QRX3000, QRX7500, lots to do on these ones among other jobs...

Discussion in 'Exclusively Sansui' started by kevzep, Sep 9, 2017.

  1. kevzep

    kevzep Its all about the Music

    Well, I thought I might do a thread on this one, I have a very good customer who collects QRX's, and he's started bringing them to me for a good going over, I did his QRX2000 last week, didn't need too much, had a couple of blown rail fuses, very dirty switches and pots, and the tuner was Waaaaaay out of alignment, maybe the golden screwdriver had been in there, I don't know for sure though.
    It turned out very nice, it went from a scratch static-y sounding FM tuner receiving only one station (I can actually only pick up three stations here on a dipole as I am rural, 5 element high gain antenna on the way!!) to receiving 5 stations, worked so well, I have my own McInotsh MR78 in the Que for an alignment!!
    I did a quick repair and a light recap on a AU417, and a check over on a Sansui 310.

    Now I have this QRX3000 and a QRX7500 to do.
    This 3000 is humming, and the right front channel is very hot, all the switches are intermittent, and yes of course, the tuner is off as well.
    I'll start in the audio section and this one will get a decent recapping. It is very clean inside, a quick brush/vacuum has it looking pretty good....
    So I'll get into it, heres a few pics of whats been going on here lately and of course a few shots of this very fine example of a QRX3000.
    First one is my JVC 4VR5446 on the bench for lamps, bias, DC offset, switch cleaning, tuner alignment.
    Second shot shows the lamps all fitted courtesy djwojo, I always get the lamps from Dave, he is very helpful and knows his lamps!!
    Third shot shows one of the 10 Crown Macrotechs 5002VZ's I am fitting some new poweramp sections to, the original ones have a corrosion issue, so our parent company has a tech who redesigned the poweramp basically, and now boards are manufactured and improvements for reliability have been made, there are a lot of steps to do as I assemble the boards then have to do all sorts of "factory" settings and tests, it takes a good 4 hours to run one amplifier up....I think in this pic I was setting the dynamic balance and the error amp sensitivity...
    Shot 4,5,6 is the QRX3000, you can see how clean and nice this example is....very nice.
    Last shot is the QRX2000 during tuner alignment...
    So there it is, a busy week...
    IMG_4925.JPG IMG_4927.JPG IMG_4928.JPG IMG_4931.JPG IMG_4932.JPG IMG_4934.JPG IMG_4922.JPG
     
  2. BLAH BLAH

    BLAH BLAH AK Subscriber Subscriber

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  3. JOMARK911

    JOMARK911 Super Member

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  4. stereofun

    stereofun AK Subscriber Subscriber

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    It's nice that you get to work on and test out all these different Sansuis - are any of the QRX cap coupled ?

    Cheers and thanks for sharing your endeavors :thumbsup:
     
  5. kevzep

    kevzep Its all about the Music

    What is interesting Tom, is the little QRX2000 which is, and I hope you're sitting down, 7watts per channel, is in fact direct coupled.
    The 3000 is as well.
    These receivers are built very well, must be around the same period as the single digit series I'd say.
    I like the green lighting.
     
  6. stereofun

    stereofun AK Subscriber Subscriber

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    7 Watts ! - wow, that turns my lowly 505 at 23 w, into a monster amp :rockon: Interestingly the QRX 6500 appears to be cap coupled, perhaps it was right around the time when they left the cap scheme and began direct coupling. We kind of see that with the 7000 / Eight - they look identical on the outside, but the 7000 is cap coupled and the Eight, Direct....

    Are you still waiting for a 999 balance pot to test out the recent 999 rebuild, curious how it came out sonically ?
     
  7. kevzep

    kevzep Its all about the Music

    I thought it was interesting these two QRX's weren't cap coupled. Minuscule amount of power output isn't it...
    A friend of mine has a Quadraphonic test record, so I thought I might get that off him and get a quad cartridge so I can properly test and set up that part of them.

    Yes we are still trying to locate a balance pot, the owner is in Japan at the moment searching for rare and interesting HiFi gear, and he says he's found a source for spare parts so thats good, once hes back we'll finish the job and assess the work done.
     
  8. rcs16

    rcs16 Super Member

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    Hi kevzep,

    Nice bench setup
    What are you using for equipment to do this. I think I see a HP 8656B RF SG?
    I have a HP 8656B and a new to me, HP8904A as a mpx sig gen, it was suggested to me by Bob at fmtuners forum as a good unit to have. It works real well, I have measured a Kenwood KT-8300 at 0.04% THD in wide BW mode.
    Interested to hear your results using quad phono, what is the record encoding type, QS,SQ,CD4?

    Cheers
    Rick
     
  9. kevzep

    kevzep Its all about the Music

    Thanks Rick, the HP is a 8675A, 1.04ghz RF gen, underneath it is a Marconi 2018, 520mhz which is the back up.
    Then there is a Panasonic Multiplex Gen sitting on top, it also has the pre-emphasis so I can check frequency response, there's a couple of VTVM's there, I used the RCA the heathkit is the spare but its fully functional and calibrated.
    I have been using the Siglent function gen to sweep the IF and Discriminator as well as basic stereo audio functions as well....but I have a sweep gen with markers on the way, I find its not an exact science trying to center an IF without markers.
    I will be honest I do need to land a distortion analyzer into the setup, and of course the big one is I will be adding a spectrum analyzer too as I repair Wireless microphones, and wireless Personal In Ear monitoring systems, hence having a signal gen which goes up to 1ghz....they run in the 500-700mhz range.

    I have a test CD4 record which came my way by chance, of course the early Sansui stuff is QS and SQ so I wasn't able to test the decoder in the 2000, however these two QRX's have CD4 so I will use it to do these ones.
    I need to get a better cartridge though ...

    There's always more gear to add to the setup, it never stops!!
     
  10. rcs16

    rcs16 Super Member

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    Thank kevzep, I'll have to look at the specs on a 8675A.
    As for thd analyzers, I use a Amber 3501, old but it works great for me. One option for you is a low thd source ( victor on diyaudio has some good ones for sale) and a 24 bit sound card as a cheaper solution.
    If you are really adventurous, could build Bob Cordell thd analyzer from the past, available sch on his web site, cordellaudio.com
    I also have a HP 3325A for a sweeper, you can find these cheap these days too.
    keep up the good work
     
  11. kevzep

    kevzep Its all about the Music

    Thanks Rick, I just checked out the 3325, I think I might get one of those, I like the HP gear....inutitve and easy to use...
    I will also check out those Dist analyzers too, thanks for the tips...
     
  12. rcs16

    rcs16 Super Member

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    Must be a 8657A, never made a 8675A :)
     
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  13. kevzep

    kevzep Its all about the Music

    Hahaha, yes you are right, its either my lightning fingers on the keyboard or a touch of dyslexia!!

    They are very nice gen's though.
     
  14. rcs16

    rcs16 Super Member

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    I use to service/cal them many moons ago when I worked as a tech at Motorola in the test lab.
     
  15. kevzep

    kevzep Its all about the Music

    Oh, well, now you've done it, PM's will be flying your way!! I have a spare 8657A under the bench with an output level issue which I wanted to get going and sell. The fault is eluding me at this point.
    When I have a bit of free time I will get it back on the bench.
    The one I have in service was a parts or repair purchase, the fault with it was simply a couple of Tantalum caps had exploded in one of the supplies....easy fix.
     
  16. Overundr1

    Overundr1 AK Subscriber Subscriber

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    Those natty tantalum tantrums :biggrin:
     
  17. rcs16

    rcs16 Super Member

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    Will see what I can do to help you out. I have the service manuals for my 8656B's, not sure how much difference a 8657A is, not a whole lot I would think, I would have to look further. Certainly a lot easier to fix if you have a working one to compare against. IIRC, leveling is done with a bunch of PIN diodes. Could be an attenuator issue as well.
    About a year ago, I was using the 8656B and the levels were wrong, so I looked at it, I found that one of the control wires to one of the attenuators was loose connecting to a feedthough cap , a poor solder joint from the factory I suspected, after all these years, a simple fix, I was lucky on that one.
    I bought my unit from a EE that got it at a Motorola auction when they closed a lab in Toronto, it failed cal for no AM modulation, it happened to be a MC3410 10-bit DAC, that I was lucky enough to have as a spare part.
    I have a old HP 436A power meter and a 8484A sensor/cable, another cheap eBay find, this equipment is required to test the attenuators and leveling ckts.
     
    Last edited: Sep 14, 2017
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  18. kevzep

    kevzep Its all about the Music

    Thanks Rick, I'd appreciate that, not exactly sure when I'll get to it but I'll flick you a PM when I'm in a good place to be able to get it on the bench. I wanted to get a level meter, I might get these things before I start the project.
    I am feeling the level is low before the attenuator, and yes they do use pin diodes, you can see at least the step attenuator is functioning. I thought it was one of those TFM2 passive RF mixers, but its not that, but because I haven't really got the correct gear to measure the RF level from the VCO its a crap shoot at best...
    Anyway, we'll have a look at it later...
    I am hoping it will be something simple, it usually is when its a global type issue such as this..
     

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