Help a newbie with a schematic

Guys,*

Its been awhile since ive delt with electronics. It's really been about 20 years. I'm getting back into it and need some help.*

What i'm doing here is just replacing some SMT capacitor's. Seems simple enough right. Well this circuit was made back in the 1980's. When taking off some of the capacitors, I really didnt have todo anything. They were just falling off with the slightest touch. Along with the capacitors, came the metal that connects it to the circuit board. So now there are a couple spots where no soldier will stick. There are a couple place where I cant trace where it would connect in the circuit because the board was messed up. I have included photos.*

Looking at the photo. I need to put a capacitor in C102 ... But where is the negative going?

A crop from the schematic is also included below.

So Looking at the crop of the schematic, I want to make sure im reading this right. So coming off the chip 380-1B at pin 20. That is the positive. the path then splits and part goes to FB5 and the other goes to the capacitor C102 (16V 10uF). The negative of the capacitor just goes to a chasis ground. So I can really tact that to any ground.*

Correct?

Once again sorry for all the newbie questions.*

Do you have complete schematic for the board which you hold? If yes check for the different ground symbols in the schematic.

Else you could take the multimeter and check for the ground pins and connect with it. Because it just seems to be the decoupling capacitor in the circuit. So nothing will harm if you just connecting it with the ground.

Looking at the photo. I need to put a capacitor in C102 ... But where is the negative going?

Click to expand...

Sorry if this sounds daft but the negative end goes to the end that isn't marked '+'. You can theoretically connect it to any ground but you would risk the differences in ground voltage around the device being conducted into the circuit. The best place is still across the two pads although the negative seems to be connected to the thick track along the edge of the board so you could scrape the green paint away and join it to that but still as close as possible to the original location.

I would guess it's a reset timing capacitor. If you do wire it elsewhere you might find the big IC resets unpredictably - making fault finding far harder.

Brian.

Since the capacitors simply fell off the board with the slightest touch along with some of the printed wiring then your soldering iron might be too cheap and gets too hot since it probably does not control its temperature.