weird repairs WTF .....

Discussion in 'Amp Tech Center' started by 24 track, May 13, 2021.

  1. 24 track

    24 track Doctor of Teleocity Ad Free Member

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    last year i did a repair to a fender super sonic amp , required an extensive general fix with a few mods i did for improvement , like the ribbon cable that goes from the front controls panel carries audio and is not shielded so i covered it with copper tape and grounded it to the chassis this quieted down a lot of the internal hum.

    after the repair and all was working I discovered the reverb circuit was not happening at all , so I replaced the reverb transformer, and the transistors in the circuit ,( I ordered the transformer in september 2020 it showed as instock with fender , it finally arrived the end of April 2021 ) after the new parts were in place , no joy , it did not work still , so i tested the return from the reverb tank it was quite alive, so i reversed the reverb cable at the amp and the tank , this tested the cable and it responded just fine , indicating the cable was OK , I measured the tank reisitence the out put was good but the input has 1.7 ohms , so I replaced the tank and it now comes alive , this is all well and great.

    but during the testing the tank starts to howl at about 6 on the dial I check the cable from the amp to tank and replace it just incase of bad continuity , pack it up and give it back to the very patient customer .

    last friday i get a call from L&M the customer brought back the amp in it is stil howling at 6 on the dial intermittently

    so today up on the bench it goes I look very closely at the reverb jacks on the amp and notice the Nylon plate that holds the RCA jacks is held in place with one screw so if by chance the screw works its way out the ground of the tank return shorts to chassis ground creating this howl, ( what a crap piece of engeneering in the design).

    My fix for this was to cut a piece of sticky 2 sided tape cut 2 holes just big enough for the RCA jacks to poke through covering the out side chassis around the jacks ensuring a zero chance of chassis contact with the jack , and every thing worked perfectly.
    The poor customer was at the whim of Fender and their bad engineering , after the repair this amp sounded outstanding and really kicked A$$ a nice sounding amp for sure.
     
    Wally, uriah1, Tommy Biggs and 2 others like this.
  2. Phrygian77

    Phrygian77 Friend of Leo's Gold Supporter

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    So, was there nothing wrong with the reverb transformer and driver circuit to begin with? You didn't explain your steps in troubleshooting it.

    Several months back, I needed a replacement toroidal power transformer for a Yorkville XS400 bass amp. That was fun. It took days to get responses from Yorkville, and also their parts retailer, Full Compass. Then, it was weeks until the part to arrived. Thankfully, my customer was patient.

    Edit: I meant to add, a six month wait is crazy though.
     
    Last edited: May 13, 2021
    24 track likes this.
  3. 24 track

    24 track Doctor of Teleocity Ad Free Member

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    Fender kept on Back stocking the transformer , right from Sept to April yet it showed as in stock the whole time
    The cutomer was so used to having the the amp with out the reverb , that he got excited when i told him i could get it back up and running, there is a known problem with the 2 transistors and the 5.00 reverb transformer in circuit with some models of fender amps , so the it is a good place to start to track it down I looked for all potential areas of concern eleiminating down the line till i found the design flaws, its silly to me how a company like fender sometimes take massive shortcuts in building some of their amps to save a buck.
    There was no return signal from the tank until i replaced the transformer and the transisitors then i got a strong signal back to the amp in the reverb return . What ever the history of this amp it obviously took some kind of hit in the reverb end of things but was weakend by a bad design.
     
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