Startup protective circuit - Luxman

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RickNel
Posts: 4
Joined: 23 Jul 2014 01:18

Startup protective circuit - Luxman

Post by RickNel » 23 Jul 2014 01:44

I have a Luxman L-505V amp with Luxman PD272 turntable - reliable service over 30years.

Recently I'm getting long delay, up to a minute, between power-on (cold) and the speaker protection relay clicking in. I've been looking everywhere but can't find a schematic for this particular model. SQ505 looks similar, but L-505 is significantly different. Eg. main power filter caps are 10,000uf, and SQ505 doesn't seem to have the same speaker protective relay circuit and all PCBs and components are laid out and numbered differently.

There has been a request for the L-505V schematic on HFE for over a year (not mine). I'd like to renew that request.

I'm interested in others' experience with these startup speaker protection delay circuits. Are they logic-timed or do they rely on caps reaching a nominal capacitance? I read a thread somewhere hinting they get feedback from the final power amp circuits. Listening for the relay to click over, I hear an increasing buzz, like voltage rising in the relay coil, for about 2secs before it trips.

I'm capable of replacing capacitors where needed, but I don't want to go fooling around without knowing where I should be looking.

Any help appreciated :?

Rick

unitecnet
Posts: 3
Joined: 10 Mar 2011 02:10
Location: Brasil

Re: Startup protective circuit - Luxman

Post by unitecnet » 24 Jul 2014 00:54

Hello, is a peculiar model, similar to sq505x/507x (power).
You have a user manual? I found some references on a French site, can be useful.
http://www.audiovintage.fr/leforum/view ... 74&t=43676
This type of malfunction is typical for damaged electrolytic capacitors, but may have leaky transistors, etc.
I hope it will be useful, greetings from Brazil. :D

RickNel
Posts: 4
Joined: 23 Jul 2014 01:18

Re: Startup protective circuit - Luxman

Post by RickNel » 24 Jul 2014 05:21

Thanks for that French link, Unitecnet. Je puis lire ca.

Yes, I have the Owners Manual and have uploaded it to HFE.

The French thread is mostly about polishing up the cabinet and chassis - but also reference to replacing capacitors based on ESR readings. Most useful to me was the reference to the L-505V being internally similar to the L-309V. HFE has the service manual for 309V, which I downloaded.

The good news is that I can see from 309 schematic that the protection circuit is controlled on the lower voltage power supply board, so I won't have to suspect the huge 10,000uf caps that serve only the +43v/-43v supply to the final power amps. I'll start by replacing all electro caps on the pre-amp supply board - not too many and largest are 100uF. If that doesn't work, I'll have to look at the power amp boards which could also be hosting leaking caps. That is a hot location so caps can lead a hard life there.

I see references that the L-505V model is considered rare in Americas and Europe. I wonder if it was sold mainly in the Asia-Pacific market where 220-240 volt AC supply is most common but also where AC supply voltages could be erratic back in the 1970s - hence high level of power filtering and protection. I bought mine in Hong Kong in 1978. It was also sold in Australia and I have seen online references in Vietnam, India and Pakistan.

Rick

RickNel
Posts: 4
Joined: 23 Jul 2014 01:18

Re: Startup protective circuit - Luxman

Post by RickNel » 25 Jul 2014 08:48

OK I've solved this now. I needed to study up on how protection circuits work, then look at a Luxman application, then compare that to my L-505V without a schematic.

A clear and thorough description of how protection circuits work can be found at http://sound.westhost.com/project33.htm. The relay that connects power amps to speakers is held closed when a particular capacitor is full. That relay stays open while the capacitor fills at startup, and can also be opened if a DC ripple above a set frequency hits the circuit from the power amps.

For the startup delay, this capacitor is filled over a few seconds from a direct feed from a secondary of the main power transformer, parallel to the rectified and filtered rail driving the pre-amps etc.

L-505V board PB1040 holds the power rectifiers for both high and low voltage rails, additional power rail filters, the protection and startup circuit, and also twin circuits for the temporary attenuation function of the amp.

Only two electrolytics are involved in the timing of the startup.
C256 is 22uf, 50v filtering the current to the startup circuit straight off the transformer via a single diode half-rectifier.

C253 is 220uf, 10v and when it fills it closes, via some transistor switching, the relay of the power circuit. Replacing both of these capacitors was enough to bring the startup delay back to normal at about 6 seconds. I pushed the voltage ratings up a level, C253 to 63v and C253 to 16v. The newer caps are smaller and run quite warm.

Thanks again Unitecnet for pointers that led me to this solution.

Rick

Coffee Phil
vinyl addict
vinyl addict
United States of America
Posts: 5840
Joined: 20 Sep 2008 08:22
Location: California

Re: Startup protective circuit - Luxman

Post by Coffee Phil » 26 Jul 2014 18:03

Hi Rick,

Capacitors should not get warm. Do make sure you did not install them backwards. If the heat is from surrounding components make sure the caps are rated for high temperatures. High temperatures will shorten the life of electrolytic caps. If the heat is coming from the caps, something is wrong and you may have a dramatic failure (capacitor exploding) in the future.

Phil
RickNel wrote:OK I've solved this now. I needed to study up on how protection circuits work, then look at a Luxman application, then compare that to my L-505V without a schematic.

A clear and thorough description of how protection circuits work can be found at http://sound.westhost.com/project33.htm. The relay that connects power amps to speakers is held closed when a particular capacitor is full. That relay stays open while the capacitor fills at startup, and can also be opened if a DC ripple above a set frequency hits the circuit from the power amps.

For the startup delay, this capacitor is filled over a few seconds from a direct feed from a secondary of the main power transformer, parallel to the rectified and filtered rail driving the pre-amps etc.

L-505V board PB1040 holds the power rectifiers for both high and low voltage rails, additional power rail filters, the protection and startup circuit, and also twin circuits for the temporary attenuation function of the amp.

Only two electrolytics are involved in the timing of the startup.
C256 is 22uf, 50v filtering the current to the startup circuit straight off the transformer via a single diode half-rectifier.

C253 is 220uf, 10v and when it fills it closes, via some transistor switching, the relay of the power circuit. Replacing both of these capacitors was enough to bring the startup delay back to normal at about 6 seconds. I pushed the voltage ratings up a level, C253 to 63v and C253 to 16v. The newer caps are smaller and run quite warm.

Thanks again Unitecnet for pointers that led me to this solution.

Rick

RickNel
Posts: 4
Joined: 23 Jul 2014 01:18

Re: Startup protective circuit - Luxman

Post by RickNel » 26 Jul 2014 23:29

Thanks Phil,
Noted about capacitor heat. They are correctly aligned. On reflection, on first test I may have felt some residual heat from the soldering operations. These things are on quite heavy solder traces from when the boards were originally floated on a solder bath. I noticed it took quite a bit of heat to get the new solder joints set properly.
Rick

unitecnet
Posts: 3
Joined: 10 Mar 2011 02:10
Location: Brasil

Re: Startup protective circuit - Luxman

Post by unitecnet » 29 Jul 2014 06:34

RickNel, Cool I could help you!!
Take care with glue (brown) in a components, over time cause damages in a leads and pbc.
Is a great site Rod Elliott!
Greetings from Brazil. :D

Dimon Hell
Posts: 1
Joined: 14 Dec 2015 19:06

Re: Startup protective circuit - Luxman

Post by Dimon Hell » 19 Dec 2015 19:06

Can cheer new member with same problem.
My L-505V have delay about 10 seconds, that became longer with every day, after that relay start working with some humming mechanical noise (like fast switching) that affects phono out with noise. And now it won't switches at all...
Maybe someone have circuit scheme of this amp?

Record22
Netherlands
Posts: 4
Joined: 07 Dec 2019 11:51

Re: Startup protective circuit - Luxman

Post by Record22 » 07 Dec 2019 11:59

Good afternoon,

At the moment I'm doing A recap on a Luxman L505V amplifier and I also didn't manage to find the service manual.
Is there maybe someone who managed to find it (or maybe a schematic diagram)?
I actually need to know the specs of the C523 and C526 on the printboard and the specs of the lamp.

Gr,
Stefan

Record22
Netherlands
Posts: 4
Joined: 07 Dec 2019 11:51

Re: Startup protective circuit - Luxman

Post by Record22 » 07 Dec 2019 12:03

Luxman L505V.jpeg
(230.67 KiB) Downloaded 44 times

Record22
Netherlands
Posts: 4
Joined: 07 Dec 2019 11:51

Re: Startup protective circuit - Luxman

Post by Record22 » 07 Dec 2019 12:08

above a picture of the inside of the L505v. the 2 capacitors of witch i'm searching for the specs are surrounded in red, right above the relay.

Stefan

kalaur
senior member
senior member
Posts: 490
Joined: 07 Apr 2014 08:24

Re: Startup protective circuit - Luxman

Post by kalaur » 07 Dec 2019 16:38

There should be markings on the side of the caps with specifications

Record22
Netherlands
Posts: 4
Joined: 07 Dec 2019 11:51

Re: Startup protective circuit - Luxman

Post by Record22 » 07 Dec 2019 19:54

i know but i'm not sure if the 2 capacitors are the right ones.. the owner before me already changed them..

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