MEP-002A Testing A1/K1 or CB1?? Huh? - Steel Soldiers::Military Vehicles Supersite

n5yzv · 10-04-2011, 11:10

While I am waiting for my replacement switch (S1) I decided to test A1 "Diode" again. In the TM, It calls it K1. Whereas, it also calls it CR1. But it seems to be on A1. Hmm..A little confused. Ok, allot.

Anyway, in the control head, A1 is in the upper right side. Eight terminals. The procedure is to disconnect 3 - 8. Testing with an ohm meter, I should get high resistance (done in the right direction) between 5 & 6 and 7 & 8. Well, I get nothing.

So i pull the A1/K1/CR1 (pick) from the block. I think this is just a DPDT switch. Dunno why the manual calls it a Diode, but ok, whatever. I test it pin to pin, same results.

Am I testing this right? Also, when I look for the part online (M5757/23-003) it comes back with a $90 item. So is this the same thing I need to replace it with, or is there an alternative that is less expensive.

Thanks for the advice!

Mark

Speddmon · 10-04-2011, 13:52

Mark,

There is a diode across some of the terminals of that relay. I do not remember which terminals right off hand, but it is there. It is on the back of the relay mount. To get to the diode you need to pull the entire mount out of the control box, not just the relay.

Keith_J · 10-04-2011, 14:32

Yes, the K1 relay is on the A1 terminal block which also has the diode mounted behind it. K1 is labeled as a start relay but in reality, it is the oil pressure/over-temperature relay. It is bypassed by terminal 28 during the start switch operation. Once the low oil pressure switch makes continuity, K1 latches closed. Only one half of the relay is used, it can be flipped over if defective on the switch

. Since the coil is 300 ohms, it rarely goes bad.

If either oil pressure is lost or over-temp condition is reached, current to K1's coil is interrupted, breaking current and stopping the engine.

n5yzv · 10-05-2011, 16:45

Well, I am still waiting for a good main switch (S1) to come in. One was delivered and it had issues. I just know I am going to be making one with a programable relay board one day.
I did manage to pull the A1 block and find both diodes are bad. I did some research and found a modern replacement. I think the manufacturer part number is 1N5404-T. It costs a whopping $0.37/ea. The original replacement, if you can find one, is like $20/ea. I hope to have the diodes and another replacement switch here by the weekend.
After this mess, I can get back to the whole battery charging / 24v issues. Then i can move on to my various leaks and then deal with the monster high voltage switch that is not turning correctly.

Keith_J · 10-05-2011, 21:29

The reason the T-diodes are so expensive is that they are toughened against radiation. That is a silicon 3 ampere power diode with 400 volt rating. Use a regular 1N5404 with absolute certainty.

The reconnection switch (120/208 3 phase, 120/240 single phase and 120 volt single phase) is an impulse type which requires motion to nearly the desired position before it reconnects with a snap. While you should never switch under load, it should be able to break a minor arc. Not that this should ever be done.

Table 6-5 in the -34 TM will show the testing for S6. Don't replace unless proven defective, it is a LOT of work. And there are two manufacturers, each with slightly different connections. I've never heard of the reconnection switch having problems but then again, I never worked in direct support.

n5yzv · 10-11-2011, 07:27

Well, it seems I got a good working switch (S1) in and my replacement diodes in. I was delayed a bit due to a nice case of food poisoning (I won't be eating at Whataburger any time soon). So hopefully today/tomorrow I can get these installed so I can re-do my testing to get things moving on.
Regarding the the reconnection switch, yeah, I don't get it. Since I don't know what it is supposed to do I can only guess that it is not working right. Once I get past some of the basic stuff (switch, diode, basic tests, 24v testing, battery recharging, fuel leaks, oil leaks) then I may take a video of it's function and post it for review before I go tearing into it. For that matter maybe a bribe of some sort and have you take a look in person.

More to come! heh

Speddmon · 10-11-2011, 17:16

The reconnection switch is a "snap" switch. You may think it is not operating properly but it very well could be doing just what it is supposed to. In order to change positions with that switch, you need to rotate the handle past the point of the next position. The switch is spring loaded and when you rotate the handle far enough the switch will "snap" into the new position. It does this in case the soldier operating it tried to reconnect it under load. By doing so you get a positive, and fast "break" and "make" of the contacts of the switch. This helps to eliminate arcing within the switch and destroying the contacts.

n5yzv · 10-11-2011, 18:48

Ok, as I think there is an issue, I took a video. The video file is 31 mb and I am sharing via my dropbox public folder. You can view it here:

http://dl.dropbox.com/u/6966525/MEP-...con-switch.m4v

Thanks for your input!

Keith_J · 10-11-2011, 20:58

Looks like you indeed have a problem. What ever you do, photograph and tag before disconnecting. Also verify wire identifications with the TM.

As the SMR code is PAFZZ, this indicates no repair authorized (Z in the 4th position). PA means stocked item so new old stock may be available but there are two types, with slightly different wiring. The 5th Z is dispose at the third (F in this case which is direct support) position level. Repair might be difficult but not impossible. Check classifieds for the generator that is being parted out.

Speddmon · 10-12-2011, 01:31

I have one if you need one, let me know.