LM338k Voltage Regulator

Thread Starter

k5 blazer

Joined Dec 1, 2019
26
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
 

AnalogKid

Joined Aug 1, 2013
11,128
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
 

Thread Starter

k5 blazer

Joined Dec 1, 2019
26
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)
 
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.IMG_4673.jpeg
 

Thread Starter

k5 blazer

Joined Dec 1, 2019
26
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
 

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sagor

Joined Mar 10, 2019
914
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.
 

dl324

Joined Mar 30, 2015
16,989
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.
TO-3-Washers.jpg
 

Thread Starter

k5 blazer

Joined Dec 1, 2019
26
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
 

Thread Starter

k5 blazer

Joined Dec 1, 2019
26
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
 

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Thread Starter

k5 blazer

Joined Dec 1, 2019
26
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?
 
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