Luxman M-03 PA problem

[radeohedca]

Hi there.
My father-in-law asked me to have a look at his Luxman M-03 power amp.
The main power indicator lights up but the power meters do not and there is no audio.
I just acquired a schematic for the unit. Before I get stuck in to this, I'd appreciate any comments, pointers etc. My suspicion is a problem in the power supply to the logic board (shorted or low esr e-cap ?).

A google search uncovered an old post from someone seeking info on the same unit with the same problem but there were no follow-up posts so I suspect it may have been a common problem with these units.

Thanks in advance, Hugh.

[singa]

Hi, First check the power supply if it is good that is ,all relevant voltages are
present and accounted for.Only then can you go on to check suspected
section of the circuit but it is also important to do visual check to see if there are any burnt or charred parts or pcb and things that are broken like pcb tracks and pads.Do forget the wiring to physical parts like meters and other things. Best if you can post the schematic so others can help you along
with your fault finding. Good luck.

[radeohedca]

I found a PDF of the M-03 service manual with schematics.

I spent a few minutes looking at it last night and I believe the problem may be the TA7313P protection IC or something in the surrounding circuitry like a bad cap.

I do not hear the relays clicking when I depress speaker A or B, hence my suspicion of the protection circuit. This would also cause the signal level displays to be off since there is a display enable signal coming off the relay board.

I'm feeling confident.... more poking around tonight.

[sakis]

be aware .... for this amplifier that is now about 20-25 yeras there is a number of problems that you need to see before powering up ...otherwise you will loose a very nice amp ....

No 1 and serious problem is that the both main pcb has loose solder joints here and there ...you will find many around

---- driver area and related conectors
---- predriver area
---- vbe multiplier and related conectors
---- block of resistors R222-227
---- local regulator transitors 216 213
---- leacky caps 205 207 211 210 213 212 217 216
---- ltp area Q201 Q202

after the above you need to find trouble free start up procedures ....

work carefully this is repair procedures beyond the above there might be other faults also

sakis

[radeohedca]

Thanks...
Your words of caution duly noted.

Resoldering will be job #1 and I already have the set of e-caps for the PS board that I will be replacing tonight.

I'm sure the years of confined heat has wreaked havoc on the electrolytics.
I'm hoping it is nothing more than a poor solder joint or shorted or low esr cap.

Hugh

[radeohedca]

Okay guys, it looks like something around the TA7317P relay driver IC (or the chip itself) isn't happy. Pin 6 (o/p) which is labeled "COM" should be +1.4V, I'm reading 12.3V. When I isolate the COM wire and pull it to ground the relays and displays come to life.
Here are the voltages that should be on the 7317 versus what I read:

1 -0.6V, I read -0.6V
2 0V, I read -0.75V
3 0V, I read -0.83V
4 0v, I read 0V
5 -0.75V, I read -0.33V
6 +1.4v, I read +12.3V
7 0V, I read 0V
8 +1.3v, I read -0.4V
9 2.8V, I read 2.9V

Pin 8 (Mute) voltage seems peculiar... In circuit it is pulled up to pin 9 through a 220K resistor. Pin 9 shows 2.9V. Pin 8 is also connected to the PRT line through a 22uF e-cap and 33K resistor.

And what about Pins 2 and 3 ? Is -0.7~ -0.8V enough to keep the relay driver from activating ?

Could the IC be smoked ?

Comments welcome.
Thanks, Hugh

[radeohedca]

BTW, I replaced all e-caps on the PSU board where the TA7317P is located.

Hugh

[ghostriderz1z]

Hello

i have the exact same problem with u.
Have you found what the problem is because i think it is the chip itself.
I am fixing this amp for a friend and i dont want to cause more damage.
Thanks

[sakis]

first of all you need to check for excessive dc offset for any of the amplifier outputs ... i have been repairing so far more that 15 Luxman m03 none of them had any 7317 issues

offset or full DC swing in the output will occur if any of the pre or drivers or VBE multiplier suffers from soldering issues .... make sure that first before anything else .

soldering is the most common failure for these amplifiers ...consider your shelf lucky if its only this ....very often a soldering in the driver or the VBE are will result blown outputs ....and these don't come any cheap...

regards
sakis

[ghostriderz1z]

hi sakis

when you say VBE multiplier??where is that?
i resoldered aalmost all of the power supply board in the back and the relay/output board.
it came back to life 2-3 times and just when i believed it was fixed it started doing it again.the main boards seem to be a little difficult to be removed so i am leaving them last for resoldering.
thanks mate