Luxman L-430 stuck in protection. Help please.

[Duffalora]

Hi all. Got a Luxman here that is stuck in protection. Problem is the service manual is so bad that there's no voltages on the schematic.

Here's what I know about it so far:


No shorts showing on the DBT.
Front lights come on but unit doesn't come out of protection.
All fuses are intact.
Voltages on output transistors are stable and identical on both sides.
Voltages on other power amp transistors are the same on both sides.
Audio tracer reveals good strong undistorted sound right around to the relay.
Relay has 8mv on one side and 10mv on the other.
New relay subbed in (no difference).
Three power supplies showing:

1) +/- 70.0v
2) +/- 60.5v (this is running pretty close to the edge with 63v main caps)
3) +32.97/-33.90


Any help on where to proceed would be appreciated. Is that third supply where I should be looking?

Thanks.

 

[chammerbeck]

Hello, first post....been reading quite a bit about this amp on here before posting. I too have a similar issue. I found two caps leaking and replaced them with spares for now. My relay never engages. I did pull the relay and test it directly and it clicks with the appropriate voltage. I pulled up all the leads for the power amp transistors mounted to the heatsink and tested them with my digital tester. The warm up light takes a long time to go out. I never hear the relay click and no sound obviously. The front panel lights all appear to work. The board is pretty clean. I looked over all the boards for bad solder joints with my jeweler's loop. Found a few but nothing alarming. Still no go...... I do have the user and service manual/print but stuck at this point. I plan to do a complete re-cap but just want to get the unit up and running first. Thanks for any help. Chris

 

[Binkman]

Welcome to ak.
The typical relay circuit consists of a transistor, a diode and cap. so trace that circuit back..if diode checks (in circuit easy and if circuit is getting power. no joy then trace further back to power supply if necessary. definitely fixable but my plate is full today. might post sm link.

 

[chammerbeck]

Thank you. Yeah, my next step was to start tracing back from the relay coil circuit like you speak of. No major hurry on my end. Just saved this awesome receiver from the e-cycler.

 

[chammerbeck]

Still no luck on my end. Hopefully getting back on this project later this week. Still looking for any comments or suggestions.
Thanks

 

[bktheking]

I have one on my bench doing the same thing, no click, just sits there- dc offset is near zero. I'll post my resolution if i fix it

 

[chammerbeck]

Excellent. Thanks for checking in. Looks like this makes three of us with this problem. I plan to jump back into mine in a few weeks. Figured some time off might help me with it.

 

[bktheking]

I swapped the 330uf cap to no avail, there's a .47 lytic i'm going to try tonight and i'll report back. Usually in these protection circuits it's something stupid that holds them up, bad cap, diode or a transistors so i figured i'd start with the simplest first.

 

[Binkman]

pdf pg. 13 relay 801. Well that 330uf was 10v rated anyway and the .47 also 10v rated. (I see 2x in series in the sm? pretty poor sm..) Anything 10-15v rated lytics that old gotta go.

The SM alt scan not too good either.. but relay 801 shows 470uf for the 2x. ?? best to check whats on the pcb.. who knows about accuracy of the schema's.
https://www.hifiengine.com/manual_library/luxman/l-430.shtml

 

[bktheking]

Yes i saw those two 470's, i'll systematically replace caps in the circuit and see where it leads. I'm thinking cap but who knows.

 

[bktheking]

Swapped the .47 uf and 2 x 470 uf = same thing, stuck in protection.

 

[Binkman]

Light tap on relay? diode checks in circuit power off is easy.. how bout the transistor?

 

[mbz]

Might have missed it, but did see any checks of power to the actual relay coil.
Measure dc voltage at coil, one side is GND, the other should be 24Vdc or 12Vdc...
with respect to chassis/GND. Then work back checking base voltages at Q833 and Q832.
Might be something simple like Q833.

 

[bktheking]

Yes I tapped the relay. Will move past caps hopefully tonight. I believe the relay in these are 24v.

 

[chammerbeck]

I just tested the two 10v 470mf caps I pulled a bit back....both are about 150mf off. I started to pull and test a bunch of other ones on the board just now.
Most were within 20mf of their rated capacity so I just put them back. Thought I found another bad solder joint. Nope.... Still in protection. Curious what voltage
we should be getting on that "TP/Warm Up plug" on the board? I get about 24.7vdc after about a minute or so. I have some good pics of these items. The new
caps are blue with a C on them. I can read schematics but the quality is a little hard to read.

 

[chammerbeck]

I'm using one of these to test with...... Prolly not the best.

 

[kramden]

No DC offset from either channel? I would check the health of C813.

 

[Binkman]

Take my word for it.. those 10v rated caps are not stable.. anything you have in there 25v-30v may work/test ok but.. hmmm iffy at power/ age.

No DC offset from either channel?

dc offset? you sure you got right thread?

 

[chammerbeck]

My caps had dried up goo coming out of them....first thing I noticed.

 

[kramden]

I have one on my bench doing the same thing, no click, just sits there- dc offset is near zero. I'll post my resolution if i fix it

You have no DC offset at the outputs but yet it stays in protect. Which I would say is incorrect. "Protect" would indicate dc at the outputs disabling the relay. Barring anything defective in the relay drive/protect circuit, it must be caused by something else. This unit uses an AC reference; hence C813.