Vintage Audio
this section covers some restoration work that I did on my vintage HI-FI gear
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Article #1 | 03:42 PM Saturday 18/01/2020

Revox B215: Introduction

I wanted a Studer A721 tape deck but I ended up acquiring a Revox B215. Not that much of a difference but still a domestic machine with studio-class pedigree. While this is one of the (if not the) most robust cassette decks out there, it still requires basic service. Not at the level I plan to do but at least electrolytic capacitors should be replaced. I will be a little bit overreaching in my approach as I want to have the best reliability in time.

It might not be the best sounding deck of them all but I like it. In my opinion an absolute best sounding deck would be a SONY in range TC-K990ES, TC-K555ESA, or TC-K555ESJ. At least these models have the sound signature I like. Ups did I just wrote signature? I feel like I am stepping on moving sands here. So I will stop using epithets and making comparisons and let the engineering side to take over.

Article #2 | 04:00 PM Saturday 18/01/2020

Revox B215: Technical Data

This cassette tape machine has the following technical characteristics.

TECHNICAL PARAMETERS
ParameterValue
Track System4 track 2 channel stereo system
Tape Transport Mechanism4-motor direct drive
Tape Speed4.76 cm/sec
Wow and Flutter<0.1% (DIN 45500)
Frequency Response30 Hz - 18,000 Hz (±3dB) - Fe2O3 tape
30 Hz - 20,000 Hz (±3dB) - CrO2 tape
30 Hz - 20,000 Hz (±3dB) - Metal tape
Distortion<0.8% - Fe2O3 tape
<1.5% - CrO2 tape
<1.0% - Metal tape
Signal to Noise Ratio>70 dB - Fe2O3 tape
>72 dB - CrO2 tape
>72dB - Metal tape
Bias Frequency105 kHz
Heads1 x Sendust record head
1 x Sendust playback head
1 x Sendust erase head
Motors2 x direct-drive linear torque BSL motor for capstan drive
2 x microcomputer controlled DC motor for reel drive
Power Voltage100 V, 120 V, 140 V, 200 V, 220 V, 240 V at 50/60 Hz
Power Consumption45 W
Dimensions / Weight153 mm (H), 450 mm (W), 332 mm (D) / 9.15 kg

Article #3 | 06:00 PM Sunday 19/01/2020

Revox B215: Parts List

I have assembled a parts list for this tape machine. My restoration targets mainly the electrolytic and tantalum capacitors but also some other components. Because I am aiming for maximum reliability and low maintenance, some of the electrolytic capacitors were replaced with film counterparts. Below you will find lists consisting of the various parts in this unit.

The schematic value corresponds to what normally can be found in the electrical schematics but the actual parts could vary. Especially electrolytic capacitor voltages -- derating (!?). The recommended value is what I replaced the former part with. The TC inscription signifies a tantalum capacitor.

The Capstan Motors Control printed circuit board is coded 1.721.260.00 and is located in the left side of the machine mounted perpendicular on the System Control board.

Note that the red lines below don't need to be ordered. I did so because I had these parts available in my parts bin as leftovers from other projects.

Capstan Motors Control (1.721.260.00)
IdentifierSchematicRecommendedMouser Number
C410 uF / 25 V10 uF / 50 V647-UPW1H100MDD
C62.2 uF / 16 V TC80-T350A225K016AT
C101 uF / 25 V1 uF / 63 V FILM505-MKS2C041001F00JA
C1122 uF / 25 V22 uF / 50 V647-UPW1H220MDD
C1410 uF / 25 V10 uF / 50 V647-UPW1H100MDD
C152.2 uF / 25 V2.2 uF / 50 V FILM505-MKS22.2/50/5
C194.7 uF / 16 V TC80-T350B475K016AT
C221 uF / 25 V1 uF / 63 V FILM505-MKS2C041001F00JA
IC1HEF4001CD4001595-CD4001BE
IC2MC14020CD4020595-CD4020BE
IC3HEF4035CD4035595-CD4035BE
IC4RC4136595-RC4136N
IC5HEF4001CD4001595-CD4001BE
IC6MC14069CD4069595-CD4069UBE
IC7HEF4035CD4035595-CD4035BE
IC8RC4136595-RC4136N
IC114-pin Socket575-199314
IC216-pin Socket575-110433161
IC316-pin Socket575-110433161
IC414-pin Socket575-199314
IC514-pin Socket575-199314
IC614-pin Socket575-199314
IC716-pin Socket575-110433161
IC814-pin Socket575-199314

The System Control printed circuit board is coded 1.721.220.00 and is located in the leftmost side of the machine, mounted vertically.

Note that the red lines below don't need to be ordered. I did so because I had these parts available in my parts bin as leftovers from other projects.

System Control (1.721.220.00)
IdentifierSchematicRecommendedMouser Number
C122 uF / 25 V22 uF / 50 V647-UPW1H220MDD
C210 uF / 25 V10 uF / 50 V647-UPW1H100MDD
C322 uF / 25 V22 uF / 50 V647-UPW1H220MDD
C410 uF / 25 V10 uF / 50 V647-UPW1H100MDD
C1010 uF / 25 V10 uF / 50 V647-UPW1H100MDD
C114700 uF / 16 V594-2222-150-55472
C122200 uF / 40 V594-MAL211817222E3
C132200 uF / 40 V594-MAL211817222E3
C15220 uF / 6 V220 uF / 25 V647-UPW1E221MPD
C1710 uF / 25 V10 uF / 50 V647-UPW1H100MDD
C2010 uF / 25 V10 uF / 50 V647-UPW1H100MDD
C2222 uF / 25 V22 uF / 50 V647-UPW1H220MDD
C24220 uF / 6 V220 uF / 25 V647-UPW1E221MPD
C2710 uF / 25 V10 uF / 50 V647-UPW1H100MDD
C2810 uF / 25 V10 uF / 50 V647-UPW1H100MDD
C2910 uF / 25 V10 uF / 50 V647-UPW1H100MDD
C3010 uF / 25 V10 uF / 50 V647-UPW1H100MDD
C3110 uF / 25 V10 uF / 50 V647-UPW1H100MDD
C3210 uF / 25 V10 uF / 50 V647-UPW1H100MDD
IC3TL7705595-TL7705ACP
IC7RC4559595-RC4559P
IC10LM339595-LM339N
IC12MC14094CD4094595-CD4094BE
IC13MC14094CD4094595-CD4094BE
IC18RC4559595-RC4559P
IC19RC4559595-RC4559P
IC18-pin Socket575-193308
IC28-pin Socket575-193308
IC38-pin Socket575-193308
IC414-pin Socket575-199314
IC528-pin Socket575-11043628
IC616-pin Socket575-110433161
IC78-pin Socket575-193308
IC828-pin Socket575-11043628
IC928-pin Socket575-11043628
IC1014-pin Socket575-199314
IC1114-pin Socket575-199314
IC1216-pin Socket575-110433161
IC1316-pin Socket575-110433161
IC148-pin Socket575-193308
IC188-pin Socket575-193308
IC198-pin Socket575-193308

The Capstan Motor Driver printed circuit board is coded 1.021.516.00. There are two independent PCBs affiliated to each capstan motor. No capacitors here but there are a few transistors which could benefit from replacing for future proofing. If you decide to swap these transistors then make sure you double order the parts below.

I decided not to replace these transistors but for the sake of completeness I'll be listing them in the table below. I'll be keeping the red color to signal that these are not mandatory for replacement.

Capstan Motor Driver (1.021.516.00)
IdentifierSchematicRecommendedMouser Number
Q1BD135-16512-BD13516S
Q2BD135-16512-BD13516S
Q3BD135-16512-BD13516S
Q4BD135-16512-BD13516S

The Input/Output printed circuit board is coded 1.721.270.00 and is located in the rightmost part of the machine. It is mounted horizontally and there are two other big vertical PCBs inserted into it.

Note that the red lines below don't need to be ordered. I did so because I had these parts available in my parts bin as leftovers from other projects.

Input/Output (1.721.270.00)
IdentifierSchematicRecommendedMouser Number
C122 uF / 25 V22 uF / 50 V647-UPW1H220MDD
C222 uF / 10 V22 uF / 25 V647-UFG1E220MDM
C322 uF / 25 V22 uF / 50 V647-UPW1H220MDD
C422 uF / 10 V22 uF / 25 V647-UFG1E220MDM
C74.7 uF / 25 V4.7 uF / 50 V FILM505-MKS2-4.7/50/10
C91 uF / 25 V1 uF / 63 V FILM505-MKS2C041001F00JA
C154.7 uF / 16 V4.7 uF / 50 V BP647-UES1H4R7MEM
C17100 uF / 10 V100 uF / 16 V647-UFG1C101MPM
C1822 uF / 10 V22 uF / 25 V647-UFG1E220MDM
C3022 uF / 10 V22 uF / 25 V647-UPW1E220MDD
C3222 uF / 10 V22 uF / 25 V647-UFG1E220MDM
C384.7 uF / 16 V4.7 uF / 50 V BP647-UES1H4R7MEM
C3922 uF / 10 V22 uF / 25 V647-UFG1E220MDM
C43100 uF / 10 V100 uF / 16 V647-UFG1C101MPM
C4422 uF / 10 V22 uF / 25 V647-UFG1E220MDM
C4522 uF / 10 V22 uF / 25 V647-UFG1E220MDM
C5410 uF / 10 V10 uF / 50 V647-UFG1H100MDM
C5522 uF / 10 V22 uF / 25 V647-UFG1E220MDM
C5710 uF / 10 V10 uF / 50 V647-UFG1H100MDM
C5822 uF / 10 V22 uF / 50 V647-UPW1H220MDD
C621 uF / 25 V1 uF / 63 V FILM505-MKS2C041001F00JA
C631 uF / 25 V1 uF / 63 V FILM505-MKS2C041001F00JA
IC1RC4559595-RC4559P
IC3RC4559595-RC4559P
IC5MC14094CD4094595-CD4094BE
IC6RC4559595-RC4559P
IC7MC14052CD4052595-CD4052BE
IC8MC14053CD4053595-CD4053BE
IC9RC4559595-RC4559P
IC10MC14066CD4066595-CD4066BE
IC11RC4559595-RC4559P
IC12MC14094CD4094595-CD4094BE
IC13MC14094CD4094595-CD4094BE
IC14TP4051CD4051595-CD4051BE
IC15TP4051CD4051595-CD4051BE
IC16RC4559595-RC4559P
IC17LF353926-LF353N/NOPB
IC18RC4559595-RC4559P
IC19MC14053CD4053595-CD4053BE
IC20MC14053CD4053595-CD4053BE
IC21RC4136595-RC4136N
IC22MC14069CD4069595-CD4069UBE
IC23LF353926-LF353N/NOPB
IC24MC14052CD4052595-CD4052BE
IC18-pin Socket575-193308
IC220-pin Socket575-193320
IC38-pin Socket575-193308
IC420-pin Socket575-193320
IC516-pin Socket575-110433161
IC68-pin Socket575-193308
IC716-pin Socket575-110433161
IC816-pin Socket575-110433161
IC98-pin Socket575-193308
IC1014-pin Socket575-199314
IC118-pin Socket575-193308
IC1216-pin Socket575-110433161
IC1316-pin Socket575-110433161
IC1416-pin Socket575-110433161
IC1516-pin Socket575-110433161
IC168-pin Socket575-193308
IC178-pin Socket575-193308
IC188-pin Socket575-193308
IC1916-pin Socket575-110433161
IC2016-pin Socket575-110433161
IC2114-pin Socket575-199314
IC2214-pin Socket575-199314
IC238-pin Socket575-193308
IC2416-pin Socket575-110433161

The Record Control printed circuit board is coded 1.721.300.00 and is located in the left part of the rightmost side of the unit, socketed in the Input/Output board.

Note that the red lines below don't need to be ordered. I did so because I had these parts available in my parts bin as leftovers from other projects.

Record Control (1.721.300.00)
IdentifierSchematicRecommendedMouser Number
C9100 uF / 25 V647-UFG1E101MPM
C10100 uF / 25 V647-UFG1E101MPM
C1322 uF / 35 V22 uF / 50 V647-UPW1H220MDD
C161 uF / 25 V1 uF / 63 V FILM505-MKS2C041001F00JA
C171 uF / 25 V1 uF / 63 V FILM505-MKS2C041001F00JA
C181 uF / 25 V1 uF / 63 V FILM505-MKS2C041001F00JA
C191 uF / 25 V1 uF / 63 V FILM505-MKS2C041001F00JA
C2122 uF / 25 V22 uF / 25 V647-UPW1E220MDD
C3522 uF / 25 V22 uF / 25 V647-UFG1E220MDM
C4810 uF / 25 V10 uF / 50 V647-UFG1H100MDM
C5010 uF / 25 V10 uF / 50 V647-UFG1H100MDM
C5610 uF / 25 V10 uF / 50 V647-UFG1H100MDM
C5710 uF / 25 V10 uF / 50 V647-UFG1H100MDM
C6122 uF / 25 V22 uF / 25 V647-UFG1E220MDM
C7910 uF / 35 V10 uF / 50 V647-UPW1H100MDD
IC1MC14094CD4094595-CD4094BE
IC3MC14094CD4094595-CD4094BE
IC4RC4559595-RC4559P
IC5LF353926-LF353N/NOPB
IC6RC4136595-RC4136N
IC7LM13700926-LM13700N/NOPB
IC9RC4559595-RC4559P
IC10RC4559595-RC4559P
IC11MC14052CD4052595-CD4052BE
IC12RC4559595-RC4559P
IC13RC4559595-RC4559P
IC14MC14052CD4052595-CD4052BE
IC15RC4559595-RC4559P
IC16RC4559595-RC4559P
IC17LM13700926-LM13700N/NOPB
IC18MC14052CD4052595-CD4052BE
IC19RC4559595-RC4559P
IC116-pin Socket575-110433161
IC220-pin Socket575-193320
IC316-pin Socket575-110433161
IC48-pin Socket575-193308
IC58-pin Socket575-193308
IC614-pin Socket575-199314
IC716-pin Socket575-110433161
IC820-pin Socket575-193320
IC98-pin Socket575-193308
IC108-pin Socket575-193308
IC1116-pin Socket575-110433161
IC128-pin Socket575-193308
IC138-pin Socket575-193308
IC1416-pin Socket575-110433161
IC158-pin Socket575-193308
IC168-pin Socket575-193308
IC1716-pin Socket575-110433161
IC1816-pin Socket575-110433161
IC198-pin Socket575-193308

The Noise Reduction System printed circuit board is coded 1.721.290.00 and is located in the right part of the rightmost side of the unit, socketed in the Input/Output board.

Note that the red lines below don't need to be ordered. I did so because I had these parts available in my parts bin as leftovers from other projects.

Noise Reduction System (1.721.290.00)
IdentifierSchematicRecommendedMouser Number
C21 uF / 25 V1 uF / 63 V FILM505-MKS2C041001F00JA
C322 uF / 25 V22 uF / 25 V647-UFG1E220MDM
C41 uF / 25 V1 uF / 63 V FILM505-MKS2C041001F00JA
C522 uF / 25 V22 uF / 25 V647-UFG1E220MDM
C6100 uF / 25 V647-UFG1E101MPM
C810 uF / 25 V10 uF / 50 V647-UFG1H100MDM
C91 uF / 25 V1 uF / 63 V FILM505-MKS2C041001F00JA
C1010 uF / 25 V10 uF / 50 V647-UFG1H100MDM
C1110 uF / 25 V10 uF / 50 V647-UFG1H100MDM
C13330 nF / 16 V TC330 nF / 50 V FILM505-MKS2B033301A00JF
C19330 nF / 16 V TC330 nF / 50 V FILM505-MKS2B033301A00JF
C24220 uF / 10 V220 uF / 16 V647-UFG1C221MPM
C25100 uF / 25 V647-UFG1E101MPM
C2622 uF / 25 V22 uF / 25 V647-UFG1E220MDM
C3010 uF / 25 V10 uF / 50 V647-UFG1H100MDM
C32680 nF / 16 V TC680 nF / 50 V FILM505-MKS2.68/50/10
C33470 nF / 16 V TC470 nF / 50 V FILM505-MKS2B034701B00KO
C344.7 uF / 16 V TC4.7 uF / 50 V FILM505-MKS2-4.7/50/10
C35680 nF / 16 V TC680 nF / 50 V FILM505-MKS2.68/50/10
C36470 nF / 16 V TC470 nF / 50 V FILM505-MKS2B034701B00KO
C374.7 uF / 16 V TC4.7 uF / 50 V FILM505-MKS2-4.7/50/10
C3922 uF / 25 V22 uF / 25 V647-UFG1E220MDM
C40220 uF / 10 V220 uF / 16 V647-UFG1C221MPM
C41100 uF / 25 V647-UFG1E101MPM
C42220 uF / 10 V220 uF / 16 V647-UFG1C221MPM
C46220 uF / 10 V220 uF / 16 V647-UFG1C221MPM
C48470 nF / 16 V TC470 nF / 50 V FILM505-MKS2B034701B00KO
C53470 nF / 16 V TC470 nF / 50 V FILM505-MKS2B034701B00KO
C594.7 uF / 16 V TC4.7 uF / 50 V FILM505-MKS2-4.7/50/10
C63470 nF / 16 V TC470 nF / 50 V FILM505-MKS2B034701B00KO
C684.7 uF / 16 V TC4.7 uF / 50 V FILM505-MKS2-4.7/50/10
C72470 nF / 16 V TC470 nF / 50 V FILM505-MKS2B034701B00KO
C77470 nF / 16 V TC470 nF / 50 V FILM505-MKS2B034701B00KO
C794.7 uF / 16 V TC4.7 uF / 50 V FILM505-MKS2-4.7/50/10
C80330 nF / 16 V TC330 nF / 50 V FILM505-MKS2B033301A00JF
C81680 nF / 16 V TC680 nF / 50 V FILM505-MKS2.68/50/10
C844.7 uF / 16 V TC4.7 uF / 50 V FILM505-MKS2-4.7/50/10
C90470 nF / 16 V TC470 nF / 50 V FILM505-MKS2B034701B00KO
C924.7 uF / 16 V TC4.7 uF / 50 V FILM505-MKS2-4.7/50/10
C93330 nF / 16 V TC330 nF / 50 V FILM505-MKS2B033301A00JF
C94680 nF / 16 V TC680 nF / 50 V FILM505-MKS2.68/50/10
C974.7 uF / 16 V TC4.7 uF / 50 V FILM505-MKS2-4.7/50/10
IC1MC14052CD4052595-CD4052BE
IC116-pin Socket575-110433161
IC228-pin Socket575-11043628
IC328-pin Socket575-11043628
IC428-pin Socket575-11043628
IC528-pin Socket575-11043628

This is a complex cassette with a very service-friendly architecture. As with all quality machines, it deserves your respect. If you decide to do the restoration then do not hurry, take your time and do the job once. And do it well. Use quality parts. And again, take your time.

Article #4 | 08:15 PM Monday 20/01/2019

Revox B215: Restoration

The modular construction of Studer and Revox gear is a joy for any service operation attempt. Whatever you need to fix implies minimal disassembly work. In contrast to Japanese gear that is filled with wires going in all directions, the Studer design philosophy is unique and highly avantgardist for the time. You have the impressions that you're working on vintage computing hardware instead. Every logical module has its own PCB. Furthermore the PCB is either socketed in a mainboard or connected with minimal wiring. It took me less than half an hour to completely disassemble every PCB in the B215.

Servicing the PCBs however implies high soldering and desoldering skills and very good tools. Word is that the Studer PCBs are very heat sensitive and also have very thin traces. While this might (and actually is) true to some extent, I've seen worse. Throughout the entire restoration I have yet to damage a single trace.

The Revox mechanical block is an engineering marvel with the four direct drive motors. The capstan motors are each PLL controlled while the reel motors are microcomputer controlled. But there is a catch. If you don't use these machines for a long time, oil tends to leak from the sintered bronze bearings. Then wow & flutter will increase drastically. And most of these decks suffer from this. The required oil is called Isoflex PDP 65 produced by a company called Klüber and it is still available. Also the pinch rollers play a very important role in minimizing wow & flutter in this type of mechanical block. So make sure you replace them. Originally Revox used sintered bronze bearings for each of the two pinch rollers. Then they updated to nylon. Any roller you find will be good as long as it is brand new.

The restoration of a Studer or a Revox machine implies almost always electrolytic capacitors replacement and possibly integrated circuits. It is not a rule to replace semiconductors though. Studer used reputable brands for all of the ICs and transistors. But somehow restoration enthusiasts tend to overreact with parts replacements.

I have to say that I haven't tackled the trimmer resistors. As much as I wanted to replace them, I haven't studied what each of them does and if I have the possibility to adjust them to factory settings. Maybe one day I will also do this.

General Considerations

I should begin by saying that working on this machine presents a very big health hazard. There are lethal voltages inside. Not knowing what you are doing might result in severe accidents and possibly death by electrocution. I am very skilled in electronics repair and I have been doing such repairs for almost 20 years. This qualifies me to work in this field. But if you do not have experience, please take this information just as a knowledge base. Do not attempt to repair something that you cannot handle as there is a big probability to severe it further while also suffering accidents.

Good working condition tools are also necessary for this restoration. I am using a quality temperature regulated soldering station with multiple tips for every situation that I could possibly encounter. Also I am using a good solder pump and quality desoldering wick in two sizes. Isopropyl alcohol is handy to decontaminate boards of old flux and other residues. I also use eutectic formulation quality solder. Every replacement part is brand new, from a reputable manufacturer, ordered from U.S.A., Japan, or Germany. Also I only use parts that are suitable as replacements in various sections of the machine, after inspecting and comprehending the original schematic. Last but not least I have the years of experience backing up every action that I take while working on this unit.

I have found out that working with a temperature of 290 degrees Celsius is sane for these Studer vintage printed circuit boards. Keep in mind that parts fitted to large ground planes require 320 to 330 degrees Celsius. I have never lifted a pad with this temperature. But it is also true that I never wait more than three seconds with the soldering tip on a pad. If you need to work on the flex boards (e.g. on tape transport and on end-of-tape light sensor) then it is advisable to use the lowest temperature able to melt the solder. I went with 270 degrees Celsius and I managed to keep the flex board intact; no damage whatsoever.

Flux fumes are extremely toxic and should be avoided at all costs. Especially toxic are the fumes released while working on these old electronic boards.

Capstan Motors Control Restoration

This is a small PCB that implements the two phase locked loops (PLL) that control the two individual direct drive capstan motors. It contains a handful of ICs and a few capacitors. I decided to replace some electrolytic capacitors with WIMA film counterparts. The old tantalum capacitors were replaced with new Kemet parts while the remaining electrolytic capacitors were replaced with Nichicon PWM parts.

While totally unneeded, I decided to replace all of the ICs with new Texas Instruments branded ones. I also added sockets to each of the integrated circuits.

This is the board prior to servicing.

Everything was replaced and overhauled. Fortunately there is enough space on the PCB to replace the small value electrolytic capacitors with WIMA film parts.

Tilted-angle view.

The solder side looks good. Almost industrial-grade.

System Control Restoration

The System Control printed circuit board contains the different power supplies, the microcomputers that govern the functions of the deck, and various additional circuits such as the IR receiver and the serial link interface.

This board contains some unobtainable ICs and all of them are ESD-sensitive. Be very careful when working on this PCB.

This is the board prior to servicing.

The three microcomputers are removed from the PCB. Their sockets as well. Due to scarcity of these ICs, this operation is not for the faint of heart types out there. Keep in mind that these are CMOS devices, very sensitive to electrostatic discharge (ESD).

All pads have been throughly cleaned. The PCB is ready to receive new precision sockets.

All parts have been replaced.

The three Philips microcomputers are installed back in their new sockets.

Detail on the connector for the flexible printed circuit ribbon that connects to the IR detectors for the reels.

I have used high quality, high temperature axial capacitors for power supply filtering purposes.

The tracks side.

Detailed view on the tracks side. There is one resistor factory-placed directly on the tracks side.

Input/Output Restoration

The Input/Output board acts like a mainboard for the NR-system and the Record Control boards. It is relatively easy to service and doesn't pose any impediments.

This is the board prior to servicing.

And after.

Detailed view. Pretty high parts density in this section of the PCB. I wanted to preventively replace that relay but I had a hard time to source a similar part.

Detailed view of the input/output section.

Unfortunately I forgot to take a picture of the solder side. But all is good there.

Record Control Restoration

There are only a handful of capacitors to change on this board. However I replaced the ICs as well.

This is the board prior to servicing.

And this is the board after the servicing operation. All new film and electrolytic capacitors, integrated circuit sockets and brand new Texas Instruments integrated circuits.

Detailed view. This unit looks very factory-original with the new WIMA capacitors. Why? Because originally they used WIMA as well.

The upper right part of the PCB contains a lot of empty holes for parts with unknown purpose. But other than that I am happy with how I serviced the PCB.

And the solder side. As always, all good. No lifted pad, no uncleaned flux, no brittle solder joints. Everything is ready for many years of continuous playback and record service from now on.

Noise Reduction System Restoration

This PCB is full of capacitors of all types. I decided to replace all tantalum capacitors with WIMA film parts. Fortunately as with all these old STUDER layout designs, the raster for the small value capacitors is 5 mm which means they provided plenty of space to easily accommodate the modern film parts.

This is the board prior to servicing.

The board after the restoration. Or should I better say ... overhaul. Capacitors have been changes and all ICs received precision sockets.

Tilted-angle view.

Detailed view.

On the solder side everything looks great.

Detailed view on the manually soldered pins of the Dolby ICs.

I found this board kind of boring to service. Normally I don't get bored that easily but this one was pretty much linear and repetitive. But I like the end results.

Aftermath

Old parts that have been removed from this unit.

Electrolytic capacitors -- there is a strong electrolyte smell emanating from the pile.

Tantalum capacitors.

Integrated circuits and sockets.

Mechanical Block Restoration

The full direct drive mechanical block of Studer A721 and Revox B215 requires only minimal maintenance. However pinch rollers are very important and even the slightest imperfection causes audible distortions. I am concentrating on the following operations:

  • oiling the capstan axles bearings;
  • replacing pinch rollers;
  • replacing defective IR-barrier sensor;
  • cleaning the IR emitter and receiver for each reel;
  • cleaning all the dust.

So let's proceed to oil the capstan motors bronze sintered bearings then. For this I used the Isoflex PDP 65 oil which I applied carefully with a small syringe. But first the capstans need to go out. Extra care should be taken to mark the position of the sprint that holds each capstan flywheel in respect to the factory mounted position. This ensures the minimum possible wow & flutter. Also special attention needs to be paid to removing the axles themselves since these are high precision fine tolerance machined parts. Force them and you might break these tolerances. The result? Increased wow & flutter. Probably irremediable.

The capstan shafts are mounted back in.

The metal springy clips were mounted exactly in the same position they were originally factory set.

The IR barrier for tape detection was not working in my unit. I have one of the first series deck that does not use red light but IR light for the detector. So there is no way to tell by naked eye if it's working or not. I used the well known trick of observing the IR emitter through a digital camera. And there was nothing. Thus I decided to switch the IR emitter to a deep red LED emitter around 660 nm.

This is the original IR barrier. The LED is easy to remove if you have a lot of patience and quick steady hands. The flexible printed circuit traces don't stand too much heat before they burn out.

The fragile flexible printed circuit traces.

The clear tinted deep red LED emitter is inserted in its place. The beauty plate is mounted as well. Besides the old pinch rollers, the mechanical block is ready to go.

The original pinch rollers in my unit were with sintered bearing hubs. The rubber was very dry and cracked. Wow & flutter is totally unbearable. So time to change them. I have sourced a pair of new sintered bronze bearing ones which I mounted carefully. A tiny drop of PDP 65 oil inside the bronze bearing does miracles in terms of audible distortions. In order to remove the small steel clips you need a set of pliers that can interface the small clips. If you don't have such a tool, I can't imagine a way to remove the clips without damaging them.

The old pinch rollers versus the new ones.

The old ones are sticky because somebody overreacted with the oil. But the shininess says that they have seen a fairly high tape mileage.

The new pinch rollers are mounted in their place.

More detailed view on the tape path.

This is all the work I did so far.

Article #5 | 07:23 PM Saturday 15/02/2020

Revox B215: Impressions

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Copyright © 1998- Alexandru Groza