Hi I have a circuit board that has blown the diode, is it due to too much voltage if so how can I find out what is too much? Thanks

 

this Is not much information to go on, for your general question, I have a good but general answer: check the datasheet of the diode.

 

Hi sorry about that, it's from a moped speedo cluster, has a 12v battery & a rectifier. Thanks

this Is not much information to go on, for your general question, I have a good but general answer: check the datasheet of the diode.

 

How do you know it’s bad?

 

The solder melted either side & it dropped off. Didn't realise it was the problem. I bought a 2nd & tge same thing happened

 

Then the problem isnt the diode... thats the symptom not the cause which is a short circuit after the diode causing it to overheat and die... rectify that problem first before replacing the diode...

 

Short circuit after the diode? Would that be on the circuit board then?

 

Sounds like a design issue that you or the manufacturer needs to figure out - diodes typically get hot when there is too much current (amperage) flowing. Too much current flows when the resistance is too low.
Have you made any modifications to the circuitry? Added any accessories, lights or buzzers?

 

Short circuit after the diode? Would that be on the circuit board then?

Hard to say without further investigation. Some good quality, hi-res photos of both sides of the board would help. Short could be on the board, quite possibly another faulty component. Though the cluster looks self contained, it could be in external wiring. Do you have overall wiring diagram to cluster (in service manual maybe)?

When does diode get hot? As soon as battery connected or after ignition switched on?

What test equipment do you have available? A good multimeter?

 

Does this speedo have an analog dial or is it digital? Original or aftermarket? Make and model of the moped

 

A quick look at the photo shows it has a motor driven rotary speedo (probably of the spring-return average current type) plus numerous LED indicators/dial lighting.

 

Nothing modified or added

 

The only thing I see is some solder spatter that may be shorting two traces...

 

I'll check that later, I've ordered a 3rd used circuit board but I don't want to plug it in till I know all is OK

 

The only thing I see is some solder spatter that may be shorting two traces...

Possibly, but that's drive to an LCD so unlikely to have the impact the TS is seeing.

I can't see any immediately obviously faulty other component either.

@Yoshi3 Can we get photos of reverse side please. Also what test gear do you have?

 

I'll have to get pics later of board & my meter, thanks

 

That seems like a very large diode for what is on the circuit board. Are you sure it's not the sort of diode put there to blow the fuse if the polarity of the supply is reversed?

 

I don't know that's something you'd have to ask the manufacturer I guess

 

I've asked for a wiring diagram. Here's some more pictures

 

Hmmm, well here is a partial cct of that area as best as can ascertain from the pictures. Apart from the overheating diode D4 the 8pin device to the left of it (U1 on diagram) looks like its blown too. Looks to me like power comes in on the connector pins 1 and 2, where pin 1 has priority over pin 2, 1 diode drop v 2 diode drops, is smoothed by the two 100uF capacitors and feeds into possibly the speedo motor from the D2/D3 junction and also carries on through D4 to other parts of the board. Looking at trace widths the connection from D4 is substantial so clearly carries some amps. I reckon something down stream has failed shortcircuit and thats whats overheating D4. Because the U1 chip is blown, but is not obviously part of that path IMHO a voltage surge well above what is normally expected has fried U1 and one or more devices downstream of D4. My guess is that the damage is catastrophic and beyond economic repair.



Edit: diagram updated following post #21 & #23