Printed Circuit Board - testing & repair

[Andy 308GTB]

Can anyone suggest where I can get a PCB from a speed sensor looked at?
I was hoping to do it myself but testing requires something way finer than any electrical metering that I own or could justify purchasing or renting.

It's a tiny little board consisting of
- 2 capacitors
- 2 resistors
- 2 transistors
- 1 diode
and a fine copper coil that generates the pulse to the speedometer.

I can buy a replacement part but it's fortunes and I'd rather not be held to ransom!

Thanks

Edited by Andy 308GTB on Thursday 21st January 19:07

[speedyman]

Why not just buy the componets and replace them. The will be part numbers on them.
All you need is a soldering iron solder and solder sucker.

[Andy 308GTB]

speedyman said:

Why not just buy the componets and replace them. The will be part numbers on them.
All you need is a soldering iron solder and solder sucker.

I did consider this, in fact I have a list of components which come with the guide on how to fix the sensor. (http://www.dinoplex.org/instruments/vegliaspeedosensor/index.html)
I started looking to buy all the bits but I got bogged down in the various tolerances etc. that each component could have when I started trying to source them. Atop of this, the copper coil could be the problem and testing that requires quite a fine ohmmeter.

I was hoping to find a small electronics outfit that could get me to a point where I can trust the sensor. Because the next stop will be pulling the dash out, which I have done before but is a horrible job.

[brman]

The trouble with finding someone to do it is (assume they have not done one before) that they will probably want to charge the overhead of working out how to test it properly. That will add up time/cost wise.

How much are you prepared to spend? £10s or £100s?

[Andy 308GTB]

brman said:

The trouble with finding someone to do it is (assume they have not done one before) that they will probably want to charge the overhead of working out how to test it properly. That will add up time/cost wise.

How much are you prepared to spend? £10s or £100s?

I have a bit of a budget... a replacement part is £207.85 + p/p + VAT (i.e. over £250)
The guide I linked to in my other post details what needs to be tested and what results are expected but as I said a normal multi-meter is too crude.

[SS2.]

Those components would cost pennies.

Even if you didn't know how to test them, it would only take 10 minutes to replace them with new.

And if you weren't happy with a soldering iron and wick / sucker, find a friendly electronics guy and offer him a few quid for him (or her) to do it for you.

[scottyp123]

You can test all the components with a multimeter but problems arise because one component could give a false reading to others if you are checking them in situ so the only sure fire way to check each one is to de-solder each one from the board and check them individually but they all look glued down with hot melt glue or some sort of resin.

It doesn't look a complicated circuit board though and Bigclive on youtube makes fixing stuff like this look ever so easy, maybe there is a schematic you can download to see how its all connected up.

[Zad]

A couple of those connections look like potential dry joints. Just sweat up all the solder joints. Also, meter the coil for DC resistance. If it is open circuit then that's going to be a bugger to replace. Make sure the module is getting power too - no point chasing a faulty module if the power isn't being supplied to it.

[Ean218]

Definitely just replace all the bits, £5 tops.

It was for fixing stuff like this that Maplins was so useful.

[timmymagic73]

I fiddle about with stuff like this, and I'd say that it's most likely you have a dry joint somewhere as previously posted - or a damaged trace on the board.

I'd start with some basic continuity between parts to check traces - if you can see where they go underneath that resin.

Then just re-flow the parts with fresh solder and test it. Of course if you're looking to bench test this then you'll probably need more specific equipment to read the pulse it generates.

[Andy 308GTB]

Thanks for the input.
Electrical component shops are few and far between - as has been said, Maplins closure compounds that. Buying components online is quite daunting because of the various different tolerances of voltage and heat etc. that are available.

I'll probably try the latest suggestions re dry joints and damaged trace first. This makes sense as I think it's an original part, so it could be over 40 years old (certainly no less than 23)