Pioneer SX-737 Restoration

Discussion in 'Pioneer Audio' started by StraightCase, Dec 28, 2018.

  1. StraightCase

    StraightCase New Member

    Messages:
    23
    Location:
    Central Ohio
    I have decided I am going to take on the restoration of my recently acquired Pioneer SX-737. This unit does not appear to have seen much use at all and I even have the original packing and box. Almost like it came out of a time capsule. :jump:

    Pictures: https://imgur.com/a/2yCpNWV

    The unit is sounding great, but I really want to get these old electrolytic caps out and replace with new to avoid trouble.

    Electronics are not new to me and I do have experience working with electricity on both standard household and industrial 3 phase circuits, but nothing quite like this. I do have some pretty decent tools for the job. Hakko 936, MG Chemicals 60/40, SRA Rosin Paste Flux, solder sucker, braid, 170 cutters, Pomona mini-grabbers for the multi-meter, surgeon's hands (welder joke) :blah:, etc. So I am off to a pretty decent start, but by no means an electrician or double E.

    So here are my questions. I have gone through many older threads on this very topic and have made a BOM (largely from Mark the Fixer's) for the components I will use in this preventative service and there are a few components that I am not going to be able to source. Any changes I am making to Mark the Fixer's BOM are marked in yellow waiting for approval from more qualified people than I; additionally there are some that are marked in red that I simply am lost on what would be a good substitute. Most of them are those film caps found on the tuner board and others. Also, mouser is out of 512-KSA1220AYS should I just wait til they arrive? I will be installing 863-1N4004RLG as my unit does not appear to have it between pins 9 and 10 on protection board banded side to 10, right?

    Is it normal to hear some crosstalk (terminology?) or bleed from the FM radio on the recording functions?

    Any recommendations on replacement main filter caps? My original caps are ELNA CE-W 50v 6800μF 85C capacitors. I am still searching for an appropriate replacement for those.

    Lastly, should really replace all these transistors? Not that it is a big deal, but do they really need it? Do they degrade like electrolytic capacitors do over time, or is it with use?

    What say ye?
     

    Attached Files:

    Last edited: Dec 28, 2018

     

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  2. Motnick

    Motnick AK Subscriber Subscriber

    Messages:
    391
    Location:
    Wyandotte Michigan
    A very good unit to start with. You will be very happy with this 737 once it’s been gone through. Many of the transistors in this unit are known to fail and should be replaced. These should all be listed in the BOM lists you’ve found.

    I don’t see a dim bulb tester listed in your post. Be sure to build one for yourself before you proceed. I was given the same advice when I was starting with my first unit, also a 737. The DBT is an essential tool which I have used on every unit that I have worked on. Only costs a few bucks to build.
     
  3. StraightCase

    StraightCase New Member

    Messages:
    23
    Location:
    Central Ohio
    That is the first thing I did. Thank you for the reminder! I am not taking any chances.
     
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  4. StraightCase

    StraightCase New Member

    Messages:
    23
    Location:
    Central Ohio
    As far as replacing the ELNA CE-W 50v 6800μF 85C main filter caps goes I have been doing some looking.

    If I wanted to stay at 6800μF it seems that either of these two may be a good choice:
    Vishay 256 PMG-SI: 594-MAL225631682E3
    Cornell Dubilier 381LX: 5985-85B-80V6800

    Digging deeper into the forum I have turned up this Nichicon UVZ at 10,000 uF being used: 647-UVZ1H103MRD

    But what about theses other 10,000 uF caps?
    Nichicon LGU: 647-LGU1H103MELB
    United Chemi-Con KMH: 661-EKMH630VSN103MA5
    Cornell Dubilier SLP: 598-SLP103M063H9P3
    EPCOS / TDK B41252: 871-B41252A8109M000
    EPCOS / TDK B41252: 871-B41252A6109M000
    Wurth Electronics WCAP-AIG5: 710-861020786030
    Wurth Electronics WCAP-AI35: 710-861140786024

    What is up with those last two Wurth leakage currents? According to mouser 12600 uA vs 2381.18 uA. That seems pretty significant! Which makes me wonder, is higher or lower leakage current better for this application?

    Will there be any harm, undue stress, or other ill iffects changing from 6800μF @ 50v to 10,000μF @ 63v?

    Sorry for all these questions. Trying to learn and think everything through as much as I can to avoid unnecessary trouble with this SX-737.
     
    Last edited: Dec 30, 2018
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  5. StraightCase

    StraightCase New Member

    Messages:
    23
    Location:
    Central Ohio
    First round of caps have come in, more on the way. Going to order the transistors too. I still need some help figuring out the few caps that I cannot source so I can make this a one timer. Don't want to have to take apart and reassemble any more than I have to. Should be a fun project and a great way to spend some time after my hernia surgery next week. Hahaha!
     
  6. markthefixer

    markthefixer On Hiatus, dealing with Dad's estate full time Subscriber

    Messages:
    21,201
    Location:
    Bensenville,Illinois
    First I don't want to reward private solicitations for help. NO private help, Public help is freely given WHEN I can find time to do it.

    This has been covered in the past, and plenty of the guys should remember.

    caps were -20% to +80% back then, so 180% x 6800 = 12,240

    going higher in capacitance MIGHT be helped by new stronger rectifier diodes between the caps and the power line to handle the increased surge.
    The e-core transformer DOES set an upper limit when saturated, unlike toroids which will surge huge amounts of power.Which is WHY the Pioneer models with Toroid transformers have power-on surge control circuits.

    Leakage is related to other things such as heating, more significant in the electromagnetic hell of a switch mode power supply. As the big caps get more expensive, they meet stricter and stricter specification relevant to these high performance power supplies.

    Other obsolete caps (not the huge main caps) have had currently available subs found.
     
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  7. StraightCase

    StraightCase New Member

    Messages:
    23
    Location:
    Central Ohio
    Thanks for the help markthefixer! I will take a look at possibly replacing that rectifier.

    Wound up going with the Cornell Dubilier SLP 598-SLP103M063H9P3 for the main filter cap replacement.

    Did a lot more digging and turned up additional results. Updated BOM has been posted. Pretty confident in this one, but if anybody sees anything strange let me know!
     

    Attached Files:

  8. pauls1

    pauls1 Active Member

    Messages:
    133
    Location:
    Essex, UK
    I'm sure that you know this already & it is something that you won't need just yet......but here it is....

    note: the DC neutral voltage and idle current procedure in the service manual incorrectly identifies adjusting VR1 (pin 3 voltage to ground) and VR2 (pin 17 voltage to ground) for 0v and VR3 (voltage between pins 2 & 1) and VR4 (voltage between pins 18 & 19) for 20 millivolts. It correctly identifies the VR1, VR2, VR3 & VR4 positions in the drawing.

    the CORRECT DC neutral voltage and idle current procedure is to adjust VR3 (pin 3 voltage to ground) and VR4 (pin 17 voltage to ground) for 0v and VR1 (voltage between pins 2 & 1) and VR2 (voltage between pins 18 & 19) for 20 millivolts.
     
  9. StraightCase

    StraightCase New Member

    Messages:
    23
    Location:
    Central Ohio
    Thanks for that! I found that out a couple days ago after trying to adjust it per the manual. Noticed they were switched around and found a thread with an updated page which I printed.

    Little off topic, but got the hernia surgery. Feels like a perpetual nut shot. Hahaha. Probably going to get started on this pioneer sometime next week depending on how I feel. Will post pics when I do.
     
  10. StraightCase

    StraightCase New Member

    Messages:
    23
    Location:
    Central Ohio
    Well I have been able to get some work done. Started on the power supply and protection boards. Definitely looks like someone has been in here before I was. There were some caps branded "Jameco" and encountered some semi-lifted pads on the power supply board. I scraped off some of the coating covering the trace, tinned it and soldered the lead onto the remaining pad and onto the newly tinned trace.

    Here is the picture album for those interested: https://imgur.com/a/uZXU0HW

    I have not thought this through thoroughly, but I have not seen of a good way to work on the tuner board without removing the string from the tuner on the board. Does anybody have any good tips to access the tuner board easily? If it comes down to it, what would the best way to remove the string from the tuner without getting things too messed up like the dial pointer be? Maybe restringing isn't that difficult, but I figured I would ask those with prior experience first.

    I understand that working on the tuner board will likely require an alignment and I will have a local shop perform that since I do not have the equipment or the desire to own such equipment.

    I have also uploaded a PDF of the BOM I am using.

    Thanks everyone for the help so far!
     

    Attached Files:

    Last edited: Jan 19, 2019
  11. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
    22,394
    Location:
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    Tape down the tuner string at the directional pulleys and the main pulley at the Vari-Cap. But 1st turn the tuner all the way to one end and two block it. Then tape the pulleys and string together. After you've loosened the wiring harnesses the tuner board should rotate toward the front of the unit (front of the board is pivot point.) . DO NOT unwrap any of the wirewrapped posts. If needed mark the lead and post with tape indicating the pin #, then De-Solder the pin from the board.
     
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  12. StraightCase

    StraightCase New Member

    Messages:
    23
    Location:
    Central Ohio
    Very smart! This way you effectively capture the mechanism at an extreme and can easily (in theory) replace it after the work is done. I will get some painters tape to avoid leaving adhesive on everything. Thanks for the tip!

    More progress has been made. The switch & volume, microphone amp, and control amp boards are finished. Pictures have been published to the album I have already linked. http://imgur.com/a/uZXU0HW
     
    Last edited: Jan 21, 2019
  13. StraightCase

    StraightCase New Member

    Messages:
    23
    Location:
    Central Ohio
    Everything up to this point has been going very well and I have been checking every time after I finish a board on my DBT. I am down to the power amp and tuner remaining.

    I am at the point where I am replacing the variable resistors VR1 - VR4 on the power amp.

    Let me use VR1 as an example.

    Here I have a picture showing the top side of the variable resistor. The red dots represent the location of each pin as seen from the same prospective. I have labeled the pin in the center as "C".

    [​IMG]

    The next photo shows the VR1 replacement next to its location on my print with the same center pin identified with "C". Am I correct in that pin "C" is going to be placed closest to C13 on the print?

    [​IMG]

    The variable resistor symbol (on the part) being on the pin "C" side is what is throwing me off. Like I said, I am not taking any chances with this amplifier and just want to be sure I am correct in the orientation of these variable resistors.

    EDIT 1: Mouser has just emailed me with an updated ETA on my back ordered KSA1220AYS for Q9 and Q10 on the power amp. June 24th......
    :eek2:

    Guess I am going to have to start searching for an acceptable substitute there. Will do that tomorrow...

    EDIT 2: Local electronics supply managed to have some in stock. No longer on the hunt there.
     
    Last edited: Jan 22, 2019
  14. ivandezande

    ivandezande Super Member

    Messages:
    2,069
    Location:
    Twin Cities
    You have the orientation correct, yes.
     
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  15. El1234

    El1234 New Member

    Messages:
    1
    Hey StraightCase,
    Can you please upload the excel file of the parts you ordered from Mouser website?
    I'm about to repair sx-737 myself.
     
  16. StraightCase

    StraightCase New Member

    Messages:
    23
    Location:
    Central Ohio
    It is already in post 10. I must let you know that I make no claim on the accuracy of the content. I will say that it is HEAVILY derived from content posted by markthefixer.

    Now, back on the topic KSA1220AYS for Q9 and Q10 on the power amp. Local electronic store told me over the phone they had some, what they actually had was an equivalent part NTE374. Went ahead and got a pair because I am SOL til June 24th.

    Now I know NTE is not exactly the most desired from previous reading, but I am SOL until June 24th. What say the forum? Should I go ahead and install them, or use something else entirely, or wait?
     

     

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  17. LesE

    LesE 110284 Subscriber

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    Location:
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    Last edited: Jan 22, 2019
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  18. StraightCase

    StraightCase New Member

    Messages:
    23
    Location:
    Central Ohio
    Yep, that looks like a winner right there! I am going to order a set. Thank you!

    Now I am just waiting on those after which I will start on the tuner.

    I went ahead and got the main filter caps in. They were smaller in diameter than the old ones. I just took the jacket off some romex that was laying around and wrapped it around the fixture a few times. It did the job nicely. The new caps were snap in capacitors. I cut the old wires at the wrap, stripped the insulation back and soldered them directly to the snap in posts. Not the prettiest job, but it will work and that is what matters. Again, pictures are in this album: http://imgur.com/a/uZXU0HW
     
    Last edited: Jan 22, 2019
  19. StraightCase

    StraightCase New Member

    Messages:
    23
    Location:
    Central Ohio
    Ok, the power amp has been completed. I installed TTA004B in Q9 and Q10 and TTC004B in Q7 and Q8.

    I turned all vr1-vr4 full ccw. (Vr3 and 4 will spin freely and have no stop) the protection relay did not kick until I turned either VR1 OR 2 up about half way. I attempted to adjust neutral voltage and idle current with no success. It seems the variable resistors have no effect on the voltage.

    Should I post voltages of pins 1-19 on the power amp measured between the pin and chassis ground? On DBT (60 watt incandescent) or full power?

    Again pictures are posted here: http://imgur.com/a/uZXU0HW
     
    Last edited: Jan 24, 2019
  20. StraightCase

    StraightCase New Member

    Messages:
    23
    Location:
    Central Ohio
    Ok, I stepped away for a while and came back to it. I didn't relize how much you had to turn these new variable resistors. Everything I have checked so far is working correctly and I have put it on main power to perform the adjustments.
     

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