Pioneer SX-737 Restoration

Discussion in 'Pioneer Audio' started by Spenser, Jan 29, 2018.

  1. Spenser

    Spenser AK Subscriber Subscriber

    Messages:
    225
    Location:
    Pittsburgh, PA, USA
    Getting going on restoration good-condition, working Pioneer SX-737.

    I'm still relatively new. That is to say just four Pioneer and Kenwood integrated amplifier repair and restores under my belt. First receiver.

    I plan to post progress reports and seek assistance from time to time. This will take several weeks. No rush -- do it right the first time.

    Comments, suggestions and questions welcome.

    Report 1:

    Switches and potentiometers cleaned and lubed. Changed out AWX-071 C5 while I was in there. Had to jockey some wires out of looms and guides to get enough slack to move the control boards. Freed the equalizer board from its mounts in the process. Left it hanging out there for when the time comes to get to it. Not going to do the microphone board.

    Lamp order in to Wojo. Going whole hog. Several were out but would have replaced all anyway. Staying all incandescent.

    The following were all good. Power supply readings; fuse continuity; protection circuit amplifier output readings; power amplifier DC neutral voltages and idle current (bias and offset).

    Note: service manual procedures for bias and offset are wrong. Link to correction.
    http://audiokarma.org/forums/index.php?threads/notice-to-all-new-sx-737-or-7730-owners.464083/

    Old fuses will stay in for the restore; will be replaced at end of project.

    Next Moves:

    Change out (electrolytic) capacitors, diodes and transistors in power supply.

    Re-check power supply readings.
     
    Last edited: Feb 5, 2018
  2. Spenser

    Spenser AK Subscriber Subscriber

    Messages:
    225
    Location:
    Pittsburgh, PA, USA
    I have a question. I'm on the power supply board. I've completed the main rectifier diodes and the three 330 uF capacitors C 7, 8, 9. Tackling hard-to-get-at stuff first.

    Were it you would you fire it up a couple times on dim bulb tester in the middle of doing the power supply to see if things are working? Poop one out there Jaybo and see where we is. I had a boss who used to say that. Mortar team reference I think.

    Two technique tips. One, you guys all know this but shoot I just recently learned that factory-tape-packaging -- diodes, transistors, capacitors whatever -- is often heat activated. Comes off easy as pie if you wave a lighter under it briefly and then pull the tape free. Jeepers.

    Two, component-lead-bender-tool is so inexpensive and nice to have especially when it comes to things like thick leads on big rectifier diodes. Take the old one you just removed and line it up on the tool to find the best spacing slot for bending the leads on the new ones and you are good.
     
    Last edited: Jan 29, 2018
  3. larryderouin

    larryderouin You can be sure if it's Westinghouse??????? Subscriber

    Messages:
    20,801
    Location:
    Glen Burnie Md.
    A lot of guys change a few parts and then test the unit. It keeps you "Honest" if you will. Actually it's easier to check after each 5 parts and find one SNAFU, than doing the whole board of 30-40 pieces and then try to figure out which one went "Tits-Up".

    I bend them by hand with a dental pick to make the bend. The tool you use is up to you. If it works for you, by all means use it.

    I just pull off the tape, and scrape off the heavy residue with fingernail. That section is 99% sure to be cut off anyway, depending on how high you mount the part. On the one's I mount high (hiwattage resistors, diodes, etc.) I dip the ends in flux and heat it slightly 1st.
     
    UncleBingo and kvining like this.
  4. Spenser

    Spenser AK Subscriber Subscriber

    Messages:
    225
    Location:
    Pittsburgh, PA, USA
    OK. Voltage readings taken again (power supply and protection), am now one third through replacing components in the power supply board. Voltages still good.

    Adding a note here on pre-existing conditions:
    A) Seems to take longer than a normal machine would for protection relay to kick in.
    B) Dim bulb tester does not dim as much as seems (to me), it should. Using 40 watt bulb. Throwing a 75 watt in there for the next go 'round.

    Stupid question: is it normal (with dim bulb tester in line), if you turn the volume up a little, bulb burns brighter and machine goes into protection?
     
    Last edited: Jan 30, 2018
  5. rcs16

    rcs16 Super Member

    Messages:
    3,184
    Location:
    Baldwin, Ontario, Canada
    Sounds like you are making good progress.
    A 40W lamp is on the low side, I use a 100W lamp as a minimum, higher for bigger units. The DBT will affect the relay turn on time esp if you are using a low W lamp. the smaller the lamp, the longer it takes for ecaps to charge and voltages to stabilize.
    The DBT is there just as a protection against a gross failure. If the lamp dims, protection relay engages, you are usually good to take it off the DBT. I have a bypass switch on my DBT, so that I do not have to re-wire my setup to take the lamp out of ckt.
    What you are experiencing is normal, so do not turn up the volume while on the DBT.
     
    Last edited: Jan 31, 2018
  6. Spenser

    Spenser AK Subscriber Subscriber

    Messages:
    225
    Location:
    Pittsburgh, PA, USA
    Good advice. Starting to better understand DBT physics. I like the DBT bypass switch idea.Thank you all for hanging in there with me.

    The seeming delay on relay kick-in is sans DBT. The delay may be imagined or normal. No prior experience with Pioneer SX-737.

    I need to find me a couple 100 watt incadescent bulbs. Haven't looked yet to see if truly thing of the past at places like Home Depot. There is a nearby "hamfest" coming up end of February could be a possibility.
     
    Last edited: Jan 30, 2018
  7. Cuppy

    Cuppy AK Subscriber Subscriber

    Messages:
    183
    Location:
    Maine
    You can try looking for a 100 watt rough service bulb as used in drop lights. If Home Depot doesn't carry them you could try a local auto parts store.
     
  8. rcs16

    rcs16 Super Member

    Messages:
    3,184
    Location:
    Baldwin, Ontario, Canada
    You can also use 150W flood or brooder lamps, certain incandescent lamps are exempt from the US DOE lamp ban.
     
  9. larryderouin

    larryderouin You can be sure if it's Westinghouse??????? Subscriber

    Messages:
    20,801
    Location:
    Glen Burnie Md.
    I've found 100W bulbs in Grocery stores, Lowes, Ace Hardware, Dollar Gen'l, etc. So don't limit yourself to H.D.

    100W is sufficient to load down the 737. 150W won't load it down at all, meaning no startup flash of any significance.
     
  10. Spenser

    Spenser AK Subscriber Subscriber

    Messages:
    225
    Location:
    Pittsburgh, PA, USA
    Thanks! Found GE model specialty 72527 "rough service 100" at a True Value hardware in Coraopolis. Pa. USA, on the way home from a job site. One of those disappearing old neighborhood hardware stores we so love.
     
    merlynski and UncleBingo like this.
  11. UncleBingo

    UncleBingo AK Subscriber Subscriber

    Messages:
    487
    Power amp transistors would be top priority for me. 2SA725 and 726 got to go. Also 2SC 1451. Very easy to access. Get them out of there. Get the other 2sa725's and 2sa726's out asap after that.

    I just rebuilt one of these. Elna Silmics in the power amp sound pretty good (where they'll fit). The Nichicons were a little bright imo.
     
  12. loweran

    loweran AK Subscriber Subscriber

    Messages:
    972
    Location:
    Austin, Texas
    Interesting UncleBingo. Did you go with Nichicons and decide to swap them out with the Elnas?
     
    UncleBingo likes this.
  13. UncleBingo

    UncleBingo AK Subscriber Subscriber

    Messages:
    487
    I used Nichicon as I had them on hand. I did all but the tuner and main Power supply cap. After rebuilding the amp was a little bright for my taste. I swapped a couple of power amp caps out with the Elna Silmic simply because those caps were the easiest to get to and it made a nice difference. I'll look up which caps. I also made sure I used Wima polypropylene films for the 1uf caps instead of the Wima polyester I accidentally ordered once before. I do wonder if the Panasonic films would be a touch warmer sounding. C7 47uf 50V C8 47uf @ 50V C9 220uf C10 220uf ( iirc only 220uf @ 50 were available from Mouser in the Silmic II- they wouldn't fit flat on the top of the board without obscuring some resistors, so I hung them from the bottom of the board and covered any exposed lead with heat shrink tube. I wouldn't do this on a clients amp, but on my own amp it was fair game for an audition. It wins and will get a dab of silicone to hold it in place.)
     
    Last edited: Jan 31, 2018
  14. Spenser

    Spenser AK Subscriber Subscriber

    Messages:
    225
    Location:
    Pittsburgh, PA, USA
    Thank you. Good thinking. I'll switch out those 2SC1451 on the power amp board first thing.

    Don't have the 2SA726 on the power amp board. Instead have the 2SA763. Same on the equalizer board. Not sure on control amplifier. Put that one back up in place after cleaning for the time being.

    On the tuner board DO have the 2SA275. I was going to ask later whether switching out those two in the tuner -- Q8 & Q9 -- is warranted; also which capacitors on the tuner board warranted. I don't mind pushing it into need for aligment-tweaking if results in significant improvement in sound quality and future trouble free operation. FM Stereo is my main mode.
     
    Last edited: Jan 31, 2018
  15. loweran

    loweran AK Subscriber Subscriber

    Messages:
    972
    Location:
    Austin, Texas
    When I did mine I just replaced all the caps, all the silicone and pretty much overhauled the power supply. Been rock solid performer since and one of my best sounding units to date.
     
  16. larryderouin

    larryderouin You can be sure if it's Westinghouse??????? Subscriber

    Messages:
    20,801
    Location:
    Glen Burnie Md.
    You can replace the 'lytics on the tuner. And the 725's. It won't hurt or improve the tuner other than making it more reliable. Lytics try as much as possible for UKL (low noise type) series Nichicons. Get those sky blue Sanyo solid Aluminium capsistors outta there.
     
  17. Spenser

    Spenser AK Subscriber Subscriber

    Messages:
    225
    Location:
    Pittsburgh, PA, USA
    Thanks Larry on the tuner-section-feedback. Thanks Loweran.

    Report 2: Finished the power supply, including the filter caps (see below component choice). Reset bias and offset. Skipped ahead into the power amplifier for a minute -- replaced those two 2SC1451 transistor known trouble makers. So far so good.

    647-LKS1J822MESC

    Pin Volts
    14 34.7
    13 -12.8
    19 13.0
    7 38.4
    9 37.1
    10 -37.0

    Next Moves: protection board and relay.

    Here's what these short fat 8200uF 63V LKS Nichicons look like mounted.
    Pioneer 737 Filter Caps 02-05-18.jpg
     
    Last edited: Feb 5, 2018
  18. Spenser

    Spenser AK Subscriber Subscriber

    Messages:
    225
    Location:
    Pittsburgh, PA, USA
    Question: How best to make connections at "snap on" terminals? I used small, 'crimp barrels' cut from little spade terminal connectors, to hold each of the four, three-lead packages together while receiving solder. Made sure to apply some rosin to the former-wire-wrap ends. Seemed to work well enough. Solicting suggestions for future.
     
    Last edited: Feb 6, 2018
  19. markthefixer

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

    Messages:
    20,889
    Location:
    Bensenville,Illinois
    Small PC board is my usual solution.
     
  20. Spenser

    Spenser AK Subscriber Subscriber

    Messages:
    225
    Location:
    Pittsburgh, PA, USA
    Thank you. That sounds like a good idea; a set of skills I would like (in time) to have. I've seen a small PC board etched in a YouTube repair and restore by X-Ray Tony B.
    I'm almost embarassed to submit the attached but thought it might be helpful in case people would like to see.
    Pioneer 737 Filter Cap Connecitons 02-06-18.jpg
     
    Last edited: Feb 6, 2018

Share This Page