Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

I need help reading this schematic

  1. Jan 31, 2016 #1

    This is a Hot Rod Deluxe amp and has a low distorted signal at the speaker. (some info on the schematic is for a Deville)

    I injected a 1000 cycle signal at 100 mVpp at J2 and have a clean signal on the grid of V1A, V1B, and V2A. There is no signal on V2B no matter what I do to the amp.

    What I do not understand is the meaning PW1A-1 and PW1B-1 or PW1B-3 and PW1A-3 or any of these PW symbols are where they go or what they are connected to.

    Is the information I need on this schematic? Am I missing something?


  2. jcsd
  3. Jan 31, 2016 #2
    PW seem to be the connector contacts on Sheet 3 of 3. If You can´t find search for the devices on the board.

    V2-B is only active when the relais contacts K2-A and K2-B are too active, otherwise the tube is fully bypassed to TL 072 U2-A, (seems to be active just for a sound effect - controlled by U3 + foot switch)

    good luck!
    Last edited: Jan 31, 2016
  4. Jan 31, 2016 #3


    User Avatar
    Gold Member

    Do you see your signal on the pre-amp out connector?

    You need to study the control logic in the lower left corner (footswitch, etc)
    Do you have a footswitch plugged in to activate K2-C? What color are the clean/drive/more drive LED? What positions are the channel switches in?
  5. Feb 1, 2016 #4
    Thanks keinstein.

    Yes,ok, that is what they are, I think. The four ribbon connectors. Now I need to take the amp apart again to check...lol
    In that case K2B is not working or R20 is open or the ribbon cable PW2A PW2B is open. That would account for no signal at V2B.

    Another thing I do not understand is where K2A and B get the voltage to open or close. As far as I can tell, that is not shown on the schematic.

    The PCB is a real pain to deal with because of the need to remove it to trace the circuit. This PCB is out of stock from Fender, otherwise I would just buy a new PCB which cost around $100.
    It is the middle of the night here....so tomorrow.

    Thanks and good night.


    EDIT: I did not see all the post so I need to read everything...Disregard most of what I said above.
  6. Feb 1, 2016 #5
    First, the PW entries are the ribbon cables and the dashed boxes around them logically link the wiring schematic with the physical layout diagram, on the last page. They also relate to specific PCB boards, as listed in the footnotes.

    As for tracing where your Amp is failing, this test probe is a handy tool. http://billmaudio.com/wp/?page_id=1254
    The videos on building and using the test probe are worth the watching. It took me about 5 minutes to assemble mine, total parts are about $3.00 at your nearest electronics supply store, most of which was the shrink tubing. For the Capacitor, you're local amp repair shop should be able to sell you one for about 25 cents if they are greedy.

    What model of Deluxe do you have and from what year? I may have a more accurate schematic for your particular amp.
    Do the volume and master controls have any effect on the loudness or shape of the hum?
    Do the tone controls change the coloring of the hum?

    And just for giggles, take a small patch cable and put one end in the jack labeled "Pre-amp out" and put the other end in the jack labeled "Power-amp in". These are switching jacks which can corrode and get stuck in the open circuit position, if this does not correct the problem then you have lost only a couple minutes. If however, the Amp does function correctly with the patch cable in, there is a process for cleaning those jacks, depending on how badly corroded they may have gotten.

    While you're there, you can also plug your instrument directly into the "Power-amp in" jack. it won't be nearly as loud as a functioning amp but if you can hear your instrument at all when connected there, it will isolate the fault to somewhere before the power section, which exists in the 2 fatter tubes on the far right, likely 6L6.
  7. Feb 1, 2016 #6
    Hi BigGuy,

    I will need to re set up the testing tomorrow to answer your question about the pre amp out. I do not have the foot switch. I see the path through R18 and K2-A must be working because I have master vol control with the slector switch in the overdrive position, so I am guessing that there will be a signal at the pre amp out. Also There must be a signal at R28 otherwise how could there be any signal at the speaker.The channel selectors are in the normal channel mode and drive switches are not pressed in. There is no need for a foot switch for the amp to work correctly.

    I had all ready put the amp back together and it is 1:14 AM here and I am a bit too tired to deal with it tonight.

    Thanks for all the help....I think I know what to do next.

  8. Feb 1, 2016 #7
    Hi Wee-Lamm,
    I understand the ribbon cable issue now. I have a test probe I made and hooked up to a small amp I have. It is much faster than using a scope which I have also.

    I see the possible jack issue you are talking about and that may very likely be part of the issue. The schematic I posted matches the PCB number. I am not sure of the exact year of the amp...B243201 serial number.

    The volume control or master have little effect on the hum and I am not getting amplification. I am getting gain through V1A to V1B and on to V2A so the pre amp section is working. I had assumed that there should be a signal at V2B and if that is not the case then the issues are after K2-A.

    Thanks again for all the help.ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ....had enough for one night...lol


  9. Feb 1, 2016 #8
    Hi guys,

    I think I have found all the issues. Now I just need to order some parts.Thanks for all the help reading the schematic.

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook