Cruise control repair - question about DIODES for you electronics experts.....?

[John E Davies]

Hi;

I rebuilt my Series 80 cruise control actuator a few years back - it has worked absolutely flawlessly until last week when it started to disconnect and shut down the system automatically (it resets after restarting the engine). I could increase road speed, but not decrease it. I opened the actuator up again and determined that one of the diodes in the motor switching circuit is shorted, so the motor only runs one direction and never shuts off with it's limit switch.

I hope some of you can help me: I don't trust a 15 year old used actuator, I certainly don't want to pay US$1700 for a new one:88002-60020 - OEM Toyota ACTUATOR SET, CRUISE. I wonder if I can replace the diodes with easily available ones from an electronic supplier.

Here is the circuit, notice pins 6 and 7, which are the power wires for the motor; their polarity is switched by the computer:

(Pins 4 and 5 is the clutch engage circuit, and 1,2 and 3 is the potentiometer circuit to tell the computer what is happening inside the actuator.)

And here is a pic showing the OEM diodes (square black thing), located between the two limit switches and that lower loop of wires:

I know _nothing_ about figuring out what individual diodes to buy, but I am pretty sure I could install them successfully, since I am a fair hand at electrical soldering. With the old one cut out and discarded, there would be plenty of room.

The original diode assembly says "EMU 12S", followed by "65 10".

Can anyone help? If I can fix this bugger with a few bucks worth of diodes, I will write up the repair and post it next to my other two articles. Just tell me what to buy, PLEASE!

Cruise Control Actuator Service

Cruise Control Troubleshooting

Thanks for your expertise and advice.

John Davies
Spokane WA

 

[psfpilot]

I think it says FMU, not EMU?

Here's a FMU-12S data sheet I found:
View attachment FMU-12S datasheet.pdf
If you know which specs are important, maybe you can get a suitable replacement from Mouser.

Good luck, and thanks for documenting these on your site.

 

[John E Davies]

I think it says FMU, not EMU?

Here's a FMU-12S data sheet I found:
View attachment 467370
If you know which specs are important, maybe you can get a suitable replacement from Mouser.

Good luck, and thanks for documenting these on your site.

Well thanks, that certainly helps..... some. I believe that part is long obsolete. I guess I will email them and see what happens...

John Davies
Spokane WA

 

[PAToyota]

Going through my suppliers, the only one that came up with a hit was Newark.

They don't stock it, but it seems that they can order it. Sometimes that doesn't pan out, though. They were able to order it the last time they tried, but it may have been awhile since they tried and they'll find out that they can't when they try now.

Won't hurt to check with them, though.

[edit] Crap! Just noticed that the minimum order was 2000 of them... [/edit]

 

[kb4mdz]

Here comes electronics man!

FMU-12S cross references to an NTE6240, which Newark says they have for $4.03 each, and Allied Electronics says for $3.81 each.

BTW, have you made sure that those switch contacts that are configured across each diode are open when you're measuring? ( I know, it seems obvious, but I have caught myself doing equally unthinking things! )

Chuk Gleason
Cary, NC

 

[John E Davies]

Here comes electronics man!

FMU-12S cross references to an NTE6240, which Newark says they have for $4.03 each, and Allied Electronics says for $3.81 each.

BTW, have you made sure that those switch contacts that are configured across each diode are open when you're measuring? ( I know, it seems obvious, but I have caught myself doing equally unthinking things! )

Chuk Gleason
Cary, NC

Most excellent! Yes, one switch was full open, for the other I placed a piece of cardboard across the contacts.

Can you tell me how you cross referenced this diode? I am interested in seeing your source.

Since I never heard back from Mouser, I will use your part numbers and see what develops. $4 plus shipping sure beats $1700 for a new actuator.....

EDIT: I found them for $3.05 each in California:
NTE ELECTRONICS NTE6240 is in stock! | Buy NTE6240 | NTE6240 | Onlinecomponents.com

If there is room, do you think it would be worthwhile adding a heat sink underneath with dielectric compound??
WAKEFIELD SOLUTIONS|273-AB|Heat Sink | us.element-14.com

Thanks for the info.

John Davies
Spokane WA

 

[kb4mdz]

Most excellent! Yes, one switch was full open, for the other I placed a piece of cardboard across the contacts.

Can you tell me how you cross referenced this diode? I am interested in seeing your source.

Since I never heard back from Mouser, I will use your part numbers and see what develops. $4 plus shipping sure beats $1700 for a new actuator.....

EDIT: I found them for $3.05 each in California:..................

John Davies
Spokane WA

You're certainly welcome, John. Yup, correct troubleshooting technique ya done dere!.

I assume by now you did something like typing "FMU-12S" into Google; very good google-fu on your part.

As far as heat sink compound, 1) take off the old one, and see if there's any heatsink compound (in certain portions of the electronics business we refer to it as 'white monkey-sh*t'; you have to be very careful dealing with it, or it will be ALL OVER THE PLACE AND IMPOSSIBLE TO CLEAN OFF!!). Number B) Just off the top of my head, I can't see a big need for heatsink compound, as I don't think the diodes would be carrying very much current at all, to get very hot. But see #1 above; maybe if they have it in little single use 'ketchup-packet' style; it'd be a shame to by a half-ounce tube of it, use it, and then have it sit idle til you pass it on to your grandkids in the will...

Good luck!!

 

[John E Davies]

Well, I have two new diodes coming (one as a spare, in case I screw up), and I will post a new follow-up thread in the Series 80 Forum if this repair works out.

I appreciate the help and comments.

John Davies
Spokane WA