Switch mode in powered mixer.

[argonrepublic]

I am working on a Powered mixer made by Phonic.
I have no power to preamp or DSP. I followed back to Primary portion of Power supply and found there a 7815 that is getting 120VAC unless I have measured incorrectly. Further, AC1 has 120VAC to chassis and AC2 has .5VAC to chassis.
Any advice would be greatly appreciated.
Thanks

 

[JOHN BALI]

Hi argonrepublic
first I will disconnect all load then measured all voltage output, are they normal?
me or other can help if there any picture of this

 

[johansen]

Assuming you live in an area where line power is 120 ac line to neutral, and neutral is connected to ground, and so is the chassis of your mixer, then your line measurements are what you would expect.

However, do not assume that the chassis is connected to the mixer circuitry. Obviously, 120vac on a 7815 should blow it open/light it on fire, that sort of failure.

 

[argonrepublic]

I was kind of thinking that I may be catching the wrong ground. I place neg probe of meter to circuit board and pos to 7815 and did not find less than 120VAC. No signs of damage. At one point I used my hand to slight bend 7815 to gain access and got 120VAC shock from to of 7815 didn't expect that. I will keep looking to find the proper ground.

 

[argonrepublic]

I was able to find a ground to get 15V from 7815. It is on the -output of a rectifier. It appears strange that when I checked the Rectifier, It is showing 27.6VAC and 320VDC. I understood that a rectifier should have more dc coming out than AC going in. What is going on here. What am I missing?

 

[argonrepublic]

I have +34VDC-ground and -34VDC on one connector.
On the other, I have 12VDC and ground.
I have been able to determine beyond doubt that I am missing +/-15VDC for TL074s as well as dsp on preamp board witch was my original concern. Please advise me what to look for. I cannot see the forest through the trees. I have no schematics and there are no obvious 7815 and 7915 regulator that I am accustomed to seeing on this type of system.
Thanks

 

[Burnedfingers]

Quote:
I followed back to Primary portion of Power supply and found there a 7815 that is getting 120VAC


I'm confused here... in the prior post of your you said there is a 7815 getting 120vac then you say I have no schematics and there are no obvious 7815 and 7915 regulator that I am accustomed to seeing on this type of system.

Is there or isn't there a 7815 and 7915 regulator?

Check the TL074's for + and - supply again got to be there but it might be down in the dumps.

 

[argonrepublic]

There is a 7815 on the power supply. I am now working on the amplifier board which has a connector that goes to the preamps. Evidently, there is 7815 and 7915. I overlooked them because they were discretely mounted between outputs.