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Luxman L-85V amp rebuild - replacement parts?

in the hifiengine manual is a 4.7 ohms in series with the driver transistor.
Now, it is not mentioned and it has no R-something number in the schematic...
Problem here, it might work with 4.7 as well as 470, even if values are 100 times apart. But it is too high if 470....

The input transistor pair usually is a suspect when output voltage is off. replace both with KSA992 or something like that preferably matched pairs.

Still, it might be one of the other transistors too, the zener diode for the input pair being defective, or other problems.


Anyway if it does not solve the problem, just make a big printout of a main amp schematic and jot down all voltages with respect to ground, probably something odd is found.
 
yes, both Q1 and Q2 (although a usual suspect does not guarantee it is faulty. BTW a lot of people on AK replace every 2SA725 or 2SA726 they encounter)
 
I replaced Q1 and Q2 with 522-ZTX795A - but maybe they are very vulnurable?
I had a bit of a mishap, first time i powered on the amp (with a dim bulb tester) - the guy i got the amp from, had apparently flipped the output transistors, which meant that when i replaced them i switched them too.
The bulb tester lighted up and i powered the amp down, but maybe this short term power-on could have damaged Q1 and Q2?
 
they are not vulnerable but many times people find the input pair more or less defective, and a source of popping and scratchy sounds.

Still, I always first measure before replacing.

Yes, a short term power up can instantly kill something. (that is why I consider the thing called DBT thing rather useless, but on AK that is probably just me...)
 
Could i try taking measurements (ECB voltages) of the transistors while in circuit, powered on - would that give a clear picture?

best regards
 
okay, measurements done:
Marking with read, where i think the difference is significant.

The Reference, original board:
Q1 E: 632mV, B: 152mV, C: 46,7V
Q2 E: 668mV ,B:152mV , C: -45V

The 'new' board:
Q1 E: 586mV, B: 156mV , C: Can't read - relay clicks in upon probing.
Q2 E: 571mV, B: 58mV, C: -41V
 
I have now replaced both Q1 and Q2, double checking the pin.-outs, the new pair that is in the machine is now allowing my to adjust Bias to 12.2-12.4 mV at the output...

I think i have solved my issue and now have a working and stable machine.
...
Yay!
 
I want that TT. One of the best looking tables from the time. Nothing flashy just quality. Well not flashy when it gets up to speed. Can't even see that indicator lamp except in a reflection in the photos.

Nice that the L85 is back in service. What speaker is that hiding in the corner?
 
congrats. You found a resistor with heat shrink on it? okay problem with your unit?
Manuals are not always in Granite... hell most unless orig in good condition suck and they don't have engineering updates. This is old stuff.

4.7 4.8... within meter range and tolerance. if 0.1 ohms can screw up a circuit? no.

a simple pic of the resistor would clean this up.. not some long shot.. need to read the bands on the resistor.
 
Hi all.
I am repairing an L85v at the moment and have both power amp boards rebuilt with zero offset and the correct bias levels- only to discover the level is way down and distorted on the left channel.
I obviously have a fault in the pre amp section just following the volume pot.
However, I can say that the resistor feeding the signal to the drive transistor Q609 is definitely 47 ohms, as this makes sense as a stability measure. 4.7 ohms would have very little affect in that regard.
The resistor fitted where D03 is marked on the board is 4.7k on my sample, but as we all know it is marked as 5.6k in the manual, D503 on one channel, D613 on the other!
Do not trust the manual 100%- be very wary. Q801 on the power supply board is drawn as a pnp transistor instead of an npn.
What were these guys on when they drew that manual?!
 
Blue Shadow said:
I want that TT. One of the best looking tables from the time. Nothing flashy just quality. Well not flashy when it gets up to speed. Can't even see that indicator lamp except in a reflection in the photos.

Nice that the L85 is back in service. What speaker is that hiding in the corner?
Click to expand...

The speakers are JBL L15 - as new and restored with original NIB recone kits. They sound remarkable considering their size!
As I have split up with my girlfriend a couple of weeks ago, I am considering L-100's again, but these will stay for sure.

The TT is a Luxman PD-441, fitted with an SME 3009 early series 2, and with an Ortofon MC-30 Supreme.I
 
Binkman said:
congrats. You found a resistor with heat shrink on it? okay problem with your unit?
Manuals are not always in Granite... hell most unless orig in good condition suck and they don't have engineering updates. This is old stuff.

4.7 4.8... within meter range and tolerance. if 0.1 ohms can screw up a circuit? no.

a simple pic of the resistor would clean this up.. not some long shot.. need to read the bands on the resistor.
Click to expand...
The issue i had was with the input transistors - the resistor was 47 ohms :)
 
Armac said:
Hi all.
I am repairing an L85v at the moment and have both power amp boards rebuilt with zero offset and the correct bias levels- only to discover the level is way down and distorted on the left channel.
I obviously have a fault in the pre amp section just following the volume pot.
However, I can say that the resistor feeding the signal to the drive transistor Q609 is definitely 47 ohms, as this makes sense as a stability measure. 4.7 ohms would have very little affect in that regard.
The resistor fitted where D03 is marked on the board is 4.7k on my sample, but as we all know it is marked as 5.6k in the manual, D503 on one channel, D613 on the other!
Do not trust the manual 100%- be very wary. Q801 on the power supply board is drawn as a pnp transistor instead of an npn.
What were these guys on when they drew that manual?!
Click to expand...
Getting very tired of the shitty manual scan - and the manual in general is very non-friendly. But always nice to have AK to help out, when everything else fails ;)
 
Luxman manuals suck and were an afterthought. They spent their money on the sound quality and build of the units in many cases. Nothing left for a small company to make nice useful and helpful manuals.

Now I know I want that table. Best cartridge I have heard in my rig is an Ortofon MC 30 Super.
 
Blue Shadow said:
Luxman manuals suck and were an afterthought. They spent their money on the sound quality and build of the units in many cases. Nothing left for a small company to make nice useful and helpful manuals.

Now I know I want that table. Best cartridge I have heard in my rig is an Ortofon MC 30 Super.
Click to expand...
Mine is of course paired with an Ortofon T-20... one of the few benefits of being in Denmark, Ortofon is cheap and plentiful! :)
 
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Bet it sounds nice.
------
Don't forget orig. manuals are usually of good quality I own a few for my good stuff. The scanned in online dl's that usually suck. of any manufacturer usually one model was already being replaced by another in any series, like cars? next year or even in months a new model. Thus why bother with a new manual vrs a service bulletin?... these are even harder to find.
 
Binkman said:
Bet it sounds nice.
------
Don't forget orig. manuals are usually of good quality I own a few for my good stuff. The scanned in online dl's that usually suck. of any manufacturer usually one model was already being replaced by another in any series, like cars? next year or even in months a new model. Thus why bother with a new manual vrs a service bulletin?... these are even harder to find.
Click to expand...

That is interesting. Let me say it again, Luxman service manuals SUCK. Look up some of them. Very basics, sort of a photocopied typewritten page, limited to the very basics without any color, completeness and in many cases no mechanical parts diagrams. Don't know if they had more than a few service manuals.

As to the already on to another, like cars, that is a change from the vintage years (for gear not cars) when the new models were made available in Sept and were simply a mild restyle from the previous year for a number of years. Now we have new models announced all year long and the cycle is about 7 years for a more completely new model with a mid-term refresh.
 
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