Modded TCM1150 APEX460 disaster

  • Thread starter Thread starter amzavareei
  • Start date Start date
no matter what pattern it's set at it's 65 volts on pin 1
 
Just to clear up, we're reffering to pin 1 on the tube?
 
yep. I'm getting 110 volts from the psu to xlr to the board
 
That sounds right. It shouldn't matter what the knob is set to, because that's the anode on the tube. It should be constant. You changed the zener diodes in the PS, right? So after the 2 resistors the voltage should drop.

I'll check mine.
 
Yup. Mine reads 61.6v at pin one. That seems kind of low, but then I wonder why it sounds so good at that level.

Hmmm.

You should be OK if you've got 6v at 4 & 5 and 65v on pin 1.
 
Hmmm... thanks for checking. Yeah, I changed the 2 diodes to get 110v. I've got those readings, but I'm getting no signal. Maybe I should put the cathode follower back on... unless anyone has any brighter ideas?
 
Are you getting a voltage reading on the front diaphragm?
 
No. How am I supposed to do that? I measured it between the capsule and ground. Just get like -300 mv, connected to the meter or not. The needle slams up when the front disconnects.
 
I measured it with the grill off, boards back on and CAREFULLY (and I mean CAREFULLY) touching the red probe to the center screw on the capsule and the black probe to any outer screw.

I read about .56v on the from capsule and 1.13 on the rear in straight cardioid mode.
 
No, I'm not getting anything. Measuring it with everything connected, and the mic on. How could the capsule be fragged? It looks fine. It couldn't have burned out, could it have? It's just a simple mechanism.
 
amzavareei said:
No, I'm not getting anything. Measuring it with everything connected, and the mic on. How could the capsule be fragged? It looks fine. It couldn't have burned out, could it have? It's just a simple mechanism.
Click to expand...

It can't be fragged. Even if something was wrong with it you would get at least some ugly noise. My bet is it has to do with the connection to the backplates. If it were one diaphragm, the other would work and you'd still have sound. My bet is the lead to the backplates. If there's something not right there, then neither side will work. trace it back through the circuit and check where each connection is.
 
Found my problem, I think. Thanks Phil! I took r10 out. It's supposed to read 1000 Mega Ohms. My meter doesn't read anything. And no continuity across it either. I guess I might have found the problem. Just hope radioshack, or some junk lying around has one. How could that happen?
 
Ooh! That's very important and they can be very hard to find. If you don't find a replacement send me a PM and I'll mail you one!

Phil

P.S. Most modern electrometers won't give a reading on those. You're talking one gigaohm!
 
amzavareei said:
No, I'm not getting anything. Measuring it with everything connected, and the mic on. How could the capsule be fragged? It looks fine. It couldn't have burned out, could it have? It's just a simple mechanism.
Click to expand...

It seems you are using a needle voltmeter. Most likely you won't read anything there--the input impedance of your VM just loads the signal.

Unless you are really talented, I don't see how you could screw the capsule (or leads).

Your voltages on the tube are correct, so not much to be found there.
Next,
1) check (from ground) that at least one of the leads on R5 shows 110V, then another should be attenuated, but you still should be able to read some voltage there.
2) The same procedure on R9 in cardioid mode.
3) From ground check resistance between either lead of C8. One reading should be infinity (or close) and another something within 100 Ohm, or so.
4) On XLR connector measure resistance between pins 5 and 6.

Report all your findings.

Don't worry about R10 1G resistor. As Phil has noticed, MOST LIKELY you don't have the right equipment to measure it.
 
OK. So I replaced R10
All these readings are with the mic in cardioid
1)Like 64 volts and 9 volts
2)0 and -.060mv
3)1.4k 800(with it on. unplugged the 800(going to R2/pin1) was 0)
4) Like .2 ohms

The PSU is still pushing 110v. Pin 1 is still showing 60ish volts, pin 4/5 6.6 volts, pin 3 like 1.2 volts.

So obviously something's wrong. None of those readings look right. I just did the CF removal as was explained earlier! So what's going on here?
 
OK, I got off this project for a while to work on some others, and now I'm back. I found that 67 and 8 were supposed to be grounded since the last test. My results came out a bit differently than last time, but still no signal. I removed pin 5 since last time too. I traced the circuit, and here it is. Anyone see anything wrong with it? <p>
tcm1150ug1.gif


R5 shows 54 volts and 9.5 volts
R9 46 and 9.5 volts
1.42k on one side / no reading on the other
XLR 5 and 6 resistance reads about .2 ohms

Thanks!

there's still 110 volts out of the PSU, and the heater is lighting.
 
The schematic looks the same, but I still have C6 in, a black gate NX, but I don't see the secondary grounded in the center, like mine is. By the primaries being grounded, do you mean the transformer's primary getting grounded, or the 6,7,8 pins, because they are. I'm getting about 65 volts on pin 1.
 
OK,that's it! The ground between c9 and c10 needed removed along with the caps. Shoulda figured that one out, I guess. I'm just gonna let it burn in overnight, and I'll check it out tomorrow. Thanks for the help!
 
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