Electronic help req'd - resistor ID.

[Gordonmc]

One for those more electronically inclined than me.
The pic below is of the small PCB behind my engine instrument panel.
Could someone confirm that the red coloured component is a fried resistor.
The circumstances are that I had a bit of excitement on a night trip which required removal of the panel. I put it back and started up, but the water temperature alarm has been continuously sounding. I traced the wiring to the engine sender. I tried another sender - no change. I have disconnected the alarm signal wire from the sender for some peace. The temperature guage works fine.
In further examination I found the guage illumination bulb holder had broken, possible shorting to earth. This is when I found the suspect resistor.

Any comments at this stage would be appreciated - next step will be to identify the resistor (10 ohm is likely) and replace it. Any other thoughts?
Another pic for context:

 

[3663Ian]

Do you think its a resitor like the one next to it that has had the coating destroyed by overheating?

 

[geoffatstanpit]

Looks more like a diode to me

 

[Sandyman]

Looks more like a diode to me

+1. A burnt out resistor would not look like that at all.

 

[starfire]

it is a diode, 1N4148 by the look of it, & it looks ok, if it was fried it would be obvious.

check it with a multimeter on diode or ohms range & no power to the panel, you should get a reading with the probes one way round & nothing the other way round

 

[halcyon]

it is a diode, 1N4148 by the look of it, & it looks ok, if it was fried it would be obvious.

check it with a multimeter on diode or ohms range & no power to the panel, you should get a reading with the probes one way round & nothing the other way round

May be a zener diode, if so it sets the reference voltage for the alarm drive circuit, thus the alarm going of.

If a zener diode it will have 5V1 or similar number on the side.


Brian

 

[lenseman]

One for those more electronically inclined than me.
The pic below is of the small PCB behind my engine instrument panel.
Could someone confirm that the red coloured component is a fried resistor.
The circumstances are that I had a bit of excitement on a night trip which required removal of the panel. I put it back and started up, but the water temperature alarm has been continuously sounding. I traced the wiring to the engine sender. I tried another sender - no change. I have disconnected the alarm signal wire from the sender for some peace. The temperature guage works fine.
In further examination I found the guage illumination bulb holder had broken, possible shorting to earth. This is when I found the suspect resistor.

Any comments at this stage would be appreciated - next step will be to identify the resistor (10 ohm is likely) and replace it. Any other thoughts?
Another pic for context:

The resistor does look like a ¼-watt 10Ω which is in series to the silver active device with the blue blob of paint on the top. What is this component and what manufacturer and what is the type?

The device below and parallel mounted 'seems' to be in parallel to the above 10Ω resistor which would be strange and as others have stated in is a diode but what type. It could be a zener (avalanche), steering or blocking diode so care needs to be exercised in your decision?

I am interested in the two other components which have been removed from the circuit board as the 10Ω resistor and diode do not seem to have 'burnt out'?

 

[mucklestone]

Looks like a diode to me too. All looks well to me..... The holes probably never had components there so not removed....

 

[Sharkx]

Not a resistor.

A burned out resistor would have a good bit of blackness around the component and the green pcb.

It doesn't look too healthy whatever it is. The other other thing it can be really is a diode.

 

[Sharkx]

http://parts.digikey.com/1/parts/421603-diode-zener-10v-500mw-do-35-1n961b.html
Tis a Zener diode.

 

[concentrik]

.

A diode yes, as others have said. Glass encapsulated and it could be a zener or plain diode as both are found in that package. You can test it as suggested with a meter, but to avoid confusing in-circuit readings you should lift one end first. That way you're only testing that component.

Just as an aside, the fault probably lies elsewhere. Failures of these components are not so common and where seen, they are often catastrophic (visually obvious)

 

[BERT T]

Can you get the part numbers of the two transistors, if you had an accidental s/c its more likely to blow one of these. the component in question is not a resistor but is as far as I can see a diode. (a burnt resistor would be a grey/black colour )

 

[Rigger Mortice]

If anything has burnt out due to a short circuit I would start with those transistors (the metal top hats with the blue spot)......if transistors they are.

What is written on the side of them?

 

[nigelmercier]

Tis a Zener diode.

Well, it's a diode without doubt. But from the picture it could be one of many.

Note that to test it with an electronic multimeter, you can't use the Ohms range, you have to use the Diode test circuit, normally marked as below

 

[William_H]

Well, it's a diode without doubt. But from the picture it could be one of many.

Note that to test it with an electronic multimeter, you can't use the Ohms range, you have to use the Diode test circuit, normally marked as below

You can use a multimeter on low ohms range. It should show very high resistance one way and a lowish resistance the other way. Typically for digital multimeter the forward resistance might be several hundred ohms. This however is not a true resistance but a reflection of the forward volt drop of the diode. (.7V for silicon diode) The reading in ohms depends on the circuitry of the meter but anything less than 1000ohms is good. You may find the resistance seems to be different on different ohms ranges.
Obviously a diode test range is best if you have it.
If it is a zener diode then you need to make a test circuit. This will compose of a 9v battery (or higher) and a resistor of 1000 ohms. Connect the resistor in series with the diode and connect across the battery. With current in one direction (band of the diode towards the -ve) you should measure around .7 volt across the diode alone as the diode conducts. Reverse the battery and you should measure the avalanche (zener) voltage of the diode which might be 5volts or whatever the diode is designed for. (3 to 75 volts) good luck olewill

 

[misterg]

...I have disconnected the alarm signal wire from the sender for some peace...

Are you saying that if you disconnect the wire from the *temperature sender* that the alarm doesn't sound?

What engine (or instrument panel) is it?

Andy

 

[nigelmercier]

You can use a multimeter on low ohms range...

Not always, modern digital multimeters don't normally put more than 0.7V on the leads, hence the need for the diode range.