Real Bull Controller box question

With the lathe running and the display flashing 8888, if I disconnect the encoder, the display returns to 0. Once reconnected, the display shows the current RPM.

The controller is the KB-240D model from KB Electronics in the US. I was worried it might be a cheap clone when I ordered the box but was happy to find it wasn't. The IC is indeed socketed and has a readable number if it should turn out to be suspect. I'm still puzzled by the fact that the fault only crops up after some time. This is why I was tempted in the beginning to think it could be a thermal intermittent problem: something gets warm then fails. Off for a few seconds then it's ok again.

I don't have a scope and frankly, wouldn't know how to use one. As I indicated, my troubleshooting abilities are as good as my Swahili! That said, I do have a multimeter and a couple of spare opto-isolators I could try. Would they have to be exactly the same part number or are they mostly interchangeable?

I'm not at home right now so it'll be a while before I can get back to it. When I do, I'll post a few images.

Once again, I'm very grateful for your help.

Trevor
 
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If you want to try swapping opto interrupters you really should try to find data sheets online first, they are similar but pinouts can vary- you can blow things up if you connect it wrong
It would be safer if you disconnect the power from the controller and tape the wires so that only the readout power supply is live when you are testing the readout
You should be able to monitor the signal from the opto either at the opto or at the connector- you might need to solder some short wires and get some alligator clip leads so that you can turn the spindle by hand while watching the meter without having to hold the test leads
 
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It might be helpful if we knew who made the tachometer board and/or integrated circuit. There could be troubleshooting info in the product manual/IC data sheet.
 
I belatedly noticed that the controller was sold by Amadeal. You might contact them to see what they have to say about the problem.
 
homebrewed said:
I belatedly noticed that the controller was sold by Amadeal. You might contact them to see what they have to say about the problem.
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That was the first thing I did but I didn't get a reply. Busy with the Xmas rush I guess.
 
Yep you may not find a lot of support from the company but if you can get the data sheet for the main chip that would be very helpful, usually they show an application circuit with interconnection details and power supply requirements
 
I really appreciate the time you're taking in helping me with this.

A test I plan to carry out this afternoon I'm hoping will narrow things down a bit. I'll fix up a bit of stock bar in the chuck and turn it with a Black and Decker drill. The motor controller will be off, only the DC feed to the display board will be on. My reasoning is that if the fault appears, that will more or less conclusively point to a fault on the display PCB or encoder (as you suspect). If it does not, then it could point to some interaction between controller/motor - possibly the EMI problem you suggested originally.

I can certainly dig out the IC and try to find a data a sheet if this proves necessary.

Now, here's another wrinkle which may clarify (or confuse) things further. Shortly after the 8888 problem surfaced, I started noticing the motor "hunting" or pulsing as if the DC feed was being interrupted. This only became noticeable in the last day or so or I would have mentioned it sooner. My first thought was worn motor brushes so I will have to eliminate that as a possible cause. Could this explain sporadic fluctuations in the load on the controller which might introduce noise into the encoder pulse train? I don't know if any of that makes sense. Anyway, I'll post the results of the test later tonight. Thanks again.

EDIT

I ran the test (see video) several times for about 5 or 6 minutes and the display behaved normally. I originally said the problem popped up after about half and hour but later said it was happening more frequently. This might mean nothing or it might simply be progressive wear of the brushes making more frequent pulses on the DC motor line and affecting the encoder signal. Is this what is known as "parasitic EMI"? Whatever. I'll run the test again several times tonight to see if the fault occurs. Next, run the motor on the lathe as normal and see what happens. It might turn out that the 8888 is a designed error signal to indicate square wave signal isn't being read or synched.
 

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homebrewed said:
It might be helpful if we knew who made the tachometer board and/or integrated circuit. There could be troubleshooting info in the product manual/IC data sheet.
Click to expand...
Thanks for the input. Finding out the OEM of all these Asian products is next to impossible. You might see "Made in China" on them somewhere if you're lucky. I received no product manual or data sheet with the box as it was supplied as a spare part. Schematics for the US made KB controller boards are readily available on the net, however. Maybe the CJ18A lathe this box is normally fitted to comes with something. This most likely would be produced by the retail seller who puts the badge on the product as it's not worth the OEM's time to write them. I doubt it would include a schematic of the display board but it's a fairly simple circuit anyway (not that I mean to imply I find troubleshooting electonics easy. Far from it:)).
Data for the IC on the tacho board should be easy to find as long as there's a readable number. OEMs often scratch them off to make it harder for others to copy the product.
 
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sacentre said:
Thanks for the input. Finding out the OEM of all these Asian products is next to impossible. You might see "Made in China" on them somewhere if you're lucky. I received no product manual or data sheet with the box as it was supplied as a spare part. Schematics for the US made KB controller boards are readily available on the net, however. Maybe the CJ18A lathe this box is normally fitted to comes with something. This most likely would be produced by the retail seller who puts the badge on the product as it's not worth the OEM's time to write them. I doubt it would include a schematic of the display board but it's a fairly simple circuit anyway (not that I mean to imply I find troubleshooting electonics easy. Far from it:)).
Data for the IC on the tacho board should be easy to find as long as there's a readable number. OEMs often scratch them off to make it harder for others to copy the product.
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Yeah, I've seen products where the IC ID's were removed. Hopefully not the situation for your board.

That was a clever way to test the tach independently of the motor controller. You might want to repeat it while heating the tach board with a hair dryer -- since the motor controller wasn't running, the box probably wasn't getting as hot as it does during normal operation. Your comments about the readout only failing after some time immediately made me think of a thermal intermittent problem. Those can be hard to troubleshoot. Freeze spray can be helpful here, but is kind of a blunt instrument. Spraying a q-tip with freeze spray and using it as a "cold probe" on components might help zero-in on the problem -- if it is a thermal intermittent. If the "blunt instrument" approach doesn't cause the tach to recover, there isn't any reason to use the q-tip scheme.
 
Good advice there from Homebrewed. I salute your courage in diving into this thing- there's a certain satisfaction in fixing something with little info to go on.
Even if the IC number has been erased, you might be able to locate it online by typing in the function "3-1/2 digit tachometer IC" or something like that.

The hunting you mentioned could be a factor or not. I wouldn't expect the brushes to be worn unless the motor has lots of hours on it.
If you can read the part # from the opto interrupter post it here- I have some opto databooks
 
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