KA-7002 protection circuit

dstariha

Active Member
I am having some difficulty with this circuit. The relay will not kick in unless I lift off one side of De9 on the Main Amp/Protection circuit board (output driver board X07-1020-00).
I have checked all the xistors, other diodes and resistors. Ce17 is new and tests OK, voltages at pin 6, 14 and 17 are as expected.
Note a couple of errors on the schematic: 1. Q2 collector is not powered from pin 8 on the PS board but from Vee (B-). Pins 18 and 19 are reversed.
The unit is in the newer series of amps, i.e., above s/n 410501. My inclination is to just leave it alone and take my chances but if anyone can help I would truly appreciate it.
Otherwise the amp works fine and can achieve full power into 8 ohm dummy loads.
The full schematic is available at: https://www.hifiengine.com/manual_library/kenwood/ka-7002.shtml
IMG_0001.JPG
 
18 & 19 are reversed? Are we to presume that Q2 base is not connected to Q12 emitter?
 
The connections are as you describe, the schematic is correct. On the circuit board connector they are reversed. It makes no difference in this instance but I had to make the correction in my mind when troubleshooting. I guess the idea stuck. Sorry for the confusion and it proves you do your homework.

Thanks, Dave
 
Pins 14 and 6 are also backwards B+ should go to 6 (including one side of the relay), relay drive is from 14, nothing else goes to 14...
My print has 2 emitters on Q16 - the parts list and common sense (at least my common sense...) says it is a PNP and the lower arrow should be the collector.
Q16 controls the circuit. Q15 will cause Q16 to conduct and shut off the relay if DC is too high.
Q13 and Q14 sense the current levels, and if there is excess current through the emitter resistors of the outputs, either will cause Q16 to conduct and shut off the relay.
I can't figure out any function for D9 or the thermistor in the protect circuit. Something may be amiss (in the schematic) there, but I don't see it. :dunno:

Edit - the schematic in 1st post has no thermistor in it so that question is moot.
 
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D6 is the flyback for the relay coil, but do we supposed D9 similarly clamps the rapid discharge of C17 when the protection goes active? I can't determine any other real reason with a resistor already present there.
 
The connections are as you describe, the schematic is correct. On the circuit board connector they are reversed. It makes no difference in this instance but I had to make the correction in my mind when troubleshooting. I guess the idea stuck. Sorry for the confusion and it proves you do your homework.

Thanks, Dave

But in order to function, Q2 base should be connected to the Q12 emitter - I'm more confused. Or are you saying that the board connection pins are simply numbered opposite the drawing?
 
D6 is the flyback for the relay coil, but do we supposed D9 similarly clamps the rapid discharge of C17 when the protection goes active? I can't determine any other real reason with a resistor already present there.
After thinking about it, my guess is that it (D9) is to keep the circuit from going negative when the power is removed. Ce17 has full voltage across it, and will go negative when the supply voltage goes down.
 
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I haven't dived into the issue the OP is having, but since you guys are noting errors I thought I'd chime in.

I was inside my KA-7002 today having a look at the bias and offset. The trimpots on the amp board itself that are labeled VR1, VR3 adjust the right channel, and VR2, VR4 the left. When looking at the board from the component side VR2,VR4 are on the left side of the board, VR1, VR3 on the right. So the labeling is a little unorthodox, but the corresponding sides make sense.

Looking at the S/M schematic from hifi engine the designations for channels shown on the schematic (If you look at the the headphone jack it actually labels them R and L) shows the reverse.

I thought this info might prove useful when making adjustments as I went turning the offset VR1 trimmer monitoring the left channel. I was not getting a change on the DMM and had a brief WTF moment.
 
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First, Watthour - the pins 18 and 19 are incorrectly labeled on the schematic, as you note and said much more clearly than my attempt, thank you.
I agree that De6 is the flyback snuffer for the relay, also I think De 9 discharges Ce17 and C307 upon shut down. I only think this because now the relay takes a couple seconds to release when power is turned off.
Second, hopjohn - yes, the unorthodox labeling had me wondering as I tried to adjust bias. Hurt my head.
Lastly, sregor, I am going to trace the wiring tomorrow to pin down the comments you have made. And will post the results here.
Sregor also noted that Qe16 appears to have 2 emitters. The print has a flaw right here; on mine it appears to be a missing connection. The transistor is a 2SA743A, PNP.

Thank you all for the assistance. I will work on this and try to confirm the correspondence between the schematic and the actual wiring. That will make this easier for us all.
 
Cleanup in Aisle Nine...

http://www.wwdsltd.com/files/KenwoodKA-7002Schematic.jpg

Any better? (Click for full-size / Right click for download)

KenwoodKA-7002Schematic.jpg
 
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Thank you Watthour, this is a better rendition than the one I posted. I am still working to confirm the actual wiring v. that shown on the schematic.
1. The positive supply to Q2 is a direct connection to C306. Not from Rk7 on the power supply board. Pretty obvious.
2. At the the output xistors the schematic is missing a 224k cap in series with a 4.7 ohm, 2W resistor to ground. I am not sure what this does, perhaps attenuate ultrasonic frequencies? However, I did notice the amp goes into oscillation at around 60 Hz without it.
3. As sregor noted, pin 6 should be B= from Rk7 on the P/S board. And pin 14 is actually wired to the "ground" side of the relay coil. This is how my older (working) unit is wired.

I rewired the relay as sregor and the older unit are. Still no relay operation. I have noticed that Re50 is quite warm, not hot. Whereas Re53 is not. I expected Qe18 to be the ground path as it seems to be on the older unit.

The 4 pins 10-13 are the output emitter voltage sensing inputs to the protection circuit. Nothing seems amiss there. It appears that these voltages drive either Qe13 or Qe14 to drive Qe16. Qe16 then, after a time delay by Ce17 drives Qe17 to to raise the voltage at the emitter of Qe18 driving it out of conduction thereby releasing the relay RL1. Frankly I am not confident I have this figured out but my guess is that Qe18 is not the problem so I will focus on the lower numbered components.

Can you confirm my thinking that Qe15 and its associated diodes operated Qe16 when the output volage exceeds some value above 20 vac at the speaker terminals (the feed is from pins 4 &18)?

Any comments as always are appreciated. And Watthour, as I noted previously your efforts regarding ignorance are indeed having an effect on me. Thanks.
 
Finally, I may be at the end of the protection circuit road. All signs pointed to Qe16 so the (previously replaced) unit was removed and its substitute installed. No change. Bewildered I looked closely at the parts list. No doubt due to my own carelessness I installed an incorrect transistor the first time around.
Now I have used a TI 511 411P unit. The unit comes on and the relay operates as expected and current flows through Qe18 and Re53 and 54 based on the warmth of 53.

Now, is it worth testing the circuit? If so, any suggestions as to method?

Also how do I interpret the TI markings so I can look up the datasheet? The unit is in a TO-39 can and marked in 3 rows: Top - Texas outline, Middle 511, last 411P. I have looked around but can not find anything definitive.

Thanks to everyone for all the help.
 
Just installed the original style output transistors, set the offset and bias and hooked it up. No need to test the protection circuit as that happened when playing Bach's Tocata and Fugue in D minor at somewhat elevated levels.

Once again thanks to all for the help with this project.
 
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