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Conference napalm::guitar

Title:	GUITARnotes - Where Every Note has Emotion
Notice:	Discussion of the finer stringed instruments
Moderator:	KDX200::COOPER

Created:	Thu Aug 14 1986
Last Modified:	Fri Jun 06 1997
Last Successful Update:	Fri Jun 06 1997
Number of topics:	3280
Total number of notes:	61432

2519.0. "amp fix help needed...." by NAVY5::SDANDREA (What, me worry?) Thu May 07 1992 14:19

    I did another dir/title and did'nt see a repair/technical note.....if
    it exists, would the moderator move this to it's appropriate home,
    please?
    
    Problem:
    
    I broke the fuse holder on my little 20w practice amp.  It was the
    black plastic kind that mounts on the "back plate" of the chassis and
    has a screw on cap.  Radio Shack was out of those so I bought and
    soldered in an "in-line" style fuse holder (the plastic "tube" with a
    wire out of each end).  The amp powers up OK, but it has NO volume!  I
    have to turn it up all the way to get a whisper out of it....it is
    amplifying my guitar signal, but all the power is gone!  What happened?
    Am I missing a ground?  Was the original fuse holder grounded to the
    chassis?  Any suggestions?  My amp is a cheap Korean solid state job...
    
    Steve

T.R	Title	User	Personal Name	Date	Lines
2519.1	Hell, if you toast it, you could always go Marshall	WEDOIT::KELLYJ	Think for yourself	`Thu May 07 1992 15:10`	11
	If the fuse holder you broke is the style I'm familiar with, it's just got an 'in' and an 'out'...no ground. You can get them locally (Boston) at You-Do-It electronics, or through the mail from Active, Sager, Newark, Gerber,... Curious symptoms. I assume the gauge of the wire on the replacement fuse holder is adequate and that you used the same fuse. How 'bout risking it and temporarily remove the fuse holder from the line? This would tell you if the new fuse holder and/or fuse is causing the problem, but you're temporarily without 'protection'..
2519.2		ZYMRGY::sam	Gonna boogie my scruples away	`Thu May 07 1992 15:25`	3
	Radio Shack sells 'em, too... -- Sam
2519.3		RAVEN1::BLAIR	What is it, Man?	`Fri May 08 1992 08:17`	3
	Steve, try re-soldering the connections. You probably got a cold joint. Heat the wire, not the solder...
2519.4	I'll try these....	NAVY5::SDANDREA	What, me worry?	`Fri May 08 1992 08:56`	5
	RE: last few... Thanks guys.....I'll give these few a try.... Stevo
2519.5	it's an "open"....	NAVY5::SDANDREA	What, me worry?	`Wed May 13 1992 09:29`	15
	I tried the re-solder, checked the fuse rating, etc...everything there is ok...... I discovered the real problem when I noticed the amp returned to full blast volume when I "flexed" the chassis that holds the circuit board. This guy operates off of 12 volts via a transformer and I was holding the amp chassis itself while out of the cab, but the speaker connections intact. I inadvertently "squeezed" the chassis frame while the guitar was plugged in and the volume up and WOW! Anyway, there seems to be an open circuit or a defective component that re-connects when I "squeeze" the chassis and/or push down on one paricular spot on the circuit board. I'm gonna let one of the techno-geeks at my wife's place of employment look at it..... Steve (Le Dawg)
2519.6	look for "cold" solder joints	MEIS::RAMSEY	It could lead to dancing	`Wed May 13 1992 11:17`	11
	Steve, Look at the solder joints in the vicinity; if they're lumpy or dull or the solder just forms a ball around the lead, it may be a "cold" joint -- no good mechanical or electrical contact. The other possibility is that you've cracked an etch -- this may be a litttle more difficult to find. Used to get a gawdawful crackle from my Ampeg until I found the lead from the input sensitivity switch that wasn't soldered to the board. Chuck
2519.7	Easy to fix when you find it...	MANTHN::EDD	It's not Manhattan...	`Thu May 14 1992 04:43`	12
	These types of failures are usually (a) hard to locate and (b) easy to fix. They require more perseverance than skill. My DEP-5 developed a problem where it would just die, then come back, then die. I removed the skins and started poking. After a few hours I noticed that applying pressure to the top of one particular cap would always bring the unit back. Assuming a bad cap, I removed it only to find a broken etch on the PCB. I flipped the board over and duplicated the electrical path with a piece of insulated single strand wire. Problem solved. Edd
2519.8		EARRTH::ABATELLI	Who knew?	`Thu May 14 1992 07:08`	15
	re: .6 I'd like to echo the "cold solder joint" reply. I had interesting problems with my PV-MX amp when it was powered up for awhile, it'd start making these very interesting noises. The noise sounded like the tube grids were shorting, so I changed the tubes with new ones, but it still didn't fix it! In checking the amp over, I noticed one specific solderjoint (a PTH on the power board) wasn't soldered completely. YIKES! I resoldered EVERYTHING and it fixed the problem! Interesting huh? Take a good look and maybe you'll find the problem yourself. Rock on, Fred
2519.9	good amp repair shop	AIAG::WISNER	Paul Wisner, TIMA/Stars V3.0 Development, Multivendor Customer Services	`Fri Jan 13 1995 13:34`	9
	Can anybody recommend a good place to get my amp fixed in (or near) Boston? It's a Fender Suepr 60 - I think it just needs some new tubes. I want a place with a decent turn around time or a maybe someplace that will give me a loaner amp. How is Wurlitzer in Brighton? -Paul