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test procedure revisited

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peter g

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hi ron, my original post asked for a circuit to test uln2003 chips. i put together the circuit you so kindly provided. i tested the circuit with a known good uln 2300. i can get all the led's to flash except for the led's connected to pins 11 & 10. tried several different new chips with same result. need help figuring this out. thanks. pg
 
I happen to stumble upon this thread because of the title. :)

I remember the old thread. I put a circuit together as I recall using a 4017 to drive the ULN2003 chip. That is strange as pins 11 & 10 would be the pins 6 & 7 inputs. See the attached as I found some remnants of the circuit I suggested. Just peculiar the first inputs / outputs work and the last two don't work. If you have a meter depending on how you are clocking the 4017 you could see if the input pins are going high when they should?

Ron
 

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hi ron, yes it is strange. i'am going to check some voltages as you suggest. will post back. i also have another question. can you explain the operation and purpose of a PC814 opto-isolator?
 
Hi Peter

If we look at the data sheet for the PC814 series we notice it has two LED emitters placed back to back. The incorporating of two LED emitters rather than a single makes it useful for AC signals. If we apply an alternating current to a single LED emitter opto coupler we get pulses out on the alternate half cycles of the AC input when the LED is forward biased. Using two emitter LEDs back to back in a single package we get a constant output for the AC input since each LED will conduct on alternate half cicles. One or the other is always on.

Ron
 
hi ron, o.k. the problem turned out to be a wiring error i made. now all led,s attached to the uln flash. i read your info on the pc814. very interesing. how and why would this opto be used? thank you.
 
Glad that worked out.

Generally in the wonderful world of opto couplers we like to think of them as used in DC applications. However, there are applications where an AC signal may be present and we need to use it. For example a ring signal on a phone line. The ring signal is an AC sine wave riding on a DC level. I could block the DC component using a capacitor to pass only the AC ring signal and divide that AC down and pass it along to the opto coupler designed for AC. I could then detect the AC ring signals on a phone line. Sort of abstract example but it came to mind. :) There are plenty of other uses, I believe the data sheet mentions common applications.

Ron
 
will check applications on data sheet. these opto's are being used in a hot tub power board. any ideas why? my problem and anyone"s problem who work on these boards is that the manufacturer of this board absolutely refuses to offer any troubleshooting or schematics for them. hence, the only thing available to a repair person is to try to understand the operation of the componets. thanks again. pg
 
Hard to call or say how they are using them without a schematic. With things like this the best shot is looking at the board and trying to map things out. From the data sheet we know the input and output of the opto so it is a matter of what feeds it and what the out is connected to. What exactly does the board do? Also, many of today's hot tubs get pretty elaborate with switching pumps etc as well as temp control.

Ron
 
hi ron, there are 2 control sections in every hot tub. one is called the topside controller. this is the owners interface to various functions. bubbles, jets, temp control, time of day, etc. this unit consists of an lcd driver, an eprom and a pic microcontroller. the second control board is called the power board. it consists of the relays that control the pumps, it consists of lots of pc814 optos, triac for blower motor, it also supplies power to the topside. it also has a pic micro. no eprom. it has a heater element that heats the water(draws tons of current 20 plus amps). thats pretty much it.
 
Hi Peter

Sans a drawing these things are almost impossible to figure out. You can look at known parts and guess how a board works but that is about as good as it gets depending on one's skill level. Like you mentioned seeing the triacs for the blower motor. Funny a hot tub came up as I see one in the near future with a new deck in the yard. :)

Ron
 
i would definitely check before you buy that service information will be available to you. the boards in hot tubs go for $300-400 apiece. it seems hot tub manufacurers would rather you change the board rather than a $5.00 part. btw on the schematic that you put together, could i just use one 30 ohm, one 560 ohm for led's and one 5.6k resistor? (uln tester circuit)
 
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Hi Peter

Sorry took awhile to get back as I lost the thread.

Yeah, it would seem hot tubs are like the new high efficiency furnaces, all you need to repair them is a $300 circuit board. When I make this buy I plan to do some homework. As to the resistors yes, it should be as drawn.

Thanks
Ron
 
hey ron, yes, sometimes i think technology is getting expensive. living in s. florida(lighting capital) it wasn't surprising my hot tub took a power surge. this was even with a surge suppressor. six componets needed to be replaced on the power bd plus the topside control panel. i was surfing the internet and came upon a hot tub manufactuer who states his hot tubs contain no expensive boards and that all the circuitry to run it is cheap and easy to repair. also states, micrcontrollers are not necessary. oh well. bye for now. pg
 
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