# Mind bending electrics....... (and some other stuff)



## 102172 (Dec 22, 2006)

Hi all,

You probably won't remember that a few weeks ago I had a mad panic when I realised, the night before driving off to a race meeting, that my water heater wouldn't work (on gas - I have since found that it seems to have a mains feed going to it, which travels via what I think is a screw in thermostat with a wire broken off, but it could be the heating element itself with an integral thermostat???). The problem was that the electronic controller (which also turns on the water pump and shows the tank levels) wouldn't supply a 12v feed to switch it on. After some superb help from Mr Star Spangled Spanner himself (what a star - I must call to arrange that service to coincide with my next race mtg) I jury rigged a 12v feed from a switch and hey-presto, working water heater. I am now in the process of working out what is wrong with that electronic controller to see if I can fix it rather than buy a new one from HR in the states.

What I have is a PCB with a quad op amp on the back, wired up as a basic analogue comparator. The op amp seems to be doing its job (although I have no oscilloscope these days and there is only so much you can do with a multimeter) but I have found a direct drop in I can replace it with, in case it has gone dead in my ham fisted attempts to diagnose the first (water heater) problem. Possible as integrated circuits can easily fail with just the slightest short across legs. But I could do with some help - how do the level systems on the tanks work??? I think I know, but would appreciate confirmation/correction. When pressing the button for a tank, on the board, it applies 12v to a wire which seems to go off to that tank. In response it seems that a voltage comes back on the other tank wire which is between 0 and 12v and proportional to the level. It looks like 12v = empty and 0v = full. I have the large copper pad on the tank and then three strips - I assume that is the normal method of sensing???? However, I can only actually find the fresh and black tanks - I have no idea where the grey is hidden! Does that sound like how they should work??? If so then I am fairly sure that the circuit board itself is causing the misreadings as when I test each tank pair independently I get the response I expect from applying 12v - but when they are all on the board I get random results. If you think I'm on the right lines I'll change that op amp and if that doesn't cure it I'll buy a new board from HR - ouch. Or I could remanufacture one from scratch I suppose......

The other problem is the continuing water heater issue. When I apply 12v, as advised, it works fine. However, when applying 12v from the board (making the board give 12v even though it doesn't always want to) I get a strange clicking noise from the heater control board and the 'lock out' light comes on at the control board. This could be another symptom of the broken board, but I want to rule out any other possibilities. I have a suspicion that the 12v out from the board doesn't go straight to the heater, but goes via another component, but I'm not sure what or why. Could that be the case? What I do know is that when the board supplies 12v it actually ends up being about 11v (could be that op amp sinking the supply) so could that cause the lock out symptom - low voltage safety perhaps? I suppose that could be why the heater control board clicks before the lock out comes on – relay chattering due to low voltage?

Any advice on that lot would be most appreciated. I'd love to think that a broken control board is the cause of all of these problems, but I'm not that optimistic so I just want to rule out other possibilities too.

On separate issues, which hopefully you can give me some steers on:

Sometimes when on gas my fridge can be heard to be clicking its ignitor furiously for a couple of minutes. It seems to work fine and gets nice and cold - is this normal or do I have a problem?? I have noticed that sometimes the check light comes on when I switch from generator back to gas, but assume that is due to the mains supply bouncing as the generator stops.

Also, one of my hydraulic jacks is getting very slow to retract. Are they pumped back up or do they just rely on the springs?? I know it has a slight oil weep around its seal (I think, but it could be a coupling I suppose). Any advice?

As always, chaps, many thanks in advance for all of your top advice. I wouldn't know where to start without you all!

Paul


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## 102172 (Dec 22, 2006)

Oh no, it looks like everyone's stumped!

Any advice at all before I go it alone???

Anything would be most appreciated.

If not, I'll let you all know how I get on........

Cheers.

Paul


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## 95633 (Jul 4, 2005)

Hi

Sorry - Im the LAST person to help with techie stuff.

But - I would suggest signing-up (free) at www.rvforum.net

It is an American forum and there are some very good tech guys on there.

Gotta be worth a try?

Paul

PS I hope I dont get told off for posting other forum details.


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## 88927 (May 10, 2005)

Hi Paul
Just noticed your thread mate..... So many questions?????
Does the comparator also work with the heater, you indicate that it is a quad input and you are only using three inputs, fresh, grey and black tanks??? Maybe the fourth input is from the heater unit (water level/thermistor etc??). If this is the case then it would strongly suggest that the IC is playing up and certainly worth changing as it is probably only a few pence compared to £000? I would change it anyway for the time/cost involved.
Have you measured the input volts to the PCB? Is it 12 volts? Is there a voltage comparator elsewhere on the board that could be in trouble? Any mini/micro transformers on board?
Don't forget that many US circuits operate by switching the return (neutral) not the live side so and bad earths can cause spurious failures.
You are saying that the water heater won't work on gas and that you have found an electrical heater with a broken wire. Is the heater feed itself broken or is it a thermostat wire that is broken? On my electrical heater system (not yet fitted due to being unable to remove the drain plug for fear of damaging the tank..) there is a mains feed from a switch to a tank mounted temperature selector (thermostat) and the power is then routed (temp dependant) on to the heater itself. If yours is fundamentally the same set up then a broken wire at any of the components will not let the system work. I do not have a 12 volt feed to mine, or is this just to operate on gas?
Ref the fridge, is it just a case of a dirty or out of position thermocouple?
We have heard our fridge "clicking" as if trying to light on gas when it is on the mains hook up, don't know what causes this either???
The jacks I know nothing about however if they are hydraulic is there a non return valve in the circuit that is sticking? Possibly crud around the seal/ram? Maybe a weak spring slowing down the return of the leg? Insufficient oil in the system / air in the system? I guess the first part of the fix is to understand how the system should work and then diagnose why it is not doing what it should do.
I hope my ramblings have been of some use and if you are passing Kettering in your travels, pop in and borrow my oscilloscope to sort out you electronic faults :lol: :lol: 

Keith


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## olley (May 1, 2005)

hi paul can't help with electronics I am afraid, regarding the jacks if they are HWH then they are spring return only, you could have a sticking solenoid or weak springs. see >>>HERE<<<

Olley


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## 102172 (Dec 22, 2006)

A-ha!

Thanks for that chaps. That has set off a few more thoughts. 

I'll let you know how I get on.

As always - much appreciated!

Keith,

Regarding the quad op-amp, the four comparators are used one for each level (1/4, 1/2, 3/4, 4/4) and are switched between the different tanks depending on which button is pressed. There are no other active components on there. But there are electrolytic capacitors which I never trust! I am going to change the op-amp - as you say £0.49 each so worth a stab! If that doesn't do the trick I'm going to remanufacture the board from scratch myself and impove the design/functionality. On the water heater, the 12v is there to activeate the gas side. The broken wire is on the end of the drain plug where I assume someone has stuffed a heating element replacement - there is a seperate 110v breaker for it in the main breaker box, so it's probably a HR fit upgrade. That I need to fix. As for the fridge - as it's working I'm not touching it! I'll get Dunc to check when he services the whole thing later in the year.

Olley,

Thanks for that - dead handy.

Paul


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## 88927 (May 10, 2005)

Got it now re the quad input, I was assuming four different devices :lol: 
Let us know how you get on with it Paul, I would try scaping all the passives off and replacing the lot wholesale tbh, if they are all leaking by say 10% that could cause your volt drop.....
Good luck

Keith


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## 99412 (May 25, 2006)

We have a HR Vacationer, and my experiences are as follows:

One of the jacks (Rear OS) was slow to retract, however after powering it up and down a few times it now seems OK. I can confirm that it is spring loaded return.

I always understood that the tank levels were simple float switches, and I have sort of confirmed this when we had a problem with the black tank never emptying. We found that it was showing 1/3 full even when nothing more came out. I coupled up the tank flush / washer to mains at 10bar and flushed it for 10 mins. After that all was well. My assumption is that something unpleasant was wrapped around a mechanical component, and once shifted the FS began to work. It all makes sense but might not apply in your case.


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## 102172 (Dec 22, 2006)

Many thanks for that. I'll give the jacks a good work out in case it is a sticking valve or similar which might free up.

On mine the tanks are definitely measured via a kind of inductance device as I can see the strips on the outside of the black tank.

Cheers.

Paul


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