Blown cap on old dwell gauge - kal equip 2851

[snakeintheeaglesshadow]

Hi,

Can anyone help ID this cap, or any tips on how to figure it out? As you can see, it's clearly fried. Unfortunately the burn marks obscured the color bands. I couldn't get a good zoom on it with my phone, so I hope the pics are enough. I can try again if not.

[petehall347]

Re: Blown cap on old dwell gauge - kal equip 2851

looks more like a resistor to me ..what does it connect to ?

[R_J]

Re: Blown cap on old dwell gauge - kal equip 2851

Looks like a resistor to me also, post a clear picture of the trace side of the board. Also post the number on the component next to the burnt resistor.

[snakeintheeaglesshadow]

Re: Blown cap on old dwell gauge - kal equip 2851

Thanks both for the quick replies. Sorry I couldn't respond until now.

Attached are pics of the trace side and (I hope) a clearer pic of the numbers of nearby components.

I believe it connects:

The very purple resistor (?) to the left of it
The black three post component (not sure what it's called)
Two white 'blocks': .1J100# and (horn?)33nJ250 (obviously not so sure on the symbols)

[stj]

Re: Blown cap on old dwell gauge - kal equip 2851

desolder it and check its resistance

[petehall347]

Re: Blown cap on old dwell gauge - kal equip 2851

looks like a track got burned through .

[redwire]

Re: Blown cap on old dwell gauge - kal equip 2851

I followed the circuit a bit, but can't tell what all the wires go to. The burnt resistor connects to the red wire near the LED, see pic.

I would say it's 82R based on the grey band and smoke, so power shorted to that wire. It's a weird fault, someone must have connected up the wires wrong to the board. +12V power is supposed to connect to the top right corner. The CD4069 IC then gets 9VDC power.

OP a resistor does not burn up unless there is an overload caused by another issue. So replacing the resistor will just smoke it again. The other resistor looks OK it just has a purple body. I can't see any cooked pcb traces, it's just solder-dipped might appear that way?
The transistor typically connects to the ignition coil/points, but here it's missing all the surge protection parts so I'm not sure where they are.

[petehall347]

Re: Blown cap on old dwell gauge - kal equip 2851

here doesn't look right ..

[petehall347]

Re: Blown cap on old dwell gauge - kal equip 2851

that transistor looking thing might be shorted ..best check its id number then test it .

[redwire]

Re: Blown cap on old dwell gauge - kal equip 2851

here doesn't look right ..

You're right trace should be flat but I have seen that as a solder blob from the tinning process, on PC boards made in the 1980's like this one.

The dwell meter reminds me of Sun, Sears Craftsman etc. circuits. PCB marked 01-4221B so it might be made by them.

[desert-rat]

Re: Blown cap on old dwell gauge - kal equip 2851

Yeah that's a res. Can you read the colors on it ? And yeah check whatever it is connected to.

[stj]

Re: Blown cap on old dwell gauge - kal equip 2851

a lot of times a resistor can get that hot and still work - it just got very hot from the real fault
so always worth metering it

[snakeintheeaglesshadow]

Re: Blown cap on old dwell gauge - kal equip 2851

Wow what great input! Very impressed by this community.

I would say it's 82R based on the grey band and smoke, so power shorted to that wire.

Can you recommend a specific resistor(s) to try?

It's a weird fault, someone must have connected up the wires wrong to the board. +12V power is supposed to connect to the top right corner. The CD4069 IC then gets 9VDC power.

I found it among my late father's hot rod stuff. No instructions of course, so I just plugged it up. Incorrectly, obviously.

The transistor typically connects to the ignition coil/points, but here it's missing all the surge protection parts so I'm not sure where they are.

Ah ha! I think I know where I went wrong attaching it. With no surge protection built-in, must be pretty easy to fry.

On the attached pic I attached the each colored lead to it's corrsponding connector on the board. I'm thinking the correct attachment points to engine are:

Red = ignition coil positive
Black = ground
Blue = ignition coil negative
Inductive pick-up = spark plug wire

desolder it and check its resistance

Would this work even if blown? I figured it stops 'resisting' when such.

[stj]

Re: Blown cap on old dwell gauge - kal equip 2851

but is it blown, or just got hot enough to burn the paint??
thats the reason to test it

[desert-rat]

Re: Blown cap on old dwell gauge - kal equip 2851

Check it with an ohm meter. If you need a new one the color bands are a key to its value.

[redwire]

Re: Blown cap on old dwell gauge - kal equip 2851

Where does this red wire go? It mistakenly got +12V power on it which is what smoked the resistor.

[snakeintheeaglesshadow]

Re: Blown cap on old dwell gauge - kal equip 2851

Where does this red wire go? It mistakenly got +12V power on it which is what smoked the resistor.

That goes to two AA batteries. Just FYI the other red wire in the pic goes to a 9v battery.

[redwire]

Re: Blown cap on old dwell gauge - kal equip 2851

Um, how many batteries are in this? A pair of AA's and a 9V?
Usually these run off the 12V power at coil(+) for tach, dwell. Maybe the battery is for small engines.
Unless... this meter must have an ohmmeter function? That would explain the smoke lol.

I would measure the burnt resistor value and see if its good for a guess at what it was or its dead. For ohms function (slide switch to the right?). One leg of the burnt resistor connects to GND.

The small transistor is the inductive pickup amp and although nearby it is not a suspect.

[snakeintheeaglesshadow]

Re: Blown cap on old dwell gauge - kal equip 2851

Um, how many batteries are in this? A pair of AA's and a 9V?

Yes indeed. Three batteries total. I would kill for a set of instructions to know why haha.

Usually these run off the 12V power at coil(+) for tach, dwell. Maybe the battery is for small engines.
Unless... this meter must have an ohmmeter function? That would explain the smoke lol.

It does have this function! I probably should have put all of the functions in the title. Attached is a pic of the front. It does dwell, tach, volts and ohms.

I would measure the burnt resistor value and see if its good for a guess at what it was or its dead.

Ok that will be my next task. I think I found a few good youtube tutorials.

For ohms function (slide switch to the right?).

Precisely! Volts/ohms. The other switch is for tach/dwell.

[desert-rat]

Re: Blown cap on old dwell gauge - kal equip 2851

Did you try to see if it would work? Volts and ohms are easy to check. For tack and dwell you would need an old car with points.