Start by uploading hi-res pics of the tops and bottoms of all the boards.Hola Comrades,
Long time lurker, first time poster...
I just built two CAPI VP312DIs... One totes works... the other ...the 1/4" DI on the front works... but the XLR part of the VP312DI does not... 48v LED doesn't light up and no signal out from VP312DI ...
verified by racking the VP312DI in my CA500R8 connecting both a dynamic and condenser mic = nada. Also routed audio out of DAW through the pre (via USB CA500R8) = nada
I know it's not my 500 rack, been using it for almost a year and all slots 100% work.
Looking at my handy work on the failed VP312DI ... no visible scorched or burned bits or bobs...
...very odd that the 1/4" DI on the front works just fine but not the XLR in/out half of the pre...?
searching this thread so far, hasn't illuminated anything yet...
Not my first DIY project (2 DIYRE color palettes, 2 Lola Pres, 2 CAPI LC40s, about a dozen DOAs).
Sincerely appreciate anyones time and suggestions.
Happy Holidays!
Thank you Ricardus... lets see if these make it onto the site here...
Having a doozy of a time getting jpegs to stick the landing here...
Verified the issue is not the DOA or HiZ Plug-in PCB (swapping both from failed unit to 100% working unit and vice versa confirmed) ...taking notes from the thread...
#56
If it's not passing a mic signal and the DOA is known to be good, I would first check the PK2 relay to make sure that with no 1/4" jack inserted, pins 8 and 10 get coupled to the input transformers primaries. With a ground signal present at PK2's VC pin, the rear mic in will be couple to the 2622. When a 1/4' jack is inserted, the normal of the sleeve's contact is broken/opened which disconnects the ground from PK2's VC pin and switches the relay to the HiZ Plug-In as the source for the 2622's input.
If all of that is good, you will have to look at the output section. That is very short and sweet really but I would make sure it is not a solder joint on either the Mute or Polarity C&K switches.
#84
Well, like I said, there will probably be no magic bullet or smoking gun fix. When having trouble like this the "pot shot" approach to finding and fixing will most times never work. The only way to find and solve is systematic and methodical.
First, common sense things with the opamp. Is it a known good solidly built opamp? Who built it? Has it been verified good in another working device? Is the voltage switch set incorrectly for the opamp installed? I never test a freshly built preamp with a freshly built opamp. Too many variables.
From there, you will need to follow the schematic like a road map. You can follow signal from the input up to the opamp with no opamp installed. When in mic mode, does injected signal get to the first relay board? Does it get past it? Keep following all the way to the opamp.
When inserting a 1/4" jack, the rear relay will switch to DI mode. Follow the signal throughout the DI signal path as well.
This may seem like a frustrating time, but the rewards when you can systematically follow signal thru an entire device and find the culprit will be very rewarding. It will only make you a better builder as well.
#85
All of the things I am about to post can be deciphered by looking at, reading or following the schematic. This will become a necessity with the amount of kits you build if it's not already. Good troubleshooting skills will out weight good build skills any day. No matter how good a builder one may be, there will always come a time when you need to sort out an issue.
So, think it may be the t-pad? Easy. Let's bypass it and see what happens. By looking at the skiz we can see that the t-pad follows the 2503 output transformer. Desolder the Blue and Orange leads from the 2503. Temporarily solder them to an XLR or whatever means you need to monitor the output. Again from the skiz, Blue will be + and Orange will be -.
What are the results? Same issues? No sound and opamp heating up? I think we have ruled out the t-pad.
In a general studying of the 312 schematic, what would happen if the 2503 is bad? What if the primaries are shorted within the x-fo? Very rare but **** does happen. Again, in following the skiz, the DOA's output would be directly shorted to ground. Not good. Would probably cause a very fast over heating of the opamp. Maybe next you should desolder all the leads from the 2503 and measure DCR to see.
What is DCR between the following: (again, that damn schematic is the key!)
Red to brown?
Blue to green?
Yellow to orange?
Violet to gray?
Make sure your DMM is set to properly measure resistance under 100 ohms. Let us know what you find.
Last thing to mention, before I would have gotten to the above, I would have injected signal and followed it all the way thru the preamp. Where it stops would be the area to look. If the above holds true, things would be fine up to the DOA's input. Would be a great help to yourself if you could verify this. You will be thanking me for it one day down the road.
#113
You can beep for continuity between the A+ pin and the O+ pin (mic mode). Next would be the B+ pin to the O+ pin (DI mode). This info is on the skiz. There is just enough room where the 90 degree header comes out of the relay PCB to get your probe tips in. If this relay is not flipping with the plug going in/out of the DI jack, it's either a problem on the PK2 relay build or the control signal which can also be followed on the schematic. You must have DC applied to the main board for this to work.
#115
The relay in question that selects what input goes to the 2622 (mic or HiZ Plug-In) is PK2 that is situated more in the center of the PCB just behind the input transformer.
PK1 routes the DI input signal to the HiZ Plug-in or to the post 2622 position. You need to flip the mini toggle on the front to get this relay to active/deactivate. This can only happen with a plug in the DI jack.
#119
Well, I can't think of any reason why the mic in won't work then. If the relay PK2 board is fine, then the only difference between the output of that relay card from DI mode to mic mode, are a few inches of PCB traces and the gold fingers #8 and #10. Is this maybe an issue that lies between the card and the mic? Meaning rack or outside cabling?
#121
Well, many things are not making sense here. My suggestion is to pull both relay boards and make sure they are working right. I test them on a breadboard. 98% of all problems on a VP312DI build are related to those little relay boards.
If Pre 2622 DI mode works, mic mode should also work.
... gonna try swapping out the DOA and HiZ Plug-in PCB from the working VP312DI into the failed one... just to rule that out...
... otherwise Jeff repeatedly points toward incorrect diodes on the relay PCBs... So I'll have to double check those little suckers...
Going off post #387...Verified the issue is not the DOA or HiZ Plug-in PCB (swapping both from failed unit to 100% working unit and vice versa confirmed) ...
I also double checked the tiny eye straining print on the diodes for both relay boards... cross referenced the relay PCB overlay...
1N749 (4V3 Zener) is in correct polarity/location and so are both 1N914's...all good there...
Verified the 1/4" DI still works as well as the Post 2622, -10 and LPF switches... but still no XLR in/out signal...
While waiting for my 500 extender card/cable to arrive...
...Might it be worth de-soldering both relay boards > swapping PK1 (DI relay) with PK2 (CA2622 relay) > solder and test..?
...or just be patient and wait for the extender to arrive and test the pins with a DMM on PK2..?
Excessively high DC offset from the 2520 opamp.I have a 312DI (rev C) where the output dropped to near-nothing. Pulled it out yesterday to start trouble-shooting, which turned into a very easy task since C10 had ballooned up significantly. I swapped it out and I'm happy to report that the preamp is now performing as it should again. Out of curiosity though: what might have been the cause of this? It didn't feel like the obvious thing to break (apart from it being an electrolytic).
Thanks Jeff, I'll measure that to see what I'm dealing with. The cap was rated higher at 16V and the one I put in now is even 20V. I have one more that I built at the same time, maybe that one is next.Excessively high DC offset from the 2520 opamp.
This is correct and normal for a VP312 or VP312DI.Hello, having trouble with my first VP312 build that I completed tonight. During "preflight" only 10 ohms across C and O plugs. Continuity breaks when I press the mute switch if that helps narrow the issue but I suspect not. Tired and putting it away for the evening, but I hoped to get a tip or two by posting for when I pick it up again tomorrow. Thanks!
To be more clear, for the VP312DI you will have around 9 ohms if the shunt jumper is set to "Output Cap Bypass". If the shunt jumper is set to "DC Block/Cap Coupled Output" then you will have a very high reading like mentioned in the VP2x Assembly Guide.Excellent. Thank you sir. I must have been referencing the wrong assembly document and thought the value should have been 200K or higher.
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