I didnt even bother re-wireing to check them; I just unsoldered all 6 opAmps. I'm pretty sure they are all bad; none of them pass the diode test on Pins1-3 or pins5-7 except for one. The one I tested before which came out of U101: diode check does not beep on pins 1 through 3. Pins 5 thru 7 diode beep-check with Com on pin 6 and 7.
Again, none of others beep-check. Am I checking these right? its basically the same thing as checking a Transistor?
Again, none of others beep-check. Am I checking these right? its basically the same thing as checking a Transistor?
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Are both resistors within tolerance?
I know of no reliable way to check op-amps with a multimeter (out of the circuit) unless they're shorted between pins. Op-amps are comprised of MANY components. Only a few of those components are connected to the terminals of the op-amp.
I know of no reliable way to check op-amps with a multimeter (out of the circuit) unless they're shorted between pins. Op-amps are comprised of MANY components. Only a few of those components are connected to the terminals of the op-amp.
R94 is measuring 469 ohms, and R93 is measuring 450 ohms so they are pretty close. i dont have any spares for replacement.
How do you think some or all of the opAmps are bad? From this matrix I posted before?
U101's pins WERE comming up like this:
2068LD Pin / vDC
1. 14.4
2. 2.4
3. 0.2
4. -14.8
5. 0.018
6. 0
7. 15
8. 15
How do you think some or all of the opAmps are bad? From this matrix I posted before?
U101's pins WERE comming up like this:
2068LD Pin / vDC
1. 14.4
2. 2.4
3. 0.2
4. -14.8
5. 0.018
6. 0
7. 15
8. 15
Hey I got sound to come out of this amp. I put back all but one opAmp - The one that was measuring 'correctly' between pins 5-7. Seems this one may have been the bad egg in the bunch. I put a different opAmp in place of the one which came out of U101. and left U103 off the PCB - So the amp is running with 5 out of the 6 required opAmps.
I get sound out of both channels now.... but R93 still gets hot 🙁
I get sound out of both channels now.... but R93 still gets hot 🙁
The voltages that you posted would indicate that the op-amp is defective. With the non-inverting input below the inverting input, the output voltage should have been near -15v.
As long as the power dissipation isn't greater than the rating of the resistor, heating is not a problem.
As long as the power dissipation isn't greater than the rating of the resistor, heating is not a problem.
How much heat can a 2w resistor handle? Using my Raytek termerature 'gun' I measured the resistor at 160 degrees F after ~2 minutes of operation, then I shut down the amp.
I swapped resistors R93 with R94 and I get the same; always the spot for R93 gets this hot. Maybe there should be some 5w resistors in R93/R94 instead of 2w.
I swapped resistors R93 with R94 and I get the same; always the spot for R93 gets this hot. Maybe there should be some 5w resistors in R93/R94 instead of 2w.
If the resistor isn't trying to desolder itself from the heat, I wouldn't be concerned about it.
The operating temperature is determined by the voltage across the resistor and the resistor value. If the resistance of the resistors is very nearly the same and the voltage across them is the same, they should be operating at the same temperature.
The materials that the resistors are made of determine the acceptable operating temperature.
The operating temperature is determined by the voltage across the resistor and the resistor value. If the resistance of the resistors is very nearly the same and the voltage across them is the same, they should be operating at the same temperature.
The materials that the resistors are made of determine the acceptable operating temperature.
Theres .5v difference across R93 and R94. ~22vDC each. and R94 is .5v higher than R93.
I'm thinking since I need to order opamps, just go ahead and replace both resistors and both diodes in this part of the circut. Also since the two resistors are measuring slightly different; 450ohm vs 470ohms.
I'm thinking since I need to order opamps, just go ahead and replace both resistors and both diodes in this part of the circut. Also since the two resistors are measuring slightly different; 450ohm vs 470ohms.
While I'm running this amp with only 5 out of the 6 opAmps, I'm finding that the neither the crossover nor the boost switches are doing anything. I bet I've got more than just one bad opAmp in this amp. I'll go ahead and check their voltages.
The boost may only work in low pass mode.
If you want to install an op-amp temporarily, you can use a DIP op-amp. Bend legs 1-4 out to the side and solder them directly in the board. Use ribbon cable (or other suitable wire) to hardwire legs 5-8 into the board.
If you want to install an op-amp temporarily, you can use a DIP op-amp. Bend legs 1-4 out to the side and solder them directly in the board. Use ribbon cable (or other suitable wire) to hardwire legs 5-8 into the board.
I picked up 6 new opAmps from Mouser for this amp. Later today I'll be working with locating the remaining failed ones; or I may just replace them all for brand new parts.
This amp is more fixed, although R94 still gets hot. Parts replaced / items fixed
1. Trace under PCB needed re-attaching
2. RCA input terminals were physically shorted and required seperation
3. Diode near R94 was close-shorted. 1n4744 replaced
4. All 6 opAmps replaced for new parts
The output from this amp sounds pretty bad - almost like the Bias is too low or not engaging at all. This amp is supposed to be a Class AB but there are no Bias pots. I think this makes sense - on an amp with bias pots if set to fully counterclockwise the output sounds distorted or 'trumpeting' like what this amp is doing. There must be something in the driver circuits which controls bias.
1. Trace under PCB needed re-attaching
2. RCA input terminals were physically shorted and required seperation
3. Diode near R94 was close-shorted. 1n4744 replaced
4. All 6 opAmps replaced for new parts
The output from this amp sounds pretty bad - almost like the Bias is too low or not engaging at all. This amp is supposed to be a Class AB but there are no Bias pots. I think this makes sense - on an amp with bias pots if set to fully counterclockwise the output sounds distorted or 'trumpeting' like what this amp is doing. There must be something in the driver circuits which controls bias.
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