Turns out to be a limiting type resistor, goes between 15amp breaker and transformer on the bottom board next to output trans heat sink. Also ordered 3 small transistor and this limiting resistor. I'm still blowing fuses. Pulled all output Transistor and checked and Put 4 new 2200 caps.
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REMOVE ALL OF THE PS CAPS FROM THE BOARD.
Install 2 + 2 new caps on the board (pair on each rail)
Turn on. If it doesn't blow fuses, find the shorted PS caps, or better still go ahead then and replace them all.
High probability.
ALSO, if it is blowing fuses, you can use ur ohmeter to find the very low resistance, starting on the filter side of the rectifier bridge (which is also a suspect to start with).
_-_-bear
Install 2 + 2 new caps on the board (pair on each rail)
Turn on. If it doesn't blow fuses, find the shorted PS caps, or better still go ahead then and replace them all.
High probability.
ALSO, if it is blowing fuses, you can use ur ohmeter to find the very low resistance, starting on the filter side of the rectifier bridge (which is also a suspect to start with).
_-_-bear
The power supply caps... remove all the old ones.
Install 2 of ur new caps in the "+" side.
Install 2 of ur new caps in the "- " side.
More if you bought more... in pairs, one for the + and one for the - ...
Get the polarity right.
You will have empty holes where caps go. Power supply caps.
IF necessary, and it still blows fuses, remove the power transistors entirely and see that you can turn it on and make B +/-
Now you should know if it will turn out without blowing fuses.
So, likely you can then conclude that , and have one or more shorted outputs or drivers or both, and/or shorted PS caps.
As I said you can make the amp operate with just one pair of outputs - you just can't drive a load to full power - but it will operate with no load just fine... a scope would help of course.
The little transistors will not likely cause it to blow fuses, it won't kick the relay in the first place with bad low level transistors, iirc.
So, get the PS working right, the filter caps not shorted, and the outputs not shorted.
BOTH need to be known to be good first.
After this you can sniff around for low level bad parts... which there may well be.
_-_-bear
Install 2 of ur new caps in the "+" side.
Install 2 of ur new caps in the "- " side.
More if you bought more... in pairs, one for the + and one for the - ...
Get the polarity right.
You will have empty holes where caps go. Power supply caps.
IF necessary, and it still blows fuses, remove the power transistors entirely and see that you can turn it on and make B +/-
Now you should know if it will turn out without blowing fuses.
So, likely you can then conclude that , and have one or more shorted outputs or drivers or both, and/or shorted PS caps.
As I said you can make the amp operate with just one pair of outputs - you just can't drive a load to full power - but it will operate with no load just fine... a scope would help of course.
The little transistors will not likely cause it to blow fuses, it won't kick the relay in the first place with bad low level transistors, iirc.
So, get the PS working right, the filter caps not shorted, and the outputs not shorted.
BOTH need to be known to be good first.
After this you can sniff around for low level bad parts... which there may well be.
_-_-bear
Tried new E7n8 and E11n12.Tested all the output transistors, replaced small ones too. I got my variac today and tried turning it up to 20watts. noticed r47 and r48 smoking. Removed them and I have burn marks. Bad resistors or what! This thing gonna drive me crazy. Rectifier bridge test? Link 2 schematic
http://www.qscaudio.com/support/library/schems/Discontinued/USA%20Series/usa1300.pdf
http://www.qscaudio.com/support/library/schems/Discontinued/USA%20Series/usa1300.pdf
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One more time:
- REMOVE ALL OF THE POWER TRANSISTORS
then make sure the PS is functioning.
IF it is, then you have to test the transistors, by installing them one pair (one per rail) and retest.
Check them with an ohmeter for dead shorts when they are out. B-E, E-B, and B-C, C-B, then E-C and C-E.
The diode check function is useful too...
Unless you have or make another way to check the transistors.
The variac shows volts not watts... you should install (buy) an AC ammeter or else create one by putting a voltmeter across a low value high power resistor - like a 1 ohm or a 0.1ohm. Then the voltage reading on either an analog voltmeter or a DVM clipped in is proportional to the current. Now you turn up the variac and watch the current, if it starts to soar then you have a shorted component. Normal current draw on this sort of amp is about 1 - 3 amps plugged in turned on, no signal.
The resistor goes in series with one leg of the AC mains going to the DUT (device under test).
Make sure you make it so you can't short it to ground, or touch it yourself, etc... The resistor should be large... work it out using ohms law P = I x E, where E = 120volts AC (you could take the RMS of that, but it's close enough without). I is the max current you expect to draw - a fuse in series with it will protect it against a major short out, unless the variac has its own circuit breaker. The good part is that you don't need a 1kw resistor for this, since you should figure it out with the resistance plugged into the equation, less current if the resistor is smaller... which is good. P = E^2/R or P = I^2 x R. So if I = 10 amps then it's 100/1 = 100 watts. If you use a 0.1 ohm resistor then it is 10 watts.
that will keep you from smoking too many more components...
Change the 5532 for good luck, and put a set of SIP pins or a socket in there too...
_-_-bear
- REMOVE ALL OF THE POWER TRANSISTORS
then make sure the PS is functioning.
IF it is, then you have to test the transistors, by installing them one pair (one per rail) and retest.
Check them with an ohmeter for dead shorts when they are out. B-E, E-B, and B-C, C-B, then E-C and C-E.
The diode check function is useful too...
Unless you have or make another way to check the transistors.
The variac shows volts not watts... you should install (buy) an AC ammeter or else create one by putting a voltmeter across a low value high power resistor - like a 1 ohm or a 0.1ohm. Then the voltage reading on either an analog voltmeter or a DVM clipped in is proportional to the current. Now you turn up the variac and watch the current, if it starts to soar then you have a shorted component. Normal current draw on this sort of amp is about 1 - 3 amps plugged in turned on, no signal.
The resistor goes in series with one leg of the AC mains going to the DUT (device under test).
Make sure you make it so you can't short it to ground, or touch it yourself, etc... The resistor should be large... work it out using ohms law P = I x E, where E = 120volts AC (you could take the RMS of that, but it's close enough without). I is the max current you expect to draw - a fuse in series with it will protect it against a major short out, unless the variac has its own circuit breaker. The good part is that you don't need a 1kw resistor for this, since you should figure it out with the resistance plugged into the equation, less current if the resistor is smaller... which is good. P = E^2/R or P = I^2 x R. So if I = 10 amps then it's 100/1 = 100 watts. If you use a 0.1 ohm resistor then it is 10 watts.
that will keep you from smoking too many more components...
Change the 5532 for good luck, and put a set of SIP pins or a socket in there too...
_-_-bear
Q3 4v, R16 2v, R17 4v Also 4v at base and emitter from mj15022 output transformers. the mj15023 on the other half of rail is .50mv
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Hi,
By checking your reading something is not right. R16 voltage should read same as the base of Q3. R16 read 2volts and Q3 read 4volts. They are tied to the same point. Both should read 2 or 4 volts. I need 3 more reading. Read the base voltage of Q1 & Q2 and also the speaker output voltage. I think with no input signal the base of Q1 & Q2 should be zero then the output should be High in both transistor collector. Right now both are low 4 volts. I think you do not want R16 enable all the time.
tauro0221
By checking your reading something is not right. R16 voltage should read same as the base of Q3. R16 read 2volts and Q3 read 4volts. They are tied to the same point. Both should read 2 or 4 volts. I need 3 more reading. Read the base voltage of Q1 & Q2 and also the speaker output voltage. I think with no input signal the base of Q1 & Q2 should be zero then the output should be High in both transistor collector. Right now both are low 4 volts. I think you do not want R16 enable all the time.
tauro0221
okay lets see if I got this. R16 and Q3 are 1.5v same. R17 and Q11 1.9v (remeasured) , speaker 39mv, Q1 700mv and 29mv, Q2 2.5v and1.8v, D4 1.8v on grd side and 5.5v on other side could D4 be problem?Thanks
Hi,
Checking your reading if the base of Q1/Q2 are 700mv and 2.5 volts the collectors for both transistor should be 93 volts. You should read the same voltage that is at the base of Q1/Q2 coming out from the emitter to R12/R13. Both voltage should read the same. In the way I understand the circuit worked is by increasing the base voltage of Q1 will ground the 93 volts thru the .47 resistors causing the caps voltage to discharged and this will send a voltages to the speaker. In other word the capacitors will blocked the dc and let pass thru the AC. Same for the negative side of the input signal for the Q2. The Q1 and Q2 collectors should read 93 volts with a zero signal input. Check Q1 /Q2 for a short between collector and emitter. Did you check all the transistors/diodes with a ohmmeter for short?
Checking your reading if the base of Q1/Q2 are 700mv and 2.5 volts the collectors for both transistor should be 93 volts. You should read the same voltage that is at the base of Q1/Q2 coming out from the emitter to R12/R13. Both voltage should read the same. In the way I understand the circuit worked is by increasing the base voltage of Q1 will ground the 93 volts thru the .47 resistors causing the caps voltage to discharged and this will send a voltages to the speaker. In other word the capacitors will blocked the dc and let pass thru the AC. Same for the negative side of the input signal for the Q2. The Q1 and Q2 collectors should read 93 volts with a zero signal input. Check Q1 /Q2 for a short between collector and emitter. Did you check all the transistors/diodes with a ohmmeter for short?
I'm using a variac and setting it at 20-25v. Q1 and Q2 i have relpace with new.I have not replaced any diodes yet. What about d4 5v on + side?
Hi,
If you are using 25 volt AC at the input then you should see close to + 35V DC and -35v DC on both collector. The anode of the D4 should read negative since is connected to the -93 rail and the cathode to ground. Should read -5 V no +5 v. You can remove one side of the D4 and check it with ohmmeter on diode test. With the pos lead at the anode and the neg lead at the cathode should read around .5. Reversing the leads should open. Check the both rail voltages when you applied the voltage. Should read +/- 35 volts. If you are using a 25 volts AC input you should see about 1.4 X 25 = 35 volts DC. If you do not see it something is loading down the voltage. Also check the resistance with no power at the +93 volt rail and at the -93 volt raid to ground.
If you are using 25 volt AC at the input then you should see close to + 35V DC and -35v DC on both collector. The anode of the D4 should read negative since is connected to the -93 rail and the cathode to ground. Should read -5 V no +5 v. You can remove one side of the D4 and check it with ohmmeter on diode test. With the pos lead at the anode and the neg lead at the cathode should read around .5. Reversing the leads should open. Check the both rail voltages when you applied the voltage. Should read +/- 35 volts. If you are using a 25 volts AC input you should see about 1.4 X 25 = 35 volts DC. If you do not see it something is loading down the voltage. Also check the resistance with no power at the +93 volt rail and at the -93 volt raid to ground.
Tried Pt out and Pair at a time and no luck. Tried caps pair no luck. Repalced Q1 and Q2 no luck. Fried R47 and R48 at 25v on variac. 5v across R41 n R42 etc, Read meas on previous post. Any Ideas? 5532? Thanks
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Sure - first off this amp is a royal PIA to fix...
But you are not being clear about what procedure you are using here, while you mention parts, it is unclear what tests you've done on the parts, or what sequence you are doing things.
Putting in shorted transistors, no matter what order you do it in won't work no matter what.
The steps are:
make sure the PS works ALONE
Test the output transistors - remove ALL of them first.
IF you find a pair that seem to be ok put that pair in.
Retest...
IF you have a working channel, I'd pull a pair of outputs from there and use them as your "model" for doing resistance and diode checks of the ones from the bad channel.
IF you fried a pair of emitter resistors, that is a sure sign of a dead short, OR that side being driven super hard. But I don't know from what you have said how many transistors were IN the board when you fried the two resistors!
As I mentioned just above, if you have one good channel, you have a model for how the voltages should be at say "20" vac on the mains...
You can jumper or open the cube relay and force the contacts together so you can watch the DC offset at the output, etc...
At this point in your troubleshooting career you might invest in a decent <$100 'scope on fleabay...
_-_-bear
But you are not being clear about what procedure you are using here, while you mention parts, it is unclear what tests you've done on the parts, or what sequence you are doing things.
Putting in shorted transistors, no matter what order you do it in won't work no matter what.
The steps are:
make sure the PS works ALONE
Test the output transistors - remove ALL of them first.
IF you find a pair that seem to be ok put that pair in.
Retest...
IF you have a working channel, I'd pull a pair of outputs from there and use them as your "model" for doing resistance and diode checks of the ones from the bad channel.
IF you fried a pair of emitter resistors, that is a sure sign of a dead short, OR that side being driven super hard. But I don't know from what you have said how many transistors were IN the board when you fried the two resistors!
As I mentioned just above, if you have one good channel, you have a model for how the voltages should be at say "20" vac on the mains...
You can jumper or open the cube relay and force the contacts together so you can watch the DC offset at the output, etc...
At this point in your troubleshooting career you might invest in a decent <$100 'scope on fleabay...
_-_-bear
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