Blues Deluxe Channel Problem

[eeijcon]

Hi,

Apologies for hi-jacking previous thread on similar issue, I'm new to this stuff.

I seem to have the same problem as Steve. 1995 Tweed Blues Deluxe that goes silent (if playing the clean channel the channel light comes on). It either goes away intermittently or sometimes seems to responds to a gentle thump. Seems to become less of a problem the longer the amp is on/more it's heated up but yuou never know when it's going to happen.

I've checked R71 value and it's rated at 10k ohms but only reads 6.2k (?). Should I replace with 100k? The 2 R85 & R86 resistors are 470 ohm big boxy things (no, I don't know much about these things). Perhaps I should try re-soldering?

Any advice would be much appreciated.

BRs,
John.

[Don Symes]

The 2 R85 & R86 resistors are 470 ohm big boxy things (no, I don't know much about these things). Perhaps I should try re-soldering?

Rather than just resoldering, does it look like you can run a piece of wire from the big boxy things' legs to the nearest other component on each of those 4 traces?

[52 Bill]

John:
I would pull out the board and replace R71 with the new 100k value. The symptoms that you describe, seem to fit exactly what the tech note describes.

While the board is out I'd also check the solder joints on the 2-470 ohm resistors just to see what shape the're in. While you're at it, check the solder joints on the input jack, ft. switch jack, etc. These are all common problem areas on these amps.

Just a thought: If the solder joints on the dropping resistors are overheated, try cleaning off all of the existing solder with a solder sucker, and resolder these joints with silver bearing solder. It is electronics safe, and has a higher melting point than normal 60/40 solder and may hold up better here.

Hope this helps,
Bill

[eeijcon]

Bill/Don,

Thanks very much for your replies and advice.

I whipped out the board just now and removed R71 and it's ready for it's replacement when it arrives probably tomorrow.

I checked the 2 470 ohm resistors and they look OK but on close inspection there's circular fracture around 2 of the leads where they push through the solder on the underside on. I might just re-solder them, they may be the problem but since they lasted for nearly 12 years I'm guessing a good fresh solder joint might hold them for another few years. Silver bearing solder is in the post too!

Thanks again - I'll let you know how I get on.

BRs,
John.

[pabothecat]

DEFINITLY resolder those 470 ohm resistors. I tried to touch up my solder joints and the solder was just plain nasty. I used solder wick and removed all of the old solder. I used the regular 60/40 solder. I didn't know about the silver bearing stuff. I did this about 2 weeks ago and have played on the amp
almost every day for at least 30 minutes and have left the amp on stand by all day long 3 or 4 times, and I haven't had a problem yet.

good luck!!

Steve

[Enzo]

The problem builds up over time. Each cycle of heat up and cool down causes thermal expansion and contraction in the metal of the component legs. AS it expands, it pushes away the solder all around it, and when it shrinks, it tends to contract away from the walls of the solder connection. over time the solder loses its grip on th wire leg.

DEfinitely resolder those resistors. That little crack is indeed failed solder. A simple resolder might last several years or not long at all, hard to say. Adding defensive measures as discussed will help.

I always visualize the failed joint as a volcano. The solder on the board slopes up to the wire, so the cone shape is there. When the solder lets go of the wire, there is a crack all around the wire. SO to my weird eyes, I see a little volcano with a wire coming out.

Train yourself to look for that tell tale crack around wires at solder joints. A common problem in electronic stuff.

[eeijcon]

Hi All,

She's back! I replaced R71 with 100k and resoldered the 470 ohm resistors and everthing is working great since the weekend.

Many, many thanks for your advice. You've saved me a trip to Dublin and probably a hundred quid or so not to mention an unwanted separation from my amp.

Kindest regards,
John.