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Post subject: Princeton 650 keeps fading out, cranked volume fixes it?
Posted: Tue Jan 18, 2011 6:22 am
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Hey there fellow Fender people,
I got my first good amp the other day and I love it - the Dyna-Touch III Princeton 650. I bought it from a pawn shop. And it was priced at only $170 and I thought I stole it for $130 (about half the price of a decent used one.) But after playing it for about a half hour the sound gently faded out over several seconds, yet the speaker still had the same sound as if the volume on the guitar was all the way down. And it keeps doing this, *#?%. It seems fade to quiet more when there's more gain and it's louder. To get the sound of the guitar back you turn the amp's volume knob up high (usually I bypass the speaker with the built-in tuner while doing this to avoid going deaf). It seems like when it comes back on after turning the volume up there are some crackling pop sounds like there's a short in the cable, but it's not the cable. Turning it a little higher or lower won't correct it. If you keep turning the volume up and back down to get the sound back not letting it rest the intervals that you can play for become shorter; after about the 4th time you fix it, it only plays for about a minute. Sometimes when it's turned on after being off for hours it's already quiet.

Extra touble shooting info:
We've tried to check whether it was the preamp or poweramp by using the jacks on the back (poweramp in & preamp out). Yet, they don't seem to work. Anything plugged into the "poweramp in" produces a loud buzzing sound and static. And the preamp out doesn't seem send sound, but oddly when it's setup for this and you turn the Princeton 650 off, for just a second you can hear your guitar on the other speaker. Also, I fixed a buzzing sound by tightening the input from the front correcting the ground. It should be at least 8 years old.

Do I need an exorcist, trash can, or master electrician? Any feedback would be helpful in traking down the problem!

Manual: http://support.fender.com/manuals/guita ... manual.pdf

Schematic: http://www.schematicx.com/schematic/fen ... schematic/


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Post subject: Re: Princeton 650 keeps fading out, cranked volume fixes it?
Posted: Tue Jan 18, 2011 9:35 am
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Hi wvchile,

Your SS amp is not as easy to troubleshoot as a tube amp. The best thing that you can do is to check all of the solder joints in the amp, and re-solder any bad ones that you find. Short of finding bad solder joints, you should probably have a tech look at it, as it sounds like you have more than just a simple problem. :idea:

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Post subject: Re: Princeton 650 keeps fading out, cranked volume fixes it?
Posted: Wed Jan 19, 2011 6:26 am
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Thanks for the reply. I've still yet to open it up, but it looks like someone else has in the past, maybe a number of times, as the screws are somewhat rounded off and contain have some rust.


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Post subject: Re: Princeton 650 keeps fading out, cranked volume fixes it?
Posted: Thu Jan 20, 2011 10:14 am
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Sadly, it sounds as if this amp is suffering from high frequency parasitic oscillations. A sort of instability that starts to rob the amp of audible power. Since you tried plugging into the amp section and get a squeal, my guess is that the culprit may lie there.

The cause of this instability could be a number of things. Best tracked down with a signal generator/scope diagnosis, section-per-section. A good tech knowledgeable with such equipment maybe able to help.


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Post subject: Re: Princeton 650 keeps fading out, cranked volume fixes it?
Posted: Thu Jan 20, 2011 12:19 pm
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wvchile wrote:
Thanks for the reply. I've still yet to open it up, but it looks like someone else has in the past, maybe a number of times, as the screws are somewhat rounded off and contain have some rust.


Hence, the cheap price.
Try stuff before you buy it, especially at a pawn shop.

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Post subject: Re: Princeton 650 keeps fading out, cranked volume fixes it?
Posted: Thu Jan 20, 2011 9:18 pm
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Well I fixed it... Thanks to most of you who replied!

I did try it out just not for twenty minutes...

One of two things fixed it. first I unplugged it while it was still on, to reset it, but what I really think fixed it was moving one of the small transistors on the board (labeled Q) back to the heat sink. The heat conduit goo had developed a small crack and needed to be pushed closer to the thick metal heat sink. If it does it again in the future I'll just go get some more conduit goo.


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