Did some work with OP via PM.
Just to clarify, removed pre-out/main in links then amp powered up/relay engaged normally.
Luxman L-100 woes
- Thread starter quadmatrix82
- Start date
Just to clarify, removed pre-out/main in links then amp powered up/relay engaged normally.
There’s 5v on the left channel pre out main in rear link
I just got done working on one of these. It was a pain in the @$$. Wires kept breaking off and the Molex connectors making bad contact. Wires going all over the place. Every time I put it back together it would fail again. With voltage on the pre out I would step back through the stages to see where the DC goes away then look at that stage. These sound great when working.
Tony
Tony
With the link removed I measure 0v on start up and when it clicks out of protection it spikes to between 5v and 15v and after a few seconds clicks back into protection and drops 0v
On the outer pre out it stays at 0v
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Here’s a photo of the refurbed flat amp pb640
It has all new capacitors and 2sc1345 replaced with bc550 and 2sa640 replaced with ksa992.
I managed to make measurements of c01f and c10f with links in
C10 starts at 0v relay clicks spikes to 2.3v clicks back into protection
C01 start up 10.1v relay clicks to protection drops to 6v
With links out c01 measurements almost same 10 v and 7v
C10 stays almost same 0 to 3v
It has all new capacitors and 2sc1345 replaced with bc550 and 2sa640 replaced with ksa992.
I managed to make measurements of c01f and c10f with links in
C10 starts at 0v relay clicks spikes to 2.3v clicks back into protection
C01 start up 10.1v relay clicks to protection drops to 6v
With links out c01 measurements almost same 10 v and 7v
C10 stays almost same 0 to 3v
Attachments
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With plug c-11-18s removed and c07s-c10s from the power supply it stays out of protection with links in or out but the front light keeps flashing
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I found a broken wire on the eq board which I was able to resolder but no change in symptoms
That is starting to sound familiar! I didn't have any issues with DC offset. Just the broken wires and bad relay on the phono board. The replacement relay I bought also had dirty contacts. After some thinking I recalled someone once saying relays should be somewhat self cleaning if working under the correct load. I pulled some current through the contacts and operated the relay a bunch of times and the contacts started to work. It is not easy to follow the signal on the schematic the way it goes from one board to another and back again.
Tony
Tony
Cheers Thankyou! I’ll check these and report back
Good news! I replaced q504 and q501, q504 had a pretty low hfe about 200 the rest circa 500, I know what you mean about broken wires I had to resolder half of them back to this board, upon power up it’s stayed out protection for 10 minutes and no dc on the links. Dc offset is steady now too. I ran out of time to do anymore testing today and I don’t want to call it a complete success yet, I’m going to do more testing tomorrow and re do the power supply and bias adjustments first and see if it holds up but looking positive!! Will report back tomorrow
So my joy was short lived again, after 5 minutes or so the protection kicks again I noticed the voltage on the pre amp links has reduced and spikes about 1.5v now, bias current remains steady and dc offset at the speaker terminal spikes approx 5v…
I will go replace the rest of the transistors on pb639 and see if that helps
Yes I think so too the only ones left I haven’t changed are on the eq phono board I’ll start there and try not to break any more wires!
So the latest update, PB639 has all new transistors and I reflowed the wires to this board, the amp now stays out of protection for around 10 minutes but something is randomly spiking dc offset on the left channel to trip the protection relay, I noticed as well bias current starts to run away, I switched it off after it drifted to approx 90ma
it has all new outputs for and drivers and matched differential transistors. I had initially ruled out the amp modules as I was always getting pre amp voltage spikes on the left side however after further checking I realised sv03 diode on the amp module was almost shorted and later shorted completely causing the dim to flow bright - finally found the culprit!
After replacing with 3 x 1n4150 diodes the bias and offset is steady on both channels for the past few hours!
Will try with some music tomorrow but thinking this is it and we are back to enjoying the
it has all new outputs for and drivers and matched differential transistors. I had initially ruled out the amp modules as I was always getting pre amp voltage spikes on the left side however after further checking I realised sv03 diode on the amp module was almost shorted and later shorted completely causing the dim to flow bright - finally found the culprit!
After replacing with 3 x 1n4150 diodes the bias and offset is steady on both channels for the past few hours!
Will try with some music tomorrow but thinking this is it and we are back to enjoying the
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So to close this out for anyone who experiences any similar issues to my journey with the Luxman l-100, I found the sv-03 diode on the other channel also faulty, after replacing it and readjusting bias the amp stayed out of protection and worked great.
In addition to this it had an intermittent transistor fault on the tone board, as per previous restorations it’s great to replace all the 2sc1345 transistors if I did this all up front would have not had to do so much troubleshooting.
When removing the tone board it’s easy to damage the wires that solder to the tone controls, I recommend de soldering these when working on the board or even better rewire them with slightly longer wiring which gives more give when moving the board around
I found a factory repair to a trace on pb637a I reflowed and repaired it helped reduce hum
Last tip - when working on pb640 it’s very likely you’ll damage wiring to it and the on pb637a and the mute switch board pb638 as the access is so tight and wiring doesn’t have much give…take photos so you know what goes where doesn’t hurt to rewire the really tight wires too…thanks again to everyone who helped along the way
In addition to this it had an intermittent transistor fault on the tone board, as per previous restorations it’s great to replace all the 2sc1345 transistors if I did this all up front would have not had to do so much troubleshooting.
When removing the tone board it’s easy to damage the wires that solder to the tone controls, I recommend de soldering these when working on the board or even better rewire them with slightly longer wiring which gives more give when moving the board around
I found a factory repair to a trace on pb637a I reflowed and repaired it helped reduce hum
Last tip - when working on pb640 it’s very likely you’ll damage wiring to it and the on pb637a and the mute switch board pb638 as the access is so tight and wiring doesn’t have much give…take photos so you know what goes where doesn’t hurt to rewire the really tight wires too…thanks again to everyone who helped along the way