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Pioneer RT-707 Capacitor Upgrade and Service

Discussion in 'Tape' started by Trevor White, Oct 4, 2017.

  1. Trevor White

    Trevor White Classic not Plastic Subscriber

    Messages:
    250
    Location:
    Adelaide, South Australia
    Hi everyone,

    I am embarking on a major service and restoration of my Australian delivered, Multi-Voltage, Pioneer RT-707. I thought that many of you might find this exercise interesting, and possibly helpful.

    I have always had an analog stereo system. In 1974 I bought a brand new Sony TC-377, a fabulous machine at that time. I still have that machine, and after a recent lube and belt replacement it works well. But I had always wanted a better Reel to Reel machine. And then just a few months ago I was able to purchase an Australian delivered RT-707 that was in cosmetically outstanding condition, but had been stored in a humid environment (Queensland) for many years.

    The machine was in desperate need of dismantling, cleaning and lubrication. The heads were heavily tarnished, but responded well to a good clean and polish. In fact after polishing I discovered that the heads had only a nominal amount of wear, and that the wear was very even. There was no evidence that the head alignment had ever been touched, so I was doubly lucky there. The two reel motors were in excellent condition without any sign of the corrosion found elsewhere. Unfortunately the Capstan motor was not so lucky. It was noisy, and the capstan shaft itself where the pinch roller runs was actually corroded and the corrosion had pitted the shaft! I have now been able to source another Capstan motor, which was in excellent condition, nice and quiet and with a perfect capstan shaft. Along with this I have also been able to replace the Pinch roller tyre.

    The machine now works extremely well, plays (in both directions) and records with fantastic quality, and makes my old Sony seem a bit ordinary in the recording quality stakes.

    But, my intention was always to overhaul the machine in more than just a mechanical sense. But I did not want to embark on a re-cap etc if the basic machine was not already in pretty good condition, and to my considerable good luck, it is very good. This gives me a solid base on which to perform an electronic overhaul which should then give this machine many years of additional life.

    And so that brings me to the beginning of this adventure. There are a number of great threads on this topic, one in particular that has been of immense value to me by Smurfer77.
    http://audiokarma.org/forums/index.php?threads/pioneer-rt-707-service-rebuild.702717/

    As I progress, if you compare my machine with the pictures in Smurfers thread you may notice a few subtle, and some not so subtle, differences in the layout of the circuit boards with different implementations. There are obviously a few variations in circuit layout in actual service. I don't actually know what year this machine was manufactured. I'm hoping I may find something during the re-cap that might help me determine it's age.

    EDIT: Turns out to have been manufactured in May 1981

    (I have not started this pictorial thread with pictures of the machine itself. I'm sure everyone knows what a nice RT-707 looks like)

    So, I have decided to start with the Power and Oscillator board, RWR-050 and it's embedded Equaliser board RWX-154.

    Here is the board in situ. The rear panel is still in place here. The green, purple and brown wires in the foreground are going to the voltage selector on the rear panel.
    [​IMG]

    Now with the rear panel removed.
    [​IMG]

    Here are the transistors mounted on the heat sink.
    [​IMG]
    If you look closely at this shot, and then look at a similar one by Smurfer in his thread, you will see that my board has a resistor just below the heat sink between the two righmost transistors. On Smurfers system there is a capacitor in this location!
    http://audiokarma.org/forums/index....07-service-rebuild.702717/page-3#post-9586163

    And now with the heat sink removed.
    [​IMG]
    You can see more clearly now the different circuit layout between the two rightmost transistors.

    The heat sink with the Mica shims ready to be cleaned.
    [​IMG]

    The Power board from the other side.
    [​IMG]

    The foil side of the power board with the EQ board pins de-soldered, ready to pull out.
    [​IMG]

    And with the EQ board removed. It just slid out without any issues.
    [​IMG]

    The EQ board RWX-154 in it's original form.
    [​IMG]

    And with all the .01uF ceramic caps removed. The lovely little WIMA film caps lined up ready. I left all the Mylar caps alone. No real need to touch them.
    [​IMG]

    And finally with the WIMA caps in place. This is the very first time I have performed this kind of job. I was more than pleased with how well it went, and how nicely the soldering went. It has given my confidence a good boost.
    [​IMG]

    [​IMG]

    The Caps used on the RWX-154 EQ board were:
    8 x WIMA .01uF 100V: http://mouser.com/ProductDetail/WIMA/MKS2D021001A00JSSD

    So, that's it for my first post in this saga. On to the main Power and Oscillator board next

    :)
     
    Last edited: Oct 11, 2017

     

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  2. phantomrebel

    phantomrebel Serial Tapist Subscriber

    Last edited: Oct 4, 2017
  3. Trevor White

    Trevor White Classic not Plastic Subscriber

    Messages:
    250
    Location:
    Adelaide, South Australia
  4. phantomrebel

    phantomrebel Serial Tapist Subscriber

    They made them from 1977-1982 so you have a "newer" model. Just curious, how do you know the caps are bad? I have 3 of these (two manufactured 1979 and one 1980) and they all are fine, electrically. They all needed new rubber, contact deoxidation, cleaning of hardened grease, basic adjustments/calibration, and fresh lubrication. They test and play beautifully and all caps are original.
     
  5. Trevor White

    Trevor White Classic not Plastic Subscriber

    Messages:
    250
    Location:
    Adelaide, South Australia
    No real indication that the caps are 'bad' per se.

    But after 35+ years all electrolytics should be considered questionable. My machine also sounded fantastic with all original components. But a re-cap now will bring the machine back to like 'new' and give it a new lease of life.

    Cheers.
     
  6. Trevor White

    Trevor White Classic not Plastic Subscriber

    Messages:
    250
    Location:
    Adelaide, South Australia
    I was delayed in my work on the Power and Oscillation board by the arrival of a spare part for the machine.

    [​IMG]

    [​IMG]

    I had been searching for a nice set of heads to put away for the proverbial 'rainy day'. Some of the heads I had seen were dreadful, but this set came up, still on the original base plate, with the original Pioneer lacquer sealing the adjustment screws. They have some wear, of course, but are actually very good. Certainly candidates for re-lapping.

    So I may look into shipping them back to the U.S. and get them re-lapped. Who would you all recommend for that kind of work?

    Cheers.
     
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  7. Trevor White

    Trevor White Classic not Plastic Subscriber

    Messages:
    250
    Location:
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    So, here is the continuation of the work on the Power and Oscillation board RWR-053.

    After managing to remove the larger electrolytics on this board I was left with some lovely goo that Pioneer used to glue them down. I had to use some spray alcohol to soften this stuff before I could get the caps off the board.
    [​IMG]

    Here we are after a bit of a cleanup. I have also replaced the ceramic caps and some of the smaller electrolytics at this point. I don't think I will bother re-gluing the large caps in place.
    [​IMG]

    Now with everything populated. Like Smurfer77 I have chosen to use Nichicon FG electrolytic caps and WIMA film caps (in place of the old ceramics).
    [​IMG]

    Here is the heat sink refitted with new thermal paste applied and of course the Mica shims in between.
    [​IMG]

    And from above with the heat sink refitted. If you compare this shot to a similar one from Smurfer77's machine you will see that the WIMA film cap immediately behind the heat sink is actually on the other side of the heat sink on his machine. Slightly different board layouts.
    EDIT: In the image below the two 100uF caps immediately above the leftmost DEC relay were originally replaced with 35V parts, as per original spec, I have now been able to source 50V UFG parts and have upgraded these to this higher voltage part. The parts list at the and of this post has been edited accordingly.
    [​IMG]

    And now with the EQ board RWX-154 refitted. All ready for testing
    [​IMG]

    [​IMG]

    They have done their job well. But after 35+ years it was time to retire them all.
    [​IMG]

    Phew!!! No smoke :banana:
    [​IMG]

    Next on to the Servo and Amplifier board. This one should be interesting as this board also has an alternative layout/implementation in this machine.
    [​IMG]

    The caps used on the Power & Oscillator board were: (in no particular order)

    1 x Nichicon FG 10uF 50V: http://mouser.com/ProductDetail/Nichicon/UFG1H100MDM
    2 x Nichicon FG 100uF 50V: http://www.mouser.com/ProductDetail/Nichicon/UFG1H101MPM
    1 x Nichicon FG 220uF 35V: http://mouser.com/ProductDetail/Nichicon/UFG1V221MPM
    1 x Nichicon FG 22uF 50V: http://mouser.com/ProductDetail/Nichicon/UFG1H220MEM
    1 x Nichicon FG 330uF 63V: http://mouser.com/ProductDetail/Nichicon/UFG1J331MHM
    2 x Nichicon FG 470uF 100V: http://mouser.com/ProductDetail/Nichicon/UFG2A471MHM
    1 x Nichicon FG 470uF 63V: http://mouser.com/ProductDetail/Nichicon/UFG1J471MHM
    2 x Nichicon FG 2.2uF 50V: http://mouser.com/ProductDetail/Nichicon/UFG1H2R2MDM
    2 x Nichicon 4.7uF 50V: http://mouser.com/ProductDetail/Nichicon/UFG1H4R7MDM
    2 x Nichicon 47uF 25V: http://mouser.com/ProductDetail/Nichicon/UFG1E470MEM
    1 x WIMA 100pF 100V: http://mouser.com/ProductDetail/WIMA/FKP2D001001D00JSSD
    1 x WIMA .047uF 100V: http://mouser.com/ProductDetail/WIMA/MKP2D024701C00JA00
    2 x WIMA 47pF 1kV: http://mouser.com/ProductDetail/WIMA/FKP2O100471D00KSSD

    And for interests sake, here are the measured values of the old electrolytics:
    470uF 63V - 545 & 554
    470uF 35V - 468
    330uF 50V - 363
    100uF 35V - 112 & 113
    220uF 16V - 257
    22uF 16V - 30
    47uF 10V - 69 & 64
    10uF 35V - 12.35
    4.7uF 35V - 5.89 & 5.68 (One of these was actually a 25V part even though the specs define 35V)
    2.2uF 50V - 2.72 & 2.70

    Cheers, until the next installment.
     
    Last edited: Oct 16, 2017
  8. phantomrebel

    phantomrebel Serial Tapist Subscriber


    JRF Magnetic Sciences http://www.jrfmagnetics.com
     
  9. dhnash

    dhnash Well-Known Member

    Messages:
    553
    Location:
    Wildwood, MO
    Yes, John French is an expert at doing this type of work.
     
  10. phantomrebel

    phantomrebel Serial Tapist Subscriber

    Hi Trevor, now that the old caps are out, have you bench tested any of them to see where they are after 35+ years? It'd be useful info for those of us with original caps in our decks.
     
  11. Trevor White

    Trevor White Classic not Plastic Subscriber

    Messages:
    250
    Location:
    Adelaide, South Australia
    Good Idea. I'll do that and report back.

    PS: I have now added the old values to the post above.
     
    Last edited: Oct 6, 2017
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  12. Trevor White

    Trevor White Classic not Plastic Subscriber

    Messages:
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    Location:
    Adelaide, South Australia
    Well, I have struck a bit of a hurdle in regard to the Servo Amplifier board.

    The example in my machine seems to be stamped as an RWG-091-0. It's layout is quite different from the version in the service manual. I am not keen on starting to remove components without a decent diagram, especially the foil side that really helps me locate the item to be replaced.

    Some time ago Buffdriver kindly posted updated circuit diagrams for this newer board, but they are no longer accessible on PhotoBucket. I have left a comment for Buffdriver in that other thread, hopefully he may still have those updated diagrams.
     
  13. Trevor White

    Trevor White Classic not Plastic Subscriber

    Messages:
    250
    Location:
    Adelaide, South Australia
    Here we go with the Servo Amplifier board.

    On my machine this circuit board is identified as an RWG-091-0. It is a different shape and the components are in a slightly different layout. With help from Buffdriver and GPS16 I pressed on with re-capping this board, although this was much trickier than the Power and Oscillation board. Without an accurate foil side diagram identifying the components from the back of the board was a bit tricky. But I only made a couple of mistakes in de-soldering a leg on something that was not a capacitor. Easily and quickly rectified.

    Here you can see the Servo board and its alloy mounting plate. The screws are hidden under the foam rubber.
    [​IMG]

    Here is the board and the alloy bracket dismounted.
    [​IMG]

    The board itself is mounted to the bracket by four screws. Once released you can turn the board over. You can then flip the board for soldering etc.
    [​IMG]

    Here is the different version of the Servo board in my machine. This is a RWG-091-0.
    EDIT: Take note of the four Orange Low Leakage caps on this board.
    [​IMG]

    The factory soldering on this board was tricky to desolder. You can see how the legs of the components have almost all been bent over before soldering.
    [​IMG]
    [​IMG]

    So after some hours of careful removing and replacing of components. I chose to use electrolytics for all the caps on this board. If you see Smurfer77's thread you will see that he chose to use some film caps in place of the small value electrolytics.
    [​IMG]

    EDIT: Note that the four Orange Low Leakage caps were replaced by Nichicon UFG's. I have now changed this and installed UKL Low Leakage caps instead. I think this is closer to the intention Pioneer had in using those Orange LL caps.
    [​IMG]

    The original 3.3uf 350V cap on this board I chose to replace with a 400V version. When I removed the original 3.3uF cap I found a lovely brown crust under the base of the cap. No sign of trouble on the top though. This cap measured at only 1.03uF, so definitely reached it's use by date.
    [​IMG]

    Now with the board remounted but before I replaced the section of foam rubber.
    [​IMG]

    Here are the old electrolytics. The 350V 3.3uF cap was definitely in need of replacement.
    EDIT: Originally I replaced the four Orange Low Leakage caps with Nichicon UFG's. I have now changed them for Nichicon UKL equivalents.
    [​IMG]
    [​IMG]

    And here is the output from the Frequency Generator at 7.5ips (19cm/s). Now indicating a nice 1360Hz. At 3.75ips speed the frequency is exactly half. (After some careful adjustment)
    [​IMG]

    Checking the capstan speed with a digital tacho gave 455RPM, which calculates out as 19.05cm/s, spot on!
    (A big thank you to Smurfer77 for providing the formula for this calculation in his thread)
    [​IMG]

    When I first hooked up the scope I was alarmed to discover that the FG was actually running fast, at 1400Hz. I had checked the machine before touching it and it had been correct before the re-cap. I can only assume that at some time the machine was calibrated with the Servo board in its questionable state? I had to use the two trim pots on the top of the board to slow the FG down for both 7.5ips and 3.75ips. The manual tells you to use a special test tape (STD-101) but in the absence of one of those I used the scope. When playing a tape at either speed it sounds fantastic, exactly right. The Speed control pot works correctly also (and was in the correct centered position when performing the tests)

    The caps used on the Servo Amplifier board were: (in no particular order)
    1 x Nichicon PW 3.3uF 400V: http://www.mouser.com/ProductDetail/Nichicon/UPW2G3R3MPD
    1 x Nichicon FG 47uF 50V: http://www.mouser.com/ProductDetail/Nichicon/UFG1H470MPM
    2 x Nichicon FG 33uF 50V: http://www.mouser.com/ProductDetail/Nichicon/UFG1H330MPM
    2 x Nichicon KL 4.7uF 50V: http://www.mouser.com/ProductDetail/Nichicon/UKL1H4R7KDDANA
    2 x Nichicon FG 10uF 50V: http://www.mouser.com/ProductDetail/Nichicon/UFG1H100MDM
    3 x Nichicon KL 2.2uF 50V: http://www.mouser.com/ProductDetail/Nichicon/UKL1H2R2KDDANA
    3 x Nichicon FG 0.1uf (100nF) 50V: http://au.rs-online.com/web/p/aluminium-capacitors/6022494
    1 x Nichicon FG 0.47uF (470nF) 50V: http://au.rs-online.com/web/p/aluminium-capacitors/6022646

    EDIT: The parts list above has been edited to specify the Low Leakage caps I have now used.

    And here are the measured values of the old electrolytics:
    3.3uF 350V - 1.03 (This cap was also bulging at its base and had a brown crust oozing from it)
    47uF 35V - 58
    33uF 25V - 42
    33uF 16V - 44
    4.7uF 25V - 5.9 & 5.10
    10uF 16V - 14.47 & 14.56
    2.2uF 50V - 2.38 & 2.30 & 2.33
    0.1uF 25V - 0.125 & 0.130 & 0.122
    0.47uF 50V - 0.967

    So that's it for today.
     
    Last edited: Oct 15, 2017
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  14. Trevor White

    Trevor White Classic not Plastic Subscriber

    Messages:
    250
    Location:
    Adelaide, South Australia
    One question for the boffins though. The manual tells you to use the two trim pots to adjust the speed, which I have done with success. However, what is the third trim pot for? On my version of the Servo board the third trim pot is mounted behind and below the two speed control trim pots. Does anyone know what that third adjuster is for?

    You can see the third trim pot behind and below the two 2K pots in this picture:
    [​IMG]

    Cheers.
     
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  15. buffdriver

    buffdriver AK Subscriber Subscriber

    Messages:
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    Location:
    Seguin, Texas
    The third pot is VR904, which is rough speed control, and it affects both speeds. Though the calibration instructions don't mention it, this pot can be used to "get close" with VR902 and VR903 in their center positions. Each speed is then fine tuned with VR902 (19cm/sec) and VR903 (9.5cm/sec). BTW, VR902 is called VR202 on the schematic, but is correctly labeled on the board diagram.

    VR904 is a 10k VR, same as the pitch control; however, VR904 is effective for both play and record. Pitch control only works for playback.

    Very nice pictures and writeup, Trevor!
     
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  16. GPS16

    GPS16 Well-Known Member

    Messages:
    699
    Location:
    UK Manchester
    Hi Trevor,

    It has always been my understanding that the 3rd pot is to adjust the Span of the pitch pot to give +/- 6%. Once this has been set it is pretty much set up once and forget it.

    The 3.3uF cap is across the regulator transistor so will be seeing high currents and high voltages depending on whether the motor is on or off (accel/decel).

    When you get to the Power Supply/Control PCB, make sure that C408 is a quality device. This cap determines the end voltage on the solenoids once the initial pull in voltage time constant has passed.

    Good job. Nice pickys.

    GPS16
     
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  17. Trevor White

    Trevor White Classic not Plastic Subscriber

    Messages:
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    Location:
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    Thanks for your replies guys.

    I think I shall leave that third pot alone. I seem to have got the speed adjusted nicely using the two 2K pots. Although foolishly I forgot to make a recording of a 1kHz and 3kHz tone before embarking on the recap. When Smurfer77 did his he reported that there was no change after the re-cap. To my horror mine was quite different! Too late then, but luckily having a scope, and the RPM gauge means I think I have been able to get it set nicely anyway.

    Hopefully it will all be OK.

    Cheers,
    Trevor
     
    Last edited: Oct 8, 2017
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  18. Trevor White

    Trevor White Classic not Plastic Subscriber

    Messages:
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    Location:
    Adelaide, South Australia
    Hi All, so today I started looking at the Control Assembly RWG-070, which on my machine is actually a RWG-087-B. Yet another variation.

    Anyway, I have a nice big Nichicon cap (22uF 100V or 400V) to replace C408, a 22uF 35V cap that GPS16 has alerted me to as being very important. However the axial caps on this board I wanted to ask about.

    There are two big axial caps, a 470uF 35V and a 1000uF 63V. I have some Vishay 470uF 63V axials to replace the 470uF cap, but with the 1000uF cap I have a choice. I can either use a Vishay 1000uF 63V, or a Nichicon VX series 1000uF 63V. The Nichicon is a little smaller (physically) than the Vishay. I reckon Smurfer77 used Vishay components on his Control board, but do you guys have any preference? Would you use the Nichicon over the Vishay?

    Thanks for any input.
     
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  19. GPS16

    GPS16 Well-Known Member

    Messages:
    699
    Location:
    UK Manchester
    Hi Trevor,

    if the caps in question are reservoir caps then debating over which is the better one is not really relevant. In this application a cap is a cap. There is no audio going through it which may be coloured. The only preference I have is I usually go for the 105 Deg spec as theses are aimed a Switch Mode PSUs which are a bit more affected by ESR due to the high frequencies involved. If they work there then in a bog standard linear supply this should be a breeze!!! If you feel the need to upgrade then do it on voltage working only. If you increase capacitances then you could end up stressing silicon elsewhere such as the rectifiers. I tend to check the physical dimensions and take things from there!!!. C408 is a bit more demanding as it is part of an RC time constant. If this cap gets leakage then the final voltage on the solenoids will increase giving un necessary dissipation in the solenoid coils. Bear in mind that any small increase in voltage will be a V squared increase in power dissipation as the current will have increased with it!!!

    Cheers.

    GPS16
     
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  20. Trevor White

    Trevor White Classic not Plastic Subscriber

    Messages:
    250
    Location:
    Adelaide, South Australia
    Cheers, thanks for that mate.

    Indeed, I never upgrade or change the rated capacitance, but I will always go up at least one level in voltage spec, sometimes more, as in the C408 cap.
     
    Last edited: Oct 9, 2017
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