Omnistor Omni-Step Double inoperative on Hymer 644B 2005

[plwsm2000]

Whiskeymac - 2019-07-21 4:17 PM

I've discovered the diode testing position on my meter, which is a revelation.  All 4 small diodes test ok, but one of each pair of large ones gives a warning screech both ways so is open circuit.  The other two are fine.  In both cases it the the diode that is closer to the centre of the board that is faulty.  They are IN5402.

The transistor tests out ok.

I will pm you a sketch of the circuit taken from your photos.The two diodes you say are faulty (short circuit) are probably ok as they are wired across the relay contacts and so will be short circuited by the normally closed contacts. I now understand how the prioritization circuit works. The emitter of the transistor is pulled low when the "open" button is pressed, the base of this transistor is connected to the "close" relay coil through a 3K9 resistor and the collector drives the "open" relay coil. If the "close" button is operated, the "close" relay coil is pulled low to operate the relay. This will also remove the base drive to the transistor so switching it off and disables the "open" relay. If you want to bypass this function, you just need to short out the emitter and collector of the transistor. I didn't realize that the fuse keeps blowing. Does this blow immediately or just when one of the buttons is pressed? If it only blows when you try to close the step, I think you may have a short on one of the motor wire to 0V. Could you try removing the ST2 connector (4 pins) and check for a short between pin 2 (0V) and pin 1 (motor wire) and also between pin 1 (0V) and pin 3 (other motor wire). Note check this is on the connector with the wires on it - not on the EMS02 pins. Both motor wires must be insulated from 0V since each one with be switched to +12V or 0V when the motor is operated in either direction..

[Alanb]

Hi,

 

I was looking at the interesting photos, and starting to sketch out a circuit when plwsm2000 posted. as he seems to be further along that path than I am, I will now stand back, as I have more than enough tasks on my job list.

 

However may I draw attention to the possibly confusing error in the final paragraph of pwlsm2000's post above. The tests for an earth fault on the motor connections should read ......" Could you try removing the ST2 connector (4 pins) and check for a short between pin 2 (0V) and pin 1 (motor wire) and also between pin 2 (0V) and pin 3 (other motor wire)."

 

Alan

 

(Edited to clarify potential error - Keithl)

[Whiskeymac]

The following steps might help - 1) Connect 12V power to ST2 pins 2 & 4 as per the sketch that Keith posted. 2) Connect DMM set to measure DC VOLTS on ST2 pins 1 & 3 (in place of the motor wires) 3) The DMM should read 0V in this state (nothing connected to ST1 yet)

My DMM records 0 O between pins 1,2 and 3.  In my test reported on 16 Jul, I put 12v down the cable that I now know goes to ST2 and it blew the inline fuse I had put in my power line.  (Suggestion by AlanB 11 Jul.)  I think that the connection I made to the removed plug at the electrobloc corresponds to ST2 1&3 rather than 2&4 but I'll have to rig a long cable to check with the DMM, rather than rely on plug shapes

[Whiskeymac]

Whiskeymac - 2019-07-22 8:59 AM

I think that the connection I made to the removed plug at the electrobloc corresponds to ST2 1&3 rather than 2&4

No I was wrong.  I put a short on the plug and then tested at the EMS 02 plug and the 12v feed that blew the fuse was connected to ST2 2&4

[Whiskeymac]

I didn't realize that the fuse keeps blowing. Does this blow immediately or just when one of the buttons is pressed? If it only blows when you try to close the step, I think you may have a short on one of the motor wire to 0V. Could you try removing the ST2 connector (4 pins) and check for a short between pin 2 (0V) and pin 1 (motor wire) and also between pin 1 (0V) and pin 3 (other motor wire). Note check this is on the connector with the wires on it - not on the EMS02 pins. 

There are no shorts on the cable, tested as directed. on the EMS there is a short between ST2 pins 1, 2 and 3.  When I stuffed 12v down the cable with the EMS connected, the fuse blew immediately, no buttons pressed.  When I repeated this with the EMS unplugged, the fuse was uneffected.

[Whiskeymac]

Alanb - 2019-07-21 9:40 PM However may I draw attention to the possibly confusing error in the final paragraph of pwlsm2000's post above. The tests for an earth fault on the motor connections should read ......" Could you try removing the ST2 connector (4 pins) and check for a short between pin 2 (0V) and pin 1 (motor wire) and also between pin 2 (0V) and pin 3 (other motor wire)." Alan (Edited to clarify potential error - Keithl)

There is a short between pins 1, 2 and 3 in any combination on the EMS.

[plwsm2000]

Whiskeymac - 2019-07-22 11:06 AM

Alanb - 2019-07-21 9:40 PM However may I draw attention to the possibly confusing error in the final paragraph of pwlsm2000's post above. The tests for an earth fault on the motor connections should read ......" Could you try removing the ST2 connector (4 pins) and check for a short between pin 2 (0V) and pin 1 (motor wire) and also between pin 2 (0V) and pin 3 (other motor wire)." Alan (Edited to clarify potential error - Keithl)

There is a short between pins 1, 2 and 3 in any combination on the EMS.

There should be a short on pins 1,2,&3 ON THE EMS02 pins but not on the plug side that connects to it. As mentioned before, with both relays de-energized, the normally closed contacts will short both motor wires to 0V so this is quite normal.(Thank you Alan for correcting my error).If there are no shorts on the motor wires, and you have previously proved that the motor is ok (works in both directions), the only things left that I can think of are -1) There is short on the button(s) that opens the step (the motor would just stall and take a high current). You could try disconnecting the ST1 connector (that goes to the buttons) to rule this one out.2) One or both of the 1N5402 diodes that are connected to 12V has gone short, but did you say these diodes are ok? I have highlighted these diodes in the pic. below. The other 2 similar diodes will show a short due to the relays (this partial schematic should help)3) One of the relays has an internal short between its coil or normally open contacts to its normally closed contacts. I have never seen this happen before though (NO, NC and Common all shorted) - relays usually fail if the contacts get welded together (NO to Common or NC to common) and sometimes open circuit if there is enough current to fuse and blow the moving contact. Coils also fail, but this would not cause this particular issue.4) Swapping 12V and 0V on pins 4 and 2 would cause the 1N5402 diodes to conduct and short the 12V. I don't suppose this has been done during testing? With European vans, the blue wire is normally 12V and brown is 0V (it is an easy mistake to make to get these wrong)

[Whiskeymac]

plwsm2000 - 2019-07-22 2:08 PM  4) Swapping 12V and 0V on pins 4 and 2 would cause the 1N5402 diodes to conduct and short the 12V. I don't suppose this has been done during testing? With European vans, the blue wire is normally 12V and brown is 0V (it is an easy mistake to make to get these wrong)

I fear I have to fess up, having checked my test connection to the plug, dicovering that I connected red to brown.  I was unaware.  I'll correct this and retest.  If no short I can proceed with the other test you suggested.  Doh! 

[Whiskeymac]

1) Connect 12V power to ST2 pins 2 & 4 as per the sketch that Keith posted. 2) Connect DMM set to measure DC VOLTS on ST2 pins 1 & 3 (in place of the motor wires) 3) The DMM should read 0V in this state (nothing connected to ST1 yet) 4) Temporarily short pins 1 & 2 on ST1. You should hear one of the relays click and the DMM should now read either +12V or -12V (I don't know what the polarity will be). 5) Remove the short on 1 & 2 and now short 1 & 3. Again you should hear a relay click and this time, the voltage on the DMM should be the opposite polarity to the previous step (ie change from +12V to -12V or vice versa). 6) Repeat 4 & 5 using the other switch on ST1 pins 4,5 & 6 Obviously the relay contacts are not taking much current with just a DMM "load" so you could add a 12V lamp to increase the load.

On the job again.  I have carried out the tests as in the quote, shorting out pins on ST1, 1&2, 1&3, 4&5 and 4&6, and testing at ST 2 pins 1 & 3.  On every occasion the DMM reading at ST2 1&3 was 0V and no relay clicking at all.  So that's 5 tests in all.

In view of the symptoms, this comes as no surprise.  I suppose I could connect 12v across ST2 1&3 plug terminals to check that the motor is powered, thus confirming the wiring on that end of the system.

[plwsm2000]

Whiskeymac - 2019-07-23 4:15 PM

1) Connect 12V power to ST2 pins 2 & 4 as per the sketch that Keith posted. 2) Connect DMM set to measure DC VOLTS on ST2 pins 1 & 3 (in place of the motor wires) 3) The DMM should read 0V in this state (nothing connected to ST1 yet) 4) Temporarily short pins 1 & 2 on ST1. You should hear one of the relays click and the DMM should now read either +12V or -12V (I don't know what the polarity will be). 5) Remove the short on 1 & 2 and now short 1 & 3. Again you should hear a relay click and this time, the voltage on the DMM should be the opposite polarity to the previous step (ie change from +12V to -12V or vice versa). 6) Repeat 4 & 5 using the other switch on ST1 pins 4,5 & 6 Obviously the relay contacts are not taking much current with just a DMM "load" so you could add a 12V lamp to increase the load.

On the job again.  I have carried out the tests as in the quote, shorting out pins on ST1, 1&2, 1&3, 4&5 and 4&6, and testing at ST 2 pins 1 & 3.  On every occasion the DMM reading at ST2 1&3 was 0V and no relay clicking at all.  So that's 5 tests in all.

In view of the symptoms, this comes as no surprise.  I suppose I could connect 12v across ST2 1&3 plug terminals to check that the motor is powered, thus confirming the wiring on that end of the system.

Peter, As per my email, you should measure the resistance of the relay coils and check these are about 90 ohms. The easiest way to measure these is across each of the 2 diodes that are to the right of the bottom relay between the two resistors. Each diode is wired in parallel with the relays coils.It would be very unusual for both relay coils to fail, but if the "close" relay went open circuit (the one at the top in your photo), the transistor would not enable the other relay to function.The other posibility is that you have a bad solder joint on the diodes connected to ST1. Looking again at the solder side photo, the leads of the 4 small diodes connected to ST1 look a bit suspect to me (although the photo is not sharp enough to be sure). On a good solder joint, you should not be able to clearly see where the solder meets the component lead. On these diodes, I think I can see a ring around the lead where it meets the solder joint. It could just the photo quality but it might be worth pointing this out to your friend with the soldering iron.

[Whiskeymac]

plwsm2000 - 2019-07-23 8:06 PM  As per my email, you should measure the resistance of the relay coils and check these are about 90 ohms. The easiest way to measure these is across each of the 2 diodes that are to the right of the bottom relay between the two resistors. Each diode is wired in parallel with the relays coils. It would be very unusual for both relay coils to fail, but if the "close" relay went open circuit (the one at the top in your photo), the transistor would not enable the other relay to function. The other posibility is that you have a bad solder joint on the diodes connected to ST1. Looking again at the solder side photo, the leads of the 4 small diodes connected to ST1 look a bit suspect to me (although the photo is not sharp enough to be sure). On a good solder joint, you should not be able to clearly see where the solder meets the component lead. On these diodes, I think I can see a ring around the lead where it meets the solder joint. It could just the photo quality but it might be worth pointing this out to your friend with the soldering iron.

We have inspected the soldering of the small diodes and concluded that your concern was unfounded, due to shadow/reflection picked up by the photo.  I have tested thoroughly continuity from the ST1 seats and the diode legs and on the other ends, from the legs to various points on the board, with no problem found.

Measuring resistance across the two relays seated between the relay and resistors, the result was 89.5O across the one nearest the relay, but across the other there is a reading which quickly disappears to no reading. The reading is different each time and wide ranging, the largest being 89.5O.  The same is true when tested from vaious connected points on the board.

[plwsm2000]

You should be getting a steady 90 ohms across both diodes (89.5 is close enough !). The fact that you sometimes get the correct reading suggests to me that you either have an intermittent open circuit inside the relay or an intermittent solder joint. If you can, it might be worth applying the +12V and 0V to ST2 as before and link pins 1&3 on ST1 (that ought to switch the top relay) and then "wiggle" the relay and the components to see if it switches and so get an idea of where the problem is.

 

The part that looks like a resistor between the two relays is a zero ohm link and is in the top relay coil circuit.. You can replace this with a bit of wire instead if it is bad (unlikely though).

 

As mentioned previously, if the top relay coil is open circuit the transistor will disable the bottom relay so it could be just the one relay that is faulty.

 

[Alanb]

While I have been engaged on other tasks, I have been loking in from the sidelines with keen interest.

 

Whiskeymac,

 

Can you please clarify as to what you mean by "no reading" in the following clause. It can be read as either infinity, or zero ohms.

 

"Measuring resistance across the two relays seated between the relay and resistors, the result was 89.5O across the one nearest the relay, but across the other there is a reading which quickly disappears to no reading. The reading is different each time and wide ranging, the largest being 89.5O. The same is true when tested from vaious connected points on the board."

 

Thanks for the PM.

 

Alan

 

Thanks

[Whiskeymac]

I have been off-piste having been invadated by 3 grandchildren and parents from Cyprus.  The sound levels have been huge, particularly from 4 year old grandson who demands answers to constant questions.  They are now away with my motorhome so I can return to some considered thought with my EMS 2 and DMM.

I discovered that the scatty reading across the winding of one relay was caused by me selecting too low a resistance setting on by DMM, so it was trying to measure a resistance that was off-scale.  I have now boiled it down to:

The apparently significant difference of readings seems to be 619 ohms in one direction only across the lower relay and 89 ohms both ways across the upper one. (Upper and lower, with plugs on the right).

I'm not clear on what this points to, but I think it may well be the nub of the problem.

[Whiskeymac]

I forgot to add that when I say that resistance is one way across one relay, the reading is zero in one direction.  The DMM gives the same reading of 1 as when not connected at all, when the red probe is on the contact with the dots around it and 619 ohms when the probes are reversed.

 

[Alanb]

The relay coil across which you are measuring 619 Ohms is prbably open circuit. I think that the indicated 619 Ohms in one direction only is the parallel diode biased in the forward direction . (Not a true resistance as the diode will not start to conduct until there is about 0.6V across it. Your meter will see this as a higher than actual resistance.)

 

The quoted coil resistance for these relays is 90 Ohms. Your readings across the other relay coil, are within the limits of error.

 

To confirm that the relay coil is open circuit you could unsolder one end of the parallel diode, and lift it from the PCB. I would then expect your meter to indicate "1" in both directions across the relay coil.

 

Alan

[plwsm2000]

Peter, I agree with Alan that it would appear that the relay coil is open circuit (or there is a bad solder joint). Did you measure across the relay pins directly? (I highlighted these on one of the PMs I sent you) BTW, the "common" contact has 3 pins all joined together inside the relay so the part actually has 7 pins that need soldering not 5 as per the circuit.

Just for the benefit of others who did not see the email exchanges, the above measurements that Peter made were taken with the DMM set to a manual 2K ohm range (autoranging switched off) as he was getting confusing readings with autoranging on. The DMM kept switching ranges when trying to measure "resistance" of now just a diode.

 

Just out of curiosity, do you ALWAYS release the button IMMEDIATELY the step reaches the end of its travel? If you don't and the fuse trips, there might be enough voltage generated by the stalled motor to blow the relay coil (just a theory)

 

[Whiskeymac]

Thank you both for your help in directing and analysing my test readings.

My soldering iron is on board so 2 days away from returning to me.  I'll then check read with the diode lifted.  Meanwhile I'll place an order for a replacement relay today.

Regarding button release as soon as the steps are at the end of travel, I suspect that my wife has been overzealous in this regard, being keen to ensure that hey are right down. We'll ensure we open the door to have sight of them going down in future.  Raising them is less of an issue.

Thanks again.  I'll report on how this goes, for completion of the thread and repect for the kind help given.

[Whiskeymac]

Alanb - 2019-08-01 7:12 PM To confirm that the relay coil is open circuit you could unsolder one end of the parallel diode, and lift it from the PCB. I would then expect your meter to indicate "1" in both directions across the relay coil. Alan

The replacement relay arrived from Germany today, in a 1ft square 5in deep box!  I popped one leg of the diode as suggested and proved the winding was reading 1 on the meter in both directions.

I'm seeing my soldering friend this evening so will take in the EMS 02, with suitably marked relay and hope she will be able to lift out the old and solder in the new.  Not an easy job.

[Alanb]

No not easy, a solder pump would help. I have from many years ago somthing called "Solder Wick". I would liken it to a piece of TV coaxial cable outer copper braid, stretched out and impregnated with resin flux. The imethod of use is to apply it to the solder to removed with a soldering iron, and letit soak up the solder, cutting off any used pieces as necessary.

As a parallel technique try gently levering up any loosened areas while solder is still molten.

 

Alan

[Whiskeymac]

Alanb - 2019-08-08 3:31 PM "Solder Wick". Alan

Looks very useful and cheap from RS, post free. Sent to my pal for consideration.  Thanks.

[Whiskeymac]

I'm glad to report that my friend, who used to solder circuits for fighter jets, managed to remove my faulty relay quite easily, using a new soldering iron with temperature control, allowing use as cool as possible. I checked the meter resistance readings across the windings and they were the same for both relays.  The box was plugged back in, the steps checked to ensure the motor could run freely and pressed the up switch and was overjoyed to hear it working.  The steps are now reconnected and alls fine.  I have just to rescrew the relay box back in the cupboard.  Since unscrewing took over half an hour and lots of blue language, this will be a loathsome task.  I may try to shift its location if the cables will allow. Now I think about it, I may well velcro it back in place!! 

I attach the circuit board photo with relay connections tested for resistance between, as marked for me by Phil, to whom I am much indebted.

Thanks to everyone who contributed and hopefully this thread will be uuseful to someone else in the future.

[Alanb]

Peter,

 

I am gratified to read that you have eventually succeeded.

 

Alan

[StuartO]

So, for the benefit of the non-experts among us, the fault was in the step relay (located behind the fridge) which needed replacement. Is that correct?

[Whiskeymac]

StuartO - 2019-08-12 10:27 AM

So, for the benefit of the non-experts among us, the fault was in the step relay (located behind the fridge) which needed replacement. Is that correct?

 

No. The fault was in one of two relays in the EMS 2 box which was located on the back of the front of the heater enclosure, to the right of the door.  The EMS 2 (or later similar units) controls the electric steps, but is not shown on the Omnistor/Thule circuit diagram that comes with the steps.