JustGreg
Joined: 07 Mar 2006
Posts: 3098
Location: Kenosha, WI
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| Posted: Fri Jun 18, 2010 7:24 am Post subject: 50-2330-02P VDM Troubleshooting |
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I'm going through this VDM piece by piece...not so much in hopes of fixing it but to learn basic board level testing.
I discovered from the prints that R67 became DNP (Do Not Populate) as a rev. This resistor is a 680K .5W that's in the FBControl circuit coming off pin 11 of U12. (VDM schematic page 2, section 6C).
1) Can I assume FB stands for FeedBack?
2) What is the function of the FB Control circuit? I haven't tracked it back but I would think it provides information to the CLM? (I've already swapped in another CLM with no change in HV dropout)
3) Are there versions of other boards that wouldn't be compatible with this rev'd version of VDM that might be contributing to the HV dropout I'm seeing? I doubt this as the pj worked with the current configuration but it can't hurt to ask.
What's interesting is as I slowly ramp up or down SKEW or PIN click by click (from the default null of 50), the pattern begins to go away from the bottom up until half of it's gone and then one more click and HV shuts down totally. SKEW and PIN is acting like a variable power supply controller (of sorts).
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Greg
"Is it ignorance or apathy? Hey, I don't know and I don't care!" --Jimmy Buffett
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