Kenwood KR-6030 (stinky!)

[gpounce32768]

I found this basket-case on ebay, I had high hopes for a hacked up mess, but this one looks fairly good inside. OTOH its easily the stinkiest set I've worked on, smells like a <lot> of deep, ancient B.O. and marijuana smoke. Sure glad I was not involved in removing it from wherever it was. It reminds me of my college dorm room a million years ago

The power cord is replaced and cut, so maybe I'll be lucky and things will be blown up- but it could just be an oddball wiring job, a preliminary look shows no signs of knuckledragger repairs, blown/replaced parts or overheat. I just gave it the usual bath, hot water w/ dish detergent and scrubbed with a paintbrush, then rinse in hot water, then a final rinse with 90% isopropyl alcohol. The basement still has the reek in it, so the unit might need a 2nd bath later.

Knobs are thin aluminum w/ plastic hubs. Its a very nicely engineered set though. The amp board is fitted to the heatsinks, with removable headers for interconnect so I think the amp & heatsink will come out as a unit for service. I'll start digging in soon as it dries out.

 

[sregor]

Nearly all these have Alps power switch problems. If the contacts on the switch aren't too scorched, I would recommend cleaning and adjusting contacts, then use a triac mod like in this thread: http://www.audiokarma.org/forums/in...orth-5-and-an-hour-or-so-of-your-time.504673/
Except for the switch problem, these were very nice units and reasonably priced.
Power switch symptoms are arcing sounds and flickering lights when turned on. I believe the Alps switch is gray module at the end of the speaker switch wafers. (been a while since I opened one up - like 35 years....)

 

[sregor]

One more caveat, if you don't already know. The heatsinks are connected to the + and - supplies, so don't ground them or touch them together, and be aware of it while measuring voltages.

 

[gpounce32768]

Saw the warning label- but thanks, have not dug into the isolation scheme. That probably explains the plastic brackets that mount the heatsinks to the chassis = isolation, I was wondering why. Definitely going to do the triac upgrade for the power switch, have not had a system which needed it before. Happily the bath seems to have worked- only a trace of odor remaining.

 

[Watthour]

Wait until it gets warm. Some of that old aroma will escape from its hiding places.

I'll second the switch service, whether it needs or or not, but would advocate a relay instead of the triac for several reasons already posted.

 

[gpounce32768]

I replaced the power cord, even set the polarization correctly and powered up on the dim bulb; good news- flickery dim illumination of the dim bulb so at the very least the power switch is bad. Also removed the amplifier board, very easy- just remove 4 screws on the plastic isolator brackets and demate the headers. Also found one of the STV-4 modules was broken, so have to make a couple replacements- so now its a project

 

[gpounce32768]

I installed the "unobtanium power switch" mod, using T3050H triac & 120 ohm resistor (didn't have 100 ohm 1/2 watt). A suitable location was fairly easy- one corner of the power supply board has a sheet metal screw mount well clear of the circuitry, so I found a longer screw and ran it thru the T3050 w/ tab isolating collar & silpad on a biggish heatsink to secure the works. That location permits removal of 1 foot of old stiff wiring, and a smaller pair running to the switch- I found it convenient to locate the resistor at the switch instead of at the triac.

I cleaned up the alps switch which was quite a mess- lots of arc damage and soot but it cleaned up and is reliable now.

Power-up on the dim bulb was clean with the bulb fading to dark orange but no protection relay click so theres work to do deeper in- all bulbs but one look like they're blown I guess this is a fairly high hours unit.

Watch out for sharp edges on the frame- the transformer's weight can turn them into knives as you move the unit around.

 

[UncleBingo]

I have a couple people that bring me stuff to work on that always smells like some kind of Indian Food or incense. Same smell, different people...much preferable to BO smell.

 

[petes'picks]

Thats what you get for outbidding us. Good luck getting it up to spec, always wanted to hear one from that series of Kenwood.

 

[Mike Sweeney]

I've gone a slightly different direction with my switch mods . I still try to fix/salvage the switch but even then, I've found a cool wifi smart power strip with indepently control outlets. I've got my Kenwood stack on the switches in the ON position all the time and I just use my phone to power them up or down as needed. A bennie is my schedule is set to on the weekend, my office lights come at at a certain time and then the radio/amp kicks on so it's ready when I walk in with my coffee

 

[gpounce32768]

I like to work on these busted systems, fix all the issues, improve specs/implementation where indicated- so getting normal function from the power switch is high on the list. OTOH in the basement I have the whole setup- amp, mixer, tv, etc on a circuit controlled by the wall switch so its easy to turn on/off- not so much for me but the wife & daughter are not into complexity.

 

[gpounce32768]

Sheesh so nearly 9 months on the bench thats what having a life will do to you lol. Anyhow, I finally made some progress on this unit. The triac mod to the power switch is working great- definitely a good fix for this application. I replaced all the bulbs with LED- the only good lamp was the stereo indicator. The original scale lamps had blue filters, I have white ones in there till I can figure out a good filter- but the white looks pretty good. Tuner is looking good on the meters anyhow, so likely not much to do there. The tuner cord is moderately fiendish to re-string, so the hifi manual is a must, as is taking photos on the way in. The fancy ganged rotary switch will take a good bit of cleaning. THe service manual details how easily its wafers can be replaced, it does come apart easily enough but unobtainium barely describes how impossible replacement would likely be lol.

Once I got to the amp module, I found it would not come out of protection on the dim bulb, though nothing blown on the amp board. It comes out of protection with a quiet buzz on the right at 0 volume and lamps are flickering- so still probing around in there. The amp module sort-of has enough harness length so it can be removed from the chassis with all but the audio in headers connected, somewhat awkward but the board is accessible front and back. The audio in cable is way too short for any testing with amp unmounted, so either rig a 3 wire extension or a cliplead for audio input ground from the tone board- chassis ground is needed for the input preamps, the power section has its own ground.

Since the OEM power transistors are all good, I'm somewhat on the fence about the upgrade to MJ21193G/MJ21194G- probably will do it in the end since the replacements are such a better spec. But there is presumably recapping to do first. Its an easy unit to work on, though Kenwood used its fixed resistor bias scheme on this unit the instructions for inserting a variable resistor are straightforward- certainly a worthwhile upgrade. Mercifully, with the variable resistors mounted, they will be easy to adjust from the bottom. As found the bias was a bit over 20mv both channels- service manual states readings from 20mv to 200mv as OK.

Happily the gross smell hasn't returned

 

[avionic]

service manual states readings from 20mv to 200mv as OK.

Nope.. Manual states 20 -- 200 ma or 8.8 -- 88 mv 20mv is still in the ballpark.

 

[gpounce32768]

Well crap, totally right, I clearly haven't read the manual closely enough... thanks! lol

 

[gpounce32768]

Did some more work on this unit, finally I removed the fixed bias resistors, since the measured bias voltages were quite a bit different- the manual suggests putting a 68ohm in parallel with a 200ohm pot- I ended up just putting in 15 turn pots (500 ohms I had on hand). A 25mv or so measurement is obtained at the low end of the adjustment so 100 ohm would probably work better. Happily the tuner is plenty strong, FM muting works great

The eq is simple and effective- right before the volume control, nice they include a tone defeat switch too. The tone controls sound a bit weird but I've not even looked at the caps in that circuit and these test speakers are terrible, so will get into that soon enough. The amp uses simple DC feedback thru a resistor. Overall it looks a conventional design but they did put some effort into the speaker protection circuits- the relay would click in and out while working on the bias; it wants the two channels to be pretty close and not too far out of spec.

I think the buzzing and audio issues above were poor contact in the jumpers I had arranged- system is sounding OK on my test junk speakers but I've only just started the recap. The blue tinted bulbs on the tuner scale were both burned out so replaced them with white, which looks nice but these bulbs are a bit too dark. Will put in something brighter wrapped with blue gel...

The power control is a little cumbersome; from off, to phones then to A spkrs, then B, then A+B. OTOH the Nikko 6065 goes from off to A, then B, then speakers off, then A+B; presumably phones are always available so use the speakers off position when listening with them... equally arbitrary lol. I prefer the amps with separate power and speaker controls.

The amp module design is convenient, using plugs so not wire-wrapped all over. Once jumpers for the two shorter cables are figured out, the board and heatsink can reasonably be set on the bench fully wired and operational, affording full access to both sides of the board.