If it's a VB and not a knock-off, the correct part is a 7406. The 7409 isn't even remotely similar. Start with the obvious.
Your comment about Q2 implies a spot killer issue (not sure how to reconcile that with your 7409). If so, C10 (or whatever that is on your board) may be shorted or installed backwards. If so, and the cap hasn't already exploded, you probably have a Xentek PS, and F2 (1/2 amp) is blown. Again, start with the obvious and check the fuse.
- Mark
On Mar 26, 2013, at 7:14 AM, Carlos Rubio <csrubio@gmail.com> wrote:
> Hello, I'm working on a Vectorbeam monitor on which I've replaced about 90% of the components. This monitor is the "discrete" version with the HV components on the monitor PCB. It also uses the older part numbers.
>
> Currently the screen is blank, but I'm not sure if it's a problem with the intensity circuit or a legitimate spot killing. Jumpering Q2 (labled Q24 on my board) causes the picture to appear and reveals that the top half of the image is missing. All transistors have been replaced.
>
> I should also mention that this monitor has a 7409 at IC7 (labeled U6 on my board) instead of the 7406 referenced in every document and schematic that I've seen. There are diodes between pins 1 and 8 and 3 and 8 as seen here. I've replaced the 7409 and the diodes with new ones, exactly as they were. The symptoms were the same before and after.
>
> I'd appreciate any insights in understanding if one problem is related to the other, and how to narrow down the fault(s). Thanks,
>
> Carlos
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Received on Tue Mar 26 10:06:04 2013
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