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what are these?

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qwikv6

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I joined the board hoping you guys could help me out in a hurry. I've got a GMC Jimmy with a digital dash. I've pulled it apart and repaired bad solder joints but they dont last. I think the capacitor(i maybe wrong) is getting too hot and causing the solder joints to fail around it. I've found some pictures of replacement circuit boards guys are selling on ebay and compared them to mine. I see three components that they are changing out, although I don't know what any of them are called or where to find a suitable replacement.
here are some pictures.
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So pretty much what I'm asking is what are these things called, and where can i find updated replacements?
Thanks for any help you guys can offer.
 
The blue device is a capacitor of metallised polyester/polypropelene construcion. The other devices are transistors. For the capacitor, look for a 0.047uF capacitor rated at at least 400v (I think thats right, 47nF). I have not heard of those transistors, but will try to find them, or someone on here will know.
 
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They're probably just general purpose medium power transistors.

What does this circuit actually do, it looks like some sort of power supply, is it part of another appliance?
 
It's the power supply for a digital speedometer on a GMC Jimmy. It piggy backs one of the two main circuit boards that makeup the instrument cluster. I'm not sure what else if anything it supplys power to, because my speedo display is the only one giving me problems. Could it possibly control the other displays as well off of another circuit on that board? I really dont know what I'm looking at or how it works, but I know how to solder so i figure I can fix it and learn something along the way.
As far as a bad capacitor goes would that cause it to work intermittently? If you look closely in the unrepaired picture you can see that it was glued to that square yellow and black component. Could that have caused it to fail? It will work for a few days after I take it apart and resolder the connections, which i find kinda odd. I know my solder joints are good and not failing overtime. Maybe the heat fuses the inside of the capacitor back togethor temporarily(if thats even possible). And the first time i took it apart I didnt even touch the capacitor or the transistors. Just resoldered two resistors that had come loose.
I really appreciate the help and sorry if I sound like a complete idiot. I need to get a book so i can find out how all these components work and what they actually do.
 
Dr.EM said:
0.047uF capacitor rated at at least 400v (I think thats right, 47nF). QUOTE]

Which would be the better choice?
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i'm leaning towards the polyester film since the wires look like they'd match up with the circuit board a lot better.
 
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A capacitor would have to have a pretty massive failure to melt the solder. I've never seen a poly cap break, but I imagine it would show signs of burning/melting long before melting solder off the pads.

Power transistors are much more failure prone and it's completely plausible that they'd melt the solder.
 
in the automotive world, larger electronic components are either glued in place or potted in encapsulating compound to eliminate vehicle vibrations from working them loose from the circuit board. That small yellow square left of the capacitor is a transformer and provides a good anchor to glue the cap to it. In electronics and especially in portable or mobile devices, all electronic components MUST be physically or mechanically welll attached to the circuit board or to a strip, etc. before it is soldered. Soldering provide nothing but the electrical path for connectivity. Solder is too soft to support heavier components and when poor mechanical anchoring is used, often the components will break loose from the solder pads. The replacement capacitor can be glued in place using a hot glue gun and the matching glue sticks. As for the transistors, the newer replacements look to be substantially larger w/ built-in heat sink on their backside to handle the current that apparently GM under estimated. The small circuit board you have pictured is a power inverter board which mounts to the main instrument cluster board, not the standard power supply type as often thought of.

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The only component I've ever seen unsolder itself was a power resistor. Silicon transistors tend to short when they fail and as such, will dissipate very little power (heat), so I wouldn't expect them to unsolder themselves.

Capacitors tend to often be heavy components and in automotive applications, you see them soldered to the circuit and then a big dollup of RTV (silicone) is added to anchor the part to the PCB and to keep it from moving and vibrating and fracturing the solder joints.

I appears that the "new" parts (the transistors) are beefier versions of the originals, indicating the GM was having a few reliability problems.

Dean
 
Dean Huster said:
The only component I've ever seen unsolder itself was a power resistor. Silicon transistors tend to short when they fail and as such, will dissipate very little power (heat), so I wouldn't expect them to unsolder themselves.

Dry joints commonly occur on large components, transformers, power transistors, large resistors, large capacitors - due partially to mechanical stress, heat in the component, and expansion and contraction due to heat changes.

Power transistors and particularly voltage regulators are probably the most common places?.
 
I appreciate all the help guys but I'm still unsure about what to replace those two transistors with. I've tried cross referencing it through the web and even searched some component suppliers for a transistor with 3328 but no luck. Is C3328 a brand specific part number(TDK i believe)? Or is there another way to determine what size/type transistor I need? Maybe something a little bigger than the C3328?

Also what kind of solder would be best to use? I've got 60/40 and 96/4(silver solder). The 96/4 seems to be a bit stronger and higher temp.

Thanks again
joe
 
qwikv6 said:
I appreciate all the help guys but I'm still unsure about what to replace those two transistors with. I've tried cross referencing it through the web and even searched some component suppliers for a transistor with 3328 but no luck. Is C3328 a brand specific part number(TDK i believe)? Or is there another way to determine what size/type transistor I need? Maybe something a little bigger than the C3328?

Try 2SC3328, Japanese transistors all start '2S' so they don't print it on the transistors - it's NPN, 80V, 2A, 900mW.

Also what kind of solder would be best to use? I've got 60/40 and 96/4(silver solder). The 96/4 seems to be a bit stronger and higher temp.

High melting point is better, as it's harder!.
 
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They eliminated stamping the prefix on to that Xistor which is a common practice. It is a 2SC3328 and two suitable alternatives are 2SC4489 and 2SC4721.
The specs for the 2SC3328 are: NPN Silicon type 80volts 2amps 0.9watts 100MHz TO-92 case CLICK HERE for data sheet on that Xistor
It's really a Toshiba transistor but TDK must have been licensed to produce them as well. What you need to find out is the number of the upgraded replacement for it or search the Xistor datasheets for a suitable alternative that has higher current/wattage spec..
 
PCB-mounted power transformers and large connectors certainly do have their problems, but they're either cold (disturbed) solder joints, flux joints or stress fractures. I was referring to compontents that got hot enough to actually unsolder themselves. The older Tektronix T922 oscilloscopes were notorious for fractured joints on the power supply to interface board connector. I guess that there was just too much movement there for the joints to withstand.

Dean
 
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