Dynaload DLF 100-100-1500 (100V / 100A /1500W DC load) teardown & repair

[nctnico]

I know I'm really late to the party.  I have one of these that works great. I also have the DLF 100-600-4000 big brother that has also worked great up until I went to test it for selling.  It has 10 Module Status LED's for each of the 10, 400 Watt modules.  The LED for Module #2 is on full-time now.  The load seems to work fine although I have not tried it near it's max power.  Anyone had any experience with this load and my issue?  I can't find any troubleshooting charts nor much info at all on the unit.  I have the operation manual but there's nothing in there.

Most of these loads are built exactly the same with slightly different components so very likely you can use the schematics of similar loads to fix your load (see link below). However, I'd start by reseating all connectors.

You can download a zip file with the service manuals here:
http://www.ko4bb.com/getsimple/index.php?id=manuals&dir=06_Misc_Test_Equipment/Transistor_Devices

[BVH]

Thanks for your quick reply.  I did pull the two module multipin header connectors to verify their cleanliness and used Deoxit gold on all contacts when replugging them.  I haven't removed the module yet to inspect for any obvious signs of burning/failure.  I will admit I am able to follow schematics somewhat but probably not able to determine the monitoring system components on the module.  I'm more or less an electronics novice, maybe just above novice.

[BVH]

Well, I thought I had it twice yesterday.  I removed the module and upon close inspection with a mag glass, I noticed that about 1/3 of the solder joints on the main transistor studs looked radially cracked so I resoldered all 24 of them, then saw a couple diode and resistor joints that looked suspect so did those too.  Fired it up and no change.  Then I was going to Ohm all the temp sensors on the board heat sinks to see if #2 was open or out of spec.  When I touched the #2 board sensor, one of the wires that lands on the board was loose in it's thru hole.  "Well, that's got to be the problem".  Soldered it, fired it up and no joy.  I'm disappointed.  Noting else on the board looks suspect.

[BVH]

I had some down time after a surgery so I set out to get this thing fixed.  I found a schematic in my manual and there is a dedicated module fault PC board.  It consists of the module fault leds 1-10 that light upon a fault and two each, 5 unit, 470 Ohm resistor arrays.  Pretty simple, even for me.  So I first removed the arrays and Ohm'd them.  All 10 checked out between 469 and 471 Ohms.  Disappointing.   So I ordered some new arrays anyway and while waiting, decided to simply swap the arrays to see if the problem moved and sure enough, the Number 2 led was now not lit and the Number 7 led is lit.  So the problem followed the resistor array.  Not sure why if all Ohm'd OK.  So here I stand until the arrays arrive in the next couple days.  This is still fun even if I am not successful.