FYI for anyone with a first-gen Variax who can't get communications on the VDI cable. I bought an older Variax 300 electric off ebay. Problem: Could not get any communications over the VDI cable but the TRS analog cable worked great. Variax Workbench did not see the Variax plugged in to my HD500. HD500 would not see any signal when input was set to Variax. Tried three different RJ45 cables, same problem. Tried plugging in TRS cable with VDI cable already plugged in and heard a plunk/pop out of the speakers like you would when you plug in your analog guitar cable to the HD500. That indicated that the VDI interface was working but not 100%.
So I started taking the Variax 300 apart. The first step was to verify that signal was getting through the RJ45 jack on the side of the Variax through the circuit board to the 8-pin blue wire connector going to the main electronics. Using my digital voltmeter, I found an open circuit on one of the pins (Pin 2 I believe). Surface-mount inductor L9 was open circuit at 20 MOhms. When a tech at work attempted to reflow the solder on the inductor ends, it split in half. So, if you have strange communications problems, you may want to check the capacitors and inductors on the input connector board. Just ohm out each path and see if you get conductivity through the connector and board.
Oh, and BTW, Ebay Variax warning: I hope you can avoid my ebay experience. Seller had 96.4% positive feedback and music equipment was not his forte.
1. Wrong nut installed on Variax - was not glued in and was rocking back and forth in slot! Let's not even mention the 8-gauge First Act strings on it that felt like plastic.
2. "Gig Bag" was a worn out no-name piece of junk. Seller claimed it was for shipping protection only (you know, like the same kind of protection you get with panty hose!) Get photos of gig bag.
3. Large dings on back of guitar body, seller did not disclose and did not photograph.
4. "Included Variax digital cable" is missing the metal ends of the Neutrik RJ45 connectors! It's unusable as-is.
5. No digital communications due to inductor problem noted above.
Hope this helps.
Just a follow up - the tech bypassed the inductor and I put the guitar back together after work. I was instantly able to communicate over the VDI and was also able to use Variax Workbench. I did have a few "loss of communication" events but they were the exception. I will post up any updates.