Presonus TubePre repair issue

[famous beagle]

Hey y'all,

I picked up one of these for cheap on eBay, and upon testing it out, everything worked perfectly, except that the meter bulb had burned out.

I think I tried my best to find out what the specs were on a replacement bulb, but I never did. I had some bulbs lying around from a repair I did on an old Audio Technica 4-track (AT-RMX64), and they looked very similar at least. So I figured I'd give it a shot. Aside from not having the blue covering on, and therefore just glowing white instead, it seemed to work perfectly.

However, ever since I did that, I'm not getting any signal. The meter (though lit now) is not registering, and I'm not getting any audio---from the XLR or 1/4" inputs (and nothing's coming out the outputs either).

I checked the PCB for any trace of scratches I may have inadvertently made. I found a few suspect-looking spots, but when I tested for continuity, everything checked out.

So ... my question is:

Is it possible to cause this issue by using the wrong type of bulb? Or would installing it backwards (the bulb is different on each end) possibly cause this issue?

I'm just kind of stumped at this point.

Thanks for any tips

 

[famous beagle]

Well I kind of answered my own question I guess. I took the bulb out completely, just to make sure that wasn't causing something, and I still had the same issue. I also noticed that the LEDs that backlight the tube aren't glowing, so it must be something. I tried switching out the tube just to be sure, and that wasn't it.

At this point, what do you do? Just start checking continuity everywhere until you find the culprit?

Thanks

 

[Steenamaroo]

If everything worked perfectly until you had a hoke, I'd be looking at all connectors/connections.
I duno what it's like in there but I guess there are a few ribbons and what not?

 

[famous beagle]

Yeah, I compared it side by side with my second (working) TubePre, and I couldn't find anything wrong. There are some ribbons, and I did re-seat a few that I had disconnected just to make sure, but no luck.

 

[Bbbent]

Time to start tracing with your multimeter. Something is shorted somewhere.

 

[famous beagle]

Time to start tracing with your multimeter. Something is shorted somewhere.

I've never made a repair before where the problem wasn't obvious. Do you mean basically just checking continuity of everything until I find the problem spot? Thanks!

 

[Blue Jinn]

I've never made a repair before where the problem wasn't obvious. Do you mean basically just checking continuity of everything until I find the problem spot? Thanks!

Sorry to come to this late in the game. Still trouble?

A few simple things come to mind:

1. Do you have a schematic? That would really help. I have one of those ART "tube" preamps, had a (very simple fault after all, bad connector) but I emailed ART and they emailed me back a schematic

2. Power supply, is probably the best place to start. Does this thing provide phantom power? You could plug a dynamic into there and see if that works. Does the tube glow? If so you're getting the heater voltage. You could remove the tube and check to see if you're getting voltages at the tube, I think these are prob 12AX7 starved plate "" so shoiuld be about 35v or so on the plate; guessing there are some IC's in there, so see if they are getting power if you can squeeze in a test probe in there without shorting anything. You;ll need to look up pinouts on the tube and IC's. Opamps should have something like 9-15v on the V+side, depending on how they are used, -9-15v on the V-side. That is not the + and - inputs on the actual opamps. Find the pinout, the power supply connectors are usually labled something like Vcc or V+ or somesuch.

3. Connectors, that ART I was talking about had one of those dual use jacks. It was bad, the XLR part worked hte phone didnt.