Preamp Studio Projects VTB-1 - No signal, only hum.

[tempus]

You might want to hold off on that order until we get a better idea of what all needs replacing. You may get your order and find that you still haven't found all the damaged components. We may need to replace caps as well.

Are the + and - regulators still out of the circuit? If so, can you check the voltages at the inputs of the 7805 and the 7915? Did you check the TIP to see if it was functioning properly?

[stonerbox]

You might want to hold off on that order until we get a better idea of what all needs replacing. You may get your order and find that you still haven't found all the damaged components. We may need to replace caps as well.

I ordered a lot resistors and caps too, just in case. Better safe than rory (mccann).

Are the + and - regulators still out of the circuit? If so, can you check the voltages at the inputs of the 7805 and the 7915? Did you check the TIP to see if it was functioning properly?

I @#$%ed up and broke off two legs on the 7915 but the 7815 is still intact. Yes, you read that right, the 7805 was another typo, I probably need glasses.

Tested the 7815 with +23v (handles up to +35v) on input and the meter read 11.5v on the output.

Tip122 was acting very strange, identical voltages (example: 12v) on emitter (according to the datasheet should be 5v) and collector. The base than had a couple volts lower (If it had 12v on E and C, Base had 9v).

[tempus]

What do the voltages read on the board at those points with the regulators removed? Also, can you update the schem so that the pin connections of the 2 regulators are correct? If you follow the current flow from +12vAC, it goes to D9, which should give around -16vDC (you're currently reading -11.5 vDC), then goes to the 7915 in. -16vDC is not enough to allow the regulator to actually regulate, so I'm wondering if there's a labeling error or you've misread the traces (you're still verifying all this with a meter right?). Also, if what you've got here is actually correct, and there is still only -11.5 without the regulator attached (and assuming that diode isn't connected to anything other than what you've drawn), then either the diode or C34 is faulty because you should be reading a higher, not lower DC value from the rectified AC. You also have the input of the 7815 connected to C38, but with no voltage source attached to it.

[stonerbox]

What do the voltages read on the board at those points with the regulators removed? Also, can you update the schem so that the pin connections of the 2 regulators are correct? If you follow the current flow from +12vAC, it goes to D9, which should give around -16vDC (you're currently reading -11.5 vDC), then goes to the 7915 in. -16vDC is not enough to allow the regulator to actually regulate, so I'm wondering if there's a labeling error or you've misread the traces (you're still verifying all this with a meter right?). Also, if what you've got here is actually correct, and there is still only -11.5 without the regulator attached (and assuming that diode isn't connected to anything other than what you've drawn), then either the diode or C34 is faulty because you should be reading a higher, not lower DC value from the rectified AC. You also have the input of the 7815 connected to C38, but with no voltage source attached to it.

Oh man.. I've drawn the layout wrong again. You should be awarded for your patience, good sir. I've checked all diodes with meter and updated the layout.

Ok, D9 got -14DCV on positive side and +13ACV on negative side.

REG 1 Input(7812): +15.5dcv
REG 2 Input (7815): +27dcv
REG 3 Input (7915): -14dcv
Tip122 Collector: +65dcv (around there, hard to tell exactly with analog)

[duck_arse]

I dunno if it's been mentioned yet, but the 1N5265 (Z5) is rated 62V, so you've got a voltage close to right, but wether it's in the right place ....

[stonerbox]

I dunno if it's been mentioned yet, but the 1N5265 (Z5) is rated 62V, so you've got a voltage close to right, but wether it's in the right place ....

It's has not been mentioned before, thank you for the usefull info Duck! I've triple checked the position and connections to Z5 and they are correct according to the latest layout (above).

95% of the layout is now done and all new components have arrived.

[stonerbox]

oh, or did you mean voltage in the right place?

[stonerbox]

This update is gonna feel good, real good. The beta layout is finally finished!
I've swapped all voltage regulators, voltage multiplier diodes and Q8 (2n3906) for brand new ones. All issues still present.
-Updated voltages on everything-

What a rat's nest...

[stonerbox]

Updated C8, C9, C31 and all 10k potentiometer connections.

[stonerbox]

So, I'm back again.. I've been trying really hard find out what's wrong with this thing but I'm getting nowhere.

-Recap-
Studio Projects refused to give me the schematic so I had to draw the layout myself from looking at the circuit board, it looks like sh*t I know..

I've swapped all voltage regulators, all electrolytic caps and 4004 diodes in the power section (top/left), all the ops, the 339N and it's still dead quiet.
If I tap into the output 1 of any of the op amps (except U5) I get signal with a lot of hum and distortion. When I connect output of U6,U2 or U1 to the output op amps (U5) input I also get signal, but again with distortion and hum. When I use a condenser I only get signal with hum but no distortion.

There is a lot of weird values here and there but I can't seem to figure out what is causing them, check them out in the layout.


Please help me, I've been at this for over a week without any major progress and got an album to finish by end of December.
Diodes
1n4004: http://www.alldatasheet.com/datasheet-pdf/pdf/14621/PANJIT/1N4004.html
1n4148: http://www.alldatasheet.com/datasheet-pdf/pdf/33884/WTE/1N4148.html

Quad Single Supply Comparator
LM339n: http://www.alldatasheet.com/datasheet-pdf/pdf/3071/MOTOROLA/LM339N.html

Op Amps
NE5532: http://www.ti.com/lit/ds/symlink/ne5532.pdf
OP275: http://www.alldatasheet.com/datasheet-pdf/pdf/49047/AD/OP275.html
LM4562: http://www.ti.com/lit/ds/symlink/lm4562.pdf

Transistors
C9015: http://vovnutri.ru/shem/detali/transistor/sc9015.html
2N3906: http://www.alldatasheet.com/datasheet-pdf/pdf/110693/STMICROELECTRONICS/2N3906.html

Voltage Regulators:
Tipp122: http://www.alldatasheet.com/datasheet-pdf/pdf/2770/MOSPEC/TIP122.html
7815: http://www.alldatasheet.com/datasheet-pdf/pdf/131200/ETC1/7815.html
7915: http://www.alldatasheet.com/datasheet-pdf/pdf/432062/SEME-LAB/LM7915.html
7812: http://www.fairchildsemi.com/ds/LM/LM7812.pdf

Tempus, if you see this, I've updated the rectifier diodes connections.

[tempus]

Have you updated the voltage readings on your schem, or are those the old ones? If they are current, we obviously still have issues in the power supply section, because none of the regulators are getting enough voltage to actually make them work, and the 7815 is mysteriously putting out more voltage than it's getting in. Can you find connections for pins 1, 7, and 8 on the tube?

[stonerbox]

Yeah, all the voltages is up to date on the current layout. I bet the voltages is set to the wrong pins.
ReG3 7915
Ground: 0
Input:-12VDC
Output:-10VDC

I can't for the life of me figure out where pin 7 and 9 on the tube goes. Pin 7 reads +9VDC and pin 9  +4.5VDC. The meter does not give any resistance readings on any resistor, cap, amp, transistor or ground?? Same thing goes for pin 1, but at least pin 1 does not give off any voltage which could indicated it is grounded?

Updated layout (the tube voltages are back, had by mistake hidden that layer in Photoshop).

[tempus]

OK 1st things 1st. We need to diagnose the power supply problem. According to your diagram. the input of 7815 is connected to the cathode of D10, which has 12v on it. It's also connected to the anode of D6 (through the 39 ohm resistor) which has 24v sitting on it. Somehow, the input of the 7815 only has 10v on it. Let's sort that out 1st. Is the pinout/voltage reading on the current schematic correct? If so, can you remove (carefully) the cathode end of D10 from the board and take a measurement on the cathode with it removed?

Next, the input of the 7915 is connected to the cathode of D9, which reads 0v DC. However, we can see that the anode of D9 has 12vAC, which should give us some DC on the cathode. Further, the anode of D9 has -13vDC, but the cathode of D8 (which according to your schem it is connected directly to) shows 11vDC. Something is clearly wrong there. In this order, can you:
1. remove the D9 cathode from the board and check the anode and cathode voltages (AC and DC) with it disconnected
2. remove the 7812 from the board and check the voltages (AC and DC) at the cathode of D8

Don't reconnect anything until we sort that out.

As for the tube, pins 1 and 6 are the plates, which I'm pretty sure should have a much higher voltage on them. I'm no tube expert, but if there is supposed to be 90v in this circuit, it's probably on the plates. Pin 1 should not be grounded.

[stonerbox]

The input on 7815 reads 12V, the voltage values was in reversed order, now fixed. I removed the cathode side of D10 but R32 and the 7815 input still reads +12V.

Ok, another error in the layout. It's hard to find all connections on this board since it is both connections underneath and above the board (under the components) making it real hard to spot some of them. Please take another look.

[tempus]

I think you misunderstood me. Can you measure the voltage on the cathode i.e., touch the probe of your meter to the leg of the diode that you disconnected from the board. Same thing with the other measurements - measure the leg of the diode that's been removed.

[stonerbox]

oh, sorry my bad.   The voltage on the cathode of D10 reads +4VDC/+13VAC.
D9 +2VDC/+7.1VAC and D8 +6.1VDC/+14VAC.

I burn my finger when touching the 7812, even though it only regulate the voltage down 3v. Hm..?

[tempus]

Something's got to be shorted somewhere, I would think. That regulator will get hot when too much current is being drawn, and of course voltages sag when too much current is drawn as well. On top of that, it's not getting the 15 or so volts it should be to actually regulate. Try and check for shorts or too low resistances across any of the power lines (with the power off though), and I'll mull over this diode stuff and decide our next course of action.

Is C27 testing OK?

[stonerbox]

I'll check the power lines for anything strange. The resistance through C27  (brand new cap, 25v 1000uF) drops after awhile but very slow and very little, I'll change it for another one and see what happens.

..Nope, made no difference.

[stonerbox]

Found something strange here.. when I checked resistance/connections on the board I found out that all U4s ( LM339n ) pins are more or less connected to every single pin of U3 ( NE5532 ).

[tempus]

What voltage readings to you get at the power supply pins of those 2 ICs? What about the other pins?