need help again with a kx1200.1 (red board) with no audio out. power supply is fine, input board is fine, i get audio into the main board and the relay cliclks on without protection light lit but i get no audio out of it. papazbill can oyu help me again please?
U14 is the chip I was referring to in previous post.
Measure the frequency w/o signal at the input to the output coils with one probe on neg spkr terminal (black or red probe is not important since you will be using the AC function), should be 80Khz.
If you are able to measure duty cycle you should see a 50% duty cycle, if you then apply signal using a 100hz test tone you will see the duty cycle vary slightly as you turn volume control through it's range. Or you can measure the frequency on the output of output coils which should be 100hz if the class D circuit and outputs are passing a modulated drive.
This may be premature, so only if you have modulated drive to the coils and coils are not open, which is not likely to have two open coils the signal is not passing through the relay. Which means the relay contacts are corroded or pitted, bad or cold solder or relay turn on circuit is bad.
Do you hear the relay click ? Is there approx. 14 volt drop across D92 when amp is fully powered up?
i don't get 80khz at the output coils like you asked, but i do get it at pin #4 of the lm361. also, remember that i've changed the Q104, Q113, Q126, Q135 drivers as well as the D107, D108, D120, D121 diodes. all resistors have been checked and are within tolerance. also, here are some pics:
replaced u11 with a known working one because i didn't have any new ones in stock. fired the amp up with a speaker in place, inputs plugged in and all i get is a touch of static on the bass hits of the music, silence between bass hits. gain up or down, xover up or down and bass up or down changes nothing. lm361 was already replaced with new also, it was the first thing i did.
Check and reflow solder to all parts replaced, particularly IC's and transistor drivers.
There are 5 resistors and 1 inductor that should be checked. For Q113,135-A1381 they are 1 ohm,120 ohm,2k ohm,910 ohm,180 ohm. For Q104,126-C3503 they are 1 ohm,220 ohm,2k ohm,910 ohm,180 ohm.
L101,102,103,104 can be checked with an ohmmeter and as long as they are a couple of ohms they should be good.
Do the Zener diodes you replaced all have a 12 volt drop across them?
I realize you may have done all this, but it's easy to overlook something, especially in this complex circuit. If U11 is in fact good and we know that the U14 is based on grounding Pin 3 test you performed, it's hard to pin down the problem, because it lies in the feedback loop, such as bad solder, broken trace or a defective replacement part.
BTW, Q105-108,Q114-117,Q127-130,Q136-139 should be checked with an ohmmeter. compare one bank to another and if you see any discrepancies, you should change all 4 sm transistors in a bank. Each bank consists of two KTC4373y's and two KTA1661y's.
Also, It occurred to me that one of the output mosfets maybe be weak or open. You may be able to detect with an ohmmeter, but you should remove outputs and see if the LM361 is outputting 80khz and if its getting through the drivers to the gate resistors. You can do this one bank at a time to save on parts, or remove all at once and replace with fresh batch matched mosfets.This would be my choice.
The 3.3kohm 5w resistors next to D108 & D121 should have the -rail voltage on one side. To illustrate look at the the two 3.3kohm resistors feeding D107,D120. The voltage on one side will be the + rail (71volts with a 14.4 battery term voltage) the other side will be 12volts less or approx 59 volts,using the transformer center tap.
Okay, so the reason why you are not seeing the 12 volt drop across D108,D121 is either two open resistors (not likely) or the -rail is missing. Dollars to Doughnuts you have broken leg/s on the power supply filter inductor. Fairly common issue with this amp. If this is the case, you may be able to stuff leg/s back in board and resolder.Keep your fingers crossed.