Philips FR-740 working but no audio output

[seve91]

Hi everyone,
i got this Philips FR-740...it powers on, i can see the front display, but no audio output at all.
No burning components on the motherboard. Any suggestions?

Here there is the service manual

https://elektrotanya.com/philips_fr7.../download.html

thanks

[CapLeaker]

Does it power on normally, or is it some error like protect? If it powers up with no error, maybe something is stuck in the head phones jack?

[R_J]

plug in some headphones to see if there is sound from the headphone jack

[seve91]

Originally Posted by CapLeaker

Does it power on normally, or is it some error like protect? If it powers up with no error, maybe something is stuck in the head phones jack?

Originally Posted by R_J

plug in some headphones to see if there is sound from the headphone jack

No, it powers on normally, no errors.
No items or other stuff inside the headphones jack.
Inserting IN and OUT the headphones is correctly detected.
For example with headphones connected, i cannot enable the surround mode, because it says (take out headphones first).
If i disconnect headphones, then i can enable surround mode.
Headphones are working good, very good and clean sound.

[R_J]

Looks like if it has audio to the headphones, there should be audio getting to the input of the stk ic's. Did you try all the outputs? meaning the sorround speakers as well.
I guess check and make sure you have + & - 40 volts to the ic's, then I would check the solder connections on the ic's sometimes they break
Since its not in protect I would think there is 0 volts at the + of all the speaker terminals, maybe check and make sure.

[seve91]

Originally Posted by R_J

Looks like if it has audio to the headphones, there should be audio getting to the input of the stk ic's. Did you try all the outputs? meaning the sorround speakers as well.
I guess check and make sure you have + & - 40 volts to the ic's, then I would check the solder connections on the ic's sometimes they break
Since its not in protect I would think there is 0 volts at the + of all the speaker terminals, maybe check and make sure.

Yes i tried all the output speaker (2 front, 2 rear, 1 center).
+40V and -40V is present in both STK, solder connection looks perfect.

These voltages are printed in the philips schematic:

STK496-070 (i have STK496-090 in the pcb):
9 = 39,5V
3 = 40V
8 = -39.5V
12 = -33.6V
1,2 = -40V
4,5,6,7,10,11,13,14 = 0V

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

Measured those values, all verified. But -33.5V and +-39.5V is a little bit higher, cause voltages are 40.2V.

[seve91]

advices?

[seve91]

please any help?

[stj]

any schematics around?
philips used to sell the service manuals so someone must have scanned one!

[seve91]

sure, here is the link:
https://elektrotanya.com/philips_fr7.../download.html

but can't figure it out what is the problem. Voltages seems to be all present. Maybe the final amplifier are broken

[stj]

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!

[seve91]

Originally Posted by stj

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.

[R_J]

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

[seve91]

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

[seve91]

any help?

[R_J]

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]

Originally Posted by R_J

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]

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]

Pin 6 always 0, pin 7 alway 4.9V

[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)