Suprima 120 ignites and then goes out

[russell.townsend]

Thanks again,

I understand what you mean about a 10M resistor shouldn't work, but it seems to defeat the circuit.

I'm going to thoroughly check and test the polarity - you're right - that would be embarrasing.

I didn't know what a "gas valve offset" was, bit it seems to be the difference between the reference output and the actual output of the gas valve.
It is also difficult to measure and if adjusted requires the measuring and adjusting of the CO and CO2 content in the flue gas.
I can do that (I have a CO and CO2 analyser for my car) - but I don't know what values it shoud be set to.
So my thought is "Best left alone".
I found this info in http://weil-mclain.com/professionals/services/Bulletins/SB0501.pdf

 

[baxpoti]

What the frig is a gas valve offset.

-0.29mbar +/-0.04

 

[ChrisR]

it seems to be the difference between the reference output and the actual output of the gas valve.

Might be more info on the SIT website.
SOunds like the extent to which a zero governor isn't a zero governor...

Can you explain further baxpoti?

I wondered when I'd find a need for my manometer's 0.001mbar resolution!

 

[Bambergaspipe]

Suprima 120:

Started cutting out: Ignited, but spark generation continued, then shut down (after 2-3 secs).
Assumed that PCB was faulty, so I have put in a new one.
(I put in a complete ignition kit, inc. electrodes and adjusted fan speeds)
Problem continues - exactly the same.

At first I thought that new PCB was faulty, but when I think about it - perhaps something else is at fault. I'd like to confirm before I send the PCB back as faulty.

Found some detail on an old post about measuring the flame sensor, but not enough to help.
How can I measure to see if the flame sensor is working ?
Could it be anything else ?
Is there a circuit diagram of the PCB ?

Very admirable. Do like every other breakdown engineer does, phone the Manufacturers helpline.

 

[russell.townsend]

Wow, Really thanks for all the help. Really useful.

I've found the problem:
First I did as suggested and used my blowlamp on the electrodes - and the ignition still failed.
I assumed that it was the PCB failing, so I started off with my old PCB and used an oscilloscope to find that C28 was failing.
This capacitor is 10nF at 630 volts. It works OK at low voltages, and fails when tested at 240v.
Now the interesting bit: the identical capacitor on the new board had exactly the same problem.
Hmmm...

I feel like sending it back & moaning, but that seems a bit self defeating now it works OK.

Haven't dared touch the Gas Valve Offset or Throttle !

Thanks again for all your help.