You can check the voltage level for the receiver on the + and -. The output ( a ) will vary depending on the amount of light it sees.
When adjusting the alignment, you want to see the maximum voltage it will produce.
Here's an example, say you have 5v on the + and -, there will be a 0.7v drop due to the gate voltage, max output for a perfectly aligned detector will be 4.3v.
I got waylayed yesterday and was unable to test. I hope to get in there today or tomorrow.
I got my testing done today. Using the staple wire probe and my meter, I am getting power out to both the emitter and receiver. Both read 3 volts. I tried various alignment positions and got no response, neither on the meter, nor any indication from the machine that it is detecting a sheet. It is either a bad emitter or receiver. I went on Mouser and was inundated. Bonz, could I impose and ask you to help me select the appropriate range of products? I would have to make the final selection based on fitment, but if you can show me to the aisle I can find the pew!
3v seems awfully low, especially on the receiver. I would have guessed they feed 5v and have a dropping resistor inline to the emitter.
Did you get 3v on the (a) terminal?
I see a 24v marking on the board, did you probe it? I'm leaning toward a problem with a power supply.
What make printer is it?
Have you tried to find schematics for it online? It sure would be handy to troubleshoot with.
The word of the day should be "confounded". After your last post I decided to test again and got something completely different. This time the receiver read 1.276v. The sender read .695v. The "a" read .648v and did not vary. Yes it is volts DC. After getting these readings this afternoon I went through and probed them all over again. The results were exactly the same.
When I had taken the readings this morning my DMM was swinging pretty wildly between 0 and 3v so I thought the voltage supply was going on and off with the rotation of the press and assumed 3v was the reading. This appears to be untrue.
One of two things that I can think of must be going on. Either the meter is bum or the other press running next to where I was testing this morning was causing the fluctuation. All other variables were the same and the connection of my probes was checked and rechecked. Confounding. I'll take my other meter in the morning and try again.
The press is a Ryobi 3300. If you can find an electrical schematic for that model online I'll eat my hat. Model 3200, 3302, and 3304 are completely different animals. This press is at least 20 yrs old and they only put this sensor on a few hundred of them. My authorized tech is trying to get the elec. manual for it but I haven't heard anything from him yet.
I haven't probed the 24v terminal. It is an unused terminal. It's hard to tell from the pic but there is no pin going into it.
Thanks again for following this!
Sounds like the battery is run down in the meter.
Have you looked here?
Don't forget the supply to the emitter is usually modulated not straight DC, this helps prevent ambient light/IR interfering with the beam. It might be 5V peak but the meter will read a screwy RMS value. That may account for the 3V. The other later readings are a little odd, was the negative probe properly connected?
I've been around IR sensors my whole career and have never seen a pulsed voltage on them. I don't think his would be since there is an adjustment pot to set the sensitivity.
I have seen ambient light problems though. On this machine (worked on these back in the mid 80's) the sensors would loose their selective wavelength filters and our high pressure sodium lights would shine on the receivers causing intermittent mis-sorts. The triangle shaped plates down the middle had two pairs of sensors under them for tracking. That was a bitch finding the problem.
Those machines were replaced with these.
And these were in use when I got into maintenance. Funny it's in the Smithsonian archives.
Things went from mechanical nightmares to electronic nightmares.
I am inserting my wire probes into the back of the connectors shown in the first post. I took readings on two different occasions. Once in the morning and once in the afternoon. On both occasions I inserted and reinserted multiple times, particularly in the afternoon when I got identical numbers each time. So I'm reasonably certain I had good contact.
Originally Posted by Peedee
Bonz mentioned a dropping resister between the board and the emitter. That adds another variable to the equation. I assume that's the modulated power you're referring to. I haven't seen anything between the terminal and the emitter. Are you suggesting that power may be modulated before it reaches the output pins on the board? So I may in fact be trying to measure a voltage that is unknowable without the schematic? Believe me, I hear these guys calling for a schematic. I wish I had one, and my tech is trying to get one too, but I'm getting the idea I may be chasing my tail without it.