Studer B67 MKII: Restoration
There are a lot of printed circuit boards that require removal before attempting any parts exchange. Some are insanely easy to remove and service, and some are a little bit more difficult. There are single layer and double layer boards. Some have solder mask on both layers, some have only on one layer. Desoldering might be tricky at times. But nothing to be scared of if you have the right tools and the necessary patience. Thankfully everything is serviceable. However note that there are a few integrated circuits that cannot be obtained anymore. I am talking about the TDA 1000 capstan motor controller circuit and the tape transport command mask programmed circuit. Of course both can be emulated with modern microcontrollers. TDA 1000 would be harder to emulate but the other one is simpler and requires only a very good understanding of the electrical schematic. However I am not planning to emulate anything. I'm pretty sure I could do both of them but the amount of work is inhuman. I'd better prefer designing microcomputers instead.
Sure there are other vintage ICs that once fried you will have a hard time getting them. But not as hard as the ones mentioned above. And they can be easily substituted, even though pin-compatibility will be compromised. But this is another subject. Some integrated circuits in my unit presented some sort of corrosion on their terminals: they turned black. This kind of corrosion is easily removed by scraping the leads. But from my experience with older Japanese parts that suffer from a similar disease, it is better to replace these with new parts. So I did. I also replaced the sockets wherever I found appropriate (or not).
One thing I like is that I found the service manual easily on the Internet and it is very comprehensive. Furthermore some of the schematics are hand drawn. Very human-esque. However in my unit on some of the printed circuit boards I have found some electrolytic capacitors with double the voltage specified in the schematics. Not a problem by all means, but so that you know.
An annoying fact is that the Studer engineers have used a lot of axial capacitors on various printed circuit boards. Sure these can easily be changed with radial types with insulated leads. But in order to keep originality I am going to use axial types as well. Vishay still makes them in high quality.
This machine is made in 1982, judging by the dates stamped on various printed circuit boards. Some boards are stamped 1981. The motors are built in 1982, so is the chassis. I think this is one of the latter revisions of the deck because I can see that they have improved the quality of some of the electronic components inside. There are absolutely no red tantalum capacitors and in some places where FRAKO electrolytic capacitors would've been installed, there are Philips parts instead. Speaking of tantalum, only a few of them are made by ITT (blue colored) and are mostly installed in the audio PCB assemblies. The logic boards have green tantalum capacitors. From my experience these are very stable and there is little concern about them. But I trust modern Kemet capacitors even more so I will replace them all. In some cases I will even use MLCC parts instead of tantalum. This will ensure better stability and reliability. It might be overkill in some cases but still. This reel to reel tape deck deserves the best.
What I like most about servicing this deck is that the PCBs are of very good quality. The tracks are very resistant and the through plated holes are very sturdy. However the soldermask is very soft. Don't ever think about pressing the iron too hard on it or it will leave a scratch. But overall from the units that I fixed or restored throughout the time, this one has the best PCBs.
Let's go ahead then.
General Considerations
Working on this unit exposes you to electrical hazards. There are lethal voltages inside.
Severe accidents and possibly death by electrocution might occur. I am qualified and skilled with electronics and I have been doing audio gear repairs for over 20 years. If you lack experience, please take these articles as just a knowledge base. Do not attempt to repair something that you cannot handle as there is a high chance of doing further damage while also possibly suffering accidents.
Good tools are a must for a quality restoration. I use eutectic soldering alloy and a temperature-controlled soldering station equipped with various tip shapes. I a standard and a precision desoldering pumps and desoldering wick in various widths. To clean the flux, I use isopropyl alcohol and high purity acetone.
Empirically, I found that working with a temperature of exactly 300 °C is safe for these vintage printed circuit boards. I have never lifted any pads and I never wait more than a couple of seconds with the hot tip on any pad. While working on the chassis, I use between 360 and 440 °C. Flux fumes are extremely toxic and should be avoided at all costs.
Every replacement part is brand new, from a reputable manufacturer, ordered from the U.S.A., Japan, or Germany. In addition, I only use parts that are suitable in specific circuit sections, after inspecting and comprehending the original schematic diagrams. Last but not least, I have years of experience backing up my choices and actions.
Tape Transport Section
The tape transport section consists of restorations of the various printed circuit boards that control the operation of the machine. Think various motor control circuits, solenoid control, (variable) tape speed regulator, digital counter, power supply, and so on.
Power Supply Chassis
These three safety capacitors are located directly on the mains power supply lines. Better replace these for safety reasons. I used WIMA metalized paper (MP) series parts.
Here is a picture of the initial state. The big one had already exploded. But it did sometime in the past, while at the previous owner of this machine. The capacitor exploded in an open state. There was no noticeable short circuit when checking with the continuity tester. That's good news.
And after. The 100 nF WIMA capacitor has a different shape and terminal raster than the old RIFA part. However in this application it doesn't matter that much since I extended its leads with some heavy duty .5 mm multi-core copper wire.
The exploded 100 nF RIFA capacitor looks scary. The smaller ones are still good albeit cracked.
Power Supply / Stabilizer Restoration
This large PCB is bolted under the power transformer and is easy to remove. You just need a very long Allen key. Or Inbus as they call them in Germany.
This is the board prior to servicing.
And the solder side.
A bunch of small tantalum capacitors are decoupling the input and outputs of the stabilizer integrated circuits. I know they look like power transistors but in fact they are ICs.
The four big FRAKO capacitors have been carefully removed from the PCB assembly. I have tested all of them and -- surprise -- all are in very good shape. All are well within their factory specifications. This is unexpected. I believe this is a low mileage deck. Otherwise I can't explain. In fact they look so well on the tester that I can safely put them back. But at a second thought they are almost 38 years and I know FRAKO parts tend to fail short. I wouldn't want this to happen directly on the power supply rails.
I have found new capacitors employing the exact same fixture as the old ones. However I couldn't find a 10000 uF / 25 V capacitor with dimensions 30 x 40 mm thus I bought a 10000 uF / 40 V part which is slightly larger at 35 x 40 mm. There is enough space on the PCB for this capacitor so no problems here. Only aesthetics are a little bit impacted. If you care, that is.
New tantalum capacitors and big electrolytic capacitors are in position.
This is the solder side after servicing.
Tape Transport Control Restoration
The biggest printed circuit board of them all. It is a little bit difficult to get it out but not impossible, even without clearing the wire loom out of the way. This PCB is home to a mask programmed integrated circuit (a ROM basically) that contains the program that controls the tape transport functions. I am very curious about the internal organization of this ROM. Maybe it can be replicated? It should be a fun project.
Details on various sections of the PCB.
I have changed all but one tantalum capacitors with modern MLCC parts. I replaced one tantalum capacitor with a similar part rated higher in terms of operating voltage. Also, I added sockets to all integrated circuits, dual-mosfets, and optocoupler. I have replaced two Philips film capacitors with WIMA parts. This operation is unnecessary though. But I did it anyway.
The circuit board is restored.
Detailed view on restored PCB sections.
Solder side.
Tape Tension Control Restoration
This is a small PCB soldered directly on the tape transport control PCB. I have not removed it nor have I took pictures of it. However I have changed one tantalum capacitor rated 1 uF / 35 V with a modern MLCC part rated 1 uF / 50 V. Also, I have added sockets for the two integrated circuits. While here I replaced the old ICs with new ones built by Texas Instruments.
For pictures, please observe the images above in the paragraphs dedicated to the tape transport control circuit board.
Sensor Board Right Restoration
This is a small printed circuit board that is next to the right tape sensor assembly. It is tricky to get out without removing the tape roller but it can be done with much care. There is only one capacitor to replace on this PCB.
This is the board prior to servicing.
And the solder side.
The sole FRAKO capacitor that requires service. In the schematic it is rated 10 uF / 25 V. In my unit a 63 V part was factory-installed. I chose to replace it with a Nichicon BT series part rated 10 uF / 50 V.
After servicing.
View from another angle.
Spooling Motor Control Restoration
These two small printed circuit boards are home of the dreaded RIFA film capacitors. These have developed a habit of cracking, shorting, and eventually smoking out, causing the spooling motors to malfunction. It is recommended to replace the power resistor as well. By now it should already be fatigued. In my unit, one of those power resistors has increased its resistance and is now measuring almost 7 Ω.
This is the board prior to servicing.
And the solder side.
A close-up shot of the RIFA film capacitors. These have 20 mm lead spacing and it is difficult to find modern capacitors that don't come in 22 mm spacing. But most important is the Vac rating of the replacements. It should absolutely not be below 150 Vac. I found some Illinois Capacitor parts that come in 20 mm lead spacing and 160 Vac rating. I think these make for a good replacement.
The new Illinois Capacitor parts are all in. I have used glass beads as spacers. Power resistor has been replaced as well.
Solder side.
Detailed view.
Next up, comes the second spooling motor PCB. One of the RIFAs was measuring continuity at 2 Ω and 0 nF capacitance.
And the solder side.
New parts.
New parts have been installed in place.
Solder side is good.
Capstan Motor Control Restoration
This small printed circuit boards is home of one (shot) RIFA film capacitor. On my board the capacitor is measuring 1.5 uF and is cracked badly. The resistor measures OK however. I chose to replace it for safety reasons.
Before servicing.
And the solder side.
Cracked RIFA capacitor is out for good.
PCB is restored.
This is the solder side. I have cleaned up the old flux.
View from another angle.
Capstan Speed Control Restoration
This printed circuit board controls the speed of the capstan motor by means of a quartz locked PLL mechanism. It accepts the feedback from the capstan motor tachogenerator as speed regulation reference. It also has three switches that commute between the three speeds available. This board is also home of the very rare TDA 1000 integrated circuit.
This is the board prior to servicing.
The solder side is hidden beneath an electromagnetic radiation shield.
You can see that the integrated circuits on my PCB are all directly soldered. I decided to socket all of them in order to ease-up future maintenances.
Halfway through the socketing operation. With the right tools you can remove even the most stubborn integrated circuit without damage. I use an Engineer SS-02 solder pump and the soldering station for heating purposes. Unfortunately I don't have a desoldering station.
The precious TDA 1000 integrated circuit is removed from the PCB safely.
Delicate handling and making sure you are not statically charged is very much required when dealing with these (rare) integrated circuits.
While here, I decided to replace all operational amplifiers on this board. They show signs of leg corrosion. Better safe than sorry.
Also, I have replaced seven film capacitors. This operation is largely unnecessary but I have my doubts about Philips capacitors in general -- except SAL types. I used WIMA film capacitors of the same rating to replace C1, C2, C3, C4, C8, C9, and C10. As a matter of fact I have measured all the Philips film capacitors that I extracted and absolutely all of them are within their 5% specified tolerance. They all measure perfect. But I had some bad experiences in the past which made me want to replace these. In fact I recommend you to not touch any part (resistor, capacitor, transistor, integrated circuit, and so on) if it is not defect. You know the drill: if it ain't broke, don't fix it.
C5, C7, and C15 were originally tantalum capacitors and I decided to replace them with modern MLCC parts with a bump in operational voltage. I very much trust modern tantalum capacitors but given the fact that this PCB is so expensive, I went the reliability lane.
I couldn't source a Kemet 220 uF / 3 V tantalum capacitor at the time of this restoration. It was simply not available at Mouser. But I am keeping an open eye on them and I'll order one as soon as they come back in stock.
Supply rail filtering capacitors C18, C19, and C20 were FRAKO bombs. I replaced them all with Vishay 118 AHT series parts.
Solder side.
Metallic shield is installed back in position.
View from another angle.
Variable Speed Restoration
This circuit board is bolted to the chassis via two very long hex nuts. Thankfully these are very well secured in place thus you only need to remove two Allen screws and pull this PCB assembly gently from its socket in the distribution PCB. Also, this board has some wires soldered to it and servicing it is a little bit awkward. But there is little to do here: change only three electrolytic capacitors.
This is the board prior to servicing.
The solder side as follows.
Of course I have also added augat sockets to all integrated circuits.
Counter Restoration
The tape counter printed circuit board is constructed entirely with TTL integrated circuits. In my unit all but two of the TTL ICs are directly soldered. Some of them present black legs which is a common fault with old Texas Instruments parts. Well I hope you see the quotes, it is not a fault per se but it could be if the corrosion progresses enough. I decided to do a full scale re-socketing of all ICs. While here I chose to swap all of them with new ones that I had lying around the parts drawer. These are remnants of other digital projects that I worked on so giving them a useful life seems like a good idea.
This is the board prior to servicing.
The solder side as follows.
Main counter IC. This is a MOSTEK ion-implanted, P-channel MOS six-decade synchronous up/down counter/display driver with compare register and storage latches. Sounds impressive, eh? It should be. This is 1976 technology after all. Vacuum tubes were still around in big numbers back then.
All unsoldered and PCB pads cleaned.
Components side.
Detailed view.
Sockets are mounted. The capacitors have been changed.
Detailed view. 47 uF capacitor has glass beads as spacers.
All new integrated circuits are in position.
Tilted-frontal view.
Detailed view again.
Solder side looks good too.
This was the most tedious PCB of them all to work on. It was not bad by all means and I had a lot of fun doing it, even if it appears to be a boring job. It all depends on perspective.
Audio Section
The audio section consists of restorations of all the printed circuit boards involved in analog signal processing. That means reproduce and record amplifiers, oscillator, overload detector, and stabilizer. All these PCB assemblies are located in the audio boards tray in the lower part of the tape machine.
Reproduce Amplifier Restoration
There are two reproduce amplifiers located in positions 1 and 2 in the audio boards tray in my machine. They are fairly complicated but thankfully there is not a lot to change on them. The usual suspects are FRAKO electrolytic capacitors, old tantalum capacitors. In addition, I am going to add integrated circuit sockets. Also, I will fix the bad channel 1 reproduce amplifier because at this moment it is not working at all.
This is the channel 1 PCB before servicing.
And the solder side. Trained eyes will spot a lifted pad.
FRAKO time-bombs and mismatched axial capacitors. Somebody was here before me and replaced one of those big axial FRAKO capacitors with a blue one. He did a messy job. Also, he exchanged one of the non-polarized film capacitors next to the trimmer resistors array. It is the second one from the top. The yellow one. The technician also lifted one of the bottom pads of this capacitor and did another messy job adding a wire connector in place of the printed track. Huh...
Scorched 4.7 Ω resistors. One is measuring ~ 380 kΩ and the other one is measuring ~ 680 Ω. Way off limits.
The burned resistors were replaced by Dale RN60D series metal film precision resistors seated on glass beads for better heat dissipation. I tried to clean the PCB as much as I could but some carbonized burn residues were so stubborn that I had to leave them be. Also, somebody scratched the soldermask next to one of the 1000 uF capacitors. It wasn't me. I did my share of scratchings but in this case it wasn't me.
The restored printed circuit board looks like this.
This is the solder side after the restoration.
Tilted-frontal view.
More details.
This is the channel 2 PCB before servicing.
And the solder side.
Roederstein capacitors. This is weird but not uncommon. Both Roederstein and FRAKO were high quality at their time. But they both aged badly. Surprisingly all these Roederstein capacitors still measure up to specifications. As a fun fact, I always liked ROE (or ERO, as they called themselves at some point) capacitors.
This is the restored PCB. I have changed all Roederstein and FRAKO capacitors, one Philips Film capacitor, one ITT tantalum capacitor, and two resistors. The resistors were OK but for symmetry and looks I chose to upgrade them to Dale RN60D parts as those used on channel 1 PCB. The Philips film capacitor was OK but I changed it anyway with a WIMA polypropylene film part.
And the solder side.
View from another angle.
Overload Detector Restoration
This is the first printed circuit board that I serviced in this tape deck. I decided to replace the sockets with augat-class ones. Note that this operation is largely unnecessary but since I had these fine sockets around, why not? Note that the original sockets are made by AMP -- very good manufacturer. On this board there are some tantalum bombs made by ITT. The blue drops need to go quickly. It is unlikely that these capacitors will fail in this circuit topology but what if? Yes, they need to go.
This is the PCB before servicing.
And the underside.
Detailed view on the ITT tantalum capacitors. Notice the TBA231A integrated circuits. These are operational amplifiers that are no longer available. But they are equivalent to SN76131 parts made by Texas Instruments. You'll have a hard time sourcing these as well. The other parts around are unlikely to fail so no need to change anything else.
C3, C6, C7, C13, C17, and C18 were all tantalum capacitors rated 10 uF / 16 V. I replaced them all with modern Kemet tantalum capacitors rated 10 uF / 25 V. All these capacitors play the role of stage decoupling or functional parts of high pass filters. The AMP sockets were replaced by augat-class sockets.
Detailed view.
Overview of the serviced printed circuit board.
Detailed view of the soldering job I did on the new integrated circuit sockets. Looks industrial. However a trained eye can easily tell the solder is newer than that of the other terminals around.
Record Amplifier Restoration
There are two record amplifiers located in positions 4 and 5 in the audio boards tray in my machine. Like the reproduce amplifier, these are also fairly complicated. But nothing to be scared of. I've seen my round of printed circuit boards throughout the time.
This is the channel 1 PCB before servicing. Note that somebody before me changed an operational amplifier. I am going to probably change all of them with new parts of the same type.
And the solder side.
The 74LS02 integrated circuit presents black oxide on its legs. It is a candidate for replacement.
I added augat sockets to all integrated circuits. Also, all ICs have been replaced with new Texas Instruments parts. All tantalum capacitors were replaced with modern Kemet tantalum parts. There is nothing else to be done on this board.
The restored PCB looks as follows.
The solder side looks OK after servicing.
View from another angle.
This is the channel 2 PCB before servicing.
And the solder side.
View from another angle, just to illustrate the parts density on these PCBs.
All old parts have been changed.
Solder side now looks like this.
View from another angle.
Oscillator Restoration
This is a very simple PCB consisting of only a handful of parts. Very few capacitors need to be replaced here. No other part was touched. FRAKO electrolytic capacitors are know for failing short. In my case however I have put the FRAKOs to test after I have extracted them. To my surprise they were measuring very good, even thought the ESR was a little on the higher side. But I've seen new capacitors measuring worse than these.
Here is the board before servicing.
This is the underside.
C3 was originally rated 47 uF / 35 V and was replaced with a modern axial capacitor rated 47 uF / 63 V. C5 and C7 were rated 10 uF / 35 V in the schematic. In my unit they were at 63 V. I chose to replace them with Nichicon KZ MUSE series parts rated 10 uF / 100 V. Not that the extra voltage bump is required but I had these capacitors lying around. C8 was an electrolytic capacitor rated 1 uF / 35 V and was replaced with a Panasonic ECQ series film capacitor with glass beads as spacers.
Here is the board after servicing.
Details.
And a detailed view on the solder job.
Stabilizer Restoration
This circuit board implements the power supply for the entire audio section. Only a few parts need to be changed here. Namely two electrolytic capacitors and four tantalum capacitors.
Here is the board before the restoration.
This is the solder side.
The restored PCB looks nice with the blue-yellow contrasting colors.
I have used 6 mm height glass tubes as electrolytic capacitor spacers. Better airflow is thus assured and it looks good too.
Kemet tantalum capacitors are trusty in all environments. And this one makes no exception.
The solder side looks good.
VU-meter Bridge
The VU-meter bridge is simple to restore since it has very few parts that require replacement. Everything that needs service is located behind the monitoring speaker panel. Thus, it is best to dismantle the hinges and take out the entire speaker assembly.
Like this.
Monitor Amplifier Restoration
This circuit is a classic push-pull amplifier driven by an operational amplifier. Simple and effective. You can't go wrong with this.
And the solder side.
Electrolytic and tantalum capacitors have been changed. I added an augat socket to the integrated circuit and I have replaced the IC with a new one.
Solder side after the work is done looks like this.
Monitor Panel Restoration
The monitor panel consists of only some signal routing switches and four transistor audio buffer circuits. These filters use some small capacity tantalum capacitors that can be quickly replaced with MLCC modern parts.
This is the PCB assembly before.
I have used TDK MLCC capacitors to replace all ITT old ones. Then I brush cleaned the PCB. And it looks like this now.
All done on the VU-meter bridge. I really like the simplicity of these circuits.
The volume potentiometer is cracking a little bit. But it doesn't matter that much since I seldom use the integrated monitoring function. Most of the time, the volume is set to minimum and the input signal switch is set to Input. It is easy to omit the restoration of these small circuits. But a shorted electrolytic capacitor could jeopardize the stabilizer card in the B67 machine. Better safe than sorry.
Overview of Audio Section
Here are the audio section printed circuit boards all socketed in their corresponding place. I have replaced the long PCBs dampening sponge as well. Removing of the old one was a very tedious job and I used acetone because I had no luck with isopropyl alcohool. Acetone stinks and a very well ventilated room is required.
Aftermath
Old parts that have been removed from this reel to reel unit.
Electrolytic capacitors.
Tantalum capacitors.
Film capacitors.
Power electrolytic capacitors and integrated circuit sockets.
Integrated circuits.
Resistors.
Old parts from the VU-meter bridge.
This is all the work I did so far.
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