Hog barn ventilation controller

Thread Starter

Eversr007

Joined Apr 10, 2016
40
Hello everyone I was wondering if anyone could help with this control board. I have a friend that own several hog barns and there switches and rotary encoders are always going out. So I started fixing them and now he dropped off several and I have a couple that have same problem. They don't light up the display. I can't tell what is going on. I tested the display and it has a common anode and with meter all digits lit up individually. I have plugged other boards into the same power supply board and they worked so it has to be with that board. Could someone give me a few hints on where best place to look. I guess no one would have any idea if there would be any place to get a schematic for this would there? That would help me learn how they are all working together. They hook together by ribbon cable at J4. Also there are 2 scr 's on the bottom of the power supply board attached to a heatsink, what is there function? And if I'm going to be working with these types of circuits do I have to have an oscilloscope? If so what kind and MHZ. I was kinda looking at some Rigols. I don't know how to use them yet, I just know to watch where you attach the ground clip if it not isolated. Any help is always appreciated. Sorry if I'm kinda all over the place...IMG_6562.jpgIMG_6563.jpg
 

drc_567

Joined Dec 29, 2008
1,156
... Do the defective boards operate or permanently reside in a humid or moist environment?
... One possibility is that the J4 connector is simply not completely conductive due to moisture related oxidation or contamination. Purchase a can of electronic contact cleaner, spray all mating contacts once or twice, allow to dry, and re-assemble.
... ... This cause may not pan out, but should be checked before anything else just to make sure that power is getting to the boards.
 

Thread Starter

Eversr007

Joined Apr 10, 2016
40
I have been trying to test off of working board. And yes the boards stay in a humid enviroment but are in a plastic box sorta sealed up. The connector looks real good under microscope. But I sprayed some deoxit on them anyways. It has power going through to the top board to the voltage regulator and also is turning on the relay on bottom board for main power. So It is doing part of its job. Wondering if it is just something in the display and everything is actually working just can't see it.
 

Thread Starter

Eversr007

Joined Apr 10, 2016
40
Thanks for turning the images. It was late and didn’t even think of doing it. And the large black thing is a big coil.
 

drc_567

Joined Dec 29, 2008
1,156
... Sometimes potentiometers ... like that rotary part... labeled SW1 .. seem to absorb moisture and stop working correctly. A squirt of deoxit into the moving portion, if you can manage it, might be worth trying out. Move it back and forth several times in order to break loose any sort of contamination or fouling. Electrical contacts require a degree of cleanliness.
 

Thread Starter

Eversr007

Joined Apr 10, 2016
40
Ok so I tried everything and starred at this thing for hours. I plugged in the working board and I can see where voltages are different but can't track down why. I even reflowed every connection on the backside thinking maybe there was a cracked solder joint. I know if I can figure this one out the other one might be same fix. The seven digit display is a common anode. The anode each display got to a pn2907a pnp transistor. The base of those transistors got to 2.7k ohm resistors and then to the microprocessor. By the way I tried a microprocessor off of the working board and still nothing. I tested the displays one segment at a time and each of them lit up. There is an eprom chip on the board not sure if it could be bad. diplays goes to a 4116r resistor ic, and a sn74hc273n Octal D-Type Flip-Flop chip. Not even sure where to look now. Any ideas..... Ps I squirted some dioxin in the switch and also check continuity from center pin and then the coresponding one and when turning switch it seemed to be good.
 

drc_567

Joined Dec 29, 2008
1,156
What is that white cartridge object, next to the black coil? Can you check it for continuity if it is a fuse? Also the adjacent black cartridge parts?
 

Thread Starter

Eversr007

Joined Apr 10, 2016
40
There is continuity on the white block. But that board, with the transformer is working. Cause I have other boards that it powers on and functions fine. Probably shouldn't have put a picture of it. Can I test those small capacitors in circuit? I check every resistor on the board.
I'll give some info on the chips that are on the problem board and see if anyone has any ideas. On the bottom left is a voltage regulator and it is working. Can't remember what the x1 metal thing is on bottom right of microprocessor.

U5- 93C66LI 410046
U6 - LM339N
U7 is 74HC4051N
U8 - SN74HC273N
U9 - ULN2803A
U10- ULN2803A

R5 CHIP -4116R LF 1-221

Q8,Q9,Q10 -PN2222A
Q2,Q3,Q4 - PN2907A
VR2 - LM336 725
Q5 - 2N5087 C03
Q6 -2N7000
Q1 - PN2907A
Q7- PN2222A

Microcontroller is - PIC17C44-16/P

I'm sure I must not be checking something right. Thanks
 

drc_567

Joined Dec 29, 2008
1,156
... on old much used devices, the failures start off with the ones that require the most power. This would include the ones that are mounted on heat sinks, output stage power transistors, large electrolytic capacitors. The difficult part is checking them for continuity ... basically de-soldering and using a resistance meter and diode checker. If you can just find one defective part, you have to trace the parts that are connected, since daisy-chain type failure is typical. ...
... You mentioned SCRs ... do you have any clue as to what purpose they serve? ... Looks like two SCRs are mounted on those heat sinks.
... It would be useful to identify a point or two on the DC power bus, to confirm that you have DC power.
 

Thread Starter

Eversr007

Joined Apr 10, 2016
40
The Scr's are on the power board that is working. I took all the measurements on the Microprocessor and compared to a working board.
Some were quite a bit different and two of them where pulsing on good board but not on the bad board. I could post the pin # and measurements of both if it would help. Also where on the board would a schmidt trigger be. Just seen it on datasheet several times now.
Man this board is taking all the fun out of this stuff. Trying to learn this crap is hard. Wish I had a professional next door to me. I have a great respect for anyone that understands all this.
 

drc_567

Joined Dec 29, 2008
1,156
... on the board that is not working, can you locate any point that has DC voltage? This would be 12 or maybe 5 volts DC, and would have a trace routed around the board, and connecting to the Vcc power pins of the various integrated circuits, and possibly transistors. If a capacitor has failed, or if a trace has broke , then the Vcc power would not be getting distributed to the different parts. You might start off by checking at the voltage regulator input and output, and try to see where the DC voltage goes from there.
 

drc_567

Joined Dec 29, 2008
1,156
... a lot of the voltage regulator ICs are lettered LM7812 or LM7805 ... or 78 something, and may or may not be mounted on an aluminum heat sink.
 

Thread Starter

Eversr007

Joined Apr 10, 2016
40
Yes there is voltage at a lot of points on the board.. Coming into the regulator has 19.2V and coming out is 5V. Some places have 2.4.

voltages are different on the micro controller. Not sure how to figure out why. Here are the differences. I will put in a table with pin # on the left, Working board on the next column and bad board on last column. Pinout is off data sheet.

Pin# Good Bad

1 5V 5V
2 3.8 4.5
3 3.8 4.5
4 3.8 4.5
5 3.8 4.5
6 0 0
7 0 0
8 0 0
9 0 0
10 0 0 ground
11 .5 .006
12 4.6 5
13 4.1 5
14 0 1.7
15 3.6 5
16 0-5v pulsing 4.9 steady
17 0-5v pulsing 4.9 steady
18 0 .57
19 1.9 2
20 2.3 2.4
21 4.5pulsing 4.7 steady
22 5 5
23 4.5 4.6
24 0 4.9
25 5 4.9
26 .2 .2
27 0 0
28 0 0
29 0 0
30 0 0
31 0 0
32 5.2 1.2
33 4.8 1.7
34 .8 1.7
35 4.0 1.7
36 4.0 1.7
37 5.0 1.4
38 4.9 1.4
39 4.8 4.9
40 4.8 4.8

Does that help anything?
 

drc_567

Joined Dec 29, 2008
1,156
... was hoping for something simple.
Can you see what Pin #32 is connected to? The good board has 5.2 volts, and the bad board has 1.2 volts.

edit:
... Is it connected to a voltage source or an IC or a capacitor?
 
Last edited:

Thread Starter

Eversr007

Joined Apr 10, 2016
40
ok so if i trace pin 32 it goes to R19 which is a 2.7k ohm resistor but it measures 1.8k ohms so i thought I had it. I changed it and replaced it and the capacitor it was tied to. But out of circuit old one measured right and with new one installed it measured 1.8 also. I thought if you put the meter on both side of the resistor it only measured from those two points so why would it measure different in or out of circuit. So I traced it to other components. got to R20, R22, R8, Pin 1 of U8 , goes to R8, pin #11 on U6 which is an LM339n
R20 goes to pin 26 on micro controller U4
R22 goes to pin 24 on micro


Pin #32 on processor is MCLR/VPP which it says is a master clear (reset) input/ programming voltage input, this is an active low reset input to the chip. So does that mean with a low voltage it is stuck in reset mode or something.??IMG_6609.jpgIMG_6610.jpgIMG_6611.jpg
 

dendad

Joined Feb 20, 2016
4,451
Can you get hold of an oscilloscope? It would be good to have a look at the !MCLR line to see if it is oscillating. The voltage reading you have suggests that.
There does appear to be a problem with that and it is holding the PIC in reset. You may need to trace that part of the circuit back and see what the reset is driven by.
One part that often fails is the electrolytic capacitors.They would be the first thing I would look at. The age of the board makes them really suspect.

EDIT: If you don't have a scope, hook your multi meter to the reset via a 100nF capacitor and measure the AC volts. It should be zero if it is steady. A reading (after it settles) indicates the line is pulsing.
 
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