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Hi Jimbo –

Nice thorough debugging job. Hard to conclude anything other than the

encoder is bad.

I’d forgotten that I left the Test menu in my application. That was
something I put in place early in its development just to convince myself
that I was getting data. Glad you found it handy.

Let me know how things go when you get the new encoder and try it out under
the stars.

Dave

—–Original Message—–
From: Jimbo S. Harris [mailto:jimbo@jimbo.net]
Sent: Sunday, October 07, 2007 7:22 PM
To: David Ek
Subject: Re: DSC circuit – USB conversion?

At 10:35 AM 9/24/2007 -0600, you wrote:
>On the issue with encoder readings, it sounds like you have a problem
>with one of the two channels for the RA encoder. It’s likely a solder

>or cable issue.

Hi Dave,

You were totally correct about this diagnosis; the B channel of the RA
encoder is shorted to +5v.
I checked it out carefully, and I was getting:

Testing the RA encoder with each cable:
RA cable to RA encoder = nothing (RA encoder count flutters +/- 1 tick no

matter how far RA axis moves)
Dec cable to RA encoder = nothing (Dec encoder count flutters +/- 1 no
matter how far RA axis moves)

Testing the Dec encoder with each cable:
RA cable to Dec encoder = works (RA encoder count changes value when I move
the Dec axis)
Dec cable to Dec encoder = works (Dec encoder count changes value when I
move the Dec axis)

This is consistent with both cables working properly and all the solder
joints OK in the interface, but a dead RA encoder.

I used Hyperterminal to some effect (I could at least see the version info
print out and I’d get ASCII stuff for the return values of the encoder
counts), but the tool I actually used to figure out what was going on was
your DSC program — the “Test Interface” menu item worked like a charm! It

did not appear to be doing any extra calculations on the encoder counts,
and I could even use the counts to figure out what my encoder resolution
was (by turning the Dec Axis exactly 180deg using the manual setting
circles and seeing what counts came out).

After a lot of playing with it and convincing myself that, in fact, the RA
encoder was blown, I pulled the encoder off the mount, and tested it out
with a voltmeter. Hooking between Ch. A and Gnd and turning the encoder
made the voltmeter flicker; either ~0v or ~5v and reading ~2v as I turned.

Hooking Ch. B to Gnd I get +5v steady, turning the encoder or not. Hooking
+5v to Gnd gives +5v (duh). I checked out the solder joints on the encoder
and nothing is noticeably wrong with the solder joints.

So, I’m going to email Losmandy and see if I can get an RMA for the encoder.

Good news is, it looks like the circuit is fine.

Thanks for your help and advice. I’ll let you know once I get the system up

and running.

Regards,
Jimbo

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