Kenwood KR-9400 Multiple Issues; Help Wanted

[Shaun b]

A while back I posted this problem but life happened and I had to focus on something else for a minute but this weekend I decided to look at this thing again. I will tell you what I know and then I hope someone can/will help me get this beast going, so here we go.....
When I first got this thing it would power on but no sound from any source including headphones. I found the service bulletin with the service manual and I followed it to the letter and then turned on again. No sound still, anywhere.
so by process of elimination, I have found the problem to be in the left side output board. If I "un-seat" it from the main power board and have only the right side hooked up, it comes out of protection within a couple seconds of powering on. However I soon discovered another problem, I still get zero sound from any source.
Heres a couple other things I know or have done that may or may not be a clue to someone as to what is going on.

1. when I powered it on the first time, all lights including the small red lights for each source were working as well as both meters were working. all 4 fuses have been tested, replaced and tested again. they are good however I'm not getting but have my source lights and both meters have stopped working.

2.output transistors have matching output voltages of -68 and +68

I'm not a technician but I have a general understanding of components and their function. I have several meters and I can solder pretty good and I'm not afraid to get inside this thing as long as I have instructions. I'm pretty sure I can figure out what is going on in the output board but I'm not sure why I'm still not getting sound from the other side when it does come out of protection. Any help would be greatly appreciated. Even if it someone all the way in Honduras Also if it gets to the point where I feel I cant get this thing fixed, I would not be to proud to send this to a trusted and well known member of this site who has repaired gear for other members. If anyone has used someone from this site with positive results, I would love to hear about them also. Thanks in advance for any help.

Shaun

PS I have cleaned the pots and both pins are in the right way on the back.

 

[gort69]

I remember....if you're certain the jumpers are in correctly (on the horizontal, not the vertical) , I'd check the regulated voltages on the power supply - +14VDC at pin 57 and -14VDC at pin 60 and for +55VDC/-55VDC at the big caps

 

[rickl]

2.output transistors have matching output voltages of -68 and +68

Shaun, my KR-9400 Service manual says the collector of Q201/Q203 should be +55vcd and -55vdc for Q202/Q204. I'd suggest you measure the voltages listed in the service manual and post your findings with what is listed.

I'd focus on the power supply , pre amp , main amp boards first. As gort listed above, +/-14vdc and +/-55vdc are used throughout.

Example, pin1 on the preamp (x08-1270-00) should be -14vdc, pin2 should be +14vdc. Gort's request to measure pins 57/58 and 60/61 on the power supply board (x00-1640-10) will tell a few things. You can use pin 59 for the ground clip on your DVM.

I haven't been in my 9400 lately so I don't remember how hard this is to measure. use common sense and use the service manual for guidance.

 

[mbz]

Not familiar with the amp/Rx.
Does the unit have a mains voltage selector on the back?
Or does the voltage printed on the back plate match the mains voltage?

Is it a 100Vac unit running on 120Vac mains?
OK, it's a long shot...

 

[petehall347]

main left amp board voltages at pins 7 10 and 16 ? obviously needs board installed

 

[Shaun b]

Thanks for all the help you guys. Here is what I got so far and Im not sure exactly what it all means but here goes;

All 8 OT are + and - 62VDC
Preamp pin 1 -14.6
2 0

power supply pin 57 -0.8
58 -0.7
59 0
60 -14.8
61 -14.8

main left pin 7 59.2
10 62
16 59
I hope its not terrible but it doesnt seem good.

 

[petehall347]

no fuses blowing so check all resistors .especially any fuse ones

 

[gort69]

I would pull and test Qk1 (2sc1419) - I suspect it's fubar. (which isn't surprising)

 

[Shaun b]

Im on my way home from work now and will check that I will let you know what I find. Thanks for the help, its very appreciated

 

[petehall347]

i missed those supply voltages ..
check fk4 first .

 

[Shaun b]

I would pull and test Qk1 (2sc1419) - I suspect it's fubar. (which isn't surprising)

Fk4 is good as is all fuses.

Well if 2SC1419 wasnt my problem before, it certainly is now. It came apart rather easy and in such away that I could see inside the plastic. Im not sure what its supposed to look like but it appeared "burnt up" inside. I have already ordered a new one so now I wait. Is there anything else you think I should look at or wait until the new part is in? Thanks again.

Shaun

 

[petehall347]

check the other power supply components

 

[Shaun b]

so my part came in and i installed it last night. Now for the first time, all the lights and dials came on and it is beautiful, but still no sound. It still will not come out of protection mode. I took my readings again after replacing 2SC1419 and here they are;

all 8 output transistors are -62 and +62

pin 57 13.5
pin 58 13.5
pin 59 0
pin 60 14.6
pin 61 14.6

preamp pin 1 -14.6
preamp pin 2 0

im going to start again this morning looking for the problem but again, I would take any advice or suggestions from those who have any input.

Thanks to all who have chimed in.

 

[gort69]

As you said - multiple issues.

Re: 0V at preamp pin 2. Set your tape monitor switch to source and set the input selector to phono and recheck.

Check pin 5 on the tone board (+14VDC) and pin 6 (-14VDC)

How is your meter connected to get +/- 62VDC at the outputs? (black to chassis, red to transistor case) That's what has me puzzled - should be +/-55VDC. A volt or two either way, but 7 volts is off by quite a bit.
Measure voltage at the filter caps - black lead to chassis and red to each of the 4 lugs. 2 of them should read 0V, and the other two +55VDC and -55VDC give or take.

 

[mbz]

Regarding +/-B at +/-62Vdc.
This is an unregulated supply.
What is the voltage rating on the main filters. SM has 15000uf/50V with a +/-B at +/-46Vdc.
If main filters are 50V then it's a voltage "input/selector" problem
If mains are 63 or ...80V then it's a SM error, move on...

 

[Shaun b]

As you said - multiple issues.

Re: 0V at preamp pin 2. Set your tape monitor switch to source and set the input selector to phono and recheck.

Check pin 5 on the tone board (+14VDC) and pin 6 (-14VDC)

How is your meter connected to get +/- 62VDC at the outputs? (black to chassis, red to transistor case) .what has me puzzled - should be +/-55VDC. A volt or two either way, but 7 volts is off by quite a bit.
Measure voltage at the filter caps - black lead to chassis and red to each of the 4 lugs. 2 of them should read 0V, and the other two +55VDC and -55VDC give or take.

yes, black to chassis and red to case. Still zero at pin 2 with tape at source and input at phono. Tone board pin 5 is +14.2 pin 6 is -15
Big caps are 2 leads at 0 and back cap is -12.8 and front cap is +8.
Inow have sound coming out of right speaker if the left amp board is not seated

 

[Shaun b]

Maybe I have been staring at this thing to long or Im over-thinking this but, if it comes out of protection and I get sound from right channel when left main amp is unseated(harnesses to output trans are left connected) doesnt the problem have to be on the left main amp board? Im so danf happy to get sound out of right side I dont know how Im going to act when I get this thing going. I have a Kenwood 770D Turntable paired with KA-7300 and KR-7500 now pushing Altec Lansin Model 14s and I cant wait to get this beast inside. Again, Thanks to everyone who has offered help. you guys are why this site is so damn cool

 

[gort69]

Seems the problem is either with the left amp board or the output transistors on that channel.

Do you see any burned resistors on the left amp board?

I would be inclined to remove the left channel outputs and test them. Seat that amp board in the edge connector with the outputs still removed and power it up. If it comes out of protection you should get sound of the channel if the board is ok (use headphones and don't crank the volume)

I don't know what to make of your voltages at the filter caps - should be the same as the collectors on the outputs.

I guess the +/-55v in the manual is an error that was repeated 8 times by my count. FWIW - the manual I'm looking at shows the filter caps to be 15000uf/80V. Downloaded from here: https://www.vintageshifi.com/repertoire-pdf/Kenwood-9.php

 

[petehall347]

check emitter resistors
main fuse intact says emitter resistors or outputs failed open .
voltage on output should tell a tale or 2

 

[Shaun b]

One of the first things I did last week when I started was replace all output transistors and they tested good before I installed them. I really hope they are alright but I will check. I will also check emitter resistors.
I'm confused by the voltages at caps to. Now I'm wondering what I had connected and not connected at the time of reading.

I just walked outside rreal quick to get something for my wife out of shop and I took just a quick look at emitter resistors and they all tested at .5 ohms so they are good. I tested 2 of the 4 outputs and they were good. Ill check the other 2 in the morning.

Yes they are 15000uf 80v. Could they be that low and me still get sound from one channel?
Its got me confused so I'm gonna call it a day and think about ahain tomorrow. Thanks guys. Sound from one side was the highlight of my day!