Door interlock testing out of machine PTC versions

[shaun67]

Was looking for some kind of tester that will allow me to apply voltage to door interlock once removed from machine ( this is for work shop testing not in customers home ).

Take a metalflex zv-446 interlock for example .. now if it is labeled like the one i have here which has pins 132 ..

Now if i ohm pins 1+3 with lock removed then i get over 916 ohms and if i move to pins 1+2 then i get OL which is good.

My idea was then to supply the interlock with voltage to test the PTC which once fed with voltage and activate the latch with an insulated screwdriver for a 1 min or so and then disconnect power to lock i should then get a ohm reading on pins 1+2 closed circuit before the PTC cools down.

I know some will say just swap it out with another lock but what if you don’t have one to hand ? What i am saying is i’d rather try a few tests before just swapping out a part .

Anyone recommend a tester that will allow me to do this.

Thanks p.s i know i can bypass an interlock by placing a jumper across live and common for testing purposes on the connector block ( not at a customers may i add ) but i want to be able to try this way 😆

[leavemetogetonwithit]

Re: Door interlock testing out of machine PTC versions

You’ll find the most common locks to fail can be covered by having a very few locks in stock (I keep about half a dozen new plus a few second hand for testing). If in doubt as to whether the lock is faulty, you can usually open it up to check inside for burning of contact surfaces. I have used a simple flying lead to test locks but it’s pointless because they go intermittent so the test is not reliable.
Mike.

[shaun67]

Re: Door interlock testing out of machine PTC versions

Cheers mike , it’s a shame we cannot reliably test an interlock ..As said before i don’t like just swapping out parts . Maybe thats because i have played about with mending switch mode power supplies and computer monitors before i got into this field and was trying to pinpoint an exact failed lock with some testing . So you think my theory would not be reliable .

Shaun

p.s i have also had the lock in bits so i know where you are coming from regarding any signs of damage inside.

[Martin]

Re: Door interlock testing out of machine PTC versions

shaun67 wrote:I know some will say just swap it out with another lock

The majority will say swap it for another one Shaun. There’s a whole bunch of door interlocks covering dozens of brands and models within those brands that fail all the time. Now stocking a box full of these on your van is a cheap investment and certain to guarantee first time fixes. Now if you’re not sure what interlocks to stock, simply look at the vast range of pattern interlocks that are available and buy one of each. Your investment will return more than 100 fold in no time at all.

Also it is rare indeed ever to go anywhere near a suspect interlock with a test lead or multi-meter, there’s no real need. A simple mains sniffer to establish whether or not a live supply is getting to the switch is often all that’s required. Time is money, wasting time taking an interlock out and ‘testing it’ is all very credible I’m sure but by the time you’ve proved it to be faulty I’ve already fitted a new one, got paid and am halfway to my next job. 🙂 😉

[leavemetogetonwithit]

Re: Door interlock testing out of machine PTC versions

Taking apart the old lock after you’ve replaced it is a useful check to make sure your diagnosis was correct. Especially useful to determine whether Lux / Merloni etc. board damage was caused by lock. Also confirms to the customer that it was a necessary replacement, should they look doubtful.
Mike.

[Phidom]

Re: Door interlock testing out of machine PTC versions

On the later Hotpoint WM models without the motor pecker device the interlock nearly always damages the PCB when it fails so just swapping the interlock is misleading as the machine will still be dead. You need to also check the board, which is easily repaired.

[shaun67]

Re: Door interlock testing out of machine PTC versions

Thanks guys for the comments. I do have a few spare interlocks already 😉 and it is only a 2min job just to replace with a new one if there is a live feed to the lock as Martin says (which is how i also test as well as checking continuity ).

It was just a theory that i was playing with while at home as i enjoy testing components and looking at the way they behave.

I have read on here a few times where some one suspected a door lock only to find replacing it was not the answer as it was some think else faulty on the machine but the person was sure it was the interlock at fault at the time ( maybe not done the right tests on the lock who knows) .

I know as Phidom says that the hotpoint wm models without pecker device nearly always took the PCB with it. Not come across one yet but if i do then i will try to repair the board as i enjoy soldering .

Like i said it was just a theory i was toying with and probably will still play about in my spare time lol I know in the real world time is money and it does not take long to substitute a doorlock with another ( as long as the substitute lock is not a faulty one also ) 😉

Shaun

[leavemetogetonwithit]

Re: Door interlock testing out of machine PTC versions

PS. In most cases it’s not a live supply to the lock which is missing when the board has gone pop; the damage is normally in the neutral side and the live will still be there.
Mike.

[Martin]

Re: Door interlock testing out of machine PTC versions

shaun67 wrote:but the person was sure it was the interlock at fault at the time ( maybe not done the right tests on the lock who knows)

We’ve all been there, done that, more than a few times but in the grand scheme of all things ‘interlock’ you cannot truly ‘test’ an interlock using neither a meter or hot wiring it.

The most vulnerable device on a washing machine has got to be without doubt the lowly door interlock. Apart from the user swinging on the door and breaking the door handle, the day to day action of slamming the door shut has got to make this the front line to any potential electrical failure within the machine. And when the symptoms of any washer is that the lights come on but there’s no-one at home you can bet it’s that little lump of plastic being at fault.

Based on that scenario you likely as not can get your multimeter out and check the terminals all you like but as I posted earlier, if you’ve got 240v to it and it still don’t work, chances are it’s bu$$ered. What’s even more tragic is that often as not it blows the main circuit board in the process.!! (as our colleagues have mentioned).

Now the simple 3 pin bi-metal is currently the most common device and the greatest offender. The older ones with spade terminals a doddle to check and in the past I myself have not been avers-ed to a little light live testing in order to check them out. But beyond that, and into the 21st century, we have minuscule plug-in connector blocks that are best part of impossible to check let alone put a test meter on.

Mike mentioned Zanussi machines in his post……Those heaps of tin now use the 4 terminal ‘solenoid’ system as well as the heated bi-metal device in order they operate. These lovely devices operate in sequence, firstly the bi-metal is fired up but not until the start button is pressed does the solenoid engage raising the locking latch and then closes the circuit. Testing those devices with a multimeter or even hot wiring will tell you little or nothing, a pointless exercise overall, it really is TBH.

shaun67 wrote:Like i said it was just a theory i was toying with and probably will still play about in my spare time lol I know in the real world time is money and it does not take long to substitute a door lock with another ( as long as the substitute lock is not a faulty one also )

No harm in playing around in your spare time on that one Shaun and I wish you well. In the workplace though it’s best to go armed with a replacement interlock. Much like when the ceiling light no longer works and I’m sure you don’t fuff around with your meter on a job like that. But rather grab yourself a new bulb and see what happens when you switch back on?

leavemetogetonwithit wrote:Taking apart the old lock after you’ve replaced it is a useful check to make sure your diagnosis was correct.

I’m not at all sure what you are saying here on this one Mike? We all know that faulty interlocks blow pcbs – fact. And checking for physical damage on PCBs will prove the correct diagnosis for the greater part. (burnt tracks and black fused markings on holders etc). That in itself evidence enough therefore it’s hardly necessary to take apart a plastic interlock as well. Similarly when a machine is dead and you stuff in a new interlock to sort it, much like the light bulb job, you don’t need to take it apart to prove to the customer that it is faulty. At least I’ve never found the need and just hand over the duff interlock and cop my just reward…. 8)

[shaun67]

Re: Door interlock testing out of machine PTC versions

Thanks Martin for that insight , and i agree whole heartedly that little plastic door lock can cause a lot of damage .I do however take spare interlocks with me as it’s a 2min job to swap one around than trying to meter it like you say ( not really had to fit one yet that has took the pcb with it ,but i guess i will come across one and the board will be throughly examined for damage ) . My little idea was just for me to play about in my spare time as previously said.

@Mike. Regarding neutral side taking out pcb .I have seen others mention this as well in previous posts in the past. If i come across a faulty component i would also make sure the said component has not damaged anything else .

Shaun

[leavemetogetonwithit]

Re: Door interlock testing out of machine PTC versions

Martin wrote:

leavemetogetonwithit wrote:
Taking apart the old lock after you’ve replaced it is a useful check to make sure your diagnosis was correct.

I’m not at all sure what you are saying here on this one Mike?
Well, for example, I went to a WM series which was reported dead the other day. But when I got there it powered up fine so I wasn’t certain there might not be some other cause for the intermittent fault, e.g. faulty socket. Rather than try it a second time and risk damaging the hybrid timer, I fitted a new lock then bust the old one open to have a look at the innards. As expected, there were the usual carbon deposits and corroded heater (ptc)/bimetal contacts which were confirmation enough. Had I found a clean interior to the interlock, I would have looked further for the cause and possibly found it thus avoiding having a call back. (Not much I enjoy less in life than a call back!)
Mike.

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