Blues deluxe chan swt issue

[Stevem]

Any one have this issue on one of these they cured?
The channels will not switch and the channel LED goes from brite yellow to dim yellow when you hit the switch so I do not think it a bad relay, so what's left is the IC chip and the two transistors.
Oh well, I guess I will dive in and find out, thanks in advance for any info!

[martin manning]

I've never had the pleasure of digging into one of these, but from what I read channel switching issues are often related to the +/-15V power supply and the notoriously hot-running 470R dropping resistors desoldering themselves from the PCB.

[billyz]

Martin nails it again. These two resistors drop the 48 volts to 15 or so. I re solder every fender that has these whether they need it or not. Many of them appear cracked and not just de soldered. I think the heat combined with the rohs solder and the weight of the resistor causes the issue. I've never had one come back after applying good old lead based solder.

[xtian]

+1 on those 5W resistors. A second failure mode is when the LED stops working properly. It has two elements (red and green--they combine to make yellow) and if one element is burned, the circuit won't work.

[martin manning]

Interesting about the change in solder alloy billyz. I would think that bending the leads so as to add some length to them and elevate the resistors off the board would help too.

[Stevem]

Yup, I replaced both resistors with over kill 7 watters ( one was open ) already on that power rail and one of the Zener regulators that was shorted, oh wait !, that rail having been dead may have taken out that IC chip in that LED section from only being powered up with the still working positive rail?

[gui_tarzan]

Martin nails it again. These two resistors drop the 48 volts to 15 or so. I re solder every fender that has these whether they need it or not. Many of them appear cracked and not just de soldered. I think the heat combined with the rohs solder and the weight of the resistor causes the issue. I've never had one come back after applying good old lead based solder.

I've worked on a few of those in recent months and the factory solder sucks. I've been removing it and resoldering with regular and it seems to work well. Doing that to those resistors, tube sockets and ribbon cable solder joints seems to clear up a lot of issues.

[martin manning]

Are the ones with failing resistors and solder joints mostly the older models? Looks like on the reissue the PCB has been redesigned, and those two resistors are rotated 90 degrees to place them in a vertical orientation.

[gui_tarzan]

I haven't seen the newest ones, the ones I've worked on were older models. Same issues in all of them.

[Edit] I take that back, I did work on one re-issue and it had the same problems.

[Stevem]

Yup, they are verticle now on the newer ones.

[Reeltarded]

These amps are what took me out of the outside repair business forever.



7 nightmares in a row.

[johnnyreece]

Yeah, I wrestled with one of these for a guy. Had the typical resistor issues, but when I'd put it back together, it wouldn't work. Took a while to realize that the ribbon cable had a couple broken wires. I'd like to say never again, but I will probably end up messing with another sooner or later...

[Stevem]

Ok, got back to this last night and the issue is solved.
It turns out that when I repairing bad circuit traces that the one that feed the - supply rail to the IC chip had 3 runs that needed to be jumped and I only did two!
Had I taken the added 3 seconds to confirm that the negative power was making it all the way to the chip I would have had it resolved last week.

[bluesfendermanblues]

I've never had the pleasure of digging into one of these, but from what I read channel switching issues are often related to the +/-15V power supply and the notoriously hot-running 470R dropping resistors desoldering themselves from the PCB.

I have this issue in a Blues Deluxe - was easily repaired by securing the two 470 ohm resistors a better connection to the pcb. You might consider changing the resistor to a pair with higher wattage rating that don't get as hot.

[Stevem]

I did, if you look back in this string I posted that I upped the 5 watters to 7 and what I did not post is that when I repair issues like this I also stand them up off the board by having there leads go thru 1/2" tall 1/16" ID brass tubing!

Weather it's right or wrong, I concider the lead lenght on power resistors and diodes as part of there heat sink and try to keep there leads as long as I can without having things look like mess.