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Old 01-20-2018, 10:36 AM   #1
seve91
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Default Old Lenco R600 Stereo

Hi everyone,
got this old lenco R600 Stereo Receiver. It has worked good for all these years. Last 31st December i used it for a few hours to listen to the music.
Was working good, except for the central pot that adjust the volume and balance, if i move it i can hear some sparkling sounds, maybe the component is old and need to be replaced. Tried contacts cleaner, better but not perfect.
Anyway the day after i tried to power it on but no output sound.
It has 2 outputs: Speaker A and B, each one for 2 speakers L-R.
Usually when i select Speaker A or B i can hear the relay that powers on, this time no sound at all.
So i've disassembled it, and i've found out a very strange thing.
One pin of the coil of the relays is soldered to -40V line (tested, -40V constant).
The other pin of each coil is enabled by the control in the front of the receiver (speaker A, Speaker B).
When i power on the receiver, and i enable Speaker A for example, i have only 8VDC between the pins of the coil (same thing for Speaker B anyway), but the relay is a 24VDC one.
If i wait some time (1 min more or less) the voltage slowly increasing, and when it reaches 14V the relay powers on and all is working perfectly (both speaker A and B).
If i disconnect the power, i wait several minutes and i try again, i have to wait another minute to have the relays ON.
If i disconnect the power but i power it on again after 20 sec for example, all is working good, i suppose because the capacitor remains charged.
Looks like a capacitor problem...i replaced the ones on the left of the mainboard without success.
I didn't replace the 2 big capacitors, but i suppose their only purpose is to filter the AC power.
I don't know what to do, because i can't even find a schematic.
Maybe is due to a bad transistor? Please help, thanks



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Old 01-20-2018, 01:22 PM   #2
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Default Re: Old Lenco R600 Stereo

If the supply voltage is constant then the problem is on the switch end, could be corroded switch contacts, try working the switch back and forth a few times, or use a spray cleaner like deoxit.
Check the other end of the switch, or does the switch control a transistor? without a schematic I'm only guessing
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Old 01-20-2018, 04:57 PM   #3
CapLeaker
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Default Re: Old Lenco R600 Stereo

Check the +14V line on the regulator board. Here is a service manual for a similar unit:
https://elektrotanya.com/lenco_t-600.../download.html
you have to wait a little bit until the download button comes up.

Last edited by CapLeaker; 01-20-2018 at 04:59 PM..
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Old 01-20-2018, 07:15 PM   #4
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Default Re: Old Lenco R600 Stereo

Download the manual for the A-600, it is closer (has the A & B speaker switches) https://elektrotanya.com/lenco_a-600.../download.html

If this circuit in this schematic matches the receiver:
The relay coil connect to the -37 volts then to one side of the coil, the other side of the coil connect to a 330 ohm resistor, then to the speaker switch, then to Q133 collector, which when turned on completes the circuit to ground.

Check the cap C108 on the -6.6 volt line and C120 on the -2.62 volt line
and maybe c119 off base of Q134.
Q134 is the protection circuit, so you may want to check that the voltage on L101 & L102 is close to 0 volts
If there is too much offset Q133 will not be turned on

Last edited by R_J; 01-20-2018 at 07:19 PM..
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Old 01-21-2018, 12:18 PM   #5
seve91
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Default Re: Old Lenco R600 Stereo

thank you all for the answers.
I've already replaced some caps, also C119 and C120.
The only one i didn't replace was the C108....it's a 47uF capacitor.
Desoldered, is measuring 25pf...replaced and all is working now!
Thank you!

To make it perfect now, would be great if i can find a replacement for the volume/balance pot, but i've never seen a similar pot in my life.
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Old 01-21-2018, 03:21 PM   #6
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Default Re: Old Lenco R600 Stereo

Good to here you have it working, Try using a good control cleaner like deoxit. you need a cleaner that leaves a bit of lube behind.

Last edited by R_J; 01-21-2018 at 03:23 PM..
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Old 01-21-2018, 11:33 PM   #7
seve91
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Default Re: Old Lenco R600 Stereo

Quote:
Originally Posted by R_J View Post
Good to here you have it working, Try using a good control cleaner like deoxit. you need a cleaner that leaves a bit of lube behind.
I used this one, almost everywhere on the board and on the controls.

http://www.duecielectronic.it/index2...22&cat=pulizia

I will try deoxit, but there are many different versions....which type should i buy? thank you.

Last edited by seve91; 01-21-2018 at 11:35 PM..
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Old 01-22-2018, 10:24 AM   #8
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Default Re: Old Lenco R600 Stereo

What you used is a degreaser "It rapidly evaporates, leaving no residue" I bet the control worked better shortly after spraying but the scratchy noise came back shortly after. Deoxit D series D5, just get the smallest amount, you don't need much, a small squirt into each control is all you need.
There are other brands also like MG NU-TROL, it also works, maybe just not as good, depends on who you ask and I'm not asking

Last edited by R_J; 01-22-2018 at 10:27 AM..
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Old 01-22-2018, 01:19 PM   #9
seve91
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Default Re: Old Lenco R600 Stereo

Quote:
Originally Posted by R_J View Post
What you used is a degreaser "It rapidly evaporates, leaving no residue" I bet the control worked better shortly after spraying but the scratchy noise came back shortly after. Deoxit D series D5, just get the smallest amount, you don't need much, a small squirt into each control is all you need.
There are other brands also like MG NU-TROL, it also works, maybe just not as good, depends on who you ask and I'm not asking
buying it from Italy is quite expensive. If is that good as you said, i'll buy it.
Otherwise if you can advice me a "local" alternative products would be better.

thanks

EDIT: Bought from the US...almost 29 euros.

Last edited by seve91; 01-22-2018 at 01:23 PM..
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Old 01-22-2018, 01:57 PM   #10
R_J
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Default Re: Old Lenco R600 Stereo

I know it's not cheap, MG Chemical makes Nu-TROL which is cheaper, I just don't know what's available in Italy.
Maybe this? Kontakt Chemie Cleaner 601
https://www.thomann.de/gb/kontakt_ch...ntaktspray.htm

Last edited by R_J; 01-22-2018 at 02:01 PM..
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Old 01-23-2018, 02:34 PM   #11
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Default Re: Old Lenco R600 Stereo

looks like that all these contact cleaners evaporate without residue.
Anyway i've bought it from US, i hope to fix the issue because it's impossible to find the replacement for the volume/balance pot
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Old 01-23-2018, 04:59 PM   #12
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Default Re: Old Lenco R600 Stereo

Even the best control cleaners may not clear up all the scratchy sound, I have had a couple controls that were that way, I applied a small amount of contact grease into them and that fixed them.
I have seen others use a bit of white lithium grease also. DO NOT use WD-40

Last edited by R_J; 01-23-2018 at 05:02 PM..
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Old 01-24-2018, 11:48 PM   #13
seve91
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Default Re: Old Lenco R600 Stereo

Quote:
Originally Posted by R_J View Post
Even the best control cleaners may not clear up all the scratchy sound, I have had a couple controls that were that way, I applied a small amount of contact grease into them and that fixed them.
I have seen others use a bit of white lithium grease also. DO NOT use WD-40
which contact grease do you advice? I was thinking about WD40
Why is not suggested?
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Old 01-25-2018, 08:41 AM   #14
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Default Re: Old Lenco R600 Stereo

The contact grease I have is ment for electrical contacts, It came from Sony for use in there mode switches. I also have some that was used in the days of mechanical channel tuners in tv's. WD-40 could cause problems with the resitive carbon in the control.
They do make contact grease for use in automotive (to waterproof plug connections)
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