Studer B67 Problem

[Nickuk99]

Hi all,

My Studer B67 MK1 has been running very well until last night...

Now when you press play, rewind, or fast forward the transport stops after a couple of seconds. If you hold the transport button down it is okay, plays well, rewinds etc... however as soon as a button is released it stops.

Can anyone give me some pointers? is this a tape sensor issue?

Any help most gratefully received.

many thanks

[TIMTAPE]

It could be a problem with the electronics for tape motion sensing. Perhaps a failed capacitor in that area.

[Ted Kendall]

Agreed. The right hand drum rotation generates a tacho signal, without which the mechanism stops. The other possibility which springs to mind is the photo-electric gate at the left of the headblock. The manual shows the test points and waveforms - best to start from there.

[Nickuk99]

Many thanks for this.. I'd like to look at these two idea.. can anyone point to which capacitors I should look at first? . I can test them.. but I don't have elaborate waveform tester..

Many thanks

[Ted Kendall]

To tackle this, you really need to download the manual and get hold of a 'scope. The control logic is not getting the signals it expects to see, and whilst these are simply logic high or low, the circuitry generating them is more complex and you need to see what is going on to diagnose the fault.

[Chris55000]

Hi!

It is possible to carry out basic diagnosis on this even without an oscilloscope, and I will post back with some more detailed fault–finding analysis for the OP once I've had a chance to study the drawings!

Chris Williams

[Nickuk99]

Thank you very much.. I'll look forward to hearing about this..

I'm also wandering if the big motor caps bolted to the upper chassis needs replacing?.. wondering if that might be part of it..

[Ted Kendall]

First things first. If the thing was running OK before this fault, check the gate and the roller and sort that out. The big motor caps can be left for now, unless they are oozing black goo, when replacement is indicated. What is more of a hazard is the Rifa suppressor caps, which look like glacier mints and go off like fireworks. Replace the lot as soon as decently possible.

[Chris55000]

Hi!

Before you begin work on one of these machines, make sure you've downloaded the latest version of the B77 MkI-MkII Service Manual, Studer Document No. 10.18.0302 (Edition 0303), Edition 0197 marked on the Circuit/Layout Drawings!

This document may be downloaded from my Dropbox:-

https://www.dropbox.com/s/886q459g5q..._Serv.pdf?dl=0

The Tape Drive & Control Electronics of the B77 are dealt with on three PCBs:-

A Power Supply PCB providing +24V, +21V & +5V and also the interconnections between the Take-up, Rewind & Capatan Motor windings. The capacitors associated with each motor are mounted on the deck metalwork.

Three types of PSU are used, the original uses a double-pole on/off switch, and a 78M20 Regulator, whilst the second type uses a single-pole on/off switch and a 78M20 Regulator, the final one uses a single-pole on/off switch and an LM317T Regulator.

A defective 78M20 can be replaced with the more readily available 7815 or a 7818 PROVIDED the value of R3 is increased (use a 1k preset to set-up the value required to give +21V) to compensate!

Three Types of Tape Control Logic PCB were used, the first used a Custom Made "SC10429" mask-programmed controller, whilst the second and third type used three TTL devices with a bipolar PROM providing the logic functions.

Not withstanding this all three types operate the same way, with an amplified "y-MOVE" signal from the Tacho Sensor 1.177.320 feeding bursts of pulses (NB - it is NOT a continuous oscillation - the oscillator signal is briefly interrupted three times each capstan revolution), a forward/reverse/play/record/stop signal from the push-button control switch-bank, and a tape-end trigger pulse from the Tape-end Sensor "QP-End".

Because the control press-buttons are simple non-latching SPST push-buttons, electronic latching of the control functions has to be employed, and this is carried out by the four 2N6073B triacs Q1 to Q4 in conjunction with the logic programmed into IC4 or the PROM on the "substitution logic panel" 1.177.316.

Failure of a function to operate or latch can be caused by:-

1) Failure of the motor a.c. supplies or triacs;

2) Failure of the "y-MOVE" interrupted oscillator bursts to reach the micro/PROM;

3) The tape-end sensor permanently stuck high.

4) An internal logic failure in IC4 or the "substitution logic panel".

I will deal with these in the order given.

1) Failure of the motor a.c. supplies/triacs.

The three motors are all a.c. shaded-pole split-phase or three-phase inductors with start capacitors mounted on the deck plates, first of all, using a good quality DMM with a cap. range or a Chinese Tester test the Motor Start Capacitors, two are 4.3uF and one 3.5uF - the Chinese Tester will read this type of cap OK.

If you find a capacitor defective, DO NOT attempt to substitute small paper or non-electrolytic types from speaker-crossovers, etc., they will not withstand the starting current!

https://www.ebay.co.uk/itm/Studer-RE...AAAOSwVupTnKAQ

If the capacitors test OK, test the motor windings for continuity against the diagrams, open-circuit windings need a specialist motor-rewinder or. better, replacement motors.

If the Motors test electrically OK, I recommend a Service Kit to recondition & re-lubricate them:-

https://www.ebay.co.uk/itm/Revox-A77...2MFabWN0Oc_FHg

I realise they are nearly three figures plus postage to the UK but these machines are well worth the investment!

If you find no problem with the motor windings or capacitors from an electrical point of view, use an ordinary AC DMM to check the multiple-tapped 110V a.c. secondary winding from the mains-transformer against the circuit-diagram for the correct voltages - it's very unlikely you'll have a mains-transformer winding failure, but dry-joints on the PSU PCBs, yakky plug-socket connectors and the complex wiring all warrant a careful examination!

Triacs are best tested by substitution - I'll deal with the triac circuits in more detail later - exact replacement 2N6073B triacs readily available!

I have included eBay links to replacement parts in accordance with the thread:-

https://www.vintage-radio.net/forum/...ad.php?t=36144

Exceptions
The following are the only exceptions whereby you may provide a direct link to a current eBay listing.
You may reply to a "wanted" post for an item with a link to an example of that item on eBay.
You may inform another member that a manual for the item they're working on is available on eBay and provide a direct link.
You may inform another member that parts to resolve the fault being discussed are available on eBay and provide a direct link.

It'll ages and ages to write detailed step-by-step fault-location advice in full, so I'll stop here for now and carry on with this post tomorrow and subsequent evenings as time & tiredness permits!

Chris Williams

[Nickuk99]

wow.. thank you so much.. I didn't expect such a quick response.. I'm very grateful for the help.. I'll get stuck in to what you have written so far... thank you very much.. Nick

[jamesperrett]

Chris - before you go too far I thought it worth checking that you do realise that it is a Studer B67 being discussed in this thread - not a Revox B77.

The B67 Mk1 service manual is at ftp://ftp.studer.ch/public/Products/...kI_Op_Serv.pdf

[Nickuk99]

Yes.. it is a Studer B67 Mk1

[Michael Maurice]

When I read Chris's reply, I did wonder as I've never seen a B67 with Triacs in it.

This looks like the tape move sensor is not giving out the correct output, I think on the B67, its done optically, but its possible a tantalum capacitor has gone s/c.

[Chris55000]

Hi!

My apologies to the OP and everyone else from this thread - I downloaded the S.M. I linked from a Russian (!!) site that said it was the B67 Hk I-MkII and I didn't read the cover and first few pages closely first!

I've now downloaded the correct B67 Mk I S.M. which, as Member Michael Maurice said, does NOT have triacs in the motor control circuits!

The wrong Manual does in fact say "Studer" on the front cover and inside - Did Revox & Studer merge?

Chris Williams

[Chris55000]

PS!

I've had a quick read of the B67 Mk I Tape Transport Control Circuits and this does use the "SC10429" control chip and a basically similar type of non-latching press-button control switch circuit, (the B67 has the switches mounted on the transport control PCB) but the differences are in the supply/take-up motors which are 50/60Hz switchable, and two versions of capstan motor control circuits are used - one for 3.75/7.5/15 in/s and one for 7.5/15/30 in/s - can I ask the OP which version of speeds his faulty machine is fitted with, and also the machine's Serial No. please?

Chris Williams

[Ted Kendall]

Originally Posted by Chris55000

Did Revox & Studer merge?

They were, of course, the same company until relatively recently. Willi Studer went from making oscilloscopes to marketing and then improving a Brush derivative called the Dynavox, which was replaced by the Revox A36 in 1956. The professional Studer range was already in production by this time.

[Nickuk99]

Hi, it is a Mk1 B67.. 15 ips version (not 30ips) in a trolly with full meter bridge.. c1976.. serial number obsured.. I need to remove from trolley to find it..

I hope this helps..

Many thanks to all for help and advice

Nick

[Chris55000]

Hi!

Thanks for that Nick – I'll know which diagrams to use when I rewrite my fault–finding advice for you later!

Chris Williams

[Chris55000]

Hi!

I'm going to deal with the B67 faults in the following order:-

1) STOP/PLAY/REWIND/FORWARD control;

2) Tape Speed/Capstan Motor Control;

3) Supply/Rewind Motor Control.

The Capstan Control Servo uses a Studer-Comissioned TDA1000 chip and two TCA561s for the Capstan servo control - both do go internally defective and supplies are getting harder to find and expensive, so I'll explain the operation of the circuits in detail and how to fault-find it!

The SC10429 micro that controls the switching logic is much less likely to be a serious problem and there are alternative panels that can be fitted in place of this IC!

Chris Williams

[Nickuk99]

Thank you so much Chris..