TK RD-II SR intermittent operation

[trammd]

Got an RD-11 SR that is starting to not power up the Microprocessor and cab mounted remote control. There is Power to the Interface board, all fuses good, Fuseable link good etc.
After changing all the units drive belts upon powering on the Microprocessor switch I would receive no power to the remote controller when trying to start the unit.
I cleaned the terminals on the corroded switch and the switch harness plug and thought that fixed it, Unit started and ran fine for a couple days. No alarms USC good etc.
Now I go to turn on the unit and same trouble. No power to cab controller.
Any ideas on how to further troubleshoot?
I checked interface board for any loose harness plugs etc but all looks good except for the fact that no power to processor and cab control when the switch is cycled on.
Any help is appreciated.

[seanf]

Do you still get power to the switch?
What happens when you bypass the switch?

[trammd]

Do you still get power to the switch?
What happens when you bypass the switch?

Yes, there is battery voltage at the switch. There are 5 terminals. The lower 2 have 12 volts.

[seanf]

Not sure if this is the right manual, but....
Theres a few pages of wiring diagrams for the RD-II 30 and RD-II 50 if you click through them.

https://www.manualslib.com/manual/21...age=128#manual

If the switch is as show on the diagrams then, it looks like when the switch is off you should get battery voltage at the terminals "2" and "2A".

When on the switch puts voltage from "2" out to "2N", and from "2A" out to "PL1".

Terminal "CHP" is described as a logic ground for the Thermoguard.

Looks like "2N" could be the main power supply for the Thermoguard, and the "PL1" as a sort of on signal?

[trammd]

Not sure if this is the right manual, but this is what I'm looking at.
Theres a few pages of wiring diagrams for the RD-II 30 and RD-II 50 if you click through them.

https://www.manualslib.com/manual/21...age=128#manual

If the switch is as show on the diagrams then, when the switch is off you should get battery voltage at the terminals "2" and "2A".

When on the switch puts voltage from "2" out to "2N", and from "2A" out to "PL1".

Terminal "CHP" is described as a logic ground for the Thermoguard.

Looks like "2N" could be the main power supply for the Thermoguard, and the "PL1" as a sort of on signal?

Thanks, This gives me something to check and yes this is the correct schematic for my unit.
I can back-probe the switch harness tomorrow and see if the switch functions as you describe.
Thanks again, I will let you know what I find....

[trammd]

Just to confirm...with the switch in the ON position I should measure battery voltage (12 Volts) BETWEEN
"2" to "2N" and also 12V BETWEEN "2A" to "PL1"
In other words I think you are saying I should read battery voltage when probing both wires (terminals).
One meter lead on "2" and other lead on "2N" should read 12V. (and also 2A to PL1)

Thanks again

[seanf]

-- When the switch is in the off position. --

With one of your meter probes on gound (chassis/earth/battery negative), and the other meter probe on either terminal "2" or "2A", I would expect to see 12v.

With one meter probe on ground, and the other probe on "CHP" or "PL1", I would expect to see near 0v.

With one probe on ground, and the other on "2N" I think youll see near 0v.

-- When the switch is in the on position. --

With one probe on ground, and the other on "2", "2A", "PL1" or "2N" I would expect youll see 12v.

"CHP" should still show near 0v.

Well thats what Im thinking anyway, if everything is as the diagrams and hasnt been messed with.

[trammd]

Thanks, I will let you know what I find....

[trammd]

-- When the switch is in the off position. --

With one of your meter probes on gound (chassis/earth/battery negative), and the other meter probe on either terminal "2" or "2A", I would expect to see 12v.

With one meter probe on ground, and the other probe on "CHP" or "PL1", I would expect to see near 0v.

With one probe on ground, and the other on "2N" I think youll see near 0v.

-- When the switch is in the on position. --

With one probe on ground, and the other on "2", "2A", "PL1" or "2N" I would expect youll see 12v.

"CHP" should still show near 0v.

Well thats what Im thinking anyway, if everything is as the diagrams and hasnt been messed with.

Okay, I was finally able to troubleshoot the switch.
It does check out exactly as you described above. so the switch is (was) functioning per design.
BUT HERE IS THE WEIRD PART:
when I initially checked the switch function with my meter I was receiving battery voltage (12.5V) at the proper terminals when actuating the switch and also at the logic board.

When I went to confirm my findings all of a sudden I am only getting 3.5 Volts at the switch test and logic board. I don't understand why it checked out good with full battery voltage one minute and then the next time I check everything is under volt at 3.5V!
I checked all the fusses again and they are all good.....
Please advise further, Thanks!

[trammd]

I just checked it again and it seems to be Intermittently receiving full 12V then alternates 3.5 to 4 volts. What the heck?

[trammd]

Okay...So I tied the Voltage drop with the switch function. When the switch is in the OFF position I get good battery voltage to the switch and interface board.
When the switch is Turned ON, Voltage immediately drops from 12V to 4 volts.

Is the Processor causing this Voltage Drop? and Why?

[seanf]

Does the voltage measured at the battery terminals drop as well, or is it just dropping on the Switch/Thermoguard circuit?

While your getting these low voltages, probe along the circuit(s) to see where the voltage is dropping. Put one probe on the negative of the battery, and then start with the other probe on the battery positive terminal, and then work you way toward the Thermoguard.

[trammd]

Does the voltage measured at the battery terminals drop as well, or is it just dropping on the Switch/Thermoguard circuit?

While your getting these low voltages, probe along the circuit(s) to see where the voltage is dropping. Put one probe on the negative of the battery, and then start with the other probe on the battery positive terminal, and then work you way toward the Thermoguard.

No, The voltage does NOT drop at the battery when turning the switch ON. Just dropping at the switch.
I did try a NEW Thermo king switch just in case the old one had some crazy internal resistance when "on" causing the voltage drop...but new switch does the same thing as the original one...

[trammd]

Can you tell from the schematic which wires feed the switch harness or maybe where I can begin checking where the voltage drop out is happening? Do you think a zapped or faulty Thermo-guard processer could cause these symptoms?
Thanks for all of your help!

[seanf]

If your measuring the low voltage at the switch, I would be thinking its probably a problem with resistance between the battery and the thermoguard.

That could be a number of things, the fuse link wire FLW, the 50A circuit breaker CB1, the 3A fuse F200, any of the wires themselves (corrosion or partial break), any of the crimp connections on the wires for the harness plugs, any other wire connections.

The only info on the diagrams, I put on the little drawing. Its not the best but...

[seanf]

It could also be that a wire has rubbed or melted and its in contact with another wire or something thats grounded.

[trammd]

Shouldn't that pop a fuse? F200 fuse is good. Where is the FLW? Is it the wire on the opposite side of the reefer unit on the terminals below the maintenance area access door? Also I have NEVER been able to locate CB1(50 amp breaker). where is it? Though I assume if this breaker was tripped I would not be getting battery voltage to the switch?
Keep in mind my unit uses the original Interface board service Part # 41-2145. It was used for initial production units through 2nd Quarter 2001.

[trammd]

Wow, Things just keep getting weirder! I was out checking fuses and I noticed all of a sudden with the switch ON I retained 12 Volts for once! I pressed the ON button and the cab controller lit up showing an alarm 61 (low batt voltage) I cleared the alarm and as soon as I did the controller went blank........you guessed it , low voltage again!
The Batteries are pretty new and I load tested them good. Maybe the next step is to remove all battery cables and the thermo king 12V main battery lead and clean all the terminals etc. (They look very clean)
I am stumped....

[seanf]

Fuses normally pop when theres a current more than their rating.
How much current flows depends on the resistances in the path, in the case of a rubbed or melted wire it might not be a good ground connection.

F200 fuse is good.
Do you mean that as in theres no voltage drop over it when current is flowing, or that its resistance measurement is low?

I'm not sure where or if your unit has FLW or CB1.
The breaker may not be tripped, it could just have a resistance to current flow, giving a voltage drop.

I've not worked on a TK RD-II SR for a long time, so I can only go by whats in that manual.

[trammd]

Yes I measure equal voltage to both sides of F200 (when current is flowing)

[seanf]

Yes I measure equal voltage to both sides of F200 (when current is flowing)

Ok, so with the switch "on" and one of your meter probes always connected to the battery negative terminal.

Take voltage measurements at:

-The battery positive terminal.
-Both sides of the fuse link wire (If you find one).
-Both sides of the CB1 breaker (if you find one).
-On the five switch harness terminals CHP, 2, 2A, 2N and PL1.
-Both sides of fuse F200.
-PL1 connection on the Thermoguard.
-2P connection on the Thermoguard.

[trammd]

Will do, Thanks