Two are probably used to ensure reliable operation at the power level the resistors are operating at. SMD resistors are not as rugged as through hole types.

Timescope

 

Got another response from baldor, They had the engineer look at it and he got the correct one. https://workspaces.acrobat.com/?d=1mdOo7Fr2LUgIisNy5sZHA

This one doesn't have R36 and R37

Ya these are the correct ones, I compared it to the board and things are where they are supposed to be.

 

This file also has a sign in page.

Feedback circuit.

This supply circuit is called a switched mode power supply. The transistor is switched on and off by the UCC2804 causing current to flow through the transformer primary winding which induces voltages in the secondary windings (on the right of the schematic connected to D11 to D16). The diodes and capacitors rectify the ac voltage and produce the dc output voltages.

The output voltages are regulated by varying the ratio of the time the transistor is on to the time it is off. This is called pulse width modulation.

In your supply, the +8_KEY voltage (D12,C19) is used to provide feedback to the UCC2804: when the +8_KEY voltage rises slightly higher than 8v, the TLC431 ic (U7) switches on the light emitting diode in U2 (MOC8102 pins1 and 2). The light from the LED shines on a photo-transistor in the ic (pins 4 and 5) and turns it on. The collector of the photo-transistor (pin5) pulls the UCC2804 COMP pin (pin1) low, switching Q1 off

U2 is called an optocoupler or optoisolator and transmits a signal using light just like a fiber optic cable. It is used here to transmit the feedback signal from the low voltage part on the circuit to the dangerous mains part of the circuit.
Note that U7 and it's components and U2 (pin1 and pin2) are on the low voltage part of the circuit on the right of the schematic ("Galvanic Isolated Area") that's why these circuits are separated by dotted lines from the UCC2804 circuit.

If you do not understand anything, feel free to ask.

Timescope

 

https://workspaces.acrobat.com/?d=1mdOo7Fr2LUgIisNy5sZHA

Still doesn't work? I can email it to you. I don't know why its not working. I did everything like the first one and it worked. Its published and anyone with the link can download/see it. I signed out of my account and clicked on the link I just posted and it takes me right to it. I even tried it on another computer and it worked. Maybe its working now?

 

Thanks for explaining all that. Ya I understand most of it, but how things work is beyond me. A little black chip with a few legs can do so much. Cant beleive there is an led in there and a photo receptor type deal. Same with transistors, I read they are made up of hundreds sometime thousands of little mini switches. Just crazy, I cant comprehend it. I understand how capacitors work to store energy, diodes are basically like a check valve in a plumbing line, resistors limit the current to specified value. And just recently learned about transistors as well as triac's which current can flow both ways. But when it gets to optocoupler or optoisolator, I am so so lost. LOL

Guess it will come with time as the stuff I know now was way over my head years back when I started tinkering around. Im a self teacher, so most of the things I do auto, electronic, construction, I teach myself. As long as it interests me, I can stay motivated to learn and with a little determination and the internet I figure out how something works or how to do something. Having the right tools is a big help when talking anything.

Someday if I get a chance Id like to take a class, but don't know if its better to start in the basics even though I know a little, or take one a little more involved.

 

but how things work is beyond me.

I do not think so : you solved the Acrobat problem and I now have the "Correct Baldor Schematic".

Same with transistors, I read they are made up of hundreds sometime thousands of little mini switches

Change that to : Same with Integrated Circuits, I read that they are made up of hundreds sometimes thousands of little transistor mini switches.

I am using this on a metal cutting lathe and was adding an rpm readout which needed a 6volt input for power. I was testing to see if there was a 6-9 volt

Now you know that you can connect it to the +8_KEY supply. Just make sure you do not exceed the maximum current rating of 725mA.

Timescope

 

Good news and bad news, 6R8 resistors came today but still doesn't work. I installed them and I had 3.5 or so depending on which multimeter I use. I don't know why each multimeter is different. So I am pretty bummed, I thought this would fix it, but it looks like my dumb a$$ ruined more then meets the eye. So what would my next step be? I bought the UCC2804, should I try that? Or is there other tests I can do before I remove it? Also taking off the transistor every time I go to work on it, is it harmful to keep heating it up to remove it? I don't know what these are capable of handling.

Im still getting 120 volts on each leg of the transistor and when I check DC- to DC+ I get 350 v or so. I forgot to write down the exact voltage but it was well over 300 volts. So I assume the transformer is working. I am just so lost and confused of what could be causing the problem

I am sorry you have to deal with this and my inexperience, if you don't want to its OK.

 

Also if I followed the schematics correctly, the blue arrow should be the "+8v key" and it does not read any voltage. And the 6 flat wire connector right below that I think should have +8v feeding the second smaller speed control board that is still in the motor. I tested all 6 wires and there's no voltage going down that to feed the board. Don't know if this is part of the problem or if its something else, but there are a couple of those small led smd diodes on the speed control board that usually light up and one blinks. But these don't do anything, and without power feeding the board I assume its because of what ever is causing everything not to work. Sorry if this is more confusing, just thought id add what I found and maybe it will be of some help.

 

Here is the board I was referring to

 

Today I guess I am going to remove the transistor and retest all the spots you had me test. Maybe ill find something after replacing that resistor. Guess it cant hurt to replace UCC2804 to rule that part out.

 

Hi diebog, sorry for the late reply.

Let's sort a few things out before you fix the UCC2804.

Im still getting 120 volts on each leg of the transistor and when I check DC- to DC+ I get 350 v

Where did you connect the negative probe of the meter to take those readings ? You should have zero volts on the source of the transistor and 350 volts on the drain.
The negative probe should be connected to DC-.

Ya the tag says 230v but the place I got it from has it to run on 120 v

The 350v implies that the voltage is 230v.

Before you fix the new UCC2804, you should make sure the feedback circuit is working properly or incorrect voltages may be produced that may cause further damage.

You will need a variable power supply and a meter set on the diode test range.

1. Disconnect all power and make sure that all capacitors are discharged.

2. Set the variable supply to about 7 volts and switch it off.

3. Refer to the "correct baldor schematic" page 2.

4. Connect the negative terminal of the variable supply to the negative terminal of C19, 470uF16v (marked GND on the schematic)

5. Connect the positive terminal of the variable supply to positive terminal of C19 marked +8_KEY.

6. Connect the negative probe of the meter set on diode test range to pin 4 of U2, (MOC8102).

7. Connect the positive probe of the diode test meter to pin 5 of U2 (MOC8102)

8. Switch on the variable supply and slowly increase the output voltage to just over 8v. The diode test meter should show continuity when the voltage on the +8_KEY line is about 8v.

This test will confirm that the feedback network is operating correctly.

Timescope

 

Ok, ill give that a try. Today I was going back over the items I orginally tested and found that R24 still showed 1kΩ. So I removed it and I had to switch the miltimeeter to MΩ just to get a reading. So this for sure is toast as it should read 10Ω. R26 is a 1kΩ so sense these are in parallel, when I tested R24 it was just reading R26. Well that is what I came up with anyhow. I just learned about series and parallel circuits with resistors more in depth and understand a little more.

When I was doing my testing on the board for voltage, I was using ground coming from AC in. When I tested DC volts I tested on DC- and DC+ with test leads.

As far as a variable dc power source, whats a good way to go? Something I can grab at RS? Could I use a 9v battery with a potentiometer?

 

It's difficult to suggest a replacement without seeing the schematic.

Here ya go:https://workspaces.acrobat.com/?d=1m...2LUgIisNy5sZHA

 

As far as a variable dc power source, whats a good way to go? Something I can grab at RS? Could I use a 9v battery with a potentiometer?

A 9v battery and potentiometer will work fine.

Timescope

 

Admin, we may have a situation here:

It's difficult to suggest a replacement without seeing the schematic.
Have you tried to contact Baldor?

Originally Posted by Victoria602 View Post
It's difficult to suggest a replacement without seeing the schematic.

Timescope.

Edit: Brilliant, problem solved. Thanks

 

Im confused, something I did?

 

So the potentiometer that I have brings a 9 volt battery down to 6.6 volts, is that low enough for the test? The potentiometer is a general hobby/volume control 500kΩ. There are 37 detentes so its got a decent ranger between 6-9 volts

 

Make sure that the power is disconnected and all capacitors are discharged before you perform this test.

500k is too high to use. Instead, just connect a diode in series with the 9v battery :

[9v battery +] ----->I--- +8_KEY. (--->I--- is the diode)
[9v Battery -] to GND.

You should get 8.4 v with this arrangement and the diode test meter connected to pins 4 and 5 of the optocoupler should show continuity.

Timescope

ps.

Im confused, something I did?

Not you but a bad girl.

 

So, I replaced R34 with another 100 smd resitor and it is reading 10Ω not 1KΩ. I made a little setup with 9volt bat and a volume/hobby potentiometer and it worked out good. Ignore my previous message, I forgot you said to set it around 7v and turn off. So I double and triple checked everything was hooked up correctly, set one meeter to diode test and the other was just set up to check the voltage. I did what you said and ramped it up past 8v and nothing changed on the diode test. I tried this with 2 other meters I have and all read the same thing. It reads the small amount of voltage the multimeter puts out to run threw the diode when testing but it doesn't show continuity when there is +8.

 

Make sure that the power is disconnected and all capacitors are discharged before you perform this test.

500k is too high to use. Instead, just connect a diode in series with the 9v battery :

[9v battery +] ----->I--- +8_KEY. (--->I--- is the diode)
[9v Battery -] to GND.

You should get 8.4 v with this arrangement and the diode test meter connected to pins 4 and 5 of the optocoupler should show continuity.

Timescope

ps. Not you but a bad girl.

Woops I did the test and didn't see your responded. So that potentiometer is to high? It got the voltage down to 6.5 or so, guess I don't understand why its too high. I haven't learned about the differences between values and what they do. That must come later when you learn to design a circuit and figure out the math for what values to use.