what precautions need to be taken when working on an amp? My dad has a fender hot rod delux and I think the input jack has a bad solder point on the inside of the chassis so I will need to take it apart to get to it. Once I unplug the amp is there a cap I should discharge or anything else I should be aware of?
Amp Precautions
- Thread starter ocguy106
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Superlizard
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Any of those big electrolytic can caps (preamp *and* power) need to be discharged before you go poking around inside the chassis.
DangerousR6
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I was told you can let the amp sit for at least 24 hrs unplugged, and that should be enough time for them to bleed off...ocguy106 said:
Patrick from Davis
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Standard disclaimer. There are voltages that can kill you in a tube amp. I am not responsible if you go into this amp and touch something that fries you with electricity. By following these instructions you have also read this disclaimer and thereby release me from any responsibility for your actions. I also take no responsibility for any of your other actions.
Now that we have the disclaimer out of the way, here is how you do it...
OK, a Hotrod Deluxe, I have rooted through one of these several times. You need a multimeter and a 20k 1 watt resistor soldered between two leads covered in shrink wrap with alligator clips at either ends. Clip-wire-resistor-wire-clip. Resistor covered in shrink wrap, shrink warp essential... The electrolytic caps (the roll of dimes sized guys) will have about 70 volts on them after the amp is turned off, they have about 480 V when it is on. Deadly. Make sure your amp is unplugged before going inside the amp. You are going to want to clip the resistor drain that you have made to the ground side, and then to the positive side. It will be marked on both the cap and the board. Look at the cap, there will be a black line down the side of it. It will have a minus signs ( - ) along with arrow heads ( < ). The arrow heads point to the ground side. By the time you get your multi-meter to check the voltage it will probably have dropped to 2-4 volts and will then slowly drop to nothing readable. Now the caps are drained. Remove the drain resistor at this point. Do not leave it on the amp. If you plug the amp in with the drain resistor still in place, something will blow. Bad.
Getting the board out. It is not easy. Not at all. You have to take all of the knobs off, then unscrew all of the pots, then five or so jacks as well. Then you have to unscrew the 7 or eight screws that hold the board in place. Then unscrew the ground lead from the chassis. Now you have to really push on it to get the pots shafts out of the chassis to get to the "circuit" side of the board. I would generally ding a knuckle or two on the sharp metal edges. Careful, these always get infected if you don't put something on the cut quick. Now you get to the board inspect the solder joints. If you have a magnifying glass even better. Look for circle cracks around the joints in question. Also, you might want to reflow the two big ceramic resistors' solder joints (R78 and R79). These joints frequently go bad. I swapped out the two plastic jacks for switch craft jacks on the input jacks. Got them from Mouser with the isolation washers. To get it back in, push hard the other way until all of the pot shafts get by the sheet metal of the chassis. Get the pots lined up, then line up all of the switches and the LED's. Careful, they break easily. Get it in place and screw the board back in place. Reassemble the thing, don't forget the ground lug, and check it out for noises. Good luck.
Patrick
Now that we have the disclaimer out of the way, here is how you do it...
OK, a Hotrod Deluxe, I have rooted through one of these several times. You need a multimeter and a 20k 1 watt resistor soldered between two leads covered in shrink wrap with alligator clips at either ends. Clip-wire-resistor-wire-clip. Resistor covered in shrink wrap, shrink warp essential... The electrolytic caps (the roll of dimes sized guys) will have about 70 volts on them after the amp is turned off, they have about 480 V when it is on. Deadly. Make sure your amp is unplugged before going inside the amp. You are going to want to clip the resistor drain that you have made to the ground side, and then to the positive side. It will be marked on both the cap and the board. Look at the cap, there will be a black line down the side of it. It will have a minus signs ( - ) along with arrow heads ( < ). The arrow heads point to the ground side. By the time you get your multi-meter to check the voltage it will probably have dropped to 2-4 volts and will then slowly drop to nothing readable. Now the caps are drained. Remove the drain resistor at this point. Do not leave it on the amp. If you plug the amp in with the drain resistor still in place, something will blow. Bad.
Getting the board out. It is not easy. Not at all. You have to take all of the knobs off, then unscrew all of the pots, then five or so jacks as well. Then you have to unscrew the 7 or eight screws that hold the board in place. Then unscrew the ground lead from the chassis. Now you have to really push on it to get the pots shafts out of the chassis to get to the "circuit" side of the board. I would generally ding a knuckle or two on the sharp metal edges. Careful, these always get infected if you don't put something on the cut quick. Now you get to the board inspect the solder joints. If you have a magnifying glass even better. Look for circle cracks around the joints in question. Also, you might want to reflow the two big ceramic resistors' solder joints (R78 and R79). These joints frequently go bad. I swapped out the two plastic jacks for switch craft jacks on the input jacks. Got them from Mouser with the isolation washers. To get it back in, push hard the other way until all of the pot shafts get by the sheet metal of the chassis. Get the pots lined up, then line up all of the switches and the LED's. Careful, they break easily. Get it in place and screw the board back in place. Reassemble the thing, don't forget the ground lug, and check it out for noises. Good luck.
Patrick
Thanks Patrick,
I took everything apart and took a quick look. I was able to pull the chassis out without actually pully all the knobs and stuff off. Got it off far enough to see the solder joints anyway. the joints looked fine so I don't think that was the issue. gave it a good cleaning while I had it open. It had a intermitent problem so I don't know if cleaning it did anything or not.
The symptoms:
while playing at volume for about 10-15 mins the sound may become distorted or scratchy maybe cut out all together. I thought the first time this happened it might be a loose tube. putting pressure on the pre amp tubes while he was playing seemed to do the trick so I thought that was the problem. I checked the tubes and all seemed good. Next week we went out and it did it again this time touching the preamp tubes did nothing but pressing on the larger tubes did so I thought maybe it was just coincidece that touching the tubes did anything at all.
so I thought maybe a cold solder joint at the input. at this time I am not sure what it is I will see if the good cleaning has any effect on it.
any suggestions
Ken
I took everything apart and took a quick look. I was able to pull the chassis out without actually pully all the knobs and stuff off. Got it off far enough to see the solder joints anyway. the joints looked fine so I don't think that was the issue. gave it a good cleaning while I had it open. It had a intermitent problem so I don't know if cleaning it did anything or not.
The symptoms:
while playing at volume for about 10-15 mins the sound may become distorted or scratchy maybe cut out all together. I thought the first time this happened it might be a loose tube. putting pressure on the pre amp tubes while he was playing seemed to do the trick so I thought that was the problem. I checked the tubes and all seemed good. Next week we went out and it did it again this time touching the preamp tubes did nothing but pressing on the larger tubes did so I thought maybe it was just coincidece that touching the tubes did anything at all.
so I thought maybe a cold solder joint at the input. at this time I am not sure what it is I will see if the good cleaning has any effect on it.
any suggestions
Ken
Patrick from Davis
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While it is open, use the electronic cleaner liberally on the tube sockets, pots, and jacks. It can be surprising how much that helps. Don't forger to twiddle the pots while cleaning, use a cord with the jacks while cleaning and insert and remove the tubes from the sockets when cleaning. Do the cleaning cycle three times for good measure. If the solder joints look OK, that is good. I'd still heat them up with a little flux to be sure. The tube pressing things is odd. Either the sockets are dirty, or there is a loose joint that moving that board around fixes. Sort of. Give it a good cleaning, let the electronics cleaner evaporate in a well ventilated area, and try again.
Patrick
Patrick
So a little more info
I put everything back together and the problem is still there only now I can replicate it every time. The right most tube the small one closet to the input jacks, it is seated all the way and I pluged and unpluged it as well. If I touch it or flick it at all it causes the sound to break up or stop all together. If I apply an pressure on it side to side it will do the same thing. I swapped all the tubes around and the problem stays on that socket so I can safely remove the problem from being the tube and the problem should be that socket. When I had it apart since that was what I originaly thought the problem was I checked that socket out pretty good and it didn't have any obviouse signs of where but I guess I can check again. The good thing is that seemed to be the easiest socket to replace if it does indeed need replacing.
I put everything back together and the problem is still there only now I can replicate it every time. The right most tube the small one closet to the input jacks, it is seated all the way and I pluged and unpluged it as well. If I touch it or flick it at all it causes the sound to break up or stop all together. If I apply an pressure on it side to side it will do the same thing. I swapped all the tubes around and the problem stays on that socket so I can safely remove the problem from being the tube and the problem should be that socket. When I had it apart since that was what I originaly thought the problem was I checked that socket out pretty good and it didn't have any obviouse signs of where but I guess I can check again. The good thing is that seemed to be the easiest socket to replace if it does indeed need replacing.
It could be a loose pin holder in the socket. These can sometimes be pressed to tighten them up, but it's tricky. You need something quite thin to get into the socket to apply pressure to one side of the pin holder and gently squeeze it towards the other side. Not very well explained, but I dont have a socket handy, otherwise I'd take some pics.
Also, Sometimes it can be tricky to spot 'dry' solder joints. Normally speaking the joints should be nice and shiny, and not a 'blob' of solder. It should almost look like its part of the of the socket pin. With that said, you may have good solder to the wire running onto the socket, but not a good connection on the socket itself, which may be tricky to see. I second Patrick's advice about running over it again with a soldering iron and reheating the connections. Cant do it any harm.
If you can, try and take a close up pic of the offending socket, and post it here.
Also, Sometimes it can be tricky to spot 'dry' solder joints. Normally speaking the joints should be nice and shiny, and not a 'blob' of solder. It should almost look like its part of the of the socket pin. With that said, you may have good solder to the wire running onto the socket, but not a good connection on the socket itself, which may be tricky to see. I second Patrick's advice about running over it again with a soldering iron and reheating the connections. Cant do it any harm.
If you can, try and take a close up pic of the offending socket, and post it here.
Patrick from Davis
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The sockets are weird PCB mount things, not the ceramic ones that homebuilders are used to. They are relatively open. I would reflow the solder before trying the squeeze procedure simply because it is much easier to reflow the solder. The trick is to put a tiny dab of flux on the solder joint. It will really clean up nicely if you do that to the 9 pins and then clean it off with a little water on a q tip or something after you are done. Jim is right, solder joints are not always the easiest to spot the crappy ones. That amp has PCB's that are wave soldered. While some companies take a lot of time to do that process correctly, this amp, and Fender in general, seem to have a relatively large number of joints go bad. I suppose Fender also has about 10 time the amps out there as other companies, but there are a lot of bad solder joints in the newer PCB amps. The good news is, it is easy to fix. Good luck
Patrick
Patrick
Superlizard
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+10000000 Patrick knows his sh!te - follow his advice.
-100000000 for PCB mounted t00b sockets.
PCB mounted t00b sockets = teh suck
-100000000 for PCB mounted t00b sockets.
PCB mounted t00b sockets = teh suck
Superlizard
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Technically, yes (well, sort of). But your life is worth taking the extra effort to make absolutely sure. :sign13:DangerousR6 said:
DangerousR6
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Very true indeed.....Electricity hurts.....a lot....Superlizard said:
Superlizard
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DangerousR6 said:
I wouldn't know, and I don't wanna know.
When I bias my amps, I'm poking around in a *live*, plugged-in, turned-on chassis... and placing meter leads
on components (specifically 1 ohm resistors on the power t00b sockets to measure current/etc).
It's scary poking around in there; luckily I haven't had to do too much.
And always sit on one hand if possible.
DangerousR6
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I've only been hit with 110, and it hurt like a bitch...I don't recommend it or any other voltage...Superlizard said:
Superlizard
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DangerousR6 said:
Could put a variac on it and lower it to ~90V to give the shock the "brown sound" feel...
But c'mon - gotta admit testing 9V batteries with your tongue is fun. :icon_thumright:
