Just wondering if it could be something wrong with the protection IC HA12002. I had pulled the relay switch apart and cleaned it so, little puzzled now why its going into protection mode? I rechecked NE5532 dual amp IC on the Control amp and its running both pin 4 and 8 at 14.2v. The fuses are secure no movement in their holders at all! Thanks
We always have to be logical.
A problem with the protection circuit itself tripping the relay wouldn't account for the VU's bouncing around. They are most likely bouncing because of unwanted changes in voltage at the power amp output.
If the VU's bounced because of an issue with their dedicated drive chip then that would not affect anything other than the meters.
If turning the volume down and using the direct button stops the relay clicking and meters bouncing then that all points to the problem being something either on the tone board or, if not that then something before the volume control.
A problem with the protection circuit itself tripping the relay wouldn't account for the VU's bouncing around. They are most likely bouncing because of unwanted changes in voltage at the power amp output.
If the VU's bounced because of an issue with their dedicated drive chip then that would not affect anything other than the meters.
If turning the volume down and using the direct button stops the relay clicking and meters bouncing then that all points to the problem being something either on the tone board or, if not that then something before the volume control.
So where the speaker relay is not even kicking in now where should I be looking for the faults at on the tone board at?, or before the volume control? The volume control is an independent board with volume control switch with 7 leads going into the control board and 4 leads going into the tape dubbing and monitoring switches?
Concentrate on the relay and how it operates.
Pin 1 of IC1 has to go 'low' in order to energise the relay. That means if you see around 1 or 2 volts on that pin then the relay should be energised and on. If the voltage is nearer 40 volts then the relay is off.
It is easiest to measure this voltage on the anode of D10 which will be easy to get to.
If you have 40 volts present then you need to determine whether the protection circuit is faulty or whether the protection circuit is doing its job and not powering the relay because of a fault.
The protection IC needs four things to be correct.
1/ Its supply voltage on pin 4 which is shown as around plus 6 volts.
2/ A negative voltage of around -4 volts on pin 5. This detects the presence of AC from the transformer and is used to detect instantly when power is removed and so cut the speakers.
3/ 0 volts on pin 3. This monitors DC offset of one channel.
4/ 0 volts on pin 4. This monitors the other channel.
All the above must be correct and constant for the relay to operate. If there is a glitch on any then the relay will probably cycle through its timed delay before energizing again.
Pin 1 of IC1 has to go 'low' in order to energise the relay. That means if you see around 1 or 2 volts on that pin then the relay should be energised and on. If the voltage is nearer 40 volts then the relay is off.
It is easiest to measure this voltage on the anode of D10 which will be easy to get to.
If you have 40 volts present then you need to determine whether the protection circuit is faulty or whether the protection circuit is doing its job and not powering the relay because of a fault.
The protection IC needs four things to be correct.
1/ Its supply voltage on pin 4 which is shown as around plus 6 volts.
2/ A negative voltage of around -4 volts on pin 5. This detects the presence of AC from the transformer and is used to detect instantly when power is removed and so cut the speakers.
3/ 0 volts on pin 3. This monitors DC offset of one channel.
4/ 0 volts on pin 4. This monitors the other channel.
All the above must be correct and constant for the relay to operate. If there is a glitch on any then the relay will probably cycle through its timed delay before energizing again.
Okay Mooly trying to stay focus here and not pull to much hair out of my head. So I am assuming you actually meant pin 7 when you said, "1/ Its supply voltage on pin 4 which is shown as around plus 6 volts." So I turned on the amp of course relay switch turned on. Checked pins and Pin 1 had 1.04v, Pin 3 & 4 had 0v, pin 5 had 4.44v, pin 7 had 6.2v, and 8 had 5.2v. Checked my amp and it had 0 volume and had it switched to direct. So thought perfect oppurtunity to check see if problem was in control amp board. Switched tone on turned the volume up and immediately the VU meter started to bounce and 10 seconds later the speaker relay switched kicked off. Checked pin 1 and had 42.5v which is what I expected to see as that would indicate the relay had switched off. Went ahead and switched the tone back to direct 5ish seconds later relay switched kicked back on 1v back at pin 1 on IC-1. What you think Mooly? Has to be on the control/tone board? Thanks
Mooly yes I did replace the orginal NJM4558 chip with a NE5532 chip that I bought thru Mouser. It also seems that it is getting harder and harder to get this amp to come out of protection mode. In fact after my test of yesterday I could never get it come out of protection mode dinking around with it. Anyways I'll go ahead and pull the new chip out of it and put the old one back in to see if that changes anything! Thanks Mooly
IC1. At the times you have 0.75 volts on pin 3 and 4 you also need to check what the voltage is at the output of each power amp. That is the voltage at the junction of the two 0.47 ohms.
Pins 3 and 4 are inputs so you need to confirm whether they are being driven to 0.75 volts or whether the 0.75 is appearing internally within the chip due to a problem with or around the chip.
Pins 3 and 4 are inputs so you need to confirm whether they are being driven to 0.75 volts or whether the 0.75 is appearing internally within the chip due to a problem with or around the chip.
Okay Mooly I desolder pin 3 & 4out of circuit after pushing on the pins to make sure there was no solder left on the pins to make contact with the PCB pad the relay switched fault cleared. The relay engaged and pin 1 dropped to 1.04v. Interesting Pin 4 is being feed tracing both sides of the pad -4.26v pin 3 is being feed -2.6v? Whenever I would push on either pin 3 or 4 to read them they would make contact with the pbc pad and of coarse relay switch would go into fault with pin 1 having 44.2v. As I was trying to see if it was the same in both direct amp and tone control I hit the pcb and pad on pin 3 and it went back into fault! I at this point in the game I haven't been able to get it come out of fault. Not sure if I fried my IC-1 chip or not? Either way some thing is amiss LOL.
Thanks
Thanks
If you mean you are seeing -4.26v and -2.6 on the print of the PCB around the unsoldered pins then that is showing the power amps have a DC offset issue.
You can force the pins to zero voltage by temporarily shorting out C29 and C30. With the chip soldered back up and the caps shorted then the relay should engage.
You can force the pins to zero voltage by temporarily shorting out C29 and C30. With the chip soldered back up and the caps shorted then the relay should engage.
Yea that is what I meant. I visually look and see that pin 3 has no contact to the pad on the pcb but I am showing +3.5v while the pad is showing a -5.7v. pin 4 has 0v on it but has -4.8v on the pad. There shouldn't be any voltage at pin 3 with it out of circuit correct? So something must be wrong with it? How do I induce a short accross C29 & 30? Where would I look to see where the DC offset would be and how should I go about repairing or addressing that DC offset? Should I also look at replacing IC-1 and if so what would you recommend? Thanks Mooly hope I'm not driving you crazy
The voltages you measure on the pads alone, with the IC pins disconnected, are showing an offset issue. That's definite, and is a definite problem. That voltage can only come via R57 and R58 from the amplifier itself.
Leaving the pins of the IC floating isn't a valid operating state for the chip and the relay may or may not be triggered. That is not really telling us anything.
That is why I suggested shorting the two caps out once the IC was soldered back up. It will force zero volts on the pins and the relay should operate correctly.
We have to first of all prove where the problem is. To have both channels with random offsets is unusual (yet that is what your voltage measurements seem to show) and suggests a common cause.
I would probably begin by isolating the power amp inputs from the tone board, which is easy to do by removing C1 and C2 on the power amp board. Then see if the relay behaves, and confirm that there is no voltage on pins 3 and 4 of the protection chip.
I would probably begin by isolating the power amp inputs from the tone board, which is easy to do by removing C1 and C2 on the power amp board. Then see if the relay behaves, and confirm that there is no voltage on pins 3 and 4 of the protection chip.
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