PACE PRC2000 / TIP107 failures

[Melanie]

>>I guess the main issue is that this is the first time I've dealt with this type of transistor

Just treat it as a high-gain NPN transistor. You can use any NPN power Transistor, but it's not going to work as well, and you'll need a reverse Diode across it for protection. For the purposes of test and playing with you could try it.

>>And I can't find any extra TIP107's laying around...

Yes you have... "I've got another PRC2000 to do the rework".

>>Actually, I already checked those out of circuit

Noooo... this is still Tekkie line of thinking... remove each part, one by one and eventually I'll find the one that's duff (probably adding faults that weren't there in the first place). Whilst I'm at it, I'll use a milliohm meter to check each piece of track... trouble is, it was probably a bad joint which you've eliminated, the problem goes away but you never found the cause... Yup... I'm confident enough in my proceedures to take that job in the Pacemaker repair shop...

My line of reasoning is this... the Motor Drive and Brake both being ON simultaneously cause a short. So remove the Brake - Do I have Motor Control? No - look in the Motor Driver Circuit. Yes - Look in the Brake Driver Circuit. Let's eliminate whole chunks of the circuit and concentrate on looking at where the problem could lie.

[skimask]

Just treat it as a high-gain NPN transistor. You can use any NPN power Transistor, but it's not going to work as well, and you'll need a reverse Diode across it for protection. For the purposes of test and playing with you could try it.

That's what I'm talking about. Just get control of the workings back. Worry about the complete fix after I get a TIP107...

Yes you have... "I've got another PRC2000 to do the rework".

And smoke another one! Maybe not...

remove each part, one by one and eventually I'll find the one that's duff (probably adding faults that weren't there in the first place).

Thing is, I had to pull a load of parts out anyways since they had been charred up by the initial burnout. Bad solder joint? Sure...maybe. While I was at the 2M class, they showed us some great X-ray video of cold solder joints. Shiny on top, cracked in the middle. I've got a decent handle on those...probably moreso than 99.9% of the rest of the hobbyist world.

My line of reasoning is this...

Oh, I agree completely...if it weren't for those charred bits/pieces that I had to pull in the first place. It could've easily been a bad joint on one of the biasing resistors that locked out the drive motor that that started the whole chain of events in the first place. But, I'll never know since that particular part was charred up...

The PRC is actually on hold for a couple of days. I blew up my tractor a couple of weeks ago and just happened to come across a new engine late last night. Putting it in tonight.
The final fix will come next week....at least it had better!!!

[skimask]

I think I found the ROOT cause of the problem.
LM324, U1, pin 7 seems to be stuck high. Can't get it to go low no matter what I do to the + and - inputs, pull to ground, pull to V+, whatever. I can get the other 'sections' of U1 to do what I want using the same methods.
Swapped it out with a new one. The output at pin 7 acts like I want it to, as do the rest of them. Can't check it out completely yet, still don't have a high-gain replacement for Q22 on hand.

[skimask]

I think I found the ROOT cause of the problem.....
Can't check it out completely yet, still don't have a high-gain replacement for Q22 on hand.

Update to the update...
Finally got my hands on actual TIP107's.
Swapped 'em out, ran the microchine for about 15 minutes, works like a champ...
The original problem (besides the bad LM324) might have also had a little something to do with the fact that Q22 originally didn't have any heatsink compound under the TO-220 case at all...don't know...don't care...it's all working...