Ibanez TSA5TVR Reverb Stopped Working

Discussion in 'Amp Tech Center' started by Fumbler, Jul 17, 2019.

  1. Fumbler

    Fumbler TDPRI Member

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    I have some kind of force field that seems to knock out the reverb in my amps. I got a used TSA5TVR amp and it really is a great little unit. The other day the reverb quit. I tested the tank by pulling the return line, putting my finger on it then turning up the reverb. No hum whatsoever. To double check I swapped in the tank from a Blues Jr (which I found out was compatible) but no dice. The problem wasn’t the tank.

    You just can’t find a schematic for these amps online. I put on the jeweler’s glasses and started scrutinizing the circuit board. The reverb is driven by the same IC the Blues Junior uses. I investigated everything, nothing looked bad. I got a zero voltage reading at pin 4 on the chip but I really didn’t know what I was looking for.

    I decided it was time to look at the back of the board for cold solder joints. Once I removed the nuts for all the pots I found the problem. When I pulled the board the pots for bass and reverb fell right off. The terminals had broken off at the board!

    Just thought I’d share in case it happens to anyone else.
     

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  2. Dacious

    Dacious Poster Extraordinaire

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    Might be worth soldering back with short flying leads- this sort of thing happens to the 83+ Marshalls where the board is supported off the pots.
     
  3. Fumbler

    Fumbler TDPRI Member

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    Thanks Dacious. I did as you suggested, largely because I wasn’t sure how easily I would find new pots with the right dimension, values and shaft styles. When I put it back together I could now barely hear anything coming out of the amp and what was coming out sounded heavily distorted. Touching the volume produced erratic sound and the tube screamer switch was noisy to touch. I took it apart again and found one of the leads to the volume broken. I installed all the pots on flying leads but after reassembly still have the same problem. Very weak distorted sound, only when tube screamer is off. Strangely the volume of the sound does not seem to change, even when volume is off.

    Any ideas?
     
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  4. Fumbler

    Fumbler TDPRI Member

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    Anyone? The fact that I am getting distorted output even when volume is off makes me suspect a bad or shorting pot.
     
  5. Modman68

    Modman68 Tele-Holic

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    Have you confirmed that you did not mistakenly switch the bass and reverb pots when re-installing them?


    Sent from my iPhone using Tapatalk
     
  6. Fumbler

    Fumbler TDPRI Member

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    Great suggestion, that’s exactly the kind of thing I would do. I just checked and reverb is a 25K pot and bass 250K. This matches the pictures I took of the board early on so I don’t think that’s it.
     
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  7. LudwigvonBirk

    LudwigvonBirk Tele-Holic

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    Do

    a) each of the re-installed leads go to the right place,

    and

    b) do they all check out for continuity (meter beep)?
     
  8. Fumbler

    Fumbler TDPRI Member

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    Thanks LudwigvonBirk. I just double-checked and yes the leads are continuous and going to the right places. I’m going to test the pots when I get home today.
     
  9. Modman68

    Modman68 Tele-Holic

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    How did the testing go?


    Sent from my iPhone using Tapatalk
     
  10. Fumbler

    Fumbler TDPRI Member

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    A bit hard to tell. Everything seems to check out with correct values except the reverb pot whose values are often in range but fluctuate before my eyes, sometimes reading over 100K, sometimes reading zero even when turned fully clockwise. I’ll pick up a replacement and see what that does but first I’m going to remove the pot altogether and see what happens. When I started this the amp sounded fine but had no reverb. It doesn’t seem to me that a bad reverb pot would cause distorted super low output...
     
  11. Fumbler

    Fumbler TDPRI Member

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    Here’s something though. The ground for the pcb appears to be a solder ring on a single circuit board mount. It looks like it has been disturbed and some of the solder broken off. What do you think?
     

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  12. Fumbler

    Fumbler TDPRI Member

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    THAT WAS IT! I reflowed the solder all around the ground ring and the amp is fixed. That ground sure seems like a crappy setup.

    Thanks for the help along the way!
     
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  13. Wally

    Wally Telefied Ad Free Member

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    Good find!

    One could establish that ground with a screw at the chassis for a wire that is solder to a different point on that ground plate. There are two solder points directly above in the upper right hand corner of that PCB as we see it above.
     
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  14. Fumbler

    Fumbler TDPRI Member

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    Good suggestion Wally, thanks. If it gives me any future trouble that is what I will do!
     
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  15. Fumbler

    Fumbler TDPRI Member

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    Well now the amp has a loud hum, almost like bad filter caps. Every now and then when I turn it on though it is still quiet. I’m going to start by adding the ground as you suggested. Please forgive the question but how do I verify that those solder points you mentioned can be used as take-offs for a ground wire?
     
  16. Wally

    Wally Telefied Ad Free Member

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    Fumbler, looking at the picture of the PCB above, one can see that there is a common grounding there.....a big patch of conductive material between those two points....and you could go on and trace that ground on through the PCB if you were curious....just to get accustomed to tracing the conductive materials in a PCB just as one can trace wiring connections in a hand wired circuit. You can also use an ohmmeter to find continuity..or the lack thereof.
     
  17. Fumbler

    Fumbler TDPRI Member

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    Oh I see Wally, thanks. So there are actually 5 visible solder points in that patch, correct?
     
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  18. Fumbler

    Fumbler TDPRI Member

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    PLUS the factory ground ring. Very obvious to me now.
    Pretty dumb question but I’m glad I asked!
     
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