KENWOOD KA-701 POWERS ON, NO RELAY CLICK

[rccrasher65]

I'm looking for some help, sorting out a protection circuit fault on my Kenwood KA-701 integrated amp. The amp does turn on , but the relay don't click. It usually ends up being, a transistor, or cap on the protection circuit, DC offset problem. I can't read schematics real well, and the ones I have are really bad quality. There are no good quality one's I have found so far. Looking for some professional help. Blue Midnight helped me a lot in the laptop forums, but It's been a few yrs, like 6 or so. I don't even know if he's on here or if anyone does the amps, but any help navigating throught this repair would much appreciated. Thank you in advance.

[stj]

start by testing the relay.

[CapLeaker]

As always with amplifiers, check that all voltage rails making proper voltage.
Then check the 2 amplifiers backwards and compare one to the other. Start with the finals, the driver, then the pre-driver. Any one of them transistors are bad, you get DC on the output and thus the protection relay won't engage. Since the amp is quite old, also check the protection relay itself. Measure the voltage on the relay coil. The relay only energizes when there is no fault.

[rccrasher65]

As always with amplifiers, check that all voltage rails making proper voltage.
Then check the 2 amplifiers backwards and compare one to the other. Start with the finals, the driver, then the pre-driver. Any one of them transistors are bad, you get DC on the output and thus the protection relay won't engage. Since the amp is quite old, also check the protection relay itself. Measure the voltage on the relay coil. The relay only energizes when there is no fault.

Thanks gentlemen, I appreciate the quick response. CapLeaker thanks for the clear readable set of schematics, mine are too blurry to get readable voltages. If you have the time I would appreciate if you could mark on the schematics, these voltages you want me to check first.I have been using a dim bulb tester to power on the amp. It glows lightly for about 3seconds and off. not very bright at all, but no relay click. A very common fault from what I've been told on Kenwood amps Is it ok to power up without the DB tester to get voltages? I'm very rusty at the moment, and will need all the help I can get, if you can tell me where to start to find those voltages. I can get them for you ASAP. I need spoon fed on this one, Much appreciated, George

/

[CapLeaker]

Thanks gentlemen, I appreciate the quick response. CapLeaker thanks for the clear readable set of schematics, mine are too blurry to get readable voltages. If you have the time I would appreciate if you could mark on the schematics, these voltages you want me to check first.I have been using a dim bulb tester to power on the amp. It glows lightly for about 3seconds and off. not very bright at all, but no relay click. A very common fault from what I've been told on Kenwood amps Is it ok to power up without the DB tester to get voltages? I'm very rusty at the moment, and will need all the help I can get, if you can tell me where to start to find those voltages. I can get them for you ASAP. I need spoon fed on this one, Much appreciated, George

/

I don't think you need a total spoon feed, you just need to be able to “see through” the schematic and understand what is what and what it does. This amp got 2 PA's because it is a Stereo amplifier. A channel for the left and another one for the right. Hopefully you're lucky and only one channel is bad, plus you can compare the left channel to the right channel and distinguish which amplifier is bad first place.
first make sure you got these positive and negative DC voltages first place power supply's and voltage regulator. Then check the voltages around the output transistors and write them down. On one of them there will be DC power where it shouldn't be and thus the amplifier is stuck in protect mode, because the relay doesn't engage. Remember, it could be any transistor in the PA module creating that DC on the output.

[rccrasher65]

Cap leaker, thanks, but have to slow down. I've been away from this for a long time, and never worked on an amp before.


I'm going to look for all these voltages you have pointed out, but if you can just tell me one step at a time, and where to find the specific voltage, till I get the swing of things again. Eyes aren't that great either. so I have to open the diagram to about 150% to see, I can't read what's in green marker. give me a few. for the readings.Thanks again for your help,, it's much appreciated. This amp has a lot of sentimental meaning for me, was given to me by my father, I'm hoping to restore to working condition, Thanks again for your help, and time.

[CapLeaker]

The two words I wrote in green was “output transistors”.

while your at it, maybe take some straight shot, high resolution pictures and upload them here using the attachment function and just chose thumbnail or none on the upload.

[rccrasher65]

The two words I wrote in green was “output transistors”.

while your at it, maybe take some straight shot, high resolution pictures and upload them here using the attachment function and just chose thumbnail or none on the upload.

I got a few voltage measurements for you. I have to find all the components on the foil side because of clearance, very tight in there, plus the fact I cant see worth crap any more.Power supply voltage is pin7 -29,75V pin 8 ground pin9 29,68V RL-1 52,3V and across coil 52,3V Q16 -29.94 Q17 +29,98V I also measured DC offset from speaker terminals and got right channel 193,0mv and left 0.0mv that's it for now.I will get more this evening. let me know if this tells anything about the problem.

[rccrasher65]

Well just my luck, as I was continuing to get voltages I decided to start with Q11, being a little shaky, (should have stopped) I slipped and must of hit both pins of Q11, and a little spark, and little burn smell. Now I discover that the relay now clicks in 3 seconds as it should. How about that for some crazy crap, but I now have 048,4V on right speaker terminals, 052,4 V on the left, Dim bulb still shows a short. I do believe I blew the 2 IC's right next to Q11, on heat sink. They show continuity on all three pins, The other 2 do not have continuity between the pins, I thought Q11 was suspicious when testing without power, It showed resistance all three pins in any direction, Now I caused a more serious problem than I had. What to do next? The relay does click now, Q11 will get repaced even though it now works,

[CapLeaker]

O.k. So how this amp works is with positive and negative voltages. These have to be present, You notice that one transistor sits on the positive (Q13&14 NPN) rail and the other on the negative (Q15&16 PNP). That's why it is important for the positive and the negative voltage to be present. Each NPN is paired with a PNP transistor completing an amplification stage.
Measure DCV at R25,26,27 and R28. These should be big resistors. Also measure the resistance on them (should basically show a short as 0.33Ohms.
Also should test the Q13-16 transistors with the DMM in diode mode. See if there are shorts.
If you get in trouble measuring things in circuit (can happen) here is a little trick. “When in doubt, take it out!” …or lift one leg and measure it again.

I think with Q16 you meant actually Q18. So the regulated 30V is o.k.
Also notice that there are power supplies for the 52.7v and two power supplier for the -52.7v there. So you basically checked one power supply, because the regulated 30v and -30v is there.

[CapLeaker]

Well just my luck, as I was continuing to get voltages I decided to start with Q11, being a little shaky, (should have stopped) I slipped and must of hit both pins of Q11, and a little spark, and little burn smell. Now I discover that the relay now clicks in 3 seconds as it should. How about that for some crazy crap, but I now have 048,4V on right speaker terminals, 052,4 V on the left, Dim bulb still shows a short. I do believe I blew the 2 IC's right next to Q11, on heat sink. They show continuity on all three pins, The other 2 do not have continuity between the pins, I thought Q11 was suspicious when testing without power, It showed resistance all three pins in any direction, Now I caused a more serious problem than I had. What to do next? The relay does click now, Q11 will get repaced even though it now works,

Now you blew a transistor. probably an output transistor. Q11 is the driver stage. Q13-16 is the final power stage. All the shorted transistors have to be replaced.

[rccrasher65]

I sort of figured , I messed it up, I don't understand how testing Q11 caused the relay now to work, that's when I slipped and touched another pin on Q11, and shorted out the transistors on the heatsink. they were ok before I started, and now the have continuity between all 3 pins in every direction.I,m going to get new replacements for all the transistors,caps, and some resistors for spares, just in case, I use digikey, and mouser, Do you have any suggestions for good replacements. I'm going to list the original components on here, and If you have any suggestions for better replacements I would appreciate your suggestions. I'm going to do them all damaged or not. In the time being,is there anything I can check while we wait for replacements. I do really appreciate all your help with this amp.

[CapLeaker]

I usually don't have any luck finding original part number replacements. So I sub newer transistors into it. I guess you have to find which ones are shorted and then I hope I am able to help you finding subs. Just be warned that maybe they need to be installed 180 degrees backwards.

[petehall347]

you now somehow have problems with the protector circuit . or your meter was on millivolts .

[rccrasher65]

I usually don't have any luck finding original part number replacements. So I sub newer transistors into it. I guess you have to find which ones are shorted and then I hope I am able to help you finding subs. Just be warned that maybe they need to be installed 180 degrees backwards.

I'm going to find as many of the originals as I can, there are plenty of old stock out there, I'm replacing all of them on that board, including Q17, and 18, and caps too. I don't want to take a chance of more failure, I've done enough already. If at all possible, can we mark on the foil side, where those voltage test points are, I don't want to make any more stupid mistakes, not knowing where to place my positive probe on, I'm going to try and get a few pics on here, never was good at it even back then, when I was really active on here, thanks again,I'll post what I find,

[rccrasher65]

you now somehow have problems with the protector circuit . or your meter was on millivolts .

I have a fluke auto ranging DMM, thanks for your reply

[rccrasher65]

I'm going to find as many of the originals as I can, there are plenty of old stock out there, I'm replacing all of them on that board, including Q17, and 18, and caps too. I don't want to take a chance of more failure, I've done enough already. If at all possible, can we mark on the foil side, where those voltage test points are, I don't want to make any more stupid mistakes, not knowing where to place my positive probe on, I'm going to try and get a few pics on here, never was good at it even back then, when I was really active on here, thanks again,I'll post what I find,

I have found the replacements I need, Ordered, and on the way. Is there anything I can do while we wait for parts? I want to thank you again for your help, and Have a very Happy Easter as well.

[CapLeaker]

Upload some straight shot, high resolution pictures using the attachment function. So we can see something.

[rccrasher65]

I'm going to try and upload some pics. do you have to do one at a time or can you make a file and upload that with pics in it? Happy Easter, parts should be here this week some time. Thanks

[CapLeaker]

Just click on the “Upload Attachments” button below.