Yes.
It's likley that the diode or C301 is leaking (electrically).
Get the readings off of the transistor. If the top terminal is at 12v and the emitter (right terminal on the bottom of the transistor) is ~1/2v below the voltage on the diode, pull the diode out and check it.
Do NOT apply power with the diode out of the circuit.
It's likley that the diode or C301 is leaking (electrically).
Get the readings off of the transistor. If the top terminal is at 12v and the emitter (right terminal on the bottom of the transistor) is ~1/2v below the voltage on the diode, pull the diode out and check it.
Do NOT apply power with the diode out of the circuit.
okay well i found Q404 and it is fried.You can easily see its been burnt.The side that only has one leg i'm getting 12.6 volts. If i'm looking at the part with the two legs facing down the right leg is at 1.1 volts and the left leg is at 12.7 volts . I'm getting a short between the top leg and the bottom left leg.
Something isn't right. One side of the diode should be grounded. If you have only 0.93 across the diode, the diode either isn't grounded or there is an error in the way the voltage was measured.
Check to make sure that the striped side of the diode is connected to the left leg of Q404.
Make sure that the unstriped side of the diode is connected to chassis ground.
If the top and left legs of Q404 are shorted together, The diode is VERY likely damaged. It's a 6.2v Zener.
Check to make sure that the striped side of the diode is connected to the left leg of Q404.
Make sure that the unstriped side of the diode is connected to chassis ground.
If the top and left legs of Q404 are shorted together, The diode is VERY likely damaged. It's a 6.2v Zener.
i checked and rechecked and i still get the .93 volts no matter what side of the diode the leads are on.One side of it is grounded and the other side (striped side)connects to what used to be the left lead of Q404.There is also another small surface mounted part tapped off of the trace that runs from the diode to the leg of Q404. I'm not sure if it is a resistor or what but one side of it is tapped off of the trace from the diode to the left leg of Q404 and the other side runs to the top leg of Q404.By the way do you happen to know a part number for what q404 was?Its completely destroyed?
okay well i replaced q404 and the diode so far and still no juice.I measured 6.15 volts across the diode ,6.15 volts on the bottom left leg of q 404, 12.75 volts on the top leg of q404, and 5.57 volts on the bottom right leg of q 404. Are these numbers in order? and if so where should i look from here?
the voltages on q 102 and 103 are close on the outside pins but the middle pin on both of them is sitting at a little under 9 volts.
Which processor are you talking about Perry?Are you talking about the square one under the foam pad or are you referring to the 494? I do not own an oscilloscope but is there any other test i can do?
Which processor are you talking about Perry?Are you talking about the square one under the foam pad or are you referring to the 494? I do not own an oscilloscope but is there any other test i can do?
is 4.85 volts close enough to 5 or should it be higher? If i'm reading the leads correctly pin 30 has .015 volts on it but pin 28 has 4.85 volts on it. I see the board is labeled with a 1 which i assume is pin one of the processor.I just counted up to 30 and used that as pin 30, please tell me if this is correct. None of the indicators light up.
pin 18 4.8 volts
pin 19 .116 volts
pin 20 .176 volts
pin 21 .002 volts.
when the amp is first powered on i'd see almost nothing on the pins.Then after about 15 seconds they would all jump up and stay up for about another 15 seconds and then drop right back down to nothing and stay there.I re-checked 5 and 6 and they do the same thing. 6 will be at 4.8 volts for about 15 seconds and then drop and 5 really never has much either way , about .015 and then .001 when it drops down.
pin 19 .116 volts
pin 20 .176 volts
pin 21 .002 volts.
when the amp is first powered on i'd see almost nothing on the pins.Then after about 15 seconds they would all jump up and stay up for about another 15 seconds and then drop right back down to nothing and stay there.I re-checked 5 and 6 and they do the same thing. 6 will be at 4.8 volts for about 15 seconds and then drop and 5 really never has much either way , about .015 and then .001 when it drops down.
Everything is probably jumping up because you don't have a good ground reference point for your meter. If you use the ground pin of the processor, do you get the same readings?
6 may be going up because the voltage on your supply is dropping when you try to power up the amp.
When you try to power the amp up, does pin 30 go to ~5v for a few seconds (using the ground pin of the processor for the reference)?
What's the voltage on pins 35-37?
By the way, I'm not just having you check random points. I'm working my way through the various inputs. It would be nice if you had a scope and could check for oscillation on the xtal pins. You didn't happen to buy one in the last few days did you?
6 may be going up because the voltage on your supply is dropping when you try to power up the amp.
When you try to power the amp up, does pin 30 go to ~5v for a few seconds (using the ground pin of the processor for the reference)?
What's the voltage on pins 35-37?
By the way, I'm not just having you check random points. I'm working my way through the various inputs. It would be nice if you had a scope and could check for oscillation on the xtal pins. You didn't happen to buy one in the last few days did you?
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