Recapping SX-737

DixieMan1994

Active Member
Hey guys,

Got my caps in from mouser, so I started the recap on my 737. Everything went fine (I started on the power supply board) until in my infinite wisdom failed to make a proper soldering joint on one of the caps (the 50v 220uf cap in the middle of the board). I went to fire the unit up and ZAP, there goes the screw in 3A fuse mounted in the back panel :dammit: :sigh: So once I solder up a proper connection with a small jumper wire, where could I get said fuse?:worried:
 
Hey guys,

Got my caps in from mouser, so I started the recap on my 737. Everything went fine (I started on the power supply board) until in my infinite wisdom failed to make a proper soldering joint on one of the caps (the 50v 220uf cap in the middle of the board). I went to fire the unit up and ZAP, there goes the screw in 3A fuse mounted in the back panel :dammit: :sigh: So once I solder up a proper connection with a small jumper wire, where could I get said fuse?:worried:

Home depot,autozone,walmart just about anywhere. Does the screw-in fuse unplug from the fuse holder cap? 3A fast acting 3A AGC.
 
Home depot,autozone,walmart just about anywhere. Does the screw-in fuse unplug from the fuse holder cap? 3A fast acting 3A AGC.

Yeah the fuse holder looks like the end cap of a mag lite in a way. Has a spring that holds the fuse in. Hell if it is an AGC I should be able to get a box of them for work (I work at an electrical wholesale outfit). I just wanted to make sure I got the right fuse before I went any further.
 
I didn't see anything to give me the impression of this, but is there anything else that I could have possibly blown during this? :dunno:
 
I didn't see anything to give me the impression of this, but is there anything else that I could have possibly blown during this? :dunno:

A cap installed bass ackwards could cause the fuse to pop. A solder bridge on the circuit board could cause it to blow as well. Shorted transistors and diodes / incorrectly installed transistors and diodes. A pinched or chaffed wire. Foreign objects like lead clippings or solder drops.To name a few.
 
A cap installed bass ackwards could cause the fuse to pop. A solder bridge on the circuit board could cause it to blow as well. Shorted transistors and diodes / incorrectly installed transistors and diodes. A pinched or chaffed wire. Foreign objects like lead clippings or solder drops.To name a few.

Ok cool. Yeah I made sure that I installed all the caps in the right polarity, double checked with a photo I took with my phone right before I started. Im only a few caps in, about halfway done with the board. Havent messed with anything other than capacitors. I powered the unit up every two caps to see if everything was working properly. As soon as I powered it up the second time, I knew what I screwed up. Ill make a bridge with a bit of wire and change the fuse tomorrow. If I run into anything else I will let ya know. Thanks dude, I appreciate your help :yes: :thmbsp:
 
Yeah the fuse holder looks like the end cap of a mag lite in a way. Has a spring that holds the fuse in. Hell if it is an AGC I should be able to get a box of them for work (I work at an electrical wholesale outfit). I just wanted to make sure I got the right fuse before I went any further.

The amperage is obviously important, but make sure to use the correct voltage also. Some (car fuses) are only 32 volt and not suitable to use in ac the main.
The voltage rating will need to be 125 or 250.
 
The amperage is obviously important, but make sure to use the correct voltage also. Some (car fuses) are only 32 volt and not suitable to use in ac the main.
The voltage rating will need to be 125 or 250.


3A AGC is rated at 250vac
 
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Do you have or have you looked into a dim bulb tester? When I fired up my 737 after the recap the dim bulb tester saved me from seriously cooking the unit a second time. Cost less than ten dollars to build, and came together in 15 minutes.

Good luck! I'm in the process of troubleshooting mine after the recap. It's a fun process, go slow and look into a dim bulb tester, I bet it could save a headache
 
I don't have one but I have thought about putting one together. How does it save the unit in a situation like that? :saywhat:
 
As you're probably finding out there's a lot of different ways to skin this cat, here's the simplest dim bulb tester instructions I've found.
http://ppinyot.com/dimbulb/dim_bulb_tester.htm
All the way on the bottom based off an extension cord and lamp socket, that's the recipe I used. I mounted mine on a piece of wood and have had no problems.
 
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Well, I am having some interesting issues now. So I of course got the capacitor bridged, installed the new fuse in the screw in holder, and gave her a whirl. Nothing. So I start checking things out and I notice the inline soldered fuse leading to the screw in fuse is blown. I change it out, and success, the unit fires up and works like a charm. :banana: Then I start again working on my recap, I replaced one of the 50v 330uf caps (the one closest to the back of the unit of the three), POW! there goes the screw in fuse again. I checked the solder joints, those came out fine, then I noticed that while I had the board out of its connectors I had the back wire post on the right side (from my angle from working from the back) very close to the chassis. Ok, so I readjust the board accordingly, pop in a new fuse, and success again. :D Well then I power the unit off, then power it on again immediately. Zap! There goes the inline fuse. :yikes::screwy: I cannot see anything visually to cause that, and I have no idea what is going on, or what I possibly did. What do you all think? The whole popping fuses thing is confusing as hell now :saywhat:
 
When you work on the boards and power them up while "hanging in space", slip a piece of dual wall cardboard about the same size under the board or wherever it looks like it's gonna touch anything else. Sounds like the board shifted slightly between you moving it and you hitting the switch. Get a couple of mechanics towels as an option and use them as isolator/padding. Or just place the board on the plastic posts but don't lock them down.

When you get to the amp board, DO NOT TAKE CHANCES WITH IT HANGING. Bolt it down 1st.

what size fuse are you using in the screw in fuse? Should be a 3A AGC. DO NOT USE A LARGER FUSE. Cycling the switch can at times pop the fuse just from the voltage drop and immediate surge / shock of the current running thru it. Wait a few seconds (10 count) between off and on.

Larry
 
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When you work on the boards and power them up while "hanging in space", slip a piece of dual wall cardboard about the same size under the board or wherever it looks like it's gonna touch anything else. Sounds like the board shifted slightly between you moving it and you hitting the switch. Get a couple of mechanics towels as an option and use them as isolator/padding. Or just place the board on the plastic posts but don't lock them down.

When you get to the amp board, DO NOT TAKE CHANCES WITH IT HANGING. Bolt it down 1st.

what size fuse are you using in the screw in fuse? Should be a 3A AGC. DO NOT USE A LARGER FUSE. Cycling the switch can at times pop the fuse just from the voltage drop and immediate surge / shock of the current running thru it. Wait a few seconds (10 count) between off and on.

Larry

I will do that for sure. I got plenty of cardboard at work that I can use. I was using a 3A AGC. I got a box of them from work. They are actually a GGC, but it is the same fuse as the AGC just different brand (Gould Shawmut instead of Bussman). Ill try swapping the fuse out and powering her back on. It was running flawlessly before I cycled it, so you very well might be right. Thank you Larry, you and all the guys here rock and roll :yes:
 
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