Home audio amp wont start

[scampo77]

I have enclosed a schematic and diagrams of measurements I have taken so far. I had this on another thread and I am hoping to breath life back into it. I really would like to get this thing fixed.

on the power standby board I don't seem top have 110v going into the main transformer. (CP302) which in turn is not giving me 12v to the digital board (CP1304)

I seem to have 10v and I also found 5v on the STBY board I am just not sure where it is coming from.

I don't seem to have any standby voltage, I don't have an LED light on or anything

I could sure use a hand to chase this problem down.

[mariushm]

Re: Home audio amp wont start

AC power comes in and goes through that standby transformer PT301 and then gets rectified by those diodes D303-D308
From there, it goes to that CN701 connector CPU_ST_VCC and gives 10v or whatever is there
From the same rectified DC, it goes into IC301 , a 1117-3.3 linear regulator , which does 3.3v for [5] in CN701

This standby circuit is supposed to give power to a processor, which checks that everything's ok and when you turn the amp on, it sends a signal to the relay through [8] in cn701, making it turn on and couple the AC voltage to the big transformer for the rest of the amp.
So it's normal that you don't see 110-120v on the big main transformer, the cpu doesn't pass all tests, something's happening before that.

According to the datasheet you should have about 12v on hdmi 12v and cpu_st_vcc, they're all coming from the D303-D308 diodes. The amp may not start because the voltage is too low at 10v.

Measure AC voltage at PT301 right before those diodes D303-D308, measure the DC voltage after the diodes, check the diodes, check that 2200uF 16v capacitor right before the 3.3v regulator
It might be going bad and drag down the DC voltage from the transformer.

[scampo77]

Re: Home audio amp wont start

Thank you very much for the quick response, i have been soldering like a madman.

all of the diodes have been de soldered verified as good and re installed

I have 8.7v AC coming out of the Transformer before the diodes and I measured 9.85vDC after the diodes.

I pulled the cap out at loc 301 and that is where I measured 9.85vDC from. I left the cap out for now. I have another one here as a replacement I will put it now.

I have an ESR meter here I just need to find a 9v battery for it for any further testing.

With my black test lead on the pin "cpu gnd" and the red lead on the middle pin and tab of regulator at loc IC301 has 3.315 vDC , and 9.85vDC on the other

[scampo77]

Re: Home audio amp wont start

Here is the schematic. It is too large to upload it here directly

[mariushm]

Re: Home audio amp wont start

Ok then, looks like you really have about 10v there, not 12v. Put a capacitor there, otherwise you'll have DC voltage that goes down and up as the AC voltage is rectified, a capacitor will smooth out this voltage.

You have there in the flow pdf the no power section where it says refer to "how to cancel the status after detection of dc error"
Read what it says.
Then go with the DC Troubleshooting section but assume that anywhere it says 12v, you actually have 12v and not 10v. Check what it says on those boxes.

Alternatively, if you want to make sure it's not a 12v issue, you could get 12v from a computer power supply and power that amp from it. You would just have to pull out those cables from the connector (hdmi and cpu_st_vcc) and connect to those points in the connector 12v from your other power supply.
This would at least confirm it's not an issue of having too low voltage on that connector.

[scampo77]

Re: Home audio amp wont start

I started by applying 12v from an external source. (12.11v) I did not bother pulling the wires I just soldered it right to the board and now i have solid 12v going out to the

in section 3.4 "how to cancel the status after detection of dc error" it said hold power and advancd surround at the same time for 2 seconds. when i did this the main relay in the standby board engauged and blew a fuse. it took 3 fuses till it went back to sleep. Now I can plug it in again without blowing a fuse.

I went to the other flow chart chasing down my 12v. at pin 2 of IC1305 i have .8v

where is this 12v coming from? is there a regulator somewhere like the 3.3v?

[scampo77]

Re: Home audio amp wont start

I think I made some progress.

I unplugged the wires going to the amplifier board and left just the cpu wires hook up, to the amp board.

with 10.1v on VCC I can start the amp and get it to display "overheat" on the display. then shut off. If I hook the wires to the amp board it just instantly blows a fuse.

Also I am getting 3v on pin 85 and 0v on pin 34, 71