If you can not find the schematic, it's time for some reverse engineering, drawing the schematic yourself. First find the power supply traces then see where the source, gate and drain go to and check those circuits. If the transistor had a short circuit between drain and gate, the driver circuit may be defective.

Don't worry if you end up talking to yourself, it's perfectly normal with a double sided or multilayer board.

Timescope

 

lol, Ya I talk to my self allot when trying to figure out stuff like this. Ill give it a try. By driver circuit, do you mean the source? I am pretty sure the short was between ground and source on the transistor. And when I check the circuits, what is the best way to do this? Continuity? Some have capacitors, some have resistors or diodes. And you cant test resistors on a board correct? The would need to be removed to bet olhmed. Any sugg you have would be great. Any examples you know of to show reverse engineering?

 

So finally got the schamatics from baldor. I am no good at reading these, I would like to learn how to but for now I was wondering if anyone can make sense of my problem with these. There are two links to two different pdf files. They sent one out of the 5 total so I had to ask for the other 4. On page 3 of the first link there you can see Transistor "Q1" that I replaced. Hopefully these will make more sense to someone else as they are way over my head. LOL

https://workspaces.acrobat.com/?d=Jv1ybWpkzUnuH1HDXjTfrQ
https://workspaces.acrobat.com/?d=LlbqB-j0*LCjVn6xecsuXA

 

Q1 is the switching transistor of the switched mode power supply and drives the transformer TR1 that outputs all the DC voltages on the right of the schematic. The resistor that burnt, R11, acts as a fuse in the DC supply to the circuit (about 160v DC).

Disconnect all power from the circuit and check that no voltage is present on capacitors. Remove the transistor.

Check R28 and R29. In circuit, they should both read 3.4Ω.

Check R24, 10Ω.

I mentioned earlier that the driver circuit may be damaged which in this case is U3, UCC2804. This ic controls the operation of the supply and may have been damaged by the short circuit.

Check for a short circuit between pin 5 and pin 6. The reading in circuit should not be much lower than 1kΩ, which is the value of R27.

Timescope

 

Thanks Timescope!

Wow ya I didn't get that from the schematic which is why I was hoping someone could help me out. So thanks a bunch. Ill desolder Q1 and check those spots. So leaving the transistor in place will give incorrect readings? Just making sure before I take it off.

 

Not really because of incorrect readings but to prevent damage from static discharge.

Timescope

 

So I went ahead and desoldered Q1 and here are my findings.
R28....121 ohms
R29......7.2 ohms
R24......1k Ohms
R27......7.2 ohms
125K ohms between pin 5 and pin 6.

SO does this mean anything?

 

I use one of those wrist grounds to eliminate static discharge also. It plugs into my digital solder station and is connected to earth ground

 

Are the resistor readings in-circuit or did you remove them ? Please refer to the schematic. The part numbers do not seem to correspond : the two 7.2ohms readings appear to be R28 and R29 (6.8 ohms plus the zero error of the meter).
Is the value still visible on R24 ? It should be 10 ohms.

Confirm the part numbers using the schematic and visually tracing the connections on the board.

Timescope

 

I am checking these on the circuit board. Should I remove them? I replaced r29 when I placed a digikey order and when I had the old one off they did ohm at 6.8 but in the circuit they measure 7.2 When I decoded 6R8 the r is basically a decimal point which gives the value 6.8 so that's what I ordered.

R24 is not perfectly clear. the middle digit is a little scratched off. but it looks like 100 the 1 and the last 0 are clear. The middle digit looks like the 0 so that's the conclusion I came up with. I scanned it at high resolution and blew it up on computer and I can see even better then using a magnifine glass. Its possible the middle digit could be an 8? I am loading up the scanned pic but the file is HUGE! so its taking a long time

 

I tried 3 different testers and the both 6R8 on the board measure:

Fluke ohm/voltage multimeter: 6.9
Radio shack mini multimeter: 7.2
actron cp7665 multimeter: 7.0

So is it possible these multimeters are not accurate? The fluke I have is the most expensive so I would guess it would be a closer to the actual reading

 

So when you put 100 in this calculator: http://www.hobby-hour.com/electronics/smdcalc.php It comes up with 10Ω like you said. But it is definitely reading 1kΩ

I also was checking the schematic to the board and found r28 calls out for 6R8=6.8Ω but R28 on the board has "121" on it which is 120Ω
R27 calls out for a 1K which doesnt decode to anything but the board has 6R8=6.8Ω

I just checked the ones we were talking about, I am going to check them all right now.

 

Here is the file that finally uploaded to drop-box. Its high resolution and can be zoomed in close to see the numbers on the SMD
https://www.dropbox.com/s/mi021qjy3xqpkjq/Top (2).jpg

 

Sorry for the late reply : I have been out. I will take a look and reply later.

Timescope

 

No problem, when ever you can. I am just thankful you are helping me

 

I compared the board to the schematics more and found a few other differences. The schematics call out for a few components that are not on the board and like we already know the value differences in those SMD's. I am thinking maybe they gave me the wrong schematic again! The gal I am dealing with just cant get it right. She says she emailed my pics and emails to the factory and this is what they sent.

The pn on the board is different by one number, the last number is a "1" and the schematics show a "4" for the last number. I dont know how much this changes things but I emailed the gal at Blador again and asked for the correct one again. So now gotta play the waiting game to find out whats going on. You had any time to take a look at my findings? Do they make any sense or tell you were the problem may be? Or do you agree that these are the wrong schematics? I have a feeling the reply back will just be something like, " well that's what we have listed for that motor". I gave them clear pics of the board and of the tag on the motor as well as what the board and motors components looked like, you think they would know what they were doing. Maybe the individual put "4" instead of"1", well see

 

Hi timescope, wondering if you had a chace to look at that stuff? I know your rpobaably busy, just trying to get this goin.

 

Hi diebog, I see you have been busy while I have been away, that's great. I look through all the info you have provided and try again to download the picture.

Timescope

Edit:It's 102 MB ): Going to be here for quite some time.

 

Yup, just trying to get this figured out. I stare at the board thinking the problem is right in front of me, but I don't know how to find it. LOL.... Also I forgot to mention that "D6" on the board is a smd led that lights up red when I pug in the power cord. Its right above the WARNING HIGH VOLTAGES PRESENT. I think its letting you know there is high DC current there.

And still waiting on the slow Baldor gal that's helping me. Maybe its is the correct one, but I don't know if its normal for a few variances from the schematics to the board. One example is the pic right above shows R12-R16 in series and in the schematic there is "R33&R37" after R16 in the series. All of same value as well. But there isn't even a spot silk screened on the board for such. So maybe they revamped it before production? Hopefully you will know what that means or if this is a tell tale sign that I have the wrong schematics.

 

The download finished at 5:02 am, the resolution is fantastic.
On the circuit diagram, R16-R37 are 18k so the total resistance is 18k x 6 = 108k.
The design has been modified to use five 27k resistors : 27k x 5 = 135k.

These are called start-up resistors and supply current from DC+ to pin 7 of UCC2804 when the supply is first switched on to enable the ic to start working. The transformer pin7, D17, D10 and R17 supply Vcc when oscillation starts.

Try to locate this circuit on the schematic and the pcb.

The start-up current specified in the UCC2804 datasheet is 0.2mA. Assuming DCin is 160v, the current will be 160v / 135k ohms = 1.26mA so the change in value of the resistor does not matter



Timescope