Sony Str-Db 840 Completely Dead

[coojoe_213]

Hi everyone. My amp is dead, no std by, no relay click. All fuses is perfect, primary on main transf. is excellent.

On the AC Board, after diode on pin 2 (12V) i have 16v, pin 3 (P_OFF) i have 12 v, and pin 4 (P.RY)i have 0V. All diodes, fuses and resistors on AC Board are fine.

On IC1206 (NJM2103) pin 5 i have 16v, but on 8 pin i have 0V.
On Q1205 i don't have 6.8v/6.2v only 16v on the collector.

My question is... in this amp, which parts /elements/ responsible for stand by voltages. I have 0.7v on stand by, but i can't see on service manual, where is a stand by supply (5v)?

[redwire]

Re: Sony Str-Db 840 Completely Dead

Q1205 should always be on and making standby voltage. IC1206 NJM2103 pin 3 turns off Q1205 when the voltage is up: When the amplifier is on, then IC1205 takes over to provide +5.6V B+.
P_OFF is 1/2wave rectified pulsing DC.

If Q1205-E is 0V then R1279 should turn it on. Either Q1205 has failed or IC1206 is keeping it off. I think the transistor is bad, usually Sony has no heatsink and they run hot.

[coojoe_213]

Re: Sony Str-Db 840 Completely Dead

I don't think Q1205 is bad. If i have 5v on pin8 ic1206 decided all is normal in proccessor, after that IC1206 switch 6.8v on pin 3

[coojoe_213]

Re: Sony Str-Db 840 Completely Dead

I replace q1205, but all is the same.

[redwire]

Re: Sony Str-Db 840 Completely Dead

First, check the power supply voltages- they are always on from the +12V.
+3.3V IC1203 , +5V IC1204 , +5V IC1208 , +5V IC1207, +6.2V IC1205 which makes +5.6V

I would follow the signal from power button pg. 29 CN5106 pin 7 turns on display controller AND signals IC1201 at pin 105.

[budm]

Re: Sony Str-Db 840 Completely Dead

What DC V do you have on the Base of that Q1205?
Whar RESISTANCE do get between GND and Emitter of Q1205?

[coojoe_213]

Re: Sony Str-Db 840 Completely Dead

First, check the power supply voltages- they are always on from the +12V.
+3.3V IC1203 , +5V IC1204 , +5V IC1208 , +5V IC1207, +6.2V IC1205 which makes +5.6V

I don't have any voltages on +3.3V IC1203 , +5V IC1204 , +5V IC1208 , +5V IC1207. On service manual i will have this voltages when main transofrmer work. Main transformer will work when relay RY901 ''close contacts''.

What DC V do you have on the Base of that Q1205?
Whar RESISTANCE do get between GND and Emitter of Q1205?

- On the Base of Q1205 I have 1.28V, emitter 0.78V.
Resistance between GND/Emitter Q1205=8.3Kohm

[budm]

Re: Sony Str-Db 840 Completely Dead

Can you please report the Voltages on each pin of the IC1206?
We already know that
pin 3 is 1.28V
PIN 8 is about 5V (that is an open Collector, I wonder if that pin did go low during reset).

[coojoe_213]

Re: Sony Str-Db 840 Completely Dead

Can you please report the Voltages on each pin of the IC1206?
We already know that
pin 3 is 1.28V
PIN 8 is about 5V (that is an open Collector, I wonder if that pin did go low during reset).

IC1206 Voltages:
1 - 1.33V
2 - 0.25V
3 - 1.28V
4 - GND
5 - 16.5V
6 - 2.79V
7 - 1.26V
8 - 0.85V /When i press Power button, the voltages on pin 8 are again 0.85v/

[redwire]

Re: Sony Str-Db 840 Completely Dead

I got the wire crossed reading schematic. Transformer T902 is always powered, making +12V which goes to Digital Board ripple filter Q1205, not the Vreg cluster.

Q1205 is a 2SD1733 Darlington, but OP is measuring only 0.5V E-B voltage, so is it the correct part or it's hFE is too low?

Or with pin 3 not up, I'm wondering if the ripple filter is driving a shorted load.
Q1205 would get hot then.

IC1206 is open-collector so I can't see it pulling down to 1.28V

[coojoe_213]

Re: Sony Str-Db 840 Completely Dead

I got the wire crossed reading schematic. Transformer T902 is always powered, making +12V which goes to Digital Board ripple filter Q1205, not the Vreg cluster.

Q1205 is a 2SD1733 Darlington, but OP is measuring only 0.5V E-B voltage, so is it the correct part or it's hFE is too low?

Or with pin 3 not up, I'm wondering if the ripple filter is driving a shorted load.
Q1205 would get hot then.

IC1206 is open-collector so I can't see it pulling down to 1.28V

Q1205 is NOT Darlington

[redwire]

Re: Sony Str-Db 840 Completely Dead

Q1205 is NOT Darlington

From service manual: Q1205 8-729-048-78 TRANSISTOR 2SD1733-TL-QR
Panasonic datasheet is Darlington TO-220
Rohm datasheet is BJT 80V 1A 2W hFE 82-390 DPAK

Does Q1205 get hot?

[coojoe_213]

Re: Sony Str-Db 840 Completely Dead

2SD1733 is a NPN silicon transistor, not darlingon. You can see your web link / / is wrong. 2sd1733 is not hot, absolutly cold.

[redwire]

Re: Sony Str-Db 840 Completely Dead

Q1205 is off (and assume it is a good part), check C1218 shorted, high value R1279, C1221 low capacitance.

Or... IC1206 bad and keeping Q1205 off.

When pin 2 is above 1.235V, pin 3 goes low which turns off Q1205.
The datasheet shows the comparator used as a shunt voltage regulator, which I think is what's going on here.

Otherwise, check the 0.1uF capacitors- but I don't expect these to fail or we have to use a scope.

[coojoe_213]

Re: Sony Str-Db 840 Completely Dead

I check before 5 days c1218 and R1279, they are fine.
C1223/C1225/C1222/C1224 are SMD elements, and i can't check with my esr meter.

[redwire]

Re: Sony Str-Db 840 Completely Dead

I think IC1206 is not working, if as you say Q1205 is good.
You could put oscilloscope on pin 3 and see if it is steady DC, or oscillating if C1221 or other capacitors are bad.

IC1206 maximum VDD 20V and right now you have 16V, so a mains surge might have damaged the IC.

Maybe budm has other ideas to try.

[coojoe_213]

Re: Sony Str-Db 840 Completely Dead

I remove IC1206 to check voltages without this chip. When i remove IC1206 relay901 close contacts????
Voltages on IC1206 without IC1206:
1. - 0V
2. - 1.67V
3. - 9.07
4. - GND
5 - 9.36V
6. - 1.82V
7. - 1.51V
8. - 6.85V
What do you think?
Do you know any equavalent on NJM2103? I my country there is no any chip NJM2103.


EDIT: Now /after 20 min/ relay RY901 doesn't close contacts without njm2103

[budm]

Re: Sony Str-Db 840 Completely Dead

I wonder why the VCC pin 5 only shows 9.36V without the IC in place. I need to look at that schematic again.

'EDIT: Now /after 20 min/ relay RY901 doesn't close contacts without njm2103' Try using 100 Ohms resistor momentary between GND and the Reset pad and see what happen.

[redwire]

Re: Sony Str-Db 840 Completely Dead

Um, don't run it with the IC taken out!
Q1205 will be full on and overvoltage the standby rail. So you are getting 9V, not 6.2V at Q1205 emitter. Which means B+ is 8.4V not +5.6V
Vcc pin 5 sags down to 9-10V when loaded I think, and up to 16V with no load.

If you cannot get a new NJM2103, I would put in TL431 or a 5.6V zener to regulate Q1205 output (emitter) at 6.2V max.

Then you just need a RESET pulse circuit.

[budm]

Re: Sony Str-Db 840 Completely Dead

You can put in 6.8v Zener of the transistor so the Base Voltage will be 6.8V, that will give you about 6.2V output at the Emitter since it is an Emitter follower circuit, output = Vzener - Vbe.