Fisher 500, how much can they be improved

Discussion in 'Fisher' started by Sam08861, Jun 11, 2018.

  1. thornev

    thornev Active Member

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    373
    Location:
    Mid Hudson Valley, NY
    Good suggestion rider. If I go forward with "take 3", I'll add that picture too.
     

     

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  2. thornev

    thornev Active Member

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    373
    Location:
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    Here is the underside of the Unity Gain board I built with annotations. If you view this image along with the images in post 12 and the thread referred to in that post, maybe someone can tell me what I've done wrong to cause distortion when I installed the board into my 500-C.

    Note that there are a few places marked "GROUND". They are all connected via the grey wire that runs vertically on the underside of the board.

    I apologize for the scribbling mess. My editing program doesn't allow me to go back in time to erase stuff (I can erase only the LAST edit). I had a hard time figuring out how to represent the fact that some components are connected in parallel such that the non-ground leads are connected to each other. They are not connected to a single wire that runs across the board as it does on the schematic.

    I will post a picture of how I wired the board the next time I open the receiver. It's fairly easy to describe. I disconnected the wires from the 2 center posts on the volume control. Then I took the LEFT IN and RIGHT IN wires from the board and connected them to the center tabs. I connected the wires I disconnected from the center tabs to the LEFT OUT and RIGHT OUT leads coming from the board. The diode lead from the board was connected to the same place at which I connected the IBAM board to get current - pin 4 of V14 which is where the SDS Labs board filament wire is connected i.e. the B- (I think). The ground lead from the board was connected to the same ground I used for the IBAM board which I think is just a lug on one of the terminal boards on the chassis. I tested with a DMM to ensure there was continuity between bare metal on the chassis and the ground on the board.

    UPDATE Jun 16... I've added the annotated TOP of the board so one doesn't have to go to an earlier post, back and forth, to match components.
     

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    Last edited: Jun 16, 2018 at 11:12 PM
  3. Sam08861

    Sam08861 Active Member

    Messages:
    355
    Location:
    Northwestern NJ
    When the weather gets worse or we get a rainy weekend and I'm not compelled to be on my boat, I'll start my build. Hopefully you'll get it figured out by then :)

    If not, I'll post as I go and we'll see if we can't get this to work.
     
  4. thornev

    thornev Active Member

    Messages:
    373
    Location:
    Mid Hudson Valley, NY
    Thanks, Sam. In the meantime, I'm going to try a variety of tasks to see if I can figure it out. Thorne
     
  5. Sam08861

    Sam08861 Active Member

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    355
    Location:
    Northwestern NJ
    Do you have the data sheet with the LF353N pinout? In my limited experience the pins have been odds on one side and evens on the other, but that said, it's been very limited experience with ICs.

    Edit, never mind, this looks correct as well.
     
  6. thornev

    thornev Active Member

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    373
    Location:
    Mid Hudson Valley, NY
    Attached, Sam.
     

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  7. Sam08861

    Sam08861 Active Member

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    Thanks Thornev. Only thing I can think of is that you've jumped (connected) pins 1 and 2 and also 6 and 7 as I would have too from reading the schematic on the prior page. Wondering if this doesn't negate the internal circuit of the IC and perhaps wasn't meant to be interpreted that way. Maybe that's something to try. (removing the connections between those pins)
     
  8. thornev

    thornev Active Member

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    373
    Location:
    Mid Hudson Valley, NY
    Sam - I've attached the schematic for this mod. See if you still think those pins should be separated after you look it over. Thorne
     

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  9. Sam08861

    Sam08861 Active Member

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    Location:
    Northwestern NJ
    Yep, that's the one I was looking at. I'm not sure, but what I'm thinking is that logically, by connecting 1 and 2, the internal 1 to 2 connection is bypassed. Same goes for 6,7.

    Therefore, I was thinking that by removing the connection on the pins, one re-introduces the internal connection into the circuit and perhaps the schematic is showing this internal connection, but being a novice am not sure.

    My thought was it might be easy enough to try and see if it works.
     
  10. Sam08861

    Sam08861 Active Member

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    Location:
    Northwestern NJ
    PS, hopefully that makes sense to you and if not I can try to explain better.

    My lay theory is that the connections on the schematic between 1/2 and 6/7 are the internal connections within the chip and not at the pins (external) and so don't need to be connected at the legs.
     
  11. thornev

    thornev Active Member

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    373
    Location:
    Mid Hudson Valley, NY
    If I disconnect 2 from 1 and 7 from 6, then 2 and 6 aren't getting connected to by anything. Does that seem to make sense?

    Just read your last reply. I see what you're saying. Hmmm. Yeah, it almost looks like an infinite loop having 2 connected to 1 and 6 to 7. 2 and 6 are INputs according to the datasheet. That would mean that because 1 and 7 are OUTputs, 1 goes into 2 which outputs through 1 which goes into 2 which outputs through 1 which goes into 2 which... etc.
     
    Last edited: Jun 19, 2018 at 12:05 AM

     

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  12. Sam08861

    Sam08861 Active Member

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    I do see what you're saying now. I see that 8 goes to ground and wondering if 2 and 6 should go to ground too but am out of my depth with this to be honest.

    Hopefully someone who has been successful with this will post his/her connections to the unit and a close up of their boards front and back.
     
  13. thornev

    thornev Active Member

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    373
    Location:
    Mid Hudson Valley, NY
    Calling all Gillespies; calling all Gillespies.
     
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  14. Sam08861

    Sam08861 Active Member

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    355
    Location:
    Northwestern NJ
    One other thing you might have already confirmed is that the outer portions of the repurposed rca jacks are going to ground and have a solid connection.
     
  15. thornev

    thornev Active Member

    Messages:
    373
    Location:
    Mid Hudson Valley, NY
    I'm not using the RCA jacks. I'm just inserting the module into the circuit that is at the center tabs on the volume control. And I doubt 2 and 6 go to ground because Dave's schematic would show their going to ground and he didn't do that.
     

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