Pioneer F-91 reference tuner assistance needed

Discussion in 'Pioneer Audio' started by Roboneal91, Mar 20, 2017.

  1. Roboneal91

    Roboneal91 Member

    Messages:
    87
    I've got a newly acquired pioneer f91 it's in awesome shape powers on and shoots it's 330 hz test signal perfectly, memory buttons work, muting works perfectly and there's no hiss or hum while muted, but there's one major issue there's no radio..everything works except what it's supposed to do, no am or FM just static buzz like its not picking up any signal I've taken the top off and nothing is visibly fried, as I said with an am or FM antenna hooked up there is nothing but static and the tuner won't lock onto or find a single station, if anyone has some ideas they would be greatly appreciated, I'm attaching a quick photo of the tuner and I do have the service manual as well if anyone might need to see a photo of a certain page
     

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  2. rcs16

    rcs16 Super Member

    Messages:
    2,815
    Location:
    Baldwin, Ontario, Canada
    Near impossible to say what's wrong with it. I looked at the schematic as well. Can you understand them? There is one hell of a lot of stuff going on in there. We're are having a fun timing fixing a SX-1980 FM tuner section, let alone this mess of electronics.
    I always start with the powers supplies, you might get lucky.
    Did you know it was not working before you bought it? Good luck finding someone to fix it, I do not think it is going to be cheap.
     
  3. Roboneal91

    Roboneal91 Member

    Messages:
    87
    I actually got it for free (almost Shit when the old gentlemen said I could have it, I'd just have to find the issue) with the purchase of my new m90, these models are built like tanks that's why I wanted to see if anyone that frequents this has worked on them, the m90 is in perfectly working condition and I've got it running my Sansui sp 5000s, I'm just scared to see what it would cost to get a service tech to fish through the board on this thing and find the issue, it takes 12 screws just to get the bonnet and rosewood sides off the tuner, and I can slightly understand them, I can trace a signal path but beyond that when it comes to understanding how the resistors diodes caps ect work together to create sound I'm lost
     
    Last edited: Mar 21, 2017
  4. rcs16

    rcs16 Super Member

    Messages:
    2,815
    Location:
    Baldwin, Ontario, Canada
    Well the price is right, but if it does not work, not much use to you or anyone else unless they use it for parts to fix another one. Obviously the original owner did not mange to get it fixed, so you have to ask or wonder why that is since it is worth a fair buck if it is operating properly?
    It is a rare and complex tuner so very few would have ever worked on one. I certainly have not, but I see what I would be up against after glancing at the schematic and SM. There are many rare, hard to get or impossible to get parts in there. Hopefully it is not one of them. Do not know until you dig in there and figure out where the problem lies. If there is no AM nor FM audio then it is a common component, powers supply, controller section. If it can not scan/lock to a good input signal on AM or FM, then it sounds more like a controller/PLL section issue.
    Where are you located? Finding someone local who has the skills and equipment might be be a challenge or impossible depending where you are located. Which means the extra cost of shipping just to find out that is un-servicable, not a good proposition to be faced with. If you were local to me I'd take a look at it.
     
  5. Roboneal91

    Roboneal91 Member

    Messages:
    87
    I'm in the Hampton roads area of Virginia so there's definitely some individuals around here but as you said the issue is finding them, I know of a repair shop but it wouldn't be cool to pay 150 for labor alone and I'd love to avoid that if possible, I'm going to try to do some simple checks with my meter in the areas you said and see if it's something simple possibly another thing is there are about ten tuning "screws" inside it for bias adjustment and such, could it possibly have something to do with those not being correctly oriented?
     
  6. rcs16

    rcs16 Super Member

    Messages:
    2,815
    Location:
    Baldwin, Ontario, Canada
    Do not mess with any of those tuning coils/transformers. By the sounds of what you are saying, you do not know what you are doing, probably have never worked on one of these, or any tuner for that matter, so part from measuring the power supply voltages, I'd say leave it alone as you will probably do more damage to it by fiddling with it.
    Seriously, you would not pay someone ~$150 to service/reapair this tuner for you? You expect someone with the knowledge and equipment to repair a complex tuner like this to work for peanuts, good luck with that. I am done with this thread, if that is the case.
     
  7. Roboneal91

    Roboneal91 Member

    Messages:
    87
    Everyone on here is always so snippy, no I haven't worked on strictly a tuner, but I'm not completely incompetent, and what sucks is it's not a "friend" I'm speaking of in regards to that, it's a repair shop they charged me 75 in labor, just labor, to change 2 transistors and two caps on a Sansui b 55 those are about as simple as they come, it was a learning experience and I'll be doing that myself from now on, but when it comes to a piece such as this no I don't want to break it, so I put the issue up on here to see if the millions that frequent could point me in the right direction at least, before I do possibly pay upwards of 150 in just labor.
     
  8. rcs16

    rcs16 Super Member

    Messages:
    2,815
    Location:
    Baldwin, Ontario, Canada
    You are not going to get much help here, even if there are millions that frequent your post.
    One thing that you seem to fail to understand, it is not the cost of the "2 transistors and two caps " it is finding them.
    Your probable only and best chance to get any help or advise is to try where the real FM tuner experts reside, not here.
    https://groups.yahoo.com/neo/groups/FMtuners/info
    See where that gets you. Still you need to know how to troubleshoot a sophisticated tuner, if it is not a simple problem and have the necessary test equipment if required, which is not cheap to buy.
    If you want to part with it, PM me. It could get involved getting it fixed, certainly not an average tuner, might be impossible to repair if one of those specialized chips are dead and are unobtainable, a chancy proposition.
     
    w1jim likes this.
  9. restorer-john

    restorer-john Super Member

    Messages:
    3,684
    Location:
    Australia
    The F91 is one of the most complex tuners built. Very specialized gear needed to set it up and it will take time to troubleshoot it correctly. It is not a job for a hobbyist.
    Whatever you do, don't adjust anything inside or it will become worthless.
    Find a tuner expert and pay the money to have it fixed or unload it to someone who will fix it properly.
     
  10. Roboneal91

    Roboneal91 Member

    Messages:
    87
    I'm going to do some checking around and see what kinds of quotes I can get, I haven't messed with anything inside but there's no telling if that's the reason it won't work to begin with, someone who had it before not knowing what they were doing, it's a beautiful tuner so I do really hope I'll be able to get somewhere and I will let you know rsc16 if the costs are too pricey for me to consider, it's crazy to think I was given one of the best tuners ever built, thank the lord for 80 year old men with old values, I'm gonna update the thread once I have some new news
     
  11. I LIKE MUSIC

    I LIKE MUSIC Super Member

    Your tuner may or may not be a door stop at this time, there are a some simple tests that can be done and it might be a simple problem.

    Since it makes noise in both the AM and FM modes that would make it appear that both IF chains and detectors are working.

    On thing that is common between the AM and FM sections are the varactor tuning diode voltage. Not only does it drive the diodes in the RF front, it drives the diodes in the local oscillators. These diodes take the place of the mechanical tuning capacitor in an analog tuner.

    The circuit that drives these diodes is just a handful transistors.

    The output of which has a 2.2 microfarad capacitor (C501). If it is shorted or electrically leaky , no tuner. There is an IC (IC 501) that drives these transistors and this IC is driven by IC 502, the tuner control IC.

    I would start by measuring the voltage on C501. It should change as the tuner's frequency is changed. If no voltage there or it does not change I would check the output of IC 502 (pin 7), the voltage there should also change as the tuner frequency changes.

    This may not be the issue, but it is fairly simple trouble shooting and the AM circuit is fairly simple. It sends it detected audio to the same place the detected FM audio goes and there is noise output on both AM and FM.


    Of course start by making sure all of the power supply voltages are present and correct.

    After that a digital oscilloscope would be handy to look at the serial data and see if IC 502 is getting the correct data and clock pulses.

    This tuner is not that hard to trouble shoot if a person has had experience with both RF and digital electronics.

    I have not checked on parts availability.

    The OP has indicated that the display works, channel scan works, mute works, AM/FM switching works. This is an indication that the tuner control IC (IC502) is possibly working okay. This is the IC that drives the PLL IC (IC501) that drive the handful of transistor that drive the varactor RF front end diodes and the local oscillator varactor diodes.

    Again, one would need a way to look at the serial data lines, but that is not a big deal for someone that has a digital oscilloscope.
     
    Roboneal91 and Oldsansui441 like this.

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