Odd Relay behavior in recapped KA-7100 - Please Help!

[tusntuk2]

Here's a puzzle - I just finished recapping a KA-7100, and the relay acts kind of backwards than expected. DBT test was quickly dimmed, offset and bias set easily, LED may be suspect, although replacing LED also created a weird response. I know LED is involved in normal operation of relay and shut down (Off).

When I power up at full AC the LED glows, then dims. The Relay fires immediately with the On switch. When shutting Off, the relay (and sound) fades for about 3-4 seconds before clicking Off. Kind of the reverse timing of what you might expect the relay to do, right?

Any quick answers?

The amp plays and sounds great after the recap. I did a lot more, too, changing trans. for the relay circuit, changing all diodes and zeners, beefing up resistors where needed and completely rebuilding the power supply.
I get 7V on pin 15, 0.mv(+/-) on 16. The relay is new, flyback diode De27 is UF1004. Timing cap Ce40 is a new 100/35v UKL low leak.

I have rechecked my work, orienting diodes and caps in the relay circuit and more, checking solder joints and values, but I have not found any simple mistakes yet (darn!). Maybe the replacement trans. are suspect? I used an 1845 for Qe33, and a 2383 for Qe34.

Any ideas? I'm off to check more voltages.

Thanks for any help! Y'all are the Best!

 

[bzb882]

Did you mean to post this in the Kenwood forum?

 

[spicer]

Here's a puzzle - I just finished recapping a KA-7100, and the relay acts kind of backwards than expected. DBT test was quickly dimmed, offset and bias set easily, LED may be suspect, although replacing LED also created a weird response. I know LED is involved in normal operation of relay and shut down (Off).

When I power up at full AC the LED glows, then dims. The Relay fires immediately with the On switch. When shutting Off, the relay (and sound) fades for about 3-4 seconds before clicking Off. Kind of the reverse timing of what you might expect the relay to do, right?

Any quick answers?

The amp plays and sounds great after the recap. I did a lot more, too, changing trans. for the relay circuit, changing all diodes and zeners, beefing up resistors where needed and completely rebuilding the power supply.
I get 7V on pin 15, 0.mv(+/-) on 16. The relay is new, flyback diode De27 is UF1004. Timing cap Ce40 is a new 100/35v UKL low leak.

I have rechecked my work, orienting diodes and caps in the relay circuit and more, checking solder joints and values, but I have not found any simple mistakes yet (darn!). Maybe the replacement trans. are suspect? I used an 1845 for Qe33, and a 2383 for Qe34.

Any ideas? I'm off to check more voltages.

Thanks for any help! Y'all are the Best!

Agree, the relay seems to be working opposite from how it should. Should be delay before closure and instant open on power off. I'd say almost for sure it is the protection circuit. Did it work correctly before the recap?

 

[tusntuk2]

Yes, it's a Kenwood KA-7100 integrated amp. Yes, I believe the circuit was working with my first test before recapping. Although it was miles ago and my memory sucks, I took notes that it powered up OK with DBT and with AC, and noted it needed cleaning, etc. It was a good candidate for recapping.

 

[spicer]

Yes, it's a Kenwood KA-7100 integrated amp. Yes, I believe the circuit was working with my first test before recapping. Although it was miles ago and my memory sucks, I took notes that it powered up OK with DBT and with AC, and noted it needed cleaning, etc. It was a good candidate for recapping.

Hi fi engine has the service manual. The KA-7100 manual refers one to the KA-9100 manual for protection circuit description which provides a detailed explanation of it's operation.

 

[tusntuk2]

Thank you, Spicer, I have not seen a KA-9100 manual before. Unfortunately the circuit is different in the KA-7100, and I need advice on trouble shooting the X07-1510-10 relay circuit. Perhaps you can help explain by applying the theory to this smaller circuit, as I am not an engineer.

I have completed several KA-7100 rebuilding projects without experiencing this particular problem. Previous mistakes like polarity reversals, poor solder joints, burned or incorrect parts have been easier to detect and correct, but this time there is not a visible problem, and the amp seems to work. I do get an apparent small "pop" (voltage?) in the speakers when the amp is turned on, and when the relay opens after it is shut down. The LED glows and dims, too, which I have never seen before. Almost like a DBT would when testing a working amp.

 

[spicer]

Thank you, Spicer, I have not seen a KA-9100 manual before. Unfortunately the circuit is different in the KA-7100, and I need advice on trouble shooting the X07-1510-10 relay circuit. Perhaps you can help explain by applying the theory to this smaller circuit, as I am not an engineer.

I have completed several KA-7100 rebuilding projects without experiencing this particular problem. Previous mistakes like polarity reversals, poor solder joints, burned or incorrect parts have been easier to detect and correct, but this time there is not a visible problem, and the amp seems to work. I do get an apparent small "pop" (voltage?) in the speakers when the amp is turned on, and when the relay opens after it is shut down. The LED glows and dims, too, which I have never seen before. Almost like a DBT would when testing a working amp.

I see. Looking at both of them on different screens the two circuits are similar in their operation, Kenwood felt it sufficient to refer protection circuit description to the 9100 manual. There are a few differences but circuits are basically same. I know you've double checked your work but some mistakes have a way of repeating themselves when examined. A cap in backwards, something like that. Check it again using the schematic, silk screen on board and board diagram against each other for conformation. It's like transposing, easy to do it twice when checking. Read the circuit description given for the 9100 and you'll have an idea of how it works and the similarity between the two circuits. Also, a new part might be bad, it happens. There are voltages on the schematic for the 7100 with the relay closed. I'd do a couple basic measurements before getting too involved with theory then maybe replace or check any of the capacitors having to do with timing, like C 39, C40, or C41, and a leaky diode or one of the transistors. A collector to emitter short of Q34 would cause those symptoms... instant on and delayed off as power supply voltage falls below threshold.

 

[tusntuk2]

Thanks, Spicer, that's what I need to do. I have a few extra parts I can swap, too. I go over and over these things, I have used a careful routine to stay out of trouble, but I know these things happen. It's back to the drawing board! er, PCB and DVM.

 

[spicer]

Thanks, Spicer, that's what I need to do. I have a few extra parts I can swap, too. I go over and over these things, I have used a careful routine to stay out of trouble, but I know these things happen. It's back to the drawing board! er, PCB and DVM.

Hopefully others will get involved as all thoughts and opinions are appreciated. Check transistor Q34 for a collector to emitter short as it is the pass to ground transistor for the relay coil and could cause the symptoms you describe.

 

[tusntuk2]

Checked Q34 (the new C2383) out of circuit with DVM and a cheap tester, but it passed the tests with no short detected. Replaced it with the original, same quick relay (On), small pop and then fade out slowly (Off). Replaced with a KSC2690, still the same behavior. Haven't found any backwards parts yet, darn!

Did not try changing Ce40 yet, it's a new UKL.

I'll try checking some voltages around here, see if I can get a better picture of what's happening.

How does the LED factor in here?

 

[tusntuk2]

Found it! Turns out it was a resistor.

I use "story boards" to do this work. I take a 1/2" sheet of styrofoam and paste a paper list of parts on it, then I populate the page with the new parts. As I take each old part out I stick it in the board next to the new part to compare. I work one piece at a time to keep everything straight. When I'm done with a section, say, the Control Amp, I will have a labeled paper full of old parts. This system has worked well, and tonight it helped me find this problem.

Our attention was on the Relay Circuit, notably Qe34 and e-cap Ce40. Changing these parts did not fix the problem, and every visual check of polarity, transistor numbers, diode orientation, etc. found nothing wired wrong. The one-part-at-a-time sequence is slower, but it works for me. I started checking every part I had replaced in the circuit, and comparing it to the schematic and the old part on the story board. I found a resistor I had installed, R83, that was 56 ohms instead of 56K ohms. Yeah, you always feel stupid making that kind of mistake, but I pass it along because it's probably more common than I know, and my "story board" turned out to be the solution.
View media item 27403
Thanks to all for your kind help and thoughtful insight!

 

[spicer]

Found it! Turns out it was a resistor.

I use "story boards" to do this work. I take a 1/2" sheet of styrofoam and paste a paper list of parts on it, then I populate the page with the new parts. As I take each old part out I stick it in the board next to the new part to compare. I work one piece at a time to keep everything straight. When I'm done with a section, say, the Control Amp, I will have a labeled paper full of old parts. This system has worked well, and tonight it helped me find this problem.

Our attention was on the Relay Circuit, notably Qe34 and e-cap Ce40. Changing these parts did not fix the problem, and every visual check of polarity, transistor numbers, diode orientation, etc. found nothing wired wrong. The one-part-at-a-time sequence is slower, but it works for me. I started checking every part I had replaced in the circuit, and comparing it to the schematic and the old part on the story board. I found a resistor I had installed, R83, that was 56 ohms instead of 56K ohms. Yeah, you always feel stupid making that kind of mistake, but I pass it along because it's probably more common than I know, and my "story board" turned out to be the solution.
View media item 27403
Thanks to all for your kind help and thoughtful insight!

Wonderful! It's fixed. Great way to do a rebuild. The mistake, that is one of the easiest mistakes to make. The 56 was right, just needed some zeros.