Gas analyser board help

[Wightsparks]

Got given a broken 4 gas analyser, took a look at the boards and that would seem to be the issue.. Fried cap (?) and a burned track - I assume that LK1 is a sort of fuse, and those yellow things are capacitors






Took a hunt through some components I inherited and am I right in thinking this is the same thing - its about the same size



There were a couple of LED's that had corroded though as well - not sure on the voltage, 5v as they are board mounted?

 

[Seadog]

The LK1 and LK2 links on the board. They probably relate to a particular configuration of the analyzer. The track doesn't look like it's blown through excess current but has been deliberately cut.

The capacitor is 1nF so 100 times smaller in value than the one you have. It looks like it's a decoupling capacitor to remove noise and the IC it's associated with is a triple three-input NAND gate, so it's probably to prevent incorrect operation through spurious triggering.
I would expect there to be another fault.

 

[Wightsparks]

Thanks @Seadog I thought it said 100 on the broken one but I see now it says 1n
Looked all over the rest of the boards and apart from the Leds that have fallen off I can't see anything. It's pump powers up but no other output, probably a stuck relay

 

[MoreWellie]

they do look weird and the legs are very thick for 1nf capacitors, it might be worth pulling the good one out and measuring it to see whether it is a capacitor

Edit: just did a search and 1no is 10pF

 

[Seadog]

Edit: just did a search and 1no is 10pF

Oops, you're right. Definitely decoupling, so shouldn't affect the operation IMO.

 

[Hitch]

If you manage to repair it, make sure its thoroughly tested and checked...
I wouldn't want to rely on one that's been fished out of the bin.

 

[Wightsparks]

^ It's for car exhaust gas, nothing I'll be breathing !
Been over it again and nothing visible, one last bit to pull apart but otherwise it's scrap.

 

[Hitch]

Ahhh, I had it in my mind you meant one of the 4 in 1 gas detectors like user for confined space entry etc.

 

[Wightsparks]

well it has been used for confined space entry today - the scrap bin is now nearly full

 

[Seadog]

What a waste

 

[Wightsparks]

Unfortunately yes, but with no documentation, circuit drawings, or visible issues to help on a 30 yr old piece of kit that even working now has no value at all there is not much choice except salvage a few bits and send it to be recycled.

 

[MoreWellie]

no documentation, circuit drawings

Draw the circuit out yourself, I haven't done it for a while but on an oldish board it usually isn't that difficult.

Multilayer circuit boards are harder but hopefully this is just single sided