Everything else such as lights, horn, indys work but no lcd from either speedo

OK, and did you measure the voltage on the chip?

 

Here's the updated cct based on what we now know... D4 is indeed a transient suppressor, to catch nasty spikes from the alternator/voltage regulator. Do you have the part #, I cant read it off the photo.

I definitely think your original VR went faulty, which over-volted the board, causing D4 to go s/c until it melted off, leaving U1 at the mercy of the extra voltage and frying it, and sadly probably the main processor as well.

When the original board went faulty what were the circumstances, what was going on at the time?

 

I don't think the problem is external now. There are no outputs from this board, all the connections are inputs with the exception of the K-line diagnostic connector serial interface which is bidirectional. All the inputs are 12v/0v switches and appear to be protected by large series resistors.

 

OK, and did you measure the voltage on the chip?

Not yet, that's what I already new

 

"Then measure voltage between pin 1 (red probe) and pin 4 (black) on the 51a 8-legged chip. Should be either 3.3v or 5v"
Are you able to show me?

 

"Then measure voltage between pin 1 (red probe) and pin 4 (black) on the 51a 8-legged chip. Should be either 3.3v or 5v"
Are you able to show me?

Sure.. see pic.

• Put your multimeter on 20 DCV range.
• Put your black probe on the little hole indicated by the black arrow. Note that the board is covered in a light insulating laquer so make sure you're getting a good metal to metal contact.
• Put the red probe on the pin indicated by the red arrow. This should read approx 12v depending on how charged the battery is. Now put your red probe on the pin indicated by the green arrow (or in one of the two little holes to the left), What voltage do you get?
• If you get no voltage reading on the green arrow pin, put your multimeter on diode setting, and try again. Do you get OL, 0v or approx 0.5v? Now swap probes over, do you get OL, 0v or approx 0.5v?

 

Black & red = 11.8v
Black & green 0.02v

 

0.252 on diode 2k setting on black & green

 

0.252 on diode 2k setting on black & green

Ummm... the 2k setting measures resistance. The diode setting is the diode symbol and is a different measurement... you need to take the measurement both ways round..

 

Black on black & red on green on diode setting = 034, black on green & red on black = 002 & alarm on meter

 

Is that board 1 or 2? If you've tested only one board, repeat all the tests on the other as well..

 

That was on the board with the missing diode. Next board 0v at all & on diode setting black on black etc = 417, & swapped =1117

 

That was on the board with the missing diode. Next board 0v at all & on diode setting black on black etc = 417, & swapped =1117

That's because the diode is in backwards, need to remove it before doing that test again. There might be hope for board 2. I have a feeling board 1 may be beyond economical repair...

Whereabouts in the world are you?

 

That's because the diode is in backwards, need to remove it before doing that test again. There might be hope for board 2. I have a feeling board 1 may be beyond economical repair...

Whereabouts in the world are you?

Suffolk

 

Suffolk

Uk

 

When the original board went faulty what were the circumstances, what was going on at the time? Earth lead wasn't

Here's the updated cct based on what we now know... D4 is indeed a transient suppressor, to catch nasty spikes from the alternator/voltage regulator. Do you have the part #, I cant read it off the photo.

I definitely think your original VR went faulty, which over-volted the board, causing D4 to go s/c until it melted off, leaving U1 at the mercy of the extra voltage and frying it, and sadly probably the main processor as well.

When the original board went faulty what were the circumstances, what was going on at the time?

View attachment 243708

When the original board went faulty what were the circumstances, what was going on at the time?

Here's the updated cct based on what we now know... D4 is indeed a transient suppressor, to catch nasty spikes from the alternator/voltage regulator. Do you have the part #, I cant read it off the photo.

I definitely think your original VR went faulty, which over-volted the board, causing D4 to go s/c until it melted off, leaving U1 at the mercy of the extra voltage and frying it, and sadly probably the main processor as well.

When the original board went faulty what were the circumstances, what was going on at the time?" negative side of battery was taken off for some reason (yet to establish why) when reconnected speedo didn't work

View attachment 243708

"When the original board went faulty what were the circumstances, what was going on at the time?

 

Now diode has been reversed Black on black &
Red on red = 11.48v
Black on black & red on green = 0.93v battery is at 11.95v

 

ok, well at least its not a dead short... there may be life there after a transplant...

 

The battery was removed for charging after being left unused for awhile when earth was attached the speedo went on then off

 

Hmmm reconnecting the battery earth lead shouldn't have caused an issue. I'm assuming the engine wasn't running at the time? And no one had tried to use the kick-start while battery was disconnected?