OK, well R904 is good. And the relay works, I tested it with a 9V battery before, and the coil reads near 0 ohms. So I guess I'll just test it when I put in the new relay drive. Btw, I did order more than one, just in case something else is causing it to go bad and I need to do more troubleshooting. 
I don't know.... it's a 9V relay. But it does work. I rigged up a relay tester which applies 9VDC to the coil, and the switched connection to light an LED and it works fine. But, could the low resistance of the relay cause problems with the transistor? I also measured the resistance between the poles of the transistor and each way was about 41ohms on the poles which beeped on the diode test. Could it be that the transistor is supposed to be like that?
I think a ballpark figure for a 9v relay would be about 200 ohms out of circuit, allowing 400mW to power the coil. If the coil is near zero ohms (out of circuit) it could be drawing far too much current through the transistor. Relay coils I suppose could short, but I can say I've run across one.
Hi rkc7,
The transistor should test like a diode one way, and open the other way across each junction (E-B & C-B). The actual E-C on resistance is very low, depending on drive current. The reading you have across the coil may not be accurate. Since the relay operates, I'd say it's okay. The 1 ohm resistor is more likely to open. Check the diode (D901) for short.
I have seen transistors fail in this application. Normally they open E-B or short E-B. I've seen the odd relay coil short but they normally go open. The shorted relay coils were all overheated.
What kind of meter are you using rkc7 (make & model)?
-Chris
The transistor should test like a diode one way, and open the other way across each junction (E-B & C-B). The actual E-C on resistance is very low, depending on drive current. The reading you have across the coil may not be accurate. Since the relay operates, I'd say it's okay. The 1 ohm resistor is more likely to open. Check the diode (D901) for short.
I have seen transistors fail in this application. Normally they open E-B or short E-B. I've seen the odd relay coil short but they normally go open. The shorted relay coils were all overheated.
What kind of meter are you using rkc7 (make & model)?
-Chris
The meter I'm using is a cheap one I bought off of Ebay.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=42291&item=4321131307&rd=1
Well... D901 is shorted, on both polarities. The service manual lists it as 1SS133T-72. Would they have a replacement for this at Radioshack? I don't really feel like ordering from a company and having to wait for it, pay shipping, etc.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=42291&item=4321131307&rd=1
Well... D901 is shorted, on both polarities. The service manual lists it as 1SS133T-72. Would they have a replacement for this at Radioshack? I don't really feel like ordering from a company and having to wait for it, pay shipping, etc.
Oh yeah, and don't worry about the relay, I actually measured it out of circuit and it was about 325ohms. Sorry I'm not helping my cause out very much, I'm just a college student who's not even majoring in any sort of Engineering (Neuroscience actually ). Because of this, I don't have much prior experience with repairing and or electrical work... but I'm learning. Although I haven't quite fixed this problem yet, I sincerely appreciate all the help you guys have given me so far.
). Because of this, I don't have much prior experience with repairing and or electrical work... but I'm learning. Although I haven't quite fixed this problem yet, I sincerely appreciate all the help you guys have given me so far.
That diode failing will be what has killed the transistor Q901 as it will have been exposed to the relays back-EMF surge which will have killed it. As a quick test solder a wire betwen Q901's collector and emitter terminals, and power the amp up. If it comes on, you know you've sussed it
Q901 wont be critical. You could subsitute any transistor in there with the same package and pinout. My sources tell me the 2sc2785 has a max Vceo of 60V and a max Ic of 100mA, so a 2N2222 would do.
Q901 wont be critical. You could subsitute any transistor in there with the same package and pinout. My sources tell me the 2sc2785 has a max Vceo of 60V and a max Ic of 100mA, so a 2N2222 would do.
Hi rkc7,
Okay, the meter is a cheap copy of a Fluke 87 appearance wise. Don't trust that this meter will hold it's tolerance, and it may be out of calibration now. (I used to work in a calibration lab) Buy a real Fluke when you can, you will be glad you did. This one is still useful, just treat the reading as a ball park value and you'll do fine.
You can use a 2N2222, but the base and collector are swapped. Since you have ordered the correct part, don't worry about the pin out. I would recommend using a 1N4001 ~ 1N4007 diode for D901. The original was marginal on current and a 1N4148 won't last long as the peak current is higher from the back emf. These are available from Radio Shack.
-Chris
Okay, the meter is a cheap copy of a Fluke 87 appearance wise. Don't trust that this meter will hold it's tolerance, and it may be out of calibration now. (I used to work in a calibration lab) Buy a real Fluke when you can, you will be glad you did. This one is still useful, just treat the reading as a ball park value and you'll do fine.
You can use a 2N2222, but the base and collector are swapped. Since you have ordered the correct part, don't worry about the pin out. I would recommend using a 1N4001 ~ 1N4007 diode for D901. The original was marginal on current and a 1N4148 won't last long as the peak current is higher from the back emf. These are available from Radio Shack.
-Chris
Hi jaycee,
That's the norm. for Japanese TO-92 transistors. I have 50V, 100mA, 300mW with a DC gain of 200 for the 2SC2785. This from the 1986 Transistor Manual, Japanese.
The funny thing about Japanese companies, once they discontinue something, it ceases to exist for them. NEC make great parts, and some of the best CD transports (used to anyhow).
That's the norm. for Japanese TO-92 transistors. I have 50V, 100mA, 300mW with a DC gain of 200 for the 2SC2785. This from the 1986 Transistor Manual, Japanese.
The funny thing about Japanese companies, once they discontinue something, it ceases to exist for them. NEC make great parts, and some of the best CD transports (used to anyhow).
Yeah, I'd like to get a good meter, but they are pretty pricey and I'm pretty poor, haha. Anyway, I'm glad to hear that I can use 1N4001, because I have some of those! As for the transistor, I should receive them tomorrow, hopefully, and will be able to see if these parts cure the problem. I did try shorting the collector/emitter without a replacement diode. The relay turned on when I plugged the receiver in, but still no response from the receiver. Would this suggest something else could be amiss, or just that I should put in the proper parts? Well, I hope I can answer my own question by tomorrow. If so... I guess it's time to try testing more parts.
Well, I installed the new parts, plugged it in, pressed the power button.... and still nothing This thing just doesn't want to work. I've tried testing other diodes, capacitors, resistors in the whole area of the standby board, and everything seems OK. I started to check caps, resistors, diodes, ICs, etc on the digital board, but all seemed OK.
Here's a larger picture of the digital board which deals with the power control circuit:
digital board 2
This thing just doesn't want to work. I've tried testing other diodes, capacitors, resistors in the whole area of the standby board, and everything seems OK. I started to check caps, resistors, diodes, ICs, etc on the digital board, but all seemed OK.Here's a larger picture of the digital board which deals with the power control circuit:
digital board 2
Hi rkc7,
Okay, does the base of the new transistor change state? On the uP, first check the +3.2V supply, if that is okay then I next check to see if the crystal (or resonator) is oscillating. You really need a 'scope. Possibly one of the labs will allow you to check this out.
Since you have the diagram, check the INT and RESET pins. What are the values at pins 66, 67 and 56 (when you press the power key)?
Let us know your voltage readings, don't worry about the oscillator for now.
-Chris
Okay, does the base of the new transistor change state? On the uP, first check the +3.2V supply, if that is okay then I next check to see if the crystal (or resonator) is oscillating. You really need a 'scope. Possibly one of the labs will allow you to check this out.
Since you have the diagram, check the INT and RESET pins. What are the values at pins 66, 67 and 56 (when you press the power key)?
Let us know your voltage readings, don't worry about the oscillator for now.
-Chris
I have seen another receiver(not Sony make) schematic. For attending this problem without the diagram, u will have to follow the following path.
There will be a sub-power supply normally, with a small transformer. This psu will be of the voltage the relay coil is.
This regulated dc voltage will be connected to the main CPU through a voltage regulator(mostly 7805/type), and will also be fed to a power detect and a reset circuit, mostly designed around transistor(s). A digital transistor(like DTC144) may also be used.
Now, if u do not get hold of a schematic, trace this regulated dc supply from the sub PSU till the main CPU board and look for the faulty component in that area. This supply may be routed through multiple connectors.
Best of luck
Gajanan Phadte
There will be a sub-power supply normally, with a small transformer. This psu will be of the voltage the relay coil is.
This regulated dc voltage will be connected to the main CPU through a voltage regulator(mostly 7805/type), and will also be fed to a power detect and a reset circuit, mostly designed around transistor(s). A digital transistor(like DTC144) may also be used.
Now, if u do not get hold of a schematic, trace this regulated dc supply from the sub PSU till the main CPU board and look for the faulty component in that area. This supply may be routed through multiple connectors.
Best of luck
Gajanan Phadte
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