Volvo SX-M Trim Tilt Control Unit Problem

[ghaunhorst]

I have a trim limit control unit (black Box) #3851584 / 3855584 on a volvo penta outdrive type SX-MHP that appears to be faulty. Does anyone have information/instructions on how this system is supposed to work, have a wiring diagram, or know how it can be tested? I have tried many things as noted below and it seems that this box is the problem. But it is too expensive to just swap it out and hope.
The following should help answer some questions:
Metal Plaque on Engine reads: Prod. No. 3868850. Type SX-MHP. Serial No. 4111505473.
Have examined and tested the Pump, Motor, Relays, Cylinders, and filled reservoir. The outdrive moves up and down just fine if I apply 12 volts directly to the relays.
I have ckecked fuses and connectors. Measured resistance across sender contacts and it changes as outdrive is raised and lowered.
When moving the trim switch on the throttle, the lights on the black box light up but nothing else happens. So it seems the box is getting the signal from the switch but the signal is not getting to the relays.
Any info or suggestions would be appreciated. Thanks , Greg

 

[QBhoy]

Do you have a additional switch on the transom or bathing platform of the boat ?
Other than that having an influence, I wonder if your trim limit position is needing set up or calibrated. Could also be as a result of poor continuity in the wiring from the remotes to the unit. Finally, does it not work from the remotes in all positions of the outdrive? Nothing to do with the difference in operation between trim and trailer full tilt mode ?

 

[ghaunhorst]

Thanks for your reply QBhoy! No additional switch on transom or platform, but there is an additional white rocker switch on the throttle lever. I believe this is for full tilt mode. When pushing this white switch a light comes on the black box but nothing else. I'm thinking the wire continuity from remotes to black box is Ok because lights come on every time I push the trim or tilt switches (both switches are on the throttle lever). But that signal never triggers the motor to run, even at various positions of outdrive.
Perhaps calibration is needed, but how do I do that?
Thanks

 

[QBhoy]

Thanks for your reply QBhoy! No additional switch on transom or platform, but there is an additional white rocker switch on the throttle lever. I believe this is for full tilt mode. When pushing this white switch a light comes on the black box but nothing else. I'm thinking the wire continuity from remotes to black box is Ok because lights come on every time I push the trim or tilt switches (both switches are on the throttle lever). But that signal never triggers the motor to run, even at various positions of outdrive.
Perhaps calibration is needed, but how do I do that?
Thanks

I’m not too familiar with that system at all to be fair. But I know that on my older VP you had to hold a tilt button then the trim to go behind a certain point. But sounds like you know that anyway.
So about the trim limit. Again…not familiar with that one…but there is usually a potentiometer that can stop the trim travelling to or beyond a certain point. If that’s compromised…it may stop or working all together.

 

[ghaunhorst]

Thanks again for your comments. Haven't had time to get back to boat to try anything, but will make another post when have more to report.

 

[ghaunhorst]

So we finally got back to the boat to work on the trim system again. Since my last post I bought a Clymer manual that was very helpful in explaining how the trim limit control unit (black box) works, how to reprogram it, plus it included a wiring. Armed with this information I felt confident that we could resolve the problem.
First: we tried operating the trim system by pushing the override switch simultaneously with the up or down trim switch. Yeah, we are now able to move the outdrive up or down thru the full range, but only if the override switch is depressed.
Second: We followed the detailed instruction in the Clymer manual to reprogram the black box with outdrive at -2 degrees, then at +5 degrees, then at full tilt. During reprograming, the lights on the box lit up like they were supposed to, but still nothing works unless use override switch.
Third: We tested sender by measuring ohms across 2 black wires a described in manual. Measured 111 ohms with outdrive at -2 degree, and 145 at +5 degrees, 200 at full tilt. Ohm reading seems to change smoothly while moving outdrive thru the range.
Fourth: We Loosened the sender so it could be rotated to adjust it as described in manual. When rotated as far as it will go (opposite from where it was), the ohms drop from 111 to 66. So tried reprograming the box again with sender in a couple different positions. Still trim still not working without override switch.
Finally, while messing with the sender we noticed that the white wire was cut through...............aah, the smoking gun. So we ran a jumper wire from sender to the connector inside the bilge to essentially reconnect the cut wire. Still nothing changed even after reprograming again?????
My questions at this point:
1. What does the white wire do? Note that the sender seems to be providing variable resistance across the 2 black sender wires, in relation to changing outdrive position.
2. Do the ohm values we measured seem to be in the correct range? Note that the gage in the dash is a "Faria" brand and it has been pegged at the top throughout all of this.

Again, Any insight or suggestions would be much appreciated.

 

[Bt Doctur]

If it works hardwired when you test it, then just rewire it to mercruiser and have the switch direct to the solenoids

 

[ghaunhorst]

Thanks to Bt Doctur for your suggestions.
We finally got back to working on the boat and I'm happy to report that we have got the trim system working again by eliminating the "trim limit control unit" (Black box).
We accomplished this by doing the following:
1. Disconnected all 4 multi-wire connectors coming out of the box, plus the override switch wire. We tucked these wires/connectors out of the way. The black box is now completely disconnected from the system.
2. Connected the two remaining large diameter connectors together to create a direct connection from the trim switch to the pump unit.
3. Connected the two remaining small diameter connectors together to create a direct connection from the sender to the trim gage. (Note that the white wire on our sender is broken but it is not needed when bypassing the box.)
4. Calibrated the gage by first positioning the outdrive in the -2 degree position and putting a mark on the gage face. Then positioned the outdrive at the +5 degree position and put another mark on the gage face. These two marks now indicate the normal operating range for the outdrive on this particular boat.

Warning: By eliminating the trim limit control unit, it is now the operator's responsibility to ensure that the trim remains in the proper position during normal operation!

Thanks to all on this forum for your help!

 

[stresspoint]

Thanks to Bt Doctur for your suggestions.
We finally got back to working on the boat and I'm happy to report that we have got the trim system working again by eliminating the "trim limit control unit" (Black box).
We accomplished this by doing the following:
1. Disconnected all 4 multi-wire connectors coming out of the box, plus the override switch wire. We tucked these wires/connectors out of the way. The black box is now completely disconnected from the system.
2. Connected the two remaining large diameter connectors together to create a direct connection from the trim switch to the pump unit.
3. Connected the two remaining small diameter connectors together to create a direct connection from the sender to the trim gage. (Note that the white wire on our sender is broken but it is not needed when bypassing the box.)
4. Calibrated the gage by first positioning the outdrive in the -2 degree position and putting a mark on the gage face. Then positioned the outdrive at the +5 degree position and put another mark on the gage face. These two marks now indicate the normal operating range for the outdrive on this particular boat.

Warning: By eliminating the trim limit control unit, it is now the operator's responsibility to ensure that the trim remains in the proper position during normal operation!

Thanks to all on this forum for your help!

living dangerously .

 

[Donald0039]

Thanks to Bt Doctur for your suggestions.
We finally got back to working on the boat and I'm happy to report that we have got the trim system working again by eliminating the "trim limit control unit" (Black box).
We accomplished this by doing the following:
1. Disconnected all 4 multi-wire connectors coming out of the box, plus the override switch wire. We tucked these wires/connectors out of the way. The black box is now completely disconnected from the system.
2. Connected the two remaining large diameter connectors together to create a direct connection from the trim switch to the pump unit.
3. Connected the two remaining small diameter connectors together to create a direct connection from the sender to the trim gage. (Note that the white wire on our sender is broken but it is not needed when bypassing the box.)
4. Calibrated the gage by first positioning the outdrive in the -2 degree position and putting a mark on the gage face. Then positioned the outdrive at the +5 degree position and put another mark on the gage face. These two marks now indicate the normal operating range for the outdrive on this particular boat.

Warning: By eliminating the trim limit control unit, it is now the operator's responsibility to ensure that the trim remains in the proper position during normal operation!

Thanks to all on this forum for your help!

I hope this is temporary.