Problems with my FG085

Problems with my FG085

Postby mwm » Thu Jul 28, 2016 7:15 am

Ok, I suspect I may have caused some of these. As noted elsewhere, I managed to screw up the power switch, and then managed to strip the rings off the through holes for the switch installing the replacement. These may or may not have contributed to my problems.

Checking the schematics, I added a jumper from what I think was pin 6 (the pin closest to the corner the switch is near) to pin 1 of U2, and another from pin 5 (adjacent to pin 6) to positive output of DB1. Pin 4 is shown as disconnected. Since the unit powers on and mostly works ok, I believe those are right.

But the other pins I have no idea what to do with. I can see that I should run one line from the other output of DB1 to pin 2. But it's shown as being wired to the two sides of a pair of LED (D10), and I don't see anything that looks like that on the board. My guess was that that was a power/standby LED which is now gone, and those pins are unused..

Two problems.

1) USB isn't working. Both Windows and my Unix boxes see a device, but don't recognize it I did double check the soldering on the thing, and touched everything up, but that was no help. Beyond that, I have no idea where to start debugging this. Maybe tear apart a usb cable and check connectivity to the something on the board?

2) The servo header output is wonky. In the PWM modes, I get a solid PWM signal between Out and Gnd. But Vcc looks like a bad version of that signal, with a sharp rise line and a slow decay. For that matter, now that I think about it, I checked it with other waveforms, and the waveform is clearly shorted to the VCC output of the servo connector. I'll check for shorts tomorrow, but it would be nice to have pointers to likely places to look to start with.

Thanks.
mwm
 
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Re: Problems with my FG085

Postby mwm » Wed Aug 17, 2016 9:19 pm

Still looking for some help with this, and back to it soon. Any chance of getting a trouble-shooting guide, or a list of test points and voltages to expect, or any help at all?
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Re: Problems with my FG085

Postby jye1 » Thu Aug 18, 2016 2:55 am

The only USB function is for downloading of user waveform data. It has no other functions.

For the servo signal issue by "VCC" did you mean VRAW at J9 pin1?

Generally for troubleshooting signal can traced by following the path

U3 pin7 -> U4 pin3 -> U4 pin5 -> U3 pin3 -> U3 pin1 -> Output

Offset is generated at U13 pin7.

Make sure V+ and V- are good before checking signal at the points above.
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Re: Problems with my FG085

Postby mwm » Fri Aug 19, 2016 1:05 am

Well, if I can't use the user-generated waveform, maybe I ought to go back to the new firmware with better accuracy but breaks user-uploaded waveforms? Or have I misunderstood that? Clearly, something is shorted to the USB connector. If I plug the thing in with the FG085 turned off, my system sees the CP22102 USB/UART bridge. When I turn the thing on, my system reports that it has been disconnected. That it happens as soon as I turn on power reinforces my suspicion that it's a power issue.

Anyway, yes, the "VCC" I mean J9 pin 1, which is labelled V+ on my board & the assembly instructions.

Note that signal output - either via the BNC connector or J9 out - is fine. The pin that normally provides power to the servo isn't. Is this what is meant by possibly needing a regulator? Can I jumper a ~5V source from elsewhere to this to get power to it? Part of the justification for buying the thing was that I wanted to use it as a servo tester.

Ok, the output signal isn't quite "fine". The amplitude is a bit off, varying by about 5% from the selected value, but the waveform shape and timing are spot on.

I'm not sure what to use for ground when testing V+ and V-. Using the GND pin on J9, the two test points with those labels both show 0 volts, so I suspect I'm doing something wrong.
mwm
 
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Re: Problems with my FG085

Postby jye1 » Fri Aug 19, 2016 2:15 am

J9 was just as an alternative output connector. It was not specifically for servo. The on-board +5V has limited capacity. It might not be enough to drive a motor.
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Re: Problems with my FG085

Postby mwm » Fri Aug 19, 2016 12:43 pm

Not driving a motor power se, just a servo. The 50mA provided by an Arduino pwm pin works fine for most testing, though stalling one could be an issue. But you normally don't check that with a servo tester. Can I get that much power, or do I need to get an alternative source?
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Re: Problems with my FG085

Postby jye1 » Mon Aug 22, 2016 2:42 am

The on-board +5V power supply has 100mA current capacity in theory. But due to limited heatsink it probably can't supply that much. Now it feeds all logic circuits and LCD backlight. I don't think it has much surplus.
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Re: Problems with my FG085

Postby mwm » Tue Aug 23, 2016 3:42 pm

I hooked up a bench PS for the servo, and yeah - it's drawing 5 to 40+ mAmps under normal use, but spiking to ~120 when it stalls. I've ordered some voltage regulators; the comment about "may need it" made me think this would work.

Any chance on getting test point values for the USB issue? As noted, the serial/usb bridge works until power is supplied, which makes me think that something is shorted there. I know it's only used for user waveforms, but I'd like that to work...

Thanks.
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Re: Problems with my FG085

Postby jye1 » Wed Aug 24, 2016 2:57 am

The issue might indicate that CP2102 has been damaged. We didn't see such problem before. Maybe you can try to add isolation by insertint a 400 - 1000 ohm resistor to each line of TXD and RXD between U5 and U15. You might need to cut traces to do that.
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Re: Problems with my FG085

Postby mwm » Mon Aug 29, 2016 8:05 am

I'm a bit leery of testing this, as I think it may have fried a USB hub. Maybe not, it was new and could have been a crib death. But that level of soldering is beyond my skills, so it may not matter. Any chance there's another way to test this? Checking the USB lines in an oscilloscope doesn't show any activity or voltage, which isn't really surprising.

Second question: I added a L7805CV as a power regulator for J9 servo testing voltage. I added a 100µfarad cap across it's input. This entire structure basically parallels the 78L05 and 470µfarad cap that provides the 5V rail for he FG085. Seems to me that this shouldn't make any difference, as they are both decoupling caps. But I figured I'd check with you to make sure.

Thanks,
Mike
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