Two Kenwood KR-5600s in the house, need help on one

I messed around and picked two KR-5600 receivers last week. One is pristine and seems to work fine so I haven't messed with it. I just hooked up some speakers and have been letting it entertain me while I try to figure the other one out. The problem unit has neither AM or FM. The pointer light comes on, but nothing happens when running the tuner through the frequencies. I did notice that moving the selector into phono gets a nice hiss from the speakers, so I have started checking to see if the tuner board is getting any power. It appears that the transformer is good. Voltage reading are post 13 -39.2 post 12 +39.2 post 10 +6.8. Going to the output side of the regulator is where things go bonkers post 4 -19.6 post 3 +36.4 , 16 0, 15 0 post 5 +3.43 and post 11 8.63.. So, it looks like I have a problem that I need to fix prior to that point. I've never trouble shot any solid state components before and I'm pretty lost. Most all of my work has been done on 480 volt motor control centers (in the middle of the night to get the broken down plant running) so I'm not totally a newbie to circuits, relays, etc., just no solid state work. Any pointers on procedures to test components or suggestions for some good reading material would really be appreciated. By the way, newbie to the site and this is my first post.
 
Welcome to the forum, I am new also. I will start looking at your schematic and try to help.
In the interim get ready for some good advice from others.
 
welcome to the site.

i'd suggest you either update your profile to include your location or post it.

I recently restored a KR-5400. not sure how close they are to your 5600 but I thought it was pretty nice.

i'd start by cleaning the am/fm/aux/phono switches before poking around. I've found it might be that simple.

pull power, clean contacts and work switches 50 times. let sit for several hours (I know this is the hardest part) and plug back in and try it. Report back.
 
I'll get to the profile tomorrow. I'm heading out the door to a meeting. Thanks. All the pots have been cleaned as you suggested. I found one coupling broken on the far right hand side for the rod running to the rear. Got that fixed for now and also found that the source switch knob was not timed correctly to the switch. I have a schematic and service manual in house and I'm ready to troubleshoot and repair. One thing that I did notice is that the tuner board is a different number than what is shown in the service manual. I have a x05-1440-10 and the manual pictures a X05-1310-11. That may be fun figuring out. I can tell that someone has been into the radio as there are some missing screws that are not accessible until the covers and sides are removed. But, there doesn't appear to have been any work done on any of the boards. If there was, whoever did the work was very good at it. I see no spots that appear to have been hot so I'm guessing this problem is a component old age break down problem.
 
Hopefully you have a schematic to look at. If not you can find one here: https://www.hifiengine.com/

You should have 13.5 v at pin 5 on the power supply board. The other values look OK; did you mean pin 6 v. 16?

If you look just below Qk1 on the schematic you will see the voltage expected at that point. I suspect this may be obvious, as you, like me have some experience with MC circuits. If so, no offense meant. Since Ck11 is across pins 15 & 5 I would suspect that it may be becoming a resistor. I have found several of these on my own pair of KA-7002's.
So while you are waiting for the cleaner to evaporate trace wire no. 14 over to pin 17 on the tuner board just to make sure it has a clear path as I have seen insulation cut going around chassis partitions. At pin 17 you will both voltage and current values. These values can be checked once you resolve the power supply issue.
 
No, pin 16 is shown right next to pin 15 and should be a ground. I haven't even spotted a pin 6 on that board. (yet) Pins 15 and 16 are both marked as ground so a zero reading is good. I will have to read up on how to take an amperage reading. If my memory serves me correctly, amp readings are taken with the meter hooked in series, but I'm not 100% certain. When I check Ck11, do I have to take the capacitor loose from the board on the pin 15 side?
 
Welcome Aboard!

The diagrams at HFE show several tuner boards (3 pages of diagrams) including your X05-1440-10.
 
Here's what I gathered from your previous posts:

Power Supply X00-1730-10
Pin 3, +36.4
Pin 4, -19.6
Pin 5, +3.43
Pin 10 +6.8
Pin 11, 8.63
Pin 12, +39.2
Pin 13, -39.2
Pin 15, 0
Pin 16, 0

And here's the way I read it should be:
Pin 3, 18
Pin 4, -18
Pin 5, 13.5
Pin 6, GND
Pin 7, GND
Pin 8, 0V
Pin 9, ~5.5
Pin 10, 7VAC
Pin 11, ~2.5
Pin 12, 38
Pin 13, -38
Pin 14, GND
Pin 15, GND

If you are actually reading 36V at Pin 3 (referenced to chassis ground) that's double what should be present there. I would look closely at R1, the 390Ω/1W resistor for a possible short, and R3, the 470Ω/1W resistor for opens/bad connections. Of course, if the load from the preamp is not connected, that voltage would tend to float up to the 38V bus voltage through R1, but R3 is there to keep it from doing so.

Pin 5 (tuner power supply) should be at 13.5V, and your reading is 3.4V. That needs to be checked, and the regulator (Q1) and zener (D5) should be verified. Excessive load from the tuner board or the muting board could also be dragging this supply voltage down, but that would likely result in heating of R9 and Q1 on the power supply board.

Pin 11 supplies the STEREO indicator LED, and if the tuner board is not grounding the other end of the LED, the voltage at Pin 11 will float up closer to the 10VDC supply ahead of R7. That voltage could be completely normal.
 
Thanks Watthour, I will note your suggestions and perform those checks. Noticing Pin 3 and Pin 4, you say 18 and -18. Looking at the PC board diagram it says 14 and -14, but looking at the schematic it shows 15 and -15. I'm learning as I go so please forgive my lack of knowledge. Is it best to rely on the schematic for the numbers when testing? I'll certainly be happy when my hard copy service manual arrives as I find it rather maddening to try and work with pdf files on a computer screen. It may be awhile before I can actually start testing components as I have to either order or find some tools to aid in desoldering. I don't want to make a mess of the board.
 
IMG_3918 (1024x683).jpg IMG_3921 (1024x683).jpg IMG_3918 (1024x683).jpg IMG_3921 (1024x683).jpg
View attachment 1439835

If you have doubts, you're fortunate to have a properly working receiver to compare.

Thank you. Now I know for sure which page to use for my readings. I pulled the top board out and got a nasty surprise or two. The first surprise was the tuner cord snapping off of the pointer when I barely rubbed it with my arm. I was really trying to not do that. That nightmare can wait until I get power to the tuner. The second nasty surprise was when I flipped the board over and it looks as if someone attempted to solder using a torch. R3 was not even connected on one end, the board has a crack in it that wasn't visible from the top, and the crack appears to have possibly separated the foil in a couple of places. I will try to attach my first photos to show what is going on. I'm borderline ready to just try to find a different board.
 
Meh, that's a simple board, easily repairable. R3 open/disconnected? That was one of the guesses. I had no idea you would find THAT, however. You mentioned in an earlier post that your didn't want to make a mess of the board. Well, that ship has sailed, and you can't do any worse than what you found so you might as well get at it.

After grabbing and enlarging your photo, it appears the traces are intact, and that whole thing could be repaired. Glue up the board crack, bridge the broken traces with small pieces of solid wire, then apply solder along the trace. Once repaired, clean off all the contamination and flux residue, then seal the bare areas with a conformal coating. Check / replace the filter caps, get those hot resistors on stood well up off the board (just like they are), and you might be good to go.
 
If you are uncomfortable soldering, practice a bit on a scrap unit, such as an old PC power supply or other trashed device with through-hole mounted devices.
 
As for amperage readings; try to find a resistor in the circuit and measure the voltage drop across it then use Ohm's law to calculate the current. Usually this is much easier than breaking the circuit to install an ammeter. I also try to use my clamp-on ammeter if I can create enough slack in the wire to fit it in.
 
Soldering is a challenge for me. I have a pronounced essential tremor that makes delicate work out of the question most of the time. Doc has me on a barbiturate related drug used for Parkinson's disease to try to calm the tremor. I'm reluctant to use more than a mild dose of it, but may have to in order to do this kind of work. The resistors checked o.k. but I had issues with my meter checking the transistor and zenor diode. My thoughts are to just order new along with the capacitors and while I'm making an order I'll get a smaller soldering iron, a desoldering pen, and some supplies. I think everything that I have on hand is acid based for plumbing work. I really need to find some good study material to refresh my memory on components and circuits. This may take awhile as I really want to understand the what and why part of each circuit rather than just being a parts changer.
 
Brad, I'd clean the area on both sides of the board to fully understand what is broken or just burned. I've seen worse.

Feel free to post a new pic once you clean the area.
 
I put the board back in to run a quick check and noticed immediately that the relay did not pull in. No change in the output voltage to the tuner so I started back tracking. I found that the voltage to the base of Qk1 was way low and kept backtracking finding that input voltage on Rk4 was way off (+5.1) and output on Rk6 was low (+5.8). The way I read it, input to Rk4 should match the output of Rk2, which is does, but the input to Rk2 is reading +7.72 when it should be -38. Removing the feed wire from pin 13, the voltage reads roughly 11 volts with no load attached. I'm guessing that this means something is goofy in the bridge rectifier, probably due to a short in the power supply board. I still have +38.7 on pin 12. I'm not even clear in my thinking about how the positive voltage can still be ok and the negative voltage can invert to a positive reading.
 
Pin 12 should be about +38V, so your measurement there seems correct. The low voltage at Pin 13 could be the result of a failed bridge rectifier, or could be due to a load downstream absorbing all its energy. That line is also connected to the mute board AND the -38V supply to the main amplifier outputs. If one of those outputs is shorted E-C or has other problmes, the power would be pulled down. .

I am also curious about the power suplpy board voltage measurements across R1 and R3, and how they compare to R2 and R4.
 
R1 in 38 out19.1, R3 in 19.7 out 0, R2 in7.72 out 5.1, R4 in 5.1 out 0 I hope that I have my directions correct. I also was concerned (still am) that something down line had a direct short and perhaps knocked out the rectifier. There is no telling when someone else has been working on it. I was hoping that once I pulled that leg coming off of the rectifier loose from the board that the voltage would come back up, but it didn't by much. I have the board removed again and I'm cleaning it up and looking for tracking. I'm not finding anything that looks like it might have shorted a hot trace over to a grounded trace.

I am assuming that the bridge rectifier has failed. I'm still trying to wrap my head around how it can put out good voltage on one leg and so much less voltage on the other leg. Would one failed diode do that?
 
Well, I assumed something that was not correct. I just powered up the transformer and bridge rectifier and found that the two wires that I was assuming were the feed to the board are now dead so they are evidently tapping power for use elsewhere. If my memory is correct they are wire numbers 31 and 32. There are two green wires wrapping around that are soldered into the board at point A which is the same as pin 12 and point B which is the same as pin 13.. A wire has +39.1 and B wire has -39.1 volts. I'm thinking now that I can leave the two heavy gauge wires unattached and hook the board back up and see if the voltages across those resisters look a little better.
 
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