Set to restore a Kenwood Model 500
- Thread starter hopjohn
- Start date
Cosmin2000
Active Member
Just beautiful! Thanks for sharing your work and passion for this Kenwood model with us.
Kenwood 500/600 Restoration Resource Guide
Cdkands Model 600 Restoration
Tapeheads Model 600 Restoration thread
Hallo-Fi Electronics Model 600 Restoration
hifiengine Model 500/600 Service Manual and Schematic (free registration required)
Vintageshifi Model 500/600 Service Manual
Relevant AK threads
Power Cans for a Kenwood 500 Supreme
Kenwood-Trio Model 500 and Model 600 Power Bandwidth Tests
Yet another Kenwood 600 thread
Kenwood Model 500\600 - Trying to remove the volume knob
Kenwood Model 600 Troubles
Kenwood model 600 adjustment pots
Kenwood 500 restore advice
Kenwood Model 500 No left channel/ Right channel cuts in and out
Help me fix this Kenwood 600
Just picked up a Kenwood Model 500
Kenwood Model 500/600
Kenwood Model 600 relay disengaged delay too long after power off
Cdkands Model 600 Restoration
Tapeheads Model 600 Restoration thread
Hallo-Fi Electronics Model 600 Restoration
hifiengine Model 500/600 Service Manual and Schematic (free registration required)
Vintageshifi Model 500/600 Service Manual
Relevant AK threads
Power Cans for a Kenwood 500 Supreme
Kenwood-Trio Model 500 and Model 600 Power Bandwidth Tests
Yet another Kenwood 600 thread
Kenwood Model 500\600 - Trying to remove the volume knob
Kenwood Model 600 Troubles
Kenwood model 600 adjustment pots
Kenwood 500 restore advice
Kenwood Model 500 No left channel/ Right channel cuts in and out
Help me fix this Kenwood 600
Just picked up a Kenwood Model 500
Kenwood Model 500/600
Kenwood Model 600 relay disengaged delay too long after power off
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Thanks EW. My restoration is going nicely thanks to the wonderful documentation here. I left Qe5 in place. The power amp side of my 500 is completely finished. Moving on to the preamp next weekend. A little tip for getting to the filter cap clamp on the rectifier side. If you play with the transformer wires a bit and straighten them out you can rotate the transformer a full 90 degress inside of the chassis. It makes removing the old caps a breeze. For some reason though It was a little harder rotating it back into place and I needed to remove the back cover.
Been using 27V 1W zeners here for ages. Two 14's look sloppy to me, and with two 5% devices you end up with one 10% device.
Edit: I won't change what I wrote ('cause that makes it look like I'm pretending I didn't screw up), but I think I was actually considering a different amplifier back when I wrote this. About the only combination that has given me the desired 28V is to use two 13V 1W zeners in series. I apologize for that guys. My bad.
Edit: I won't change what I wrote ('cause that makes it look like I'm pretending I didn't screw up), but I think I was actually considering a different amplifier back when I wrote this. About the only combination that has given me the desired 28V is to use two 13V 1W zeners in series. I apologize for that guys. My bad.
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Changes again to Dz3/4. I think we've got it figured out this time with EW's help. I made changes to the list to reflect using two 1N4743A 13V 1W Zeners in series at Dz3 and Dz4 on the main power supply instead of the 1N4750A 27V 1W Zener at each position. Thanks guys.
Rodger that, thanks for the clarification. With 28.4V measured at 28V nominal using the 1W 13V parts, any further tweaking will probably only result in a debate over how big the gnat's ass is, but if you find the 2W or 3W 27V zeners more capable when you have the opportunity to experiment with them, please let us now. Your wisdom is much appreciated EW. Cheers.
Gort69 pointed out an omission in the list for the pre amp board. There should be a total of 14 caps on the board, not 12, the two missing caps were 47uf 10v x2, where I used 47uf 16v x2 Elnas. I've corrected the list to include them now (Version 1.3). Thanks gort.
Thank you for this post. I've got one that I like and I'm thinking of recapping it. It works just fine but has some static occasionally when there is no signal to it. It's not that much but I know it needs a recap before it blows something. I commend you on your parts list, and I appreciate all the information.
naveed
New Member
Filter capacitor removal and Relay / Rectifier board access.
I first disconnected the wiring from the bottom of each of the large filter caps. Then, I placed the amp atop two large books, each about three inches tall, carefully spaced such that the books are at the far ends avoiding any jacks or terminals on the back of the amp. Next, I sprayed soapy water around where the cap and bracket meet serving as a lubricant. I then gently wiggled at the two filter caps until they had become loose enough to take out by hand. With these capacitors out, it opens up easy access to the top half of the clamp and its mounting screws (shown already removed in Photo 1 below). The bottom half of the clamp was still nestled behind the transformer. To access these screws, I needed to remove it from the chassis. The transformer was held in place by four 8mm hex nuts on the reverse side which I removed with a socket wrench. Before pulling the transformer free I placed a rag beneath it to avoid any damage and freed up the wires at the back to provide a bit of slack. With the transformer off the chassis it can be maneuvered around a bit to reach to the two remaining screws left holding the clamp.(see Photo 2 below)
The second transformer is removed in the same way as the first. Access to the top screws was straight forward through the gaps to the inside of each of the rectifier heat sinks. (See Photo 3) The screws behind this transformer were a bit more challenging to reach. The capacitors are left in the way, but with a little patience and maneuvering of the transformer an opening for the screwdriver shaft presented itself. Once the clamp was freed from the chassis, getting the caps/clamp out required me to take the two screws from the relay/regulator mount out. With the screws removed, I was able push the circuit board upward slightly which provided some much needed space for the clamp/caps to slide left and then out.
With the filter caps removed and the transformers re-attached to the chassis, the amp can now be placed bottom down. The relay/rectifier board is now accessible for solder work to remove and replace the old relay. (Photo 4)
Photo 1: The Kenwood 500 atop two books backside down.
Photo 2 : Accessing the mounting screws of the filter cap clamp shown behind the transformer.
Photo 3: Removing the second transformer with the caps still in place.
Photo 4: With the filter capacitors removed the solder side of the relay/rectifier board is accessible.
deltalight
AK Subscriber
Right Channel Power Amp (X07-1440-00)
Every transistor on the right channel power amp board, with the exception of the Dual FET, was evaluated. None of them test shorted. All of the resistors were checked for value in circuit and only a couple of them weren't close to the rated value. Those two were pulled and they checked out fine.
I suspect either one of the the two 2SA810 (Qe3,Qe4) or the 2SC1452 (Qe6) were going bad though, as these are known to fail. They were replaced with KSA1381 and KSC3503 respectively. I also replaced 2SA673A (Qe7, Qe10) with KSA733C and 2SC1213A (Qe8,Qe9) with KSC945C. The heat sink mounted Qe11,Qe12 were given fresh compound.
Though they tested fine, I figured I'd replace the zener diodes while I was in there. For De1 EQA01-24 24V 500mA, I used a 1N5252B. For De2 YZ-140 14V 500mA, replaced with a 1N5244B.
R14 looked pretty shabby (see the before photo), so it was replaced with Vishay/Dale 1K metal film. Having looked at photos of other Model500/600 amp boards and also the parts list in the service manual, my board is the only one one I've seen use a 1K resistor in that position. The others all had a 100Ohm part. I verified that the left channel had a 1K installed also.
An orange low leak Elna CERB 10uf 25v capacitor is checked. Notice the ESR measures pretty poorly when compared with say a Nichicon PW of the same size and value which likely has an ESR half that. This is not an anomaly, all of the 10uf orange Elna low leak caps measure this way and seems to indicate the leakage current was of more importance to the engineers than the ESR.
One of the special features of the Model 500/600 Supreme amplfier is this Sony 2SK58 dual FET which is enclosed in this small, shielded metal case due its temperature sensitivity.
Here is the finished right power amp. I've squeezed three Wima 10uf 50v polyester caps in place of the 10uf 25v Elna CEBR caps at Ce5-8 and an Elna Silmic II 10uf 50 at Ce5. Each of the Vr trimmers were replaced with 3386H Bourns single turn. Vr1 and Vr2 got 500ohm, and Vr3 a 50K. Vr1 is the coarse adjust and Vr3 the fine adjust for the offset metered at pin 13 and set as close to 0mV as possible. Vr2 is the bias adjust set to 25mV while metered across pins 5 and 6.
After a partial reassembly and the 4 Sanken outputs reinstalled I fired the 500 back up under full power. I set the offset and bias per the service manual and then shut down long enough to hook up a CD source to Aux 1 and have a listen through the headphones. The right channel distortion is GONE, just a nice clean signal now. As I said before, I can only speculate that I had a failing transistor at Qe3,Qe4 or Qe6 as all parts tested okay. A bit anti-climatic in finding the guilty part, but you can't complain with the end result.
With the repair completed it's time to move on to the restoration.
Right Channel Power Amp (X07-1440-00)
Every transistor on the right channel power amp board, with the exception of the Dual FET, was evaluated. None of them test shorted. All of the resistors were checked for value in circuit and only a couple of them weren't close to the rated value. Those two were pulled and they checked out fine.
I suspect either one of the the two 2SA810 (Qe3,Qe4) or the 2SC1452 (Qe6) were going bad though, as these are known to fail. They were replaced with KSA1381 and KSC3503 respectively. I also replaced 2SA673A (Qe7, Qe10) with KSA733C and 2SC1213A (Qe8,Qe9) with KSC945C. The heat sink mounted Qe11,Qe12 were given fresh compound.
Though they tested fine, I figured I'd replace the zener diodes while I was in there. For De1 EQA01-24 24V 500mA, I used a 1N5252B. For De2 YZ-140 14V 500mA, replaced with a 1N5244B.
R14 looked pretty shabby (see the before photo), so it was replaced with Vishay/Dale 1K metal film. Having looked at photos of other Model500/600 amp boards and also the parts list in the service manual, my board is the only one one I've seen use a 1K resistor in that position. The others all had a 100Ohm part. I verified that the left channel had a 1K installed also.
An orange low leak Elna CERB 10uf 25v capacitor is checked. Notice the ESR measures pretty poorly when compared with say a Nichicon PW of the same size and value which likely has an ESR half that. This is not an anomaly, all of the 10uf orange Elna low leak caps measure this way and seems to indicate the leakage current was of more importance to the engineers than the ESR.
One of the special features of the Model 500/600 Supreme amplfier is this Sony 2SK58 dual FET which is enclosed in this small, shielded metal case due its temperature sensitivity.
Here is the finished right power amp. I've squeezed three Wima 10uf 50v polyester caps in place of the 10uf 25v Elna CEBR caps at Ce5-8 and an Elna Silmic II 10uf 50 at Ce5. Each of the Vr trimmers were replaced with 3386H Bourns single turn. Vr1 and Vr2 got 500ohm, and Vr3 a 50K. Vr1 is the coarse adjust and Vr3 the fine adjust for the offset metered at pin 13 and set as close to 0mV as possible. Vr2 is the bias adjust set to 25mV while metered across pins 5 and 6.
After a partial reassembly and the 4 Sanken outputs reinstalled I fired the 500 back up under full power. I set the offset and bias per the service manual and then shut down long enough to hook up a CD source to Aux 1 and have a listen through the headphones. The right channel distortion is GONE, just a nice clean signal now. As I said before, I can only speculate that I had a failing transistor at Qe3,Qe4 or Qe6 as all parts tested okay. A bit anti-climatic in finding the guilty part, but you can't complain with the end result.
With the repair completed it's time to move on to the restoration.
On the driver board, the model 600 parts list and schematic shows R14: 100-ohm 1/4W CF, yet I see 1K replacing R14. I looked at several photos on the web and see the two different values installed. What R14 value is correct?