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Help with Kenwood Receivers (KR-4070 & KR-5030)

B

bougan

New Member
I recently purchased a Kenwood KR-4070. It works great except when first turned on... it initially flickers (the lights go dim and bright repeatedly and intermittently) and the sound is garbled for several seconds to several minutes before stabilizing. The problem appears to get worse as the unit warms up and is power cycled.

I previously owned a KR-5030 that did exactly the same thing (never resolved). I see from several other posts that other owners of the KR-4070 have experienced a similar problem.

Does anyone know what is causing it and how it can be resolved?

Thanks --

Tim
 
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bougan said:
I recently purchased a Kenwood KR-4070. It works great except when first turned on... it initially flickers (the lights go dim and bright repeatedly and intermittently) and the sound is garbled for several seconds to several minutes before stabilizing. The problem appears to get worse as the unit warms up and is power cycled.

I previously owned a KR-5030 that did exactly the same thing (never resolved). I see from several other posts that other owners of the KR-4070 have experienced a similar problem.

Does anyone know what is causing it and how it can be resolved?

Thanks --

Tim
Click to expand...

Could it be a bad main power switch with worn/pitted contacts?

Lefty
 
Lefty said:
Could it be a bad main power switch with worn/pitted contacts?
Click to expand...

That's what I was thinking a well... so put down another vote for the power switch. :thmbsp:

Scott
 
Lefty said:
Could it be a bad main power switch with worn/pitted contacts?

Lefty
Click to expand...

I kind of doubt it. I turned it on and left it until it was stable and playing fine. I then unplugged it (without turning the power switch) and immediately plugged it back in. It started the flickering again. I would assume that if the power switch and contacts had not been moved that the flickering would not repeat when the power was reapplied. Also, the problem is definitely worse when the unit is warm (the first time it is turned on in the day it flickers but only for a second or two). After it is warm it can flicker for several minutes before finally stabilizing.
 
Do you hear an "electric sizzle" (read - arching) while this is happening? :scratch2:

Scott
 
SPL db said:
Do you hear an "electric sizzle" (read - arching) while this is happening? :scratch2:

Scott
Click to expand...

I do, but it seems to be coming from inside the power transformer (no where near the on/off switch).
 
Kenwood KR-4070

Hello. My father bought this receiver in the late seventies when it first came out. It died after 16 years. I still have it. It was the power supply. I hate to sound so matter of fact, but it is not worth your time. Hit the local thrifts and find something that is better. Look at the power supply inside. It could be a loose wire. Also look at the size of the power supply. Not very well made. Just not enough beef. I am sure there are people that have had success with Kenwood. The receiver that I have only got about six years of solid use. I picked up a VR 305 at the thrift two weeks ago. Works great. It also lacks in sound quality. I am waiting to find something I like by Kenwood. I haven't yet. Good luck with it, if you are that determined about it.
 
Check the mains fuse and fuse holder. Loose connection or corroded contacts.

Bad safety caps can do this too.
 
EchoWars said:
Check the mains fuse and fuse holder. Loose connection or corroded contacts.

Bad safety caps can do this too.
Click to expand...

The fuse and all associated contacts appear clean and tight. The power switch is a sealed unit so I can't do much there w/o a replacement switch. The safety capacitor is definitely a possibility... I will try disconnecting it first and see if that cleans up the problem. If so it would be easy enough to replace.

I am an EE but analog circuits like this are outside my primary area of expertise. Does it seem reasonable to you that a bad cap could be a systemic problem? As I stated earlier this appears to be a common issue with Kenwoods of that era.
 
arrow 68 said:
Hello. My father bought this receiver in the late seventies when it first came out. It died after 16 years. I still have it. It was the power supply. I hate to sound so matter of fact, but it is not worth your time. Hit the local thrifts and find something that is better. Look at the power supply inside. It could be a loose wire. Also look at the size of the power supply. Not very well made. Just not enough beef. I am sure there are people that have had success with Kenwood. The receiver that I have only got about six years of solid use. I picked up a VR 305 at the thrift two weeks ago. Works great. It also lacks in sound quality. I am waiting to find something I like by Kenwood. I haven't yet. Good luck with it, if you are that determined about it.
Click to expand...

Thanks for the input. My desire to restore this receiver (and the KR-5030 that I have coming) is sentimental as I owned the same model as a college student and I am attempting to recreate my original setup. I don't anticipate the system will get a lot of use but I do want it functioning as perfectly as possible.

Having said that, does anyone know where I can land a pair of Ultralinear 228 speakers (circa 1978)?
 
I have had this problem with several 4070, 5030 receivers.
It is almost always the power switch on the rear of the speaker selector switch.
On many of these modelsKenwood used a dual section power switch. If that is the case the rear section can be carefully removed, inverted and the wires soldered to the unused section of the switch.
If you get in a real bind, the failing switch can be disassembled,and the contact surfaces cleaned. Probably not a long lasting repair, but better than gerry rigging some other switch in its place.
 
another vote for power switch/switches

have myself a KR-6030
and friend with a KR-6050
both emmitted exact symtoms
when (sissling) was able to see voltage drop accross switch.
badly screwing up relays and power supply
was able to isolate by slightly moving switch while unit was on and symptom occurring. found that moving a little were able to close contacts better.
switch has ball and v cut stop. when moved slightly off stop, contacts slighly change position without power going out.
was able to duplicate on both recievers.
carefully cleaned mine (crusty) and have not had a problem since.
note contacts have a hardened surface with softer metal underneath.
try not to use abrasive (emory,sand paper,file)you want to keep as much of the hard material as you can or this will be a frequent problem.
this is of course if reassembly of switch is succesfull
 
morgan said:
I have had this problem with several 4070, 5030 receivers.
It is almost always the power switch on the rear of the speaker selector switch.
On many of these modelsKenwood used a dual section power switch. If that is the case the rear section can be carefully removed, inverted and the wires soldered to the unused section of the switch.
If you get in a real bind, the failing switch can be disassembled,and the contact surfaces cleaned. Probably not a long lasting repair, but better than gerry rigging some other switch in its place.
Click to expand...

Thank you for the information. It is indeed the power switch as the problem goes away when I hard jumper across the contacts.

I have been able to locate three switches NOS ("new old stock") and have ordered all three. These are Kenwood original parts and should correct the problem (at least for a few years). Because I have three switches I should be able to keep the unit operating indefinitly. These were not easy to find and I doubt if any more are available anywhere.

However, I found this interesting link for others with the same problem:

http://www.number63.ca/kenwood/kenwood.htm

Thanks for all your help!
 
Nice find. I made a pfd of that whole thing.

The only thing he forgot is a safety cap. As the contacts close and open, there is a time when they are close enough to arc. This will eventually destroy the contacts unless a safety cap is connected across the contacts to eliminate the arcing.

A safety cap is a specially designed cap, and specifically rated to be placed directly on the AC line. It's design is such that it will fail open, not shorted. Digikey sells 'em, Panasonic Type VS, 10,000pf (.01µf), PN. P11423CT-ND.
 
I had this problem with a Kenwood of which I forget the model. Wiggling the switch around was able to isolate it to the power switch.
 
Kenwood KR-5030 lamps

I've recently bought a KR-5030, exactly with the problems you described.

You can only imagine how much time I've saved following your hints: thank you very much about. The receiver works perfectly, the radio section is really good and also the sound is quite appreciable.

Some further questions:

- some lamps (FM, Phono and AUX ) do not work anymore, but I'm not able to find them here in Italy: which type have I to look for (voltage, code and so on) ? Where could I buy them from ?

- signal and tuning meters are not illuminated at all, as none lamp is fitted. After a quick analysis, I think that a lamp was originally foreseen (together with its holder) exactly between the two instruments. Is it so? Which kind of lamp is it?

Thank you very much in advance to everyone for your attention

See you soon, Paolo
 
Most of the Kenwoods I got had perfectly working dial lights and bad/dropping channels, probably got sidelined before the dial lamps blew, so unfortunately I don't know the values off the top of my head. Maybe someone else here knows otherwise I'll try and dig one out.
 
A good testimony for using a switched power strip to turn on and off your vintage stereo. This is especially true on the KR-4070 that has the power switch and phones and speaker selector switches all in one. Power strips are cheap.

Charlie
 
While you guys are thinking Kenwood, is anyone familer with a KR V7020?
I just picked up one that is in a like new condition but I don't know anything about it. Lots of switches and etc I don't understand. I'm thinking it's from the 80's. Kenwood no longer has any info and about all I can find out is that it's 100 watts per ch. I need a user manual (have a ser manual on the way) and a remote. Any help would be appreciated. RM~
 
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