Green pre woes....

[Ptownkid]

I understand the visual part of looking for shorts, but is there a way to test that?

Also, i'm still at a loss as to why I get 56v on my 48v pin.

 

[peterc]

I understand the visual part of looking for shorts, but is there a way to test that?

A short is 0 ohms or close to it. Take your meter, set it to the lowest ohms range, probably 200ohms, & test the connection you want to check.

So here we want to check to see if the power supply rails are being shorted. Take the black probe & put it on the 0v connection. Take the red probe & put it on the +ve connection. What is the reading?

Do the same with the -ve rail.

Example : If it is 1ohm, then Ohms law gives you 15v/1ohm = 15 amps. Your power supply cant handle this, hence the blown regs. OK, I dont know what the reading will be in your case, but this is the principle.

By doing this, we are purely looking for a short circuit. You cant look at the reading on the multimeter & say "this is accurate", because it will change when power is applied.

Always apply power the first time without the IC's inserted. Use the voltage chart I supplied to verify the voltages on the IC pins. This will show up power rail shorts as well. If these readings are correct, your circuit will most probably work correctly.

Also, I'm still at a loss as to why I get 56v on my 48v pin.

Some regulators need current drawn thru them to work. If you have nothing connected to the 48v rail, no current is being drawn.

Also check for a short between the input & output pins of the regulator.

Peter

 

[Ptownkid]

I don't have that voltage chart, where migght i find this.

And thank you for the detailed explaination, this is a great learning experience, frustrating, but good for me in the long run. If everything had worked perfectly I wouldn't have learned too much.

Thank you all for your patience.

 

[peterc]

It's with all the docs in the Meta on Mendelt's site

 

[Ptownkid]

ok here are the 5532 socket readings, obviously not right...

Pins 1-8 leftmost 5532, center 5532, rightmost 5532


13.3
15.3
15
-15.2
15
153
13.3
15.3

13.3
13.3
13.6
-15.2
13.2
11.4
11.5
15.3

13.7
13.8
13.8
-15.2
13.8
13.6
13.6
15.3


The only numbers that are correct are the -15.2's

I've checked everything I can think of and still no solution.

 

[Mbira]

I've checked everything I can think of and still no solution.

So does that mean that you have replaced all the bad resistors, checked for shorts, found no shorts, and that resistors don't smoke now? If so, then you have made a step in a positive direction.

Joel

 

[Ptownkid]

well, i check all the resistors, and the power supply seems fine, but all those number are hella wrong.

 

[Mbira]

Turn the Pre off.
Take the IC's out.
Disconnect the power supply.
Get out your volt-meter.
Set it to Ohms.
Put one wire on the four pin connector (where the power comes in from the power supply.).
Put that one against the ground input.(the second pin from the bottom of the four.
Put the other lead to the +15 side.
What does your meter say?
Put that wire now to the -15 side.
What does your meter say?
Is there a short?

Joel

 

[Ptownkid]

you mean on the preamp card right?

My meter doesn't read anything, right when i touch the +15 or -15 pins, a random number flashes on my meter and then ir reads nothing, no value, not zero, it just does't read anything.

 

[dustartist]

Have you been following my troubles with one of my Green channels? The thread is a few lines down. I don't have the same voltages you do, and I'm using a different version of the PCB, but I have similar problems. It seems like you are getting voltage on Pin 1 and 7 that shouldn't be there. That is getting passed along to the other ICs. If you find out where the voltage is coming from then you will be on the right track. That said, I haven't found my problem yet, but I'm working on it now.....

 

[Ptownkid]

Peter - Do you know what is causing me to get those wierd voltages?

It's one page back at the bottom.

 

[peterc]

Without having the PCB in front of me, it's impossible to tell.

With whats happened on your PCB, there could be a number of problems.

Have you built up all 4 boards yet? I think it would be best to build another, get it working, & then have the 2 side by side & where voltages differ, to then fix those areas.

Peter

 

[Ptownkid]

Ok, i'll try that

 

[HappyTom]

Are you sure you have wired the power right?
I tried to flip the four cables around and got the 48V cable where the +15V should be and the 0V where the -15V should be. A couple of caps and resistors were blown when i powered it up...

HT

 

[Ptownkid]

No, i've tested the psu extensivily, and made sure to read what wire was going to what value, not just pin 1 pin2 pin 3 and pin4.

 

[Ptownkid]

So i built a third channel tonite, and all the pin volatages are actually right, checked for shorts, scanned the whole thing at least 5 times, great time to fire her up.

Well guess what, same two freakin' 10R resistors start smoking, i don't know what the else to do. I can't find any shorts, i'm getting the right pin voltages, I'm getting the right psu voltages, withe the exception of +56 instead of +48


arrrrrrrrgggghhhhhh

 

[Ptownkid]

woooooohoooooooo


We have sound!!!!!! And no smoke!!!!!!!

Ok so are you all ready for this, I thought all the ics went in in the same orientation, i didn't realize that the ne5532's went opposite to the 339 and the 074, damn eh?

However, i get a pretty loud hum, so where do I start checking now?

I'm assuming it a grounding thing.

One of em has no hum, but lots of air, even at low gain and my leds don't work at all anymore.

 

[peterc]

Are you using the same 5532's? If you are, this is probably the problem.

Peter

 

[Ptownkid]

what do you mean by the same?

 

[Ptownkid]

I'm assuming you mean i may have hurt them? I think the problem was post ne5532 was it not? I'll try brand new ones tonite.

Also, how do i figure out how many maps the ac ffilter needs to be, i want to use one witha fuse, someone said it's Transformer Va divided by secondary voltage, is that right?