Help using Rapitest DM25 (volt tester)

[zappastix]

Hi

I need to check if I have power on a PCB (Alpha CB28).

I have replaced the Air Pressure Switch - the problem remains.

My final check before forking out £150 for a new PCB is to determine if the PCB is dead (dead feed to APS).

The manual says I should also check M5 and M6.

I have got hold of a Rapitest DM25 - but no instructions.

MY QUESTION

I need to check for 24 V DC

What settings should I set the tester at;

1) V _
...

2) V ~

number 1 OR number 2

3) Presumably I would select 200 (not 20) is this right?

4) I have got the RED PROBE in V (ohms sign)

5) The BLACK PROBE is in COM

I have got to test connector number 15 (within M5)
and number 20 (within M6).

My last question - do I hold the probes ON BOTH
connectors at the same time while testing?

On the circuit diagram the APS switch (number 14 0\ 0 number 15)
i.e. the switch is not connected at number 15.

Number 20 in M6 is one of two connectors into
Gas Valve Modulating Coil.

Any help would be really apprciated.

Thanks, Stephen

 

[Rob]

Maybe you should just explain the fault you've got first!

What is and isnt happening with the boiler. i.e when a tap is turned on or heating is put on?

 

[Gasguru]

FFS get someone in before you kill yourself.

And don't waste your time buying a PCB - you can't just plug it in...it requires test gear to set it up.

 

[zappastix]

It's an Alpha CB28 combi boiler.

Neon B flashes every 5 seconds (which is normal)

When you turn on the hot water tap, the fan runs, but the air pressure
switch does not prove.

I know this because Neon A and Neon B start flashing on/off together.

The fault finding chart says to check the flue.
I did this - I had all the fan assembly out and the flue/ventura are all
clean (fitted new fan 2 years ago).

So I fitted a new APS - but the fault remains - both lights flash.

I've blow through the tubes and the tube that goes into the hampster wheel.

So unless I've been sold a duff APS - I'm left with checking the PCB,
to see if power (24 V DC) is at the relevant connectors.

Thanks. [/wiki]

 

[wiffers2003]

Bear in mind that i have no boiler pcb experience, although i can tell you how to use a meter.

To measure 24 VDC...

V_ is Volts DC (batteries, circuits)
V~ is Volts AC (mains voltage)

Set your meter to V_

You then need to choose the next level up from what you want to measure, therefore select 200.

Black probe goes in Com (Common Ground)
Red probe goes in the hole with V next to it, it may share the same hole to measure resistance (the ohms sign) but if it doesn't (not all meters do) then make sure it goes into the V for Volts hole.

You will need to hold on both probes at same time so the meter can measure the "difference" (voltage) between them. Why not practise on a standard battery first !

Not sure about the other part of your message, but basically if the manual says, for example, there should be 24VDC between two points then touch them both with the meter on the correct settings and see what it says.

By the way if the meters says -24 VDC instead of +24VDC then you just have the probes round the wrong way on the pcb. It wont cause any damage.

Good luck.

 

[zappastix]

Thanks Wiffers2003 - that has help me alot.

Cheers.

 

[luminaire]

Also check this out on how to use a muiltmeter.

 

[cheesepuff]

the tidle (~) and the underscore (_) i think the tidle is alternating currnet (AC) and the underscore Direct Current (DC)

 

[breezer]

You only THINK it is

 

[wiffers2003]

I KNOW it is.