Signal loss and distorted problem: HELP!

[stevefunk]

Hi All - I have a Fender Performer 650 bought used. Love the amp, LOUD, great clean and using the overdrive.

Recently, the signal drops on strumming guitar harder (or jumps in level), while also being distorted (but on the clean channel). Presently it is unusable.

Frustratingly, I have taken it to two repair outfits; one flushed out the pots, said it was repaired (NOT! - which I discovered that night at sound-check!) while the next one tinkered with it for three weeks and then in the end I got them to agree they weren't able to detect problem.

Any trouble shooting tips would be greatly appreciated as this has been going on for over five weeks - I have replaced components, mod'd pedals and guitar electronics. If this can be solved I will make a decision whether to repair myself or get someone else to do it, but with more knowledge this time.

Thanks in advance!

[Roly]

Hi Steve, welcome.

stevefunk> "(but on the clean channel)"

But only on the clean channel?

First; please try injecting a signal, say from an MP3 player or the like, into the Effects Return input to confirm that the power amp section is stable and performing as expected.

Protip: don't go changing components until you are sure you have found the cause of the problem; randomly replacing stuff only muddies the waters and has the real risk of introducing new faults.  First we identify what is wrong, then we replace the faulty component.

This amp uses a switch contact on the input socket as part of the clean/drive selection.  You could have a broken solder joint where the socket mounts on the board, or the contacts themselves could be dirty.

Carefully inspect the socket solder joints and renew the joints if you find anything loose/amiss.  You could also try giving the input socket a dose of contact cleaner or a drink of metho, and work a plug in and out a few times.  This may not entirely cure a dirty contact fault, but if you get some sort of change it suggests you are on the right track.

Service manual with circuit attached (thanks Enzo)

HTH

[Enzo]

Roly, I agree it is unclear, but I read that to mean it is distorted, but he is playing through the clean channel.  Meaning he expects the channel to be clean.  As opposed to ONLY on the clean channel.

I agree to plug into the FX return.  You can even play the guitar directly into the FX return.   That will tell us if the power amp is clear or not.


First, to test this, use NOTHING but the amp and guitar.  Nothing in the FX loop, no extra pedals or effects out front.

And it takes only seconds to try this:  plug a spare cord from FX send jack to FX return jack.  Any help?

And another.  Turn down the reverb if it has one, then ball up your fist and whack the top of the amp.  Does that do anything?  That reveals loose connections.  If the amp reacts to whacking, something is loose.

When you strum, the vibration from the speaker could be triggering a loose connection to react.

On this series of amps from Fender, I see too often that the solder has cracked under the main filter caps, never hurts to resolder them.

[Roly]

"When in doubt, give it a clout!" - old techs saying.    8|

[Enzo]

If a mallet sounds too harsh, just call it a "mah-lay."

[stevefunk]

Thanks everyone for your suggestions...I will try them in a couple of days and post result. Cheers  :dbtu:

[stevefunk]

Thanks Roly and Enzo  :dbtu: for your suggestions - really appreciate your help so far.
What I have tested to date;

• Input  -wiggled cable jack in input. No difference.(No loose solder points/contact points?)
• 'Whack it' test - vol up with no reverb, No audible noise but the smack of me fist! (SO, possibly no loose connections?)
• Guitar direct in Efx Return - No difference. (points to power amp section?)
• Cable connecting/between Efx send and return - No difference.

So, by the above, it seems like the power amp section - what do you think?

Do you masters :tu: have any suggestions how I should proceed from here?
Any thoughts greatly appreciated!

AND...Merry Christmas! :cheesy:

[stevefunk]

And one more thing to add;

When strumming, and the signal distorts (when expecting 'clean') and drops, there is a buzz, particularly when strumming hard on the lower (bass) strings.

Cheers. 8|

[DrGonz78]

What year was the amp made around? Did either of the tech guys replace the main filter caps?

[stevefunk]

Hi DrGonz78

Amp made/assembled July '95.

No; neither tech even mentioned filter caps. As said before by Roly and Enzo, they advised checking for solder cracks. In reading other info here and elsewhere...it is likely, after 17yrs, they're a done thing. However, I will check with meter (after discharging).

Do you think that the filter caps are now looking like the culprit/s?
Most advice out there is just to replace ones that are this old anyway.

[DrGonz78]

I say in any amp you need to always be looking for cold/cracked solder joints and bad traces. Sometimes bad filter caps can cause some serious problems creating hum/buzz sounds or flabby sounding tone. First replace the solder completely on the filter caps. Inspect the caps to see if they are bulging on top or leaking on the bottom. Maybe the amp sat un-played for long time? Yeah ditch the caps but first just try to see if it is the solder joints.

BTW: When you did the "Whack It" test were you feeding audio into the amp? As you are trying to get the amp trigger a loose connection and see if that audio signal is interrupted by this beating.

[Roly]

If you haven't downloaded the service manual I attached above, do so.

In it you will find a circuit and a board overlay, both marked with test points.  Of particular interest are the two main supply voltages, TP23  & TP26 which should be +40 V and -40V respectively.

The other point of particular interest is the output stage half-rail, TP21, which should be no more than half a volt.  If this is significantly different you should disconnect the speaker for the moment, and you can probe the other test points around the output stage and report their values.