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Kenwood L-07M II Issues

Hey Willy. That is exactly my intention. After I get yours, I'm going to take a hard look at what both need, and then reread this thread a couple more times. If I decide not to tackle this project, I'm going to offer the pair back to the forum under the same deal. (Pay me for shipping.) :thmbsp:
 
EchoWars said:
There are two relays...one that is triggered by a remote source through the back panel or triggered by flipping the rear panel switch to 'Mains On', and there's the speaker relay, which should come on about 3 or 4 seconds after power is applied.
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Hi guys. I need help.My two L-0 MKII are working really fine but tomorrow morning when I turned on one of the units, it remains silent....
In facti I can't hear the "clicK" of the speaker relay triggering. Normally it takes only 3 to 5 seconds to trigger. I await 5, 10....5 min and nothing. Turned off,turned on again the amp with no results...the amp remains deadly silent...
Any clue please about this malfunction ????
Many thanks
 
Check fuses first. If that looks OK, and if you can find your way around the inside of the amp and own a decent DMM, then start a thread in the Kenwood forum and I'll see if I can help.
 
OK, I know this is an old thread, but a VERY GOOD one, specially for us Kenwood fans.

I just finished recapping another L-07 mII and I have some questions to whoever done this job before.

The DC offset adjustment is kinda trick. What is the correct sequence? Adjust VR1 until the lowest reading (but not zero) and then adjust VR2? I use a Fluke DMM, but sometimes I wish I used an analog one as mine displays "1" whenever is out of range. I noticed the DC offset reading is not very stable and it is very hard to reach "zero" as indicated in the SM.

As for the bias, I adjusted last night after warming the amp up for about 1/2 hour. This morning, I turned on the amp and measured again and bias was at 30 mV.

After doing all this, should I go back to point no.23 and recheck the rail voltage?
 
One offset adjust is coarse, and the other is fine. Adjust the coarse (schematic says VRe2) until it is close to 0V, and then adjust VRe1 to zero it in. Before beginning the adjustment, these two pots should be centered.

The L-07MII has a FET input stage that will drift a bit more than a bipolar stage, but it should not 'jump around' by more than a millivolt or two at any given moment (although over a longer time...15 to 45 minutes, it could drift by 10 to 15mV, which is why it should be monitored for a hour or more to make sure it is fully warmed up and settled).
 
In case anyone is still subscribing to this thread, please see a related post I made today (16 August 2013) in "Dollars and Sense."
 
I bought a L-07mII lot a few weeks ago. After about 10 minutes after being powered on, two of them heat up to the point where I cannot put my hand on the heatsink for more than a couple of seconds. Is this the typical oscillation symptom?
 
cchean said:
I bought a L-07mII lot a few weeks ago. After about 10 minutes after being powered on, two of them heat up to the point where I cannot put my hand on the heatsink for more than a couple of seconds. Is this the typical oscillation symptom?
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They run notoriously hot. They were designed to stand alone, free air circ, or mechanically vented (fan cooled). High performance from these comes with a great deal of heat generation.
 
No. They should not get anywhere near that hot under normal operation. Do not run them until you get them fixed.
 
HiFiWilly said:
They run notoriously hot. They were designed to stand alone, free air circ, or mechanically vented (fan cooled). High performance from these comes with a great deal of heat generation.
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But Echo is right.. they are not to be run so hot you cannot touch them. You do need to figure out what is causing the overheating and get them repaired. Hope you can find someone to help you. What incredible pieces of pure sound they truly are when operating properly.
 
Hello all, i also have two of this wonderful L-07 MII. I have made a total recap and cleanup to my babys. My Question:
Both of them are warming up during the first 3 Hours powerd on. They reach a temperatur where you still can put your hand on the heatsink. But it is hot. Wich Temperature should they reach?
Richard
 
One of mine had a heat rise about 2 years ago, and resoldering the main board took care of the problem. There is however another possibility to conider with this special amplifier. It was designed to have extreme bandwidth, and the output LPF was matched to the short speaker cable that was in the box with the amplifier. When you switch to conventional speaker cables, especially braded or woven designs, the amplifier may oscillate as ultra sonic frequencies. The results are a slight hiss in the tweeter and hot heat sinks. To test ths possibility, simply disconnect the speaker cable at the amp end. If everything cools, then it is time to use another cable. If the amp remains hot, (and you'd have to wait 30 minutes for the massive heat sinks to cool) then get it serviced for those solder connections.
 
EchoWars said:
No. They should not get anywhere near that hot under normal operation. Do not run them until you get them fixed.
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Echowars is right. I bought these knowing they would need the silver-mica cap replacement, better fix before I loose those precious outputs!
 
Hello,
some weeks ago i had blown away on one of my Kenny L-07 II all of the six power transistors. :(
The reason was: I switched them on when they where still warm, only one hour off- time since the last using. Lucky i am to find some NOS transistors for repair.
For that reason i recommend capton foil isolators instead of the glimmer ones between the heat sink and the body of the transistor. The heat transfer is much better so that the transistor itself will not become so hot.
Richard
 
Turning the amp on after it has been off for more than about 45-60 seconds should not be any problem for this or any other power amp.
 
Some Things i found out with my Kennys:
They still get very warm after long using Time, three or more Hours and they did not cool down again if they are once at temperature until i switch them off. I reduced the bias but i think that is not the best way.
So i decided to replace the R23 by a new one, in the SM 22 Ohm, in real sometimes 33 Ohm. I found both variants on my Kennys. The effort is a reduced temperature on the long Term with the same bias adjust. I mesured the resistors, they had shown the right values when i tested them. Maybe the old resistors increase their resistance too much by warming up. That would be difficult to find out so the test in real was the easiest way.
Hope you have fun with your Kenwoods
Richard
 
Living with the Kenwood L-07 M II,

i have some more Information’s for you. EW told us (thanks a lot for all of that to EW) to change the "black flags" , the PS capacitors on the voltage- amplifying board. I have done this and it is fine.

But you can do even more. Just change all of the Resistors and use Dale CMF Resistors on the pcb. I tried that on my daily used Kenwood L-07 M II and had he following success: It sounds much better. Quiet. More Dynamic,- just better. And: it works much cooler. I think it is a great success to use the Mica silver Glimmer as EW told at the start at this Thread and to use Dale non Magnetic Resistor. I have made an Project List in my Mouser account with all the needed Parts for one Board. Here is the Link:

http://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=e20dd50eaa

Some information: The Wima MKS2 4,7uF/63V is very expensive. So if you can get it cheaper somewhere else, be free to do so. Set a small Foil- Cap as Shunt to the following Caps: Ce6, Ce7, Ce8, Ce9. This could be an 1,0 uF Cap like in the Position 5 of the Project- List.

Richard
 
Still, eight years later, and my L-05M's run as cool as cucumbers in an October morning. They sound as good as when I recapped them with modest, but industrial sorts of capacitors. I re-soldered a lot of the board, and I improved the ground plane as well as some other wiring. I also replaced the the in/out terminals.

Maybe this was the amp in the series to get, but it was always deemed the junior partner. Relatively speaking, throughout successive decades the '5's' have had very little acclaim. The boast of the time was in BIG power, and I guess some of the contemporary speaker design feasted on it. Naturally, the L-05' was often passed over.

I drive a pair of somewhat modified Sansui SP-G88's. These are very big speakers from the power hungry era the 5's can still peel paint off the house next door without distortion and yet cause Mrs wife to go bonkers.

Maybe the 5's were really the series to have had back in the day. I am not trying to drive up the value; I'm just reporting. You couldn't pry these speakers away from me

The most salient point is — they seem to be forever trouble free!
 
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