Fender Champion 30 troubleshooting help

[nebraskaplayer]

Hi...

Looking for some help with an amp problem.  Retired now and looking to get back into some playing.  Picked up a Fender Champion 30 with a problem hoping for an easy fix for a small practice amp.

Amp has a very loud hum, unusable, when turned on.  Here is what I have observed or tried so far.
1.   Hum is present with all controls at 0, doesn't change with movement of any controls, did seem to be a pop, crackle (dirty pot type noise) with reverb control, after some movement now doesn't seem to cause any change/noise
2.   Plug in guitar hum still present at same volume, can hear guitar in/behind hum.
3.   Pulled chassis and number 1 input jack legs were loose (the 2 legs closest to front of amp) to the point the jack actually lifted slightly off of board when turned over.
4.   Resoldered jack, no change in hum level
5.   Looked for other cold solder joint, reflowed a couple, no change
6.   Disconnected reverb tank, no change
7.   Tried this speaker with a different amp, sounded fine
8.   Checked DC voltage at the speaker leads... consistently 3.6v dc when turned on, bleeds off to 0 when turned off.
9.   There are a few brown sticky dots on the transformer and a series of dark spots on the bottom of the aluminum pan in a pattern out about 8"but it doesn't look like "tar". Not knowing the former life of the amp, could be as simple as a spilled/splashed soft drink?, they wipe off with a wet cloth.

Suggestion for next steps?,  I don't have any other test equipment, but my trusty mulitmeter. Thanks for your help.

[joecool85]

First, welcome to the board!

Now, I have worked on a Champion 30 before.  This one had no sound or low volume (I don't remember now).  It turned out to be 4-5 broken solders.  But while I was in there I noticed several dozen (yeah, like 48-50) cold solders that I fixed that would have probably caused issues later.  So, first, I would start by reflowing all of the solder joints.  I know it takes time, but it's worth it.

As far as the brown spots, I'd need to see them before I could make any suggestions.  Please attach a picture of the board, or better yet, several at different angles etc.

[tonyharker]

3.4v on the output indicates that the output amplifier is faulty, possibly caused by the brown spots?  There should only be a few mV on the output - TP17 on the diagram.
Are there any spots near the output amp chip U6 a TDA1514A integrated circuit. (mounted on the Heatsink) Can you read a circuit diagram? Its available from here http://support.fender.com/schematics/guitar_amplifiers/Champion_30_schematic.pdf . This should help you.

[J M Fahey]

Disconnect the speaker and re-measure DCV at the Spkr out wire, I bet you´ll have even more than what you found now.
*Carefully* replace the TDA1514 with a new one, meaning pamper the board (you don't want to tear pads and tracks off).
If necessary, cut the TDA1514 legs , it´s much easiervto pull them one by pne.
Clean well each pad (solder sucker+ some solder wick), install a new TDA1514 with proper grease and mica and you *should* have it working.
2 suggestions:
1) build and use a bulb lamp limiter (search the Forum)
2) do not connect a speaker until you check you only have a few mV DC at the output.
Then you connect the speaker and play a little at low volume (1 or 2 W), still using the limiter.
Only when everything checks fine you can plug the amp straight in the wall.

[joecool85]

Tony and Juan, I agree that it is *probably* a blown TDA1514, but I wanted him to try the easy stuff first.  I still think that reflowing the solder joints is a good idea, then clean the PCB with water and thoroughly dry (making sure not to get water into transformer, potentiometers and the reverb tank etc, only on the PCB itself and cleaning the resistors, caps, ICs, diodes etc).

Odds are he'll still need a new TDA1514, but the stuff I suggested may fix it and would be free.  Plus, it would make it that much better for later even if he does replace the TDA1514.  Now, if time is of the essence, yeah, throw a chip in and check it.  But if he's like me and money is tight, it's best to explore all options first.

[nebraskaplayer]

Wow...

what response, I'll be away for a few days, I get the photos and upload those upon return.

I did see the light bulb limiter in a search before I posted, so I can try that as well.

I did have the speaker disconnected with the 3.4v dc read, sorry I wasn't clear, I'll try a read with the speaker connected later as well.
thanks for all the help thus far

[nebraskaplayer]

Here are a couple of pics of transformer... looks a little worse than I  thought... hmmm.

I'll get some pics of board etc, up latter.

I'll try light bulb limiter as well.

Is there anyway to check the jack that was lifting from the board intially... continuity , etc? that would tell me if it was broken as a result of only being anchored by the back "legs"

[joecool85]

Here are a couple of pics of transformer... looks a little worse than I  thought... hmmm.

I'll get some pics of board etc, up latter.

I'll try light bulb limiter as well.

Is there anyway to check the jack that was lifting from the board intially... continuity , etc? that would tell me if it was broken as a result of only being anchored by the back "legs"

You should really shrink your photos down to 1024x768 or 800x600 so they are more easily viewable.

[phatt]

Having issues with pics?  I've been using this one,,,
http://www.irfanview.com/

Resize,, resample,, change DPI
very handy program.
oh and it's free.

Phil.

[nebraskaplayer]

Thanks for help (again),  just changed laptops no photo editing programs.  Your suggestion IS very handy, (and the fact it's from CNET download),  made it feel safe.
Here are downsized pics. (hopefully)

[J M Fahey]

Don't think the transformer has a problem.
It looks like somebody sprinkled some Coke on it (see drops in the chassis itself) or simply it was in a *very* humid place (basement/storage room?), water drops condensed and rusted it somewhat.
But nothing beyond that.

[nebraskaplayer]

So...
1. I tried the light bulb limiter, with a 40w bulb, get a "low" glow when turned on.
2. Again hum is REALLY loud, unusable... didn't see to change after reflowing some more joints... but I need to get some desoldering wick... some aren't too "good" (tried to add a little solder)
3. Did plug in guitar and I can still get sound,  with enough volume (on amp and guitar) it equals or rises above the hum, since hum doesn't change with volume. The bulb didn't seem to change much/any with playing briefly.
4. Did seem to be a some amount of distortion (like  the gain channel) almost.
That's all the farther I'm going to get for a day or so, but welcome any other suggestions/next steps.
5. I did make the mistake of wiping off the thermal grease between pan and alum. block.. so if sucessful I'll need to replace.  (but it has made no difference)

[phatt]

You did well,,  :tu: Sound like the power amp is ok.

Next one is preamp PSU,, Check C37,C38 and also C39,40.
If you have a DMM then check those voltages are close to spec
If any of these caps are blown then it will hum like mad at one fixed level ,,, much like you explain.
Phil.

[nebraskaplayer]

So... I wasn't going to mess with this for a day or so (but I can't help myself with all the help)

Thanks to Tonyharker I have the schematic...  and to answer his question, I haven't read Schematics before. I am familiar with basic A/C home wiring, and D/C simple automotive type wiring. 
But I'm going to need some help, what the schematic "should" be telling me,  on the test procedures now.
I did go buy a cheap Radio Shack desoldering iron/bulb combo.
Phatt..
I'm still thinking back to the number 1 guitar input jack swinging by two legs from the board when I first opened it up.  Is there reason to think that either the soldering (that I did or a defect in the jack ) could still be causing my issue...
Otherwise
I"ve located C37,C38 and also C39,40 on both the board and the schematic.
Looking at the Fender load comments on the schematic:
To test C39 & C40:  Test DC with no input signal?
1.power amp on (speaker unhooked, and light bulb limiter not in circuit), no guitar plugged in, all knobs to 0.
Then test between ( + )  leg of each to chassis ground
and C39 should be +13v dc?, and C40 should be -13v dc?
It looks like can be done from the top of board easily, if that's what I'm really looking for.
Now... C37 & C38
C37 positive leg to chassis ground =   +15vdc
C38 positive leg to chassis ground=  -15vdc
Again little tighter but still looks like can get probe on + leg from top of board.
Pics below.
Comments/direction?
Thanks

[phatt]

Wow shinny new boards,,,

and You are catching on fast chum. :dbtu:

Yes you have the right parts and the right voltages.
Nothing there looks odd.

My guess is that you have just lost a ground connection somewhere,,, Yes likely the input sockets as these are cheaply made and prone to solder breaks as well.

With the Amp humming,, Try gently pushing down on the PCB board especially around the input sockets as sometimes these cracked solder joins are darn hard to see by sight.

Hairline cracks,,,Even with a magnifying glass they can be hard to see.

Phil.