear and simple steps for me to start checking, realligning and setting up the deck properly. I am not fussy on which cart to use though the AKG seems more even in tonal balance. The AT is new with less then 20hrs on it so that might contribute to the imbalance, maybe? No breakin?

Please gents, Steerpike, SaSi, Grainger, Peter, your skills and expertise are needed!!

Many thanks,

- Henk

 

[guiller]

As a starter, you can find the manual here: ftp://ftp.studer.ch/Public/Products/Revox/Revox_B790/

 

[Robie]

I don't really have an answer but hope you can solve this problem.

Isn't there some way to mount the cartridge more forward and backward in its mount? The Cartridge mounting kit for the Revox Linatrack arm contains a clear plastic template that tells you when the stylus tip is optimally located (both as to height, fore and aft and side to side) so it seems likely that that there would be some type of adjustment or mounting flexibility.

BTW, I have a older Grado 8MR mounted on my non functional B795.

It is likely that others with more experience with Revox will chime in. Good Luck.

 

[henkuk]

Stripped the deck down and removed all parts from the platter. Tomorrow or later this week I will remove the paints and polish this to see if that comes out nicely.

Had a closer look at the tonearm assembly and all moving parts just to understand cartridge allignment better. Can't see anything that allows the cartridge to slip back or forth. Also, from earlier posts some of you suggest it's not cartridge allignment.

Once I have stripped the deck I will go over the process of again setting up the table, alligning the cartridge and see what we get this time round.

Any thoughts or ideas some of you might have regarding this are most welcome.
Cheers,

- Henk

 

[boyerd001]

Henkuk -

PM me with your email address and I will send you a compressed RAR package of all the info you need. I've help SaSi and others here before - do a search on my name for some of this info.

The ReVox cartridge alignment kit is USELESS for all purposes except the extra tonearm weights and spacers it furnishes - these you can fabricate if needed. The cartridge's stylus is adjusted to the radial line from the turntable's spindle by rotating the eccentric at the tonearm's rotating base - it is this eccentric which determines where the arm "locks" when rotated over the record. This alignment procedure is explained in the Service Manual in sections 2.1.3 and 2.1.4.

Dale

P.S.

Here are a couple of documents I've written that may be of help to you. The "Mechanical" adjustment doc is what you want right now. The "Electrical" doc has to do with tracking adjustments made via the pots on the Tonearm PCB and may or may not be of interest to you. The Revox brochure referred to in the "Mechanical" doc - "Installing or Changing a Cartridge" can be downloaded from:

http://www.revox.name/

Go to the 7th link down, on the new page that appears, scroll down and then choose the Linatrack Tonearm document. The copy I have is too big to upload to the forum message pages.

Again, hope this helps,

Dale

 

[henkuk]

Thanks all that wrote in so far and particularly Dale who send a pile of bed time reading my way.

Since I had a few days off, I obviously spend this trying to work out various bits on the table that I thought were off or needed attention.
In my usual style I disassembled the whole thing as I was getting frustrated and also wanted to clean the platter nextel finish and maybe even strip this.

Here is the score of my adventure so far. I decided to post this for a couple of reasons:
1/ There might people out there who match me in being gung ho and exceed me in stupidity or lack of organisation (not likely). Let this be your warning.....
2/ It might have some tips for some folks who just seen a table and think, hmm not touching that, be more problems then it's worth. Believe, it was a learning curve but worth it and I love it now!

So here goes, preceeded with the warning that my skills are limited, very limited even.

1/ Nextel finish, cleaning this turned out to be a nightmare and paint starting to get flaky in one area and had clear overuse in others coming out very thin. So I thought, strip it.

Using chemical stripper and a brush to remove the stripper under hot water. The hot water scares the paint so to say and will cause it to come off easily after letting it sit with the stripper for about 30min.

Do not use sharp tools on the platter as the metal is quite soft relatively speaking and scratches easily which in turn required more and more sanding.
To much sanding is not good either as it will reveal the bottom frame molding/welding lines to come through, go easy....

You might want to polish off with some fine fluid jeweller/fine metal polish, something I still need to do.

Do not use WD40 on the stripped platter, it causes it to stain and you will have black hands for a while. Don't ask how I found this out.

I have done this to a PL12D as well and letting the surface breath for a day or two will actually improve the look.

2/ I had a minor scraping noise coming from the motor/platter assembly but could not pinpoint where from and how it was caused. I thought it was initially just the motor needing to be excercised for a bit as it seemed to disappear at times but after reassembly it reappeared and was causing the last speed digit to fluctuate quite a bit, not even staying on 33.33 steady for longer then 2 seconds. Worse then before......

It took me a while to figure out how the motor/rotor and bearing/bearing cup are designed and constructed. What I did notice is the usual Swiss/German heavy duty engineering. Much like the deck as a whole, not pretty but build to last.

When picking the motor up yesterday I sat there looking like a fool for 10 seconds, looked back at the motor and it hit me, the copper/brass bottom part is the bearing cup and the spindle coming out of the rotor is sitting on the cup.
Cleaned the cup and guess what I found, a bit of copper wire strand, solidly lodged in the bearing cup. Removed this, two drops of light machine oil and put it back together.

This might make it silent or not as the case would be for me. When spinning the first record, behavior was weird, speed fluctuating all over the place and definate scraping noises from the motor/platter combo.

Took the motor off again and spinning it by hand, I found it was the rotor scraping over the magnet internally. Since this is fixed in a way that only a crowbar could force it apart I sat there scratching my head for a minute and then did the following to force the rotor upwards on the spindle by a fraction.

Insert all three allen key bolts in the motor holes, and handtighten these against the rotor, you can still turn the rotor but it will scrape against the bolts. Then tighten each bolt in turn with a quarter turn until you actually feel that light force is needed. Do two more quarters turns per bolts and then release all the bolts, quarter turn per bolts to ensure even loosening, same as you tightened them.

When taking the motor off the platter, there are a bunch of spacers that will drop on the floor and will decide to get lost for a bit, at least until you have put it back together and find it's not quite perfect.
You will repeat this a few more times and then the spacers will reappear as if by magic.

Take this all apart, on top of an old towel as even if the spacers decide to do a runner, they can't and will stay on the towel.
To safe you all this hassle, this is what you should have as soon as you take the motor off. 3 nuts (allen key), three locking spacers in black that sit between the nut and base.

You will also have 6 copper spacers, 2 for each nut, these sit between the motor and the base to raise the motor to the right height.
These spacers have two different thicknesses. You will need one of each thickness per bolt, ie thin and thick per bolt, 3 sets of two.

To put the motor back again, you will have to drop all spacers, get very annoyed and just when you had enough of trying to get the spacers to stay on the platter when lowering to motor in this you might have the following idea.
Get a large roll of tape, put the motor upside down onto this, spindle down to the table. Tape the wires to the middle of the bearing cup so that they stay out of the way.
Get three matches and insert these in the bolt holes, head down.
Put the spacers (2 per match, both thickness) around each match.
Get the platter, turn it upside down and lower it very carefully on the motor, guiding each match through each bolt hole.
Hold this down with intermediate force, get the first bolt ensuring the spacer is one and remove the first match.
Check the hole is clear and insert and fasten the bolt lightly. Not too tight, you need room to move the platter to allign the other two as well.

Leftover issues:
As far as the imbalance in sound, there is still a very minor difference with the AKG cart but it is not as pronounced as before.
This might be due to the cleaning of the PCB's and connectors internally.
I still need to doublecheck tracking force and recheck and maybe correct the allignment, that is for this weekend.
That might take care of the problem altogether.

Cosmetics still do be done:
I still need to put the side cheeks back on.
Base needs to be painted gloss black.
Need to match the Revox grey so that the control panel can be touched up.
Platter needs final polish.

All in all, not bad for one day after a frustrating Sunday evening.

Cheers,

- Henk

 

[henkuk]

Pic

Work done so far...

 

[visto]

Hi,

I decided to put my question about my Revox B790 problem.
Here is the story :

-All electrolyts replaced
-cleaning and lubricating - done
-new stylus for factory cartridge in place

but... I have still following issues :
-platter auto stop function is not working - it continue to rotate after TT has been stopped...
-it takes about 5 - 7 seconds to lock the speed.... I think it is a bit too long.... Once it is locked i.e at 33.33 rpm speed is quite stable, popping up to 33.34 ocasionally.
-arm motor is a bit noisy when it is coming back to start position or when FF, REV button is pressed - during LP plaiying it is O.K

BIG thanks for any advise !!

 

[steerpike2]

I need to repaint my newly-bought B795 now. Today I washed it (just the plastic base) in mild soap and water, and it has turned whitish in parts. Not a disaster since it was very very badly scratched, dirty and sticky.

Methyl alcohol dissolves Nextel as easily as hot water dissolves sugar!

 

[visto]

Hi,

I decided to put my question about my Revox B790 problem.
Here is the story :

-All electrolyts replaced
-cleaning and lubricating - done
-new stylus for factory cartridge in place

but... I have still following issues :
-platter auto stop function is not working - it continue to rotate after TT has been stopped...
-it takes about 5 - 7 seconds to lock the speed.... I think it is a bit too long.... Once it is locked i.e at 33.33 rpm speed is quite stable, popping up to 33.34 ocasionally.
-arm motor is a bit noisy when it is coming back to start position or when FF, REV button is pressed - during LP plaiying it is O.K

BIG thanks for any advise !!

is this b790 and b975 close enough so i can use b975 as reference..?
searching forum and web i still got no answer what it could be with my TT...

THX

 

[Pio1980]

The exact location, number, and thickness of the washers under each location for the arm pillar base and motor mount is absolutely critical for proper relative alignment of the arm gantry and platter. Mix them up and you must start set-up from the absolute beginning of the process, EXCEPT for the B795 with the composite baseplate which sags out of alignment in time with the weight of motor and platter and MUST be checked and re-aligned during renovation. While you do not have this version the thread may be useful for full understanding of the alignment relationships.
Pertinent thread here; http://www.audiokarma.org/forums/showthread.php?t=403638
Pertinent post for procedure here; http://www.audiokarma.org/forums/showpost.php?p=5155782&postcount=43

 

[Pio1980]

Originally Posted by visto View Post
Hi,

I decided to put my question about my Revox B790 problem.
Here is the story :

-All electrolyts replaced
-cleaning and lubricating - done
-new stylus for factory cartridge in place

but... I have still following issues :
-platter auto stop function is not working - it continue to rotate after TT has been stopped...
-it takes about 5 - 7 seconds to lock the speed.... I think it is a bit too long.... Once it is locked i.e at 33.33 rpm speed is quite stable, popping up to 33.34 ocasionally.
-arm motor is a bit noisy when it is coming back to start position or when FF, REV button is pressed - during LP plaiying it is O.K

BIG thanks for any advise !!

is this b790 and b975 close enough so i can use b975 as reference..?
searching forum and web i still got no answer what it could be with my TT...

THX

Other than the general operating system design being similar, the circuit details are different for the two models.
For the electronic problems ensure that all the recommended power supply suggestions for renovation are followed and that the power out is correct after checking all the interconnecting plugs and sockets, working them with contact cleaner. I hesitate to suggest working the trimpots on the boards after applying carbon pot cleaner and then returning them to their exact prior location as their adjustment can be critical for proper operation and returning them without instrumentation can be chancy.
For the tracking motor noise try cleaning the carriage rails with WD-40 on a bit of lint free cloth, carefully lube motor shaft under pulley with a drop of light machine oil. Otherwise motor/gear running noise may be audible when in the 'fast' transit modes and is of no concern if not audible during play.

 

[henkuk]

I am out of the Revox game.
On mine, motor burned out and some electronics gave the ghost.

Instead of trying to fix this, I took the coward way out and sold the lot to a local guy who needed parts...

Been running a Dual CS 5000 in it's place for about 2 yrs now, absolutely flawless.
The Revox sounds better but the temperamental nature did not combine with my lack of skills.

 

[Pio1980]

I am out of the Revox game.
On mine, motor burned out and some electronics gave the ghost.

Instead of trying to fix this, I took the coward way out and sold the lot to a local guy who needed parts...

Been running a Dual CS 5000 in it's place for about 2 yrs now, absolutely flawless.
The Revox sounds better but the temperamental nature did not combine with my lack of skills.

Mine went back to the PO as per a pre-agreement after the alignment renovations were done. I have a number of other varied LTs to play with.

 

[jlb2]

is this b790 and b975 close enough so i can use b975 as reference..?

Hi, no need to use the B795 as reference for your B790, the service manual is available from the studer site: ftp://ftp.studer.ch/Public/Products/Revox/Revox_B790/. Except for very early B790s they are the exact same tonearm (well, except for the looks) and the electronics are practically the same too - the B795 being the same circuit as the late B790. OTOH they constantly improved their service manuals so it is a good idea to refer to the B291 manual which has essentially the same adjustment procedure - and also the same tonearm, only better explained.

-All electrolyts replaced
-cleaning and lubricating - done
-new stylus for factory cartridge in place

I don't get the "lubricating" bit. I've never seen a B790 needing lubrication. Can you elaborate on what you did?

-platter auto stop function is not working - it continue to rotate after TT has been stopped...

How skilled and equipped are you to check the electronic circuits? The B790 motor is stopped by a reversal of the driving current. You will need to check the power voltage (especially the +24V) and, if they are ok, the waveforms of the signals commanding the brake (see section 5.1.2 on page 5-2, waveforms on page 7-12 and schematic on page 7-13 of the service manual.

-it takes about 5 - 7 seconds to lock the speed.... I think it is a bit too long.... Once it is locked i.e at 33.33 rpm speed is quite stable, popping up to 33.34 ocasionally

That might confirm that the +24V voltage is too low.

-arm motor is a bit noisy when it is coming back to start position or when FF, REV button is pressed - during LP plaiying it is O.K

It is perfectly normal for the motor to make noise in fast speed. Unless it is also noisy when playing a record, don't bother. If you have swept the rails with WD40 as Pio said, my advice is to clean them thoroughly with isopropyl alcohol immediately after: the WD40 can dissolve seized lubricant or dirt, which is good, but I have constantly observed that it too seizes after a while and causes the exact problems that you wanted to avoid. These rails are designed to be oil-free.

 

[perryinva]

I agree. I would never leave any residual WD-40 on anything I cared about. I never use the stuff on anything except outside hinges, and even those, I hit with grease afterwards.

As for the rails,, when the self lubricating plastic was new, clean was the way to go. But over this many years, it really depends on the condition of the plastic at the chrome rail/slider interface, & often, it needs help, but really, a single drop of sewing machine oil, rubbed over the rail with a lint free cloth, is all that is needed to significantly reduce friction, and the sticking that goes with it during movement. Both my B791s rails were replete with hardened deposits from who knows what the PO's used. Mine have been perfect for a few years now, after cleaning and doing this, once. That super thin layer of synthetic oil never goes away, and doesn't attract any dust, covered the way they are.

 

[visto]

Hi, no need to use the B795 as reference for your B790, the service manual is available from the studer site: ftp://ftp.studer.ch/Public/Products/Revox/Revox_B790/. Except for very early B790s they are the exact same tonearm (well, except for the looks) and the electronics are practically the same too - the B795 being the same circuit as the late B790. OTOH they constantly improved their service manuals so it is a good idea to refer to the B291 manual which has essentially the same adjustment procedure - and also the same tonearm, only better explained.


I don't get the "lubricating" bit. I've never seen a B790 needing lubrication. Can you elaborate on wha

How skilled and equipped are you to check the electronic circuits? The B790 motor is stopped by a reversal of the driving current. You will need to check the power voltage (especially the +24V) and, if they are ok, the waveforms of the signals commanding the brake (see section 5.1.2 on page 5-2, waveforms on page 7-12 and schematic on page 7-13 of the service manual.


That might confirm that the +24V voltage is too low.


It is perfectly normal for the motor to make noise in fast speed. Unless it is also noisy when playing a record, don't bother. If you have swept the rails with WD40 as Pio said, my advice is to clean them thoroughly with isopropyl alcohol immediately after: the WD40 can dissolve seized lubricant or dirt, which is good, but I have constantly observed that it too seizes after a while and causes the exact problems that you wanted to avoid. These rails are designed to be oil-free.

Thanks for your post ! pls see below my answers..

I did simple clean up and lubrication of two tonearm rails...
i do not use WD 40 ... it was light oil used for cleaning first and then lubricating...
i'm O.K with all measurements (i have basic tools and can get simple oscilloscope when needed), can read simple schematics - but not understand in full how the circuit works ....

Would be great if you can support me with your know how...... from my side should not be a problem to use your advise and safely do what's necessary..

in the mean time i clean all connectors with deoxi - did not perform any measurements so far ... where to start...?

 

[jlb2]

Thanks for your post ! pls see below my answers..

I did simple clean up and lubrication of two tonearm rails...
i do not use WD 40 ... it was light oil used for cleaning first and then lubricating...

That's good. What I meant is that there is normally nothing to relube on the Revox turntables. Even the motor is as lubrication-free as advertised (good job Revox :thmbsp: ). So I would check what you have lubricated for oil spills that could cause problems and especially electrical shorts - but don't dismantle the motor!

i'm O.K with all measurements (i have basic tools and can get simple oscilloscope when needed), can read simple schematics - but not understand in full how the circuit works ....

That will do for a start First off, measure the +24V voltage on the supply PCB to make sure it is 24V. Rectifier bridge and regulator failures are not uncommon after all these years, and have a bad habit of showing up after you replaced things. Measure with the motor off, then on if ok. If ok, locate an accessible +24V point on the motor PCB and check again. While you have the turntable open, double-check the PCBs to make sure that all the new caps are mounted with the correct polarity, and that the solders are clean: no cold solders? No solder bridge? This kind of problem happens much more often that I'm willing to admit :worried:

If no problem there, things will get trickier and you will need that oscilloscope - and probably a spare day too.

Would be great if you can support me with your know how...... from my side should not be a problem to use your advise and safely do what's necessary..

No problem, I'm sure the problem can't be that bad.

in the mean time i clean all connectors with deoxi

It's most probably not the origin of the problem, but it can't hurt :thmbsp:

 

[visto]

That's good. What I meant is that there is normally nothing to relube on the Revox turntables. Even the motor is as lubrication-free as advertised (good job Revox :thmbsp: ). So I would check what you have lubricated for oil spills that could cause problems and especially electrical shorts - but don't dismantle the motor!


That will do for a start First off, measure the +24V voltage on the supply PCB to make sure it is 24V. Rectifier bridge and regulator failures are not uncommon after all these years, and have a bad habit of showing up after you replaced things. Measure with the motor off, then on if ok. If ok, locate an accessible +24V point on the motor PCB and check again. While you have the turntable open, double-check the PCBs to make sure that all the new caps are mounted with the correct polarity, and that the solders are clean: no cold solders? No solder bridge? This kind of problem happens much more often that I'm willing to admit :worried:

If no problem there, things will get trickier and you will need that oscilloscope - and probably a spare day too.


No problem, I'm sure the problem can't be that bad.


It's most probably not the origin of the problem, but it can't hurt :thmbsp:

Hi,

here is the situation :

- no oil spills on PCB, so far not noticed any cold solder too
- supply PCB +24V is actually +23,3V and is stable in STOP position and also stable during platter start up and in LOCK (both speeds 33 & 45)
- motor PCB +24V is same as on supply : 23,3V and stable in conditions as above


i noticed one thing - during platter spin up i can hear servo is working for a while (and quiet in LOCK) .. but while slowing down from 45 to 33 servo is dead silent and i have to wait quite long time to get 33 (so platter needs to slow down naturally on its own..)
I wonder if there is any signal sent to motor PCB (from tonearm PCB...? or speed buttons...?) telling servo to reverse platter spin to slow it down or stop completely...???

i can get oscilloscope on weekend - so some next steps advise is very welcome, so i can report job progress on Sunday.... !!
Thanks a lot for support .... :thmbsp:

 

[jlb2]

- no oil spills on PCB, so far not noticed any cold solder too
- supply PCB +24V is actually +23,3V and is stable in STOP position and also stable during platter start up and in LOCK (both speeds 33 & 45)
- motor PCB +24V is same as on supply : 23,3V and stable in conditions as above

Ok, so that was not the +24V supply. But check the other voltages anyway, you never know.

i noticed one thing - during platter spin up i can hear servo is working for a while (and quiet in LOCK) .. but while slowing down from 45 to 33 servo is dead silent and i have to wait quite long time to get 33 (so platter needs to slow down naturally on its own..)

All this sounds perfectly normal, considering the motor is not braking any more. You will have to check the control waveforms when you have that oscilloscope : you need to know why the reverse current is not applied.

I wonder if there is any signal sent to motor PCB (from tonearm PCB...? or speed buttons...?) telling servo to reverse platter spin to slow it down or stop completely...???

I too think it is the problem. Now you will have to find out where the link between the decision to stop and the reversed current is broken.

i can get oscilloscope on weekend - so some next steps advise is very welcome, so i can report job progress on Sunday.... !!
Thanks a lot for support .... :thmbsp:

Let me sleep over it and I will try to send you a list of things to check by then.