Philips FR-740 working but no audio output

[seve91]

Originally Posted by R_J

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

[seve91]

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

[R_J]

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]

Originally Posted by R_J

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]

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]

Originally Posted by R_J

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]

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

[seve91]

Originally Posted by R_J

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]

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]

Originally Posted by R_J

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]

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]

Originally Posted by R_J

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)

Yes exactly, test = pass and format = new.
Tried to connect anode 6305 AMP IR ON to AMP S ON that was at 5.2V, but now they are both 0.4V

I tried also to desolder the anode from the mainboard to disconnect it from the circuit, and solder the anode directly to pin 2 of 1426 (5.2V).
Now i have 4.6V on that pin, but no audio. Could 7309 be in short?

[R_J]

did you check the voltages on 7309, there should be 3.1 volts on the emitter, if not that 6304 zener could be shorted, did you check any of those transistors like 7309, 7304, 7902

[seve91]

these are the voltages measured:

7309: E= 3.4V, B= 3.05V, C= -1.4V
7304: E= -40.3V, B= -39.6V, C= -40.3V
7902: E= -40.3V, B= -39.6V, C= -40.3V

[R_J]

I wonder if 7309 is'nt bad, there should be -34.5 volts on the collector. I guess you could check the 2 100k's 3329 & 3936
-------from other post-------
ok, page 79:
A of 6305: 0V
K of 6305: 3.2V
C of 7309: 0.04V <------------the schematic indicates there should be -34.5 volts here
C of 7304: -41.5V
C of 7310: -41.5V
--------------------
I see from before
STK496-270
11 = 39,5V
14 = -33,5V
10 = -39,5V
3,4,19 = -40V
7,8,9,12,13,15,16,17,18,20 = 0V <------------pin 12 listed as 0 volts
7309: E= 3.4V, B= 3.05V, C= -1.4V
7304: E= -40.3V, B= -39.6V, C= -40.3V
7902: E= -40.3V, B= -39.6V, C= -40.3V <-------7902 (C) listed as -32V
check the voltage on resistor 3918 and then 3935

I checked a data sheet for a STK486-430 and the CCC pin only changes BY 2 volts between amp on and amp off (it uses -50v amp ON -52v amp OFF)

[seve91]

Originally Posted by R_J

I wonder if 7309 is'nt bad, there should be -34.5 volts on the collector. I guess you could check the 2 100k's 3329 & 3936
-------from other post-------
ok, page 79:
A of 6305: 0V
K of 6305: 3.2V
C of 7309: 0.04V <------------the schematic indicates there should be -34.5 volts here
C of 7304: -41.5V
C of 7310: -41.5V
--------------------
I see from before
STK496-270
11 = 39,5V
14 = -33,5V
10 = -39,5V
3,4,19 = -40V
7,8,9,12,13,15,16,17,18,20 = 0V <------------pin 12 listed as 0 volts
7309: E= 3.4V, B= 3.05V, C= -1.4V
7304: E= -40.3V, B= -39.6V, C= -40.3V
7902: E= -40.3V, B= -39.6V, C= -40.3V <-------7902 (C) listed as -32V
check the voltage on resistor 3918 and then 3935

I checked a data sheet for a STK486-430 and the CCC pin only changes BY 2 volts between amp on and amp off (it uses -50v amp ON -52v amp OFF)

the resistors are all SMD and all are in good conditions.
Voltages:
3329: -39.6V (B of 7304) and -1.44V (C of 7309)
3936: -39.8V (B of 7909) and -38.15V (to 4910)
3918: -40.28V (to 3935) and -40.27V (C of 7902)
3935: -40.16 (C of 7909) and -40.18V (to 3918)

is it possible that one of these transistors is not working good?
I don't know if it can help, but every time i touch the tip of oscilloscope probe to C of 7310 (pin 14 CCC of STK496-270) i can hear a click coming from the speaker (i have connected a speaker, just to test, to the Front L output)

[R_J]

That voltage on the collector of 7309 is way too low, the schematic says it should be -34.5 volts,
Whats on the base of 7902, it should be -35 volts
7309 could be leaky e-c killing that voltage
Like said about the other stk486-430, it seems to only take a 2 volt difference on the ccc line to turn it on or off.
You have -40v on ccc line, the schematic says it should be -33.5v

[seve91]

base 7902 = -40V

so what could be the next step? try replacing a transistor?

[R_J]

7309 could be bad cap 2365 could be bad, something is killing that voltage. all the other voltages seem to be close except this one. and it is the "AMP ON/OFF CIRCUIT"

I checked the schematic for a FR975, which is similar (more power) and that same circuit shows a negative voltage on transistor 7309 that is more than the 1.44 volts you measure there. so I assume the schematic is correct

[seve91]

i know that the voltage on C of 7309 is wrong, but i don't know how to fix it.
I'm trying to desolder and test.
Desoldered cap 2365, nothing changed. Cap tested with ESR meter, is good.
Resoldered the cap back and desoldered 7309.
So as you said, 7309 was E-C shorted, because now on C of 7309 i got -36.6V (without the 7309).
So i need to order a replacement for sure. But probably there is another fault in the main board or in the front board