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Crate G80XL fading out

Started by callanbrown, January 28, 2010, 07:29:23 PM

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callanbrown

Hi guys!

Picked up this Crate amp the other day. Seemed to be working but the sound fades to nothing. Occasionally it'll be fine for like 10 minutes, the do nothing for a few minutes, then come back to life. I also noticed that pressing in the channel select button, then pressing it again, the channel doesn't change quickly, it takes 30 seconds to a minute for B's LED to turn off and A's LED to turn back on.

I noticed that by turning up the reverb, then disconnecting and reconnecting one of the plugs to the reverb box the sound will return, however I'm fairly certain the reverb box isn't the problem.

I took a look at the electronics and it's definitely been repaired before. There is a section that looks burned (and was repaired). I tried reflowing some of the iffy looking solder points around that area but it didn't fix the problem.

This all seems to point to transistor or capacitor problems, would I be correct?

J M Fahey

QuoteThis all seems to point to transistor or capacitor problems, would I be correct?
*Maybe*, but ... which one? :-\
Start by squirting a little contact cleaner into the loop (or Pre out/Pwr In) jacks and work a plug in-out a few times.
Grime and rust on contacts cause similar symptoms.
Now that you bought that can, also clean all pots and jacks, also squirt a little on all switches and work them too.
It should work wonders.


Enzo

Also squirt some cleaner into the footswitch jack and probe a plug in and out of it a few times.  That jack could be involved in your channel switching problems.

Your problem is probably not a bad partt, more like a bad connection.

Next time this happens, ball up your fist and whack the top of hte amp.  If the amp reacts, something is loose.

phatt

If *Audio signal* is in sync with channel led issue then likely the switching relays or power supply to same.
Just my guess?
Phil.

callanbrown

Thanks guys, I'll pick up some contact cleaner today and check those jacks.

Phatt: I wouldn't say the the LED and audio problems are "in sync", it just seems like two problems that are related. For example, when the audio starts to fade out, the LED stays on fine. I just noticed when I switch channels and switch back, the LEDs seem to take time to react.

Enzo: I did whack it once, and it reacted.

phatt

hi callanbrown,
ok, then *Enzos* likely on the mark. :tu:

Start hunting the solder side of PCB board for cold solder joins or cracked tracks.
Good light, a keen eye, oh and some patience. ;)

Since RoHS the solder compounds have changed, good for the planet but not so good for long term reliability. This new solder stuff tends to *Shrink* away from joins
over time and any hot running components just speeds up this shrinking issue even more so.

Also most stuff is PCB mounted and things like input sockets and pots often crack at the solder pads.

Good hunting, Phil.

Enzo

That's why I get the big bucks here.  DOuble my pay, please.

Solder is a weak link alright.  Check solder on each and every control and jack, plus all the rectangular cement power resistors - those 5 and 10 watt things.  They vibrate and break their solder.

Crate uses those Cliff style jacks, and the cutout contacts on those is a weak link.  I automatically measure the resistance of each cutout contact.  If it is more than half an ohm it needs to be cleaned or burnished.  If it measures like 1 or 2 ohms, it will probably work fine, but the very fact the resistance is up that high means the contacts are not pristine, and 2 ohms at the moment can turn into 2000 tomorrow.

phatt

Quote from: Enzo on January 29, 2010, 11:16:01 PM
That's why I get the big bucks here.  DOuble my pay, please.

Solder is a weak link alright.  Check solder on each and every control and jack, plus all the rectangular cement power resistors - those 5 and 10 watt things.  They vibrate and break their solder.

Crate uses those Cliff style jacks, and the cutout contacts on those is a weak link.  I automatically measure the resistance of each cutout contact.  If it is more than half an ohm it needs to be cleaned or burnished.  If it measures like 1 or 2 ohms, it will probably work fine, but the very fact the resistance is up that high means the contacts are not pristine, and 2 ohms at the moment can turn into 2000 tomorrow.

Good come back Enzo, LOL.
But I think Fonzy holds the copyright on thumping juke boxes to get them to work.

Those cliff sockets USED to have a pressed carbon stud imbedded in the tang so as to make proper contact but I've not seen them for many years.
Now it's just a pressed metal tang with a bump protrusion for contact, really no better than the cheap stuff. :'(
Phil.

callanbrown

Hey guys,
Ok did some more testing. First of all the contact cleaner worked well on the pots, less random noise when changing stuff now.

The rectangular giant resistors are in the area that had been repaired, and I can see for sure that one of the feet (I believe from the 10ohm one?) has pulled off from the circuit board. I ran a jumper from the pin to next contact and put it all back together and things seem much better. Still when I had it on really high I hit a point where it gave up, so I think vibration is still an issue.

Secondly, I tried flexing the input cable a bit at the jack and it seems there's a problem with the 0db input (despite resoldering) so I think I need a replacement.

There's also a significant amount of resistor dust in that area.. will these things increase in resistance over time? Should I just replace them?

callanbrown

Ok new symptoms, new problems:

-On channel A, there is now nothing.
-On channel B, there is a very loud white noise sound. I believe it's a concoction of radio signals, occasionally you can pick out voice/music/ghosts, but the guitar has no effect.
-Plugging a guitar into Line In, it works and sound great.

Switching from channel A to B is also very slow. Finally, if I tap on one of the big wide caps with the butt of a screwdriver on channel B, the radio noise seems to go away.

J M Fahey

Your problems are mechanical rather than electronic: resolder all jacks, caps (specially the bigger ones), pots, connectors, etc. with the tiniest amount of solder and a good, hot, solderin iron.
You don't want to have big solder globs of solder everywhere but re-melt cracked solder into the factory fresh type.
Instrument amps take a beating, boards flex and vibrate, solder cracks, connectors rust or gunk, pots get dirty, copper everywhere turns at least dark brown or worse, green with corrosion, connectors loosen, etc.
You must look at it with this in mind and you'll find the trouble spots.
A 1/2 gram resistor rarely will cause trouble, but a 150 gram electrolytic, a 7W ceramic resistor, overheated and on long pins will, a chassis bolted pot with its pins soldered to a flexing board will too.

callanbrown

Thanks JM,

I was in fact doing exactly what you mentioned. Resoldered the large caps and jacks etc, and lo and behold, everything is back in order, even the channel-switching delay has disappeared (capacitor I'm sure).

One weird thing I noticed.. the input jacks and line in/out have been switched. The input jacks are stereo and the line in/out are mono. I'm pretty sure I should just replace all of them, would you agree? Will these do?

http://cgi.ebay.com/Amp-Mono-Cliff-Input-Jack-4-PC-Terminal-Mount-S-H503_W0QQitemZ170371640384QQcmdZViewItemQQptZGuitar_Accessories?hash=item27aaf0ec40

J M Fahey

If they match the board holes, change all.
You will save in shipping and it's cheap insurance.
Jacks are the most abused part.
Fill the board holes, that means that if the board has 6 holes (Stereo jack), put a stereo jack there.
No matter that the guitar signal is mono, sometimes those extra contacts are used for muting, gain switching, whatever.