testing circuit
Hi All,
Thanks mark for your help, really appreciated.
The motor was connected when measuring before. so i disconnected it;
All the IC measurements were the same as with connected.
I also swapped the IC2 and IC4 over,no change.
Am i correct that these are the main problems?
VR1 not adjusting motor + (step 7 in the FAQ testing)
VR2 not adjusting motor +
IC2 pin7, is 4v should be the same as pin3
IC4 pin 5,6,7 too much voltage, should that be 3.6v?
IC4 no control output
Can anyone confirm Q3,4,5 look ok from my measurements?
Many Thanks
webby
Hi All,
Thanks mark for your help, really appreciated.
The motor was connected when measuring before. so i disconnected it;
All the IC measurements were the same as with connected.
I also swapped the IC2 and IC4 over,no change.
Am i correct that these are the main problems?
VR1 not adjusting motor + (step 7 in the FAQ testing)
VR2 not adjusting motor +
IC2 pin7, is 4v should be the same as pin3
IC4 pin 5,6,7 too much voltage, should that be 3.6v?
IC4 no control output
Can anyone confirm Q3,4,5 look ok from my measurements?
Many Thanks
webby
Webby
Q3-5 form a Widlar current mirror which draws a current equal to 1/10 the motor current through R8 and R9. If the motor is not connected there is no current so Q3-6 have nothing to do. With no current through R9 the voltages at pins 5, 6 and 7 of IC2 should be equal but this is not the case.
There appear to be two possibilities: There could be a problem around IC2 (causing it to give the incorrect voltage with the correct inputs) or there could be a problem with Q3-5 (causing Q4 to give an incorrect input to IC2).
If replacing IC2 didn't solve the problem I suspect there's a problem with Q3-5. You could try injecting a current into the lower motor terminal and seeing how Q3-5 react.
Q3-5 form a Widlar current mirror which draws a current equal to 1/10 the motor current through R8 and R9. If the motor is not connected there is no current so Q3-6 have nothing to do. With no current through R9 the voltages at pins 5, 6 and 7 of IC2 should be equal but this is not the case.
There appear to be two possibilities: There could be a problem around IC2 (causing it to give the incorrect voltage with the correct inputs) or there could be a problem with Q3-5 (causing Q4 to give an incorrect input to IC2).
If replacing IC2 didn't solve the problem I suspect there's a problem with Q3-5. You could try injecting a current into the lower motor terminal and seeing how Q3-5 react.
PCB testing
Hi Mark, All.
I haven't given up yet! i have been going round in circles, but your hint about injecting some current gave me an idea. Put some extra load on the motor (finger on spinning pulley) and see what happens. suddenly IC4 pin1 starts putting out 11.63 volts,take finger off drops to 0 volts. I guess there must be a minimum load to get the current sensing working?
I have swapped all the transistors but don't have spare 2277`s, swapping them over doesn't change the behaviour or voltages.
IC2 pin5=6.42 6=6.42 7=7.22
IC4 Pin1=11.63 2=6.91 3= 7.21
But I still can`t vary the motor output.
Any more Ideas,
Many thanks
Webby
Hi Mark, All.
I haven't given up yet! i have been going round in circles, but your hint about injecting some current gave me an idea. Put some extra load on the motor (finger on spinning pulley) and see what happens. suddenly IC4 pin1 starts putting out 11.63 volts,take finger off drops to 0 volts. I guess there must be a minimum load to get the current sensing working?
I have swapped all the transistors but don't have spare 2277`s, swapping them over doesn't change the behaviour or voltages.
IC2 pin5=6.42 6=6.42 7=7.22
IC4 Pin1=11.63 2=6.91 3= 7.21
But I still can`t vary the motor output.
Any more Ideas,
Many thanks
Webby
I take it that the output (pin7) of IC4 jumps straight from one rail (0V) to the other (12V). Check what the voltage at the current compensation input (pin5) does when the output does this. I'm assuming it gets to a threshold voltage which causes the output to suddenly rise quickly.
Now turn VR1 all the way down and check the behaviour again. If it has stopped, turn VR1 up slowly until you get consistent motor speed with load variation. Don't forget that the compensation circuit is damped so it's normal to get some lag before it settles.
Also make sure you have R24 across the motor windings, should be 600 ohm to 1k.
Now turn VR1 all the way down and check the behaviour again. If it has stopped, turn VR1 up slowly until you get consistent motor speed with load variation. Don't forget that the compensation circuit is damped so it's normal to get some lag before it settles.
Also make sure you have R24 across the motor windings, should be 600 ohm to 1k.
For those who are interested:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=124737
Regards
http://www.diyaudio.com/forums/showthread.php?s=&threadid=124737
Regards
testing circuit
Hi Mark, all.
Sorry I haven't got back to you, been off line due to PC problems!
I have now replaced the two OPA2277 chips, but still no joy!
I can use VR3 to vary the voltages so that IC2 pin1 output also varies, and IC2 pin 7 the same.
IC4 inputs at pin 2&3 also vary, but pin1 only puts out 0.08v. Then something strange happens, if i vary VR3 up and down quickly the output briefly jumps up to over 12v and then as quick drops to 0.08v again.
I tried to follow the circuit diagram and so checked the voltages at R23;
one side is always the same as IC4 pin 1 and the other side the same as IC4pin 2,not the 4.85 as marked?
Also the base of Q7 = 0.08 the same as IC4 pin 1, i assume this is wrong.
Any more ideas would be great.
many thanks
webby
Hi Mark, all.
Sorry I haven't got back to you, been off line due to PC problems!
I have now replaced the two OPA2277 chips, but still no joy!
I can use VR3 to vary the voltages so that IC2 pin1 output also varies, and IC2 pin 7 the same.
IC4 inputs at pin 2&3 also vary, but pin1 only puts out 0.08v. Then something strange happens, if i vary VR3 up and down quickly the output briefly jumps up to over 12v and then as quick drops to 0.08v again.
I tried to follow the circuit diagram and so checked the voltages at R23;
one side is always the same as IC4 pin 1 and the other side the same as IC4pin 2,not the 4.85 as marked?
Also the base of Q7 = 0.08 the same as IC4 pin 1, i assume this is wrong.
Any more ideas would be great.
many thanks
webby
testing circuit
Hi Mark,
Thanks for the retest idea, i should have gone through it again since changing components. I charged the battery for a good few hours, so voltage = 13.16
It is IC4 pin1 that jumped up in voltage, not pin7 as suggested ( this may be the problem) . Going back and resetting VR1 to 0, and adjusting it as you instructed i managed to get PIN1 settling on 0.08v unless i load the platter slightly and the voltage increases up to 12.86v and settles back to 0.08v (DIPS not set). I measure VR1 to be 10.1K
So the compensation circuit appears to be functioning?
So then i tried setting the DIP switches as you suggested in an earlier post, thinking this will lower the voltage but the motor output stays at 12.87. but if i leave all the dip switches off and turn VR4 the motor output varies between 12.86 and 12.88?
VR3 varies the output of IC2 pin1 and pin7, also IC4 pin1 when dips are not set.
IC4 pins 5 & 6= 7.13v, pin7 =7.14 and don't change regardless.
when dips set IC2 pins 1 & 7 =6.4v and don't vary, but IC4pin1 voltage jumps about between 4.5 and 5.6 volts, hard to read as its constantly changing.
Sorry if its not clear, just trying to cram in all my observations.
Thanks again for the help.
Webby
Hi Mark,
Thanks for the retest idea, i should have gone through it again since changing components. I charged the battery for a good few hours, so voltage = 13.16
It is IC4 pin1 that jumped up in voltage, not pin7 as suggested ( this may be the problem) . Going back and resetting VR1 to 0, and adjusting it as you instructed i managed to get PIN1 settling on 0.08v unless i load the platter slightly and the voltage increases up to 12.86v and settles back to 0.08v (DIPS not set). I measure VR1 to be 10.1K
So the compensation circuit appears to be functioning?
So then i tried setting the DIP switches as you suggested in an earlier post, thinking this will lower the voltage but the motor output stays at 12.87. but if i leave all the dip switches off and turn VR4 the motor output varies between 12.86 and 12.88?
VR3 varies the output of IC2 pin1 and pin7, also IC4 pin1 when dips are not set.
IC4 pins 5 & 6= 7.13v, pin7 =7.14 and don't change regardless.
when dips set IC2 pins 1 & 7 =6.4v and don't vary, but IC4pin1 voltage jumps about between 4.5 and 5.6 volts, hard to read as its constantly changing.
Sorry if its not clear, just trying to cram in all my observations.
Thanks again for the help.
Webby
Re: testing circuit
Webby
If I'm doing the troubleshooting, please just do the tests that I ask you to and report the results.
The results of the tests I specified appear to be that adjusting VR1 has little effect on the voltage at IC4 pin7.
Change the position of the jumper and tell me the voltages on pins 1, 2 and 3 of IC4.
Turn the power off and check the resistance between pins 1 and 2 of IC4.
webby said:
Webby
If I'm doing the troubleshooting, please just do the tests that I ask you to and report the results.
The results of the tests I specified appear to be that adjusting VR1 has little effect on the voltage at IC4 pin7.
Change the position of the jumper and tell me the voltages on pins 1, 2 and 3 of IC4.
Turn the power off and check the resistance between pins 1 and 2 of IC4.
Webby
I really don't understand what's going on. It looks to me like there's something wrong with Q6, Q7 and Q8 but I understand they've already been replaced.
Can you double check all them all and measure the resistance between the three pin pairs on each transistor (eg E to C, C to B and B to E)
I really don't understand what's going on. It looks to me like there's something wrong with Q6, Q7 and Q8 but I understand they've already been replaced.
Can you double check all them all and measure the resistance between the three pin pairs on each transistor (eg E to C, C to B and B to E)
Webby sent me his PCB and I fixed for him. Problems were numerous. They were:
-Q6 defective and not correctly connected to destroyed traces. Replaced and repaired traces
-Q2 was re-solder to existing cut pins, but the middle one was broken, micro fracture into the solder joint. Unsolder it, reseated correctly without pins extensions and re-solder.
-Q8 missing trace, causing one pin not making contact. Repaired.
-Missing trace between R31-R32. Was destroyed, repaired.
-Possible bad solder joints at numerous locations. I re-done all the soldering so I fixed that too.
The pcb is all repaired. I re-did all the soldering, installed correctly the resistors and caps and the three power transistors. It is fully tested and functional.
-Q6 defective and not correctly connected to destroyed traces. Replaced and repaired traces
-Q2 was re-solder to existing cut pins, but the middle one was broken, micro fracture into the solder joint. Unsolder it, reseated correctly without pins extensions and re-solder.
-Q8 missing trace, causing one pin not making contact. Repaired.
-Missing trace between R31-R32. Was destroyed, repaired.
-Possible bad solder joints at numerous locations. I re-done all the soldering so I fixed that too.
The pcb is all repaired. I re-did all the soldering, installed correctly the resistors and caps and the three power transistors. It is fully tested and functional.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.