Fender Champion 30 troubleshooting help

[nebraskaplayer]

Thanks for everyone's help thus far...
Couple of observations.
1. Still have 3.5-3.7vdc across speaker leads (unconnected).
2. When I power down, small light pulse from gain cuircuit indicator light (maybe that's totally normal) but I thought it may mean something to someone.

3.I ran DC voltage tests on C37-40, and have one result that wasn't what I expected on C40 the (-14.2vdc showed up on negative leg not positive leg?)

attached is sketch of what I found.
(I think I have it sized ok...)

[nebraskaplayer]

And additional question...
Taking everyone's advice and trying to be very careful of the board and traces, I did notice there was a "bridged" solder joint between these two (in photo below, not sure if I caused),  used desolder iron quickly to remove most, is there a preferred method for getting the remaining that bridges between without risking damage?
I think it's between the legs of C48 and C49 (labled >IJ63 part number?)
thanks

[JHow]

Are you sure those two points aren't on the same trace?  Is that the ground end of the cap??

[nebraskaplayer]

Ah...
Younger more knowledgeable eyes, Yes I do see now looking at pic, it is on same trace, so I'll just solder back up.
The pic below show what the legs come from , white block "things", they are labeled  C48 and C48 so that means they are capacitors even though they don't have the traditional canister shape?

Still don't understand what the reading on (-and +) legs of C40 in post above means?

and why I have 3.5+ v at speaker leads... unless the TDA151 is "partially bad"?,

Also if there is any way to check number 1 input jack since that was the only visible issue when I started or remove or jumper it somehow  to eliminate that possibility. I'll try to look at schematic , (or if I can pick up a jack local might be easier to replace then troubleshoot)


thanks ALL...

[JHow]

As I read the schematic, you should have 0 zero volts on the positive side of C40 cap and minus 13V on the negative side of the cap, which it sounds like what you reported, so no problem in that case.  Zero is more positive than minus 13, so that works.

Some of the caps are in rectangular white "blocks".  Look at the top and see if it doesn't say something like ".1u" on top.

The 3 volts DC on the speaker is still a problem.  Somehow you have DC on the speaker and that shouldn't be.  The likely path is through your output device.  Maybe C46? Gurus help here.

I missed the part about your input jack.  A bad ground there can cause hum.  If you fixed it, check that the ground lug is really continuous to ground and that the "switch" lug is grounding the input lug when no plug is inserted.

[nebraskaplayer]

Thanks...
Does that make the reading on C38 in the earlier post suspect then?,  as I got a (-15.8vdc) on the POSITIVE leg?  When looking at the schematic it looks like it should test like the  C40,  you are referencing, meaning it should be testing  (-15vdc) on the NEGATIVE leg ? , or is it dependent on how it's used in the circuit? ( I'll double check readings today).
Can you provide a brief description of the DVM testing for the jack you suggest?,  here is a pic of the jack I believe is in question.

Thanks
Dave

[JHow]

C38 per schematic, should be like c40, with zero VDC on the positive end of the cap and minus 15 VDC on the negative end of the cap.  Double check this - if the cap is original its not likely to be inserted backwards.

Regarding the jack, viewed from the top, the back-left lug is the tip of the guitar cable.  If you look closely, it is a spring and it grounds itself on the righthand side of the jack.  Sometimes the spring gets weak and doesn't make contact, which can hum.  With no plug inserted, that back left lug should be continuous to ground.  With a (good) cable inserted, it should isolated from ground and continuous with the tip of the cable.  The schematic shows this relationship with the little "arrow" connections that go to ground on the two jacks.  If you experiment with your multimeter on continuity (amp off), one end to ground, one end to probe with you should be able to see if the switch/spring isn't making contact.

One afterthought, the schematic gives "TP" locations, i.e., test points, presumably marked on the board, for you to  measure VDC to ground.  Those are meant to give you convenient locations to test DC. iF you get a the appropriate reading there, you don't have to really worry, you can assume the cap is in correct place.  Personally, I always write these measurements on a copy of the schematic as I work (in pencil).  IF they (TP 3,4,5,6) are good, you can continue on in your fact-finding.  Also, later if something changes, you have a baseline to work from.

[nebraskaplayer]

I'll recheck c38, and I do (now) see the test points and values, I'll take a look and see what I find.

My wife seems to think putting a new blower motor in her car before snow flurries tonight should take priority over this IMPORTANT project...

I also see that the TDA1514A may be tough to find?,  (and a little expensive?) if I end up needing that.

[joecool85]

I'll recheck c38, and I do (now) see the test points and values, I'll take a look and see what I find.

My wife seems to think putting a new blower motor in her car before snow flurries tonight should take priority over this IMPORTANT project...

I also see that the TDA1514A may be tough to find?,  (and a little expensive?) if I end up needing that.

I hadn't realized how hard they are to find now (not the case a few years ago).  Anyway, you can still get them for $10 or so on ebay.  If you can't find a TDA1514A, the NTE7118 is apparently the substitute although it appears it is even harder to find and also $43 from mouser.com...ouch!  Another option would be to scrap the poweramp section of your current amp and feed the preamp into an LM3886 or similar board.  This would require you to get a "kit" from somewhere like chipamp.com.  I think you should be able to power the LM3886 board off your current PSU which would make this a cheap option.  $3 for the LM3886 board from chipamp.com, then just buy the components.  Should be able to do that for less than $15 or so I'd imagine.

[nebraskaplayer]

So heat in the wife's car...
Thanks again to all who have responded so far>

1.   Tested Jack Inputs with these results:
Tested with meter for continuity.
Both Input 1 & 2: W/O cord inserted both of the top "tabs" were to ground.
Both Input 1 & 2: W/ cord inserted,  front (closest to threads)  "tab" was still to ground but back "tab" was open on each.

2.    With the chassis out checked the solder joints on the "legs" of each  jack to ground.
Interesting results, I'll look at schematic and see if I can figure out if this is right... (if I need to upload sketch to make clear let me know)
   JACK 1   (bottom view)      JACK 2   (bottom view)
Leg 1   leg 2            Leg 5   leg 6
Leg 3   leg 4            Leg 7   leg 8

•   With NO cord in any Jack
Legs (2,3,4)&(5,6,7) are to ground
•   With Cord in Jack 1
Legs (2,3) & (6) are to ground
•   With Cord in Jack 2
Legs (2,3,4) & (6,7) are to ground
3.   Here are the DC test points
      S/B      ACTUAL
TP 3       +25.9      +26.4 vdc
TP 4      -25.9      +26.4 vdc
TP 5      +15.1      +15.0 vdc
TP 6      -14.8      -15.3 vdc

I rechecked the earlier test on :
      + lead   - lead
C39      +14.2      0
C40      0      -14.2

4.   I tried a couple of A/C test points:
      S/B      ACTUAL
TP1      20.3      20.2VAC
TP2      20.3      20.2VAC

Still have the 3.5 vdc on speaker leads (speaker unconnected).

I did borrow a "better" meter a UEI dm383b ... Didn't seem to make me "better"... it does have capability of mvolts... but I think it needs an input load?, and load on speaker leads to test>

Regarding the TDA1514A, I did notice the EBAY sellers before, but ALL are Hong Kong, and most are still "branding" as a Phillips part, I did see on some other places there is some complaints regarding Fakes blowing up.    I also saw there was a bunch of late 80's Phillips and Marantz CD players (of all things that used this,that foks are canabilizing).


Next steps?...

[JHow]

From the above it sounds like the jacks are fine and C39 and C40 are correct.  The voltages are pretty close to the schematic, except for the 3+ volts DC on the speaker.  I'm think we keep coming back to the chip. 

[nebraskaplayer]

Duh... might be easier if you all could hear what it sounds like.

http://www.youtube.com/watch?v=vOjYjR-2WQ4&feature=youtu.be

hopefully it's ok to post links, otherwise go to youtube and search for

troubleshooting fender 30

I did find a US repair shop that has a single td1514a available, but the $20 to buy and ship will equal the cost of the amp... so I'd like to see if we can narrow it down to that before I pull the trigger.
thanks

[nebraskaplayer]

Jhow... I posted before I read last post regarding your chip comment.

I'll let a couple of folks listen to youtube recording and see if you all agree with the testing that I/we have done, resoldering the loose jack,  still having the 3.5vdc on the speaker leads,  that I need to get the chip and replace it next..

Does only having 3.5 vdc on the speaker leads (vs. the much higher that was suggested there would be if the chip was "blown" ) mean it's "somewhat" failing?, also the fact that there is some input from the guitar that still passes through to the speaker through the chip (as shown in the youtube clip as well, although it was very weak and had to be turned all the way up).

Only other thing I noticed the guitar volume as well as the ambient noise level was higher when the gain circuit was engaged with both gain and volume  vs. the standard channel?

tks

[joecool85]

I'd say 99% chance at this point that it is a blown TDA1514A.

[J M Fahey]

As a last check before you order your TDA1514, please read and post the Dc voltage on its pins: 1/9/6/4/5. Thanks.
PD: If you can´t find it, or it´s a "Hong Kong fake", I can suggest a way to replace it with an LM3886 , but it involves some brain surgery. :duh
To see that it´s possible, i´ll need a couple sharp. well illuminated closeups of the TDA1514 mounted to its heatsink and PCB, to check available space.