How to go about checking this PCB

[david74]

Hi, I have this ignition PCB, it opens a valve but does not ignite. I bought a primitive tester for £7.99 and what I checked was the fuse and the output terminals.

The fuse is ok and output terminals show 0.05 (My Ohm meter goes from 1 to 0 and says 200kO on the selector knob dial). But I can't read anything on the input of the grey little box the output terminals are.

I went to the local phone shop and the person there poked around with the meter and spotted a blown capacitor.

He said he would be happy to swap out any faulty part but also said that he had no means of finding which one was which.

Can I find anything conclusive with a multimeter on the board?

I understand that capacitor appears as an open circuit to the 3V multimeter.

If I wanted to order the capacitor, how would I figure out its specs?

Please could anybody check out the photo?

There is a primitive diagram on the box.

 

[Spoon]

Ok, correct me if I'm wrong, but the component that you have circled is a resistor. (The one with the 4 coloured stripes)
To get the value of the resistor, you use the coloured stripes.
The stripes to me look like brown, black, brown. and the end one looks Gold. That will give you a value of 100 ohms and a tolerance of plus/minus 5%
The wattage of the resistor, you may find out by measuring the length and comparing it with the catalogue lengths.
Also the value of the resistor may be printed on the PCB when you take the damaged on off.

 

[david74]

Ok, correct me if I'm wrong, but the component that you have circled is a resistor. (The one with the 4 coloured stripes)
To get the value of the resistor, you use the coloured stripes.
The stripes to me look like brown, black, brown. and the end one looks Gold. That will give you a value of 100 ohms and a tolerance of plus/minus 5%
The wattage of the resistor, you may find out by measuring the length and comparing it with the catalogue lengths.
Also the value of the resistor may be printed on the PCB when you take the damaged on off.

Oh, thank you, it just says R42 on the board probably referring to a parts list on some schematics.

What about my other question. Should that grey box read anything on inputs? Actually!!! I pressed harder and it shows 0.01!!!

Do you think swapping that resistor out would sort the PCB? What potential other, bigger problem it could indicate to check first?

BTW, I checked the 24V power supply, and it does show 25V. I did not check it under load.

I also checked the 100 Ohm resistors on eBay but they also specify wattage e.g. 1/4 or 1.8. And the look small, mine is at least half an inch wide.

How do I check other resistors. My tester has diode continuity knob position. When I check a nearby component that looks like a diode, it gives reading jumping around upper 19 hundreds. And it does it both ways.

The other blue large resistor (R4) shows 0.05 but the yellow (R21) says 36 which means that my tester not just goes from 1 to 0 but also gives larger numbers than one.

 

[westward10]

I believe the terminals on the grey box are the 20kv output for the ignitor.

 

[david74]

I believe the terminals on the grey box are the 20kv output for the ignitor.

Yes, they are and I consulted AI and it says that the 0.5 reading on output and fluctuating reading between 0.0 and 0.1 on input is really low. Does it mean they have melted and then fried the resistor?

I ordered a pair of 3W 150 Ohm resistors on eBay because the black line Spoon took for black is actually blue.

There is a little bit of soot on the inside of the box around the 20kV terminals.

 

[mainline]

Oh, thank you, it just says R42 on the board probably referring to a parts list on some schematics.

What about my other question. Should that grey box read anything on inputs? Actually!!! I pressed harder and it shows 0.01!!!

Do you think swapping that resistor out would sort the PCB? What potential other, bigger problem it could indicate to check first?

BTW, I checked the 24V power supply, and it does show 25V. I did not check it under load.

I also checked the 100 Ohm resistors on eBay but they also specify wattage e.g. 1/4 or 1.8. And the look small, mine is at least half an inch wide.

How do I check other resistors. My tester has diode continuity knob position. When I check a nearby component that looks like a diode, it gives reading jumping around upper 19 hundreds. And it does it both ways.

The other blue large resistor (R4) shows 0.05 but the yellow (R21) says 36 which means that my tester not just goes from 1 to 0 but also gives larger numbers than one.

To be able to check most components properly you would need to take them off the pcb or at least one leg or more.

 

[david74]

I checked the other resistors and compared the readings with the stripes and they were all a match except one where AI said it should be 33K Ohm but my tester just shows that it was 32.7 without specifying that it was in K.

The problem was that the protective coating the PCB and parts are covered in are difficult to scrape through.

I could not get any readings from the relay but the board was opening the valve so if that was what relay was supposed to do, then that is ok.

 

[mainline]

I checked the other resistors and compared the readings with the stripes and they were all a match except one where AI said it should be 33K Ohm but my tester just shows that it was 32.7 without specifying that it was in K.

The problem was that the protective coating the PCB and parts are covered in are difficult to scrape through.

I could not get any readings from the relay but the board was opening the valve so if that was what relay was supposed to do, then that is ok.

You maybe lucky and it’s just that resistor gone open.

If not it could be a number of things.

 

[david74]

You maybe lucky and it’s just that resistor gone open.

If not it could be a number of things.

Well, before I cash out £83 on a new board, it is worth trying a resistor for £2.25.

 

[mainline]

Well, before I cash out £83 on a new board, it is worth trying a resistor for £2.25.

If the resistor gets hot very quickly I would unsolder the transformer and see if it does the same.
If it doesn’t then it’s more than likely the transformer is duff.
If it still gets hot then it will more than likely be the switching or both.

Because of your limited experience and lack of test gear that’s probably the easiest steps to take.

 

[david74]

If the resistor gets hot very quickly I would unsolder the transformer and see if it does the same.
If it doesn’t then it’s more than likely the transformer is duff.
If it still gets hot then it will more than likely be the switching or both.

Because of your limited experience and lack of test gear that’s probably the easiest steps to take.

If the resistor gets hot very quickly I would unsolder the transformer and see if it does the same.
If it doesn’t then it’s more than likely the transformer is duff.
If it still gets hot then it will more than likely be the switching or both.

Because of your limited experience and lack of test gear that’s probably the easiest steps to take.

Do you mean the ignition coils or the 24V one because that was hot. It was first thing I noticed when it stopped working.
The 24V one is quite massive. I can hook up to it easily and see if there is voltage drop on ignition.
Hooking up to the little ignition one is complicated.
I'm off to shops on Town street to resolve the resistor. They just arrived.

 

[david74]

The moment of truth. The guy at phone shop was off today so I bought a soldering gun for £9.99 and swapped it myself.

 

[david74]

I have a video with the resistor catching fire. If you have trouble with watching flashing videos, take migroleave in advance. The fireworks start after my phone switches to selfie mode for the second time.

 

[david74]

The aftermath. Now not only the resistor is blown but the capacitor next to it has spilled its guts.

 

[mainline]

The aftermath. Now not only the resistor is blown but the capacitor next to it has spilled its guts.

Well at least you got some ignition, pity it was from the wrong place.
The capacitor may have been the source of the short so you could change it along with the resistor again.

 

[mainline]

Do you mean the ignition coils or the 24V one because that was hot. It was first thing I noticed when it stopped working.
The 24V one is quite massive. I can hook up to it easily and see if there is voltage drop on ignition.
Hooking up to the little ignition one is complicated.
I'm off to shops on Town street to resolve the resistor. They just arrived.

The LZL-24H is a relay.

Yes I meant the ignition one.

 

[david74]

Well at least you got some ignition, pity it was from the wrong place.
The capacitor may have been the source of the short so you could change it along with the resistor again.

What I will do when I get the replacement board, first I will try it in the machine to see if that works.

If it does, then I will replace the resistor and capacitors and compare readings with working board.

Once it does match, I will try it in device again and if works, put it on eBay half price perhaps to recover some money. Or perhaps I could do something more sinister and send the new one back under 14 days return policy.

Also I will maybe develop understanding how certain electric components work together apart from one being blown out when the other is short.

 

[Avo Mk8]

What I will do when I get the replacement board, first I will try it in the machine to see if that works.

If it does, then I will replace the resistor and capacitors and compare readings with working board.

Once it does match, I will try it in device again and if works, put it on eBay half price perhaps to recover some money. Or perhaps I could do something more sinister and send the new one back under 14 days return policy.

Also I will maybe develop understanding how certain electric components work together apart from one being blown out when the other is short.

Realistically, unless you can get hold of the circuit diagram, the board is "beyond economic repair".
R41 is now a gonner. Things burning up are quite likely symptoms of a fault elsewhere, not the actual faults. You may have to detach components to individually measure them, and doing lots of that could end up damaging the pcb or components.

Some of us like dabbling with electronic repairs, and it can often be successful with simple faults like droppers in power circuits, but I suggest a reality check here, and it would be more worthwhile checking there's nothing wrong in the boiler that's going to blow up the next PCB.️

 

[david74]

Realistically, unless you can get hold of the circuit diagram, the board is "beyond economic repair".
R41 is now a gonner. Things burning up are quite likely symptoms of a fault elsewhere, not the actual faults. You may have to detach components to individually measure them, and doing lots of that could end up damaging the pcb or components.

Some of us like dabbling with electronic repairs, and it can often be successful with simple faults like droppers in power circuits, but I suggest a reality check here, and it would be more worthwhile checking there's nothing wrong in the boiler that's going to blow up the next PCB.️

That is a valid concern. But I checked the spark plugs, they are open. And the PSU did not drop the voltage on the fire if you noticed.

There are no other inputs or outputs to check.

I did similar shuffle with an Abarth Spider SatNav SD card. I bought one with valid preburned identity code, used it to download and install the latest maps, then after two weeks (from the first insertion of the card), once it encrypted the contents to my particular VIN, it allows to create and use backup on any card which I did and then restored the original contents to the original card and sold the it on eBay with 10% off. If it makes sense.

What startles me, is that during fireworks, the fuse did not go.

 

[mainline]

That is a valid concern. But I checked the spark plugs, they are open. And the PSU did not drop the voltage on the fire if you noticed.

There are no other inputs or outputs to check.

I did similar shuffle with an Abarth Spider SatNav SD card. I bought one with valid preburned identity code, used it to download and install the latest maps, then after two weeks (from the first insertion of the card), once it encrypted the contents to my particular VIN, it allows to create and use backup on any card which I did and then restored the original contents to the original card and sold the it on eBay with 10% off. If it makes sense.

What startles me, is that during fireworks, the fuse did not go.

The only reason the voltage on the power supply didn’t alter was that the power supply is obviously well regulated and working as it should.
If you had been monitoring the current it would have been another story.