Philips FR-740 working but no audio output

[R_J]

Re: Philips FR-740 working but no audio output

That does'nt seem like it works right, so TEST EEPROM = PASS
and EEPROM FORMAT = NEW
Well the reason the amp is not turned on is the missing +4.9V on diode 6306 (page79) amp lr on.
I guess you could lift the anode of diode 6305 and feed it +5 volts to see if the amp turns on and is ok. You could have a bad 7412 (hef4094bt)

[seve91]

Re: Philips FR-740 working but no audio output

That is because the scope is not grounded, if you place the probe anywhere you will see that, if you touch the probe with your finger you will see that also
Didi you ever check the voltage on (page 78) transistor 7253, base should be 0 collector 5 volts or measure on (page34) plug 1426 pin 2

Did you ever run the Service Test Program ? (page 27) and (page 28) various other tests, and run those two tests, the last one should reset to factory.

yes 0V on E and B of 7253, 5.12V on C of 7253 and pin 2 of plug 1426.
Done all the tests, all is ok except for tuner test. If i press TUNER it goes immediately in tuner mode (it exits from service mode instead of doing the test, but with headphones i'm sure that tuner is working good, i can listen to the radio).
Done the factory reset, but still no audio.

[R_J]

Re: Philips FR-740 working but no audio output

That is because the scope is not grounded, if you place the probe anywhere you will see that, if you touch the probe with your finger you will see that also
Didi you ever check the voltage on (page 78) transistor 7253, base should be 0 collector 5 volts or measure on (page34) plug 1426 pin 2

Did you ever run the Service Test Program ? (page 27) and (page 28) various other tests, and run those two tests, the last one should reset to factory.

[seve91]

Re: Philips FR-740 working but no audio output

I don't think the cpu is bad, but something is preventing it from turning on the amp.

and how i can find the fault?

I found out a strange thing when measuring pin 6 with the oscilloscope probe.
If i connect the ground of the probe to the chassis of the device, i got 0V.
If i disconnect the ground of the probe (and i leave it free, without connecting) it detects this signal from pin 6.
How is it possible?

[R_J]

Re: Philips FR-740 working but no audio output

I don't think the cpu is bad, but something is preventing it from turning on the amp.

[seve91]

Re: Philips FR-740 working but no audio output

On page 78, MFD looks like it should be 0 volts on base of 7253 (power down circuit) and the collector should be +5 volts (amp pd)
A lot of the voltages are marked so make sure they are all ok, the only one I can see that is not right is that {amp lr} line, it should be +5 and its 0 so the main amp ic's are not turned on.
That amp lr line is controlled by one of the output lines of ic7412 (page 34) and that ic takes data in to control the output lines, so something (microprocessor) must not be telling it to turn on pin 6,

Pin1,2,6 of IC7412 are 0V. So i need to replace the CPU 7415?

[R_J]

Re: Philips FR-740 working but no audio output

On page 78, MFD looks like it should be 0 volts on base of 7253 (power down circuit) and the collector should be +5 volts (amp pd)
A lot of the voltages are marked so make sure they are all ok, the only one I can see that is not right is that {amp lr} line, it should be +5 and its 0 so the main amp ic's are not turned on.
That amp lr line is controlled by one of the output lines of ic7412 (page 34) and that ic takes data in to control the output lines, so something (microprocessor) must not be telling it to turn on pin 6,

[seve91]

Re: Philips FR-740 working but no audio output

I think +4.4 for the amp protect line is for normal operation, I suspect a low would tell the amp to be in protect?
If the amp lr line is not high (+5 volts) then the amp on circuit will not be told to turn on, I can't see what conditions need to be met for the micro to say turn on the [amp lr] line?
It looks like the voltages marked on the schematic are for normal operation (bottom right of page 80)
Do you have the remote? can you turn the Mute on and off?

It sure looks like something in the menu somewhere has turned the amp off

Yes i can turn MUTE on and off with the remote. In the menu there are not many options...volume is balanced to 0 for all the speakers.

[R_J]

Re: Philips FR-740 working but no audio output

I think +4.4 for the amp protect line is for normal operation, I suspect a low would tell the amp to be in protect?
If the amp lr line is not high (+5 volts) then the amp on circuit will not be told to turn on, I can't see what conditions need to be met for the micro to say turn on the [amp lr] line?
It looks like the voltages marked on the schematic are for normal operation (bottom right of page 80)
Do you have the remote? can you turn the Mute on and off?

It sure looks like something in the menu somewhere has turned the amp off

[seve91]

Re: Philips FR-740 working but no audio output

so this means that the AMP is in protection due to a short or something?

[seve91]

Re: Philips FR-740 working but no audio output

On plug 1410 pin 11 amp prot (page 34) do you have 4.4 volts? Its hard to follow where things connect in this old type pdf (can't search)

Yes, 4.5V present

[R_J]

Re: Philips FR-740 working but no audio output

On plug 1410 pin 11 amp prot (page 34) do you have 4.4 volts? Its hard to follow where things connect in this old type pdf (can't search)

[seve91]

Re: Philips FR-740 working but no audio output

Pin 6 always 0, pin 7 alway 4.9V

[R_J]

Re: Philips FR-740 working but no audio output

looks like ic 7412 is working, Do those other lines change like the Amp lr on (pin 6 of 7412) or mute (pin 7) Those lines could be checked on plug 1410 also

[seve91]

Re: Philips FR-740 working but no audio output

It looks like the comand from the front panel is not turning on the amp, I think A of 6305 should be around 4.5 volts not 0
On page 34 the Amp lr on comand comes from ic7412, I see there are also a couple led's off that ic, dvd & Surr, is it posible to comand those led's to change from the front panel? to make sure the ic is receiving comands.

Yes, both leds are working DVD is on when input 6CH/DVD is selected. SURR is on when you push surround button (surround is not available in 6CH/DVD mode)

[R_J]

Re: Philips FR-740 working but no audio output

It looks like the comand from the front panel is not turning on the amp, I think A of 6305 should be around 4.5 volts not 0
On page 34 the Amp lr on comand comes from ic7412, I see there are also a couple led's off that ic, dvd & Surr, is it posible to comand those led's to change from the front panel? to make sure the ic is receiving comands.

[seve91]

Re: Philips FR-740 working but no audio output

any help?

[seve91]

Re: Philips FR-740 working but no audio output

ok, page 79:
A of 6305: 0V
K of 6305: 3.2V
C of 7309: 0.04V
C of 7304: -41.5V
C of 7310: -41.5V

[R_J]

Re: Philips FR-740 working but no audio output

On page 79, whats the voltage on Q7310 collector? Also check if the amp on/off circuit is working.

[seve91]

Re: Philips FR-740 working but no audio output

page 16,
make sure all 6 volume settings are centered.

page74 shows the audio leaving the input selector into the amp circuits through an electrolytic.(2541,2542)
i would scope or tap off of that to see if the audio is making it through the switching section first.
this is a complex bastard, but atleast the schem's are readable!

page 16, all volumes centered.
page 74: i have signal on both 2541 and 2542. Checked the output of the opamp (pin 1 and 7), signal is good.
page 75: i have signal on inputs of TDA7437, front and surround ok
page 76: i have signal on 2534 and 2535, no signal on 2536-2537.
page 79: i have signal on 2310-2316, and also 2334 if i enable surround. no signal on 2905-2913 even with surround on.