LM338k works with 16.79 on the input and about 16v on the output with no load. As soon as I attached the the first resistor of 866ohms, it pulls the out put down to about 420mv. Is this a indication that the LM338k is failing under load. what is expected is around 12v per the circuit

 

You probably need more voltage on the input. It needs the input to be 2.7V higher than the output.

 

You probably need more voltage on the input. It needs the input to be 2.7V higher than the output.

You might have miss understood my question. The question is why does it draw the output to zero when I connect the 866k to ground? This was a factory circuit that was working at one time

 

If it was working at one time, then it sounds like the LM338 has failed.

 

If it was working at one time, then it sounds like the LM338 has failed.

Is there a way to test that LM338k and prove it is bad Vs. Just throwing parts at it?

 

There is, but need to see a schematic of the circuit.

 

Check you pinout carefully. There are six different ways to connect three pins to three holes, and five of them are wrong. With some datasheets it is not clear if you are looking at a top side or bottom side view of the connections.

ak

 

There is, but need to see a schematic of the circuit.

Its attached above in first post

 

Check you pinout carefully. There are six different ways to connect three pins to three holes, and five of them are wrong. With some datasheets it is not clear if you are looking at a top side or bottom side view of the connections.

ak

There is only two pins on this unit as it is packaged in a T-03 housing. the current configuration is how it once worked. it was never romoved.

input pin
output pin
Ground (Housing)

 

The circuit looks very basic, so it would seem that if it was working and is not now, then the LM338 has failed.

 

The circuit looks very basic, so it would seem that if it was working and is not now, then the LM338 has failed.

Does it make sense if the LM388 was bad it would draw the out put voltage to almost nothing when connecting a resistor to it?

 

Isn’t the LM338K in a TO-3 package?
Yes it is. And legitimate devices are frighteningly expensive.
You will see advertisements on Amazon or Ebay at very low prices.
BEWARE! Those most likely are counterfeits, most likely LM317 dies.

 

Does it make sense if the LM388 was bad it would draw the out put voltage to almost nothing when connecting a resistor to it?

If something is blown inside the LM338 chip, it could.

 

There is only two pins on this unit as it is packaged in a T-03 housing. the current configuration is how it once worked. it was never romoved.

input pin
output pin
Ground (Housing)

The case is the output terminal on LM338K. From NatSemi:

 

The case is the output terminal on LM338K. From NatSemi:
View attachment 319995

You might have uncovered the information that I was over looking. So if the case is the output, how do you suppose it is isolated through the metal plate yet passing power on the bolt to the red wire with the ring terminal. I understand that the plastic spacer is a isolator (was not sure why it was there and now makes sense), the LM338k has a thin pad on the base of it but I don't know that I would trust that as a isolator from the plate witch is ground.

Thanks in advance on your feedback

 

Your first picture shows 2 different mountings. The one on the right is insulated, but has a nylon bolt holding it down, it should be a metal machine screw so it contacts the case on the other side, and the solder tab is then contacting the metal machine screw. If using a nylon screw, the solder tab is not connected to anything.
They use thin insulating pads between the TO3 case and the mounting plate to isolate it. The bushings of the plastic device keeps the mounting screws aligned to the middle of the hole, away from any metal. But like I said, you have to use metal "bolts" to pass through the hole to the solder tab so you have an electrical connection to the TO3 case.

 

So if the case is the output, how do you suppose it is isolated through the metal plate yet passing power on the bolt to the red wire with the ring terminal.

There are a number of ways of maintaining case isolation from the mounting surface: washers, spacers, etc.

I understand that the plastic spacer is a isolator (was not sure why it was there and now makes sense), the LM338k has a thin pad on the base of it but I don't know that I would trust that as a isolator from the panel witch is ground.

It doesn't take much to isolate the case.

 

Gentleman, thanks for the assistance, as I think I have some work to do when I get home. As a novice here I really appreciate the assistance.

Thank you

 

Update in, This resolved my 12v issue and I now have 12v and 5v going to this board as required. Only thing now is I am at a dead stop on how to further trouble shoot this. It appears my 12v stuff is working but the 5v stuff appears dead.

The clear bulbs are 12v and the red bulbs run on 5v along with the readouts. All solder joints look good, no obvious blown devices etc. I can trace a line on the board and check it to ground and it has 5v.

J1 in the bottom middle is where the power comes in, left to right. left pin gnd, Middle pin 12v, far right pin 5v

 

Some rudimentary testing that I did. All the small blue caps on display front side photo, one side rings to ground and 1 side rings to 5v terminal, I believe this portion is what powers the LED display driver M5450b7. The oddity that I found was the big cap on the back it rings to ground on both side of the cap and it rings to 12v terminal on both sides of the cap. Does this seem odd?