Luxman LV105 protection IC woes [not, solved]
Hi,
This thing is driving me nuts.
So I have this otherwise beautiful amp which is giving me a hard time.
It has a TA7317P chip that controls the amp's protections : DC, overheating, and so on.
The amp does actually work. I've got about 4 mV offset before the relay and nothing overheats. It even makes nice sounds! Nothing crackles or distorts.
But the damn relay won't trigger.
I can force it to do so by bringing about 2 V on pin 8 of the TA chip, then the relay engages after about 30 seconds (all I need to do is short the - good - 100k resistor between pin 8 and 9 with a low value resistor). So basically, the chip seems to work, right?
Otherwise, voltage on pin 8 is too low, but why? 😕
I checked everything around the protection circuit. I can'f find anything odd. Just the bloody pin 8 low voltage. Oh, the cap is new (the old one was fine anyway).
I also tried to lift R8325 (1k) but that didn't make any difference.
Do you have any clues please?
Thank you.
Hi,
This thing is driving me nuts.
So I have this otherwise beautiful amp which is giving me a hard time.
It has a TA7317P chip that controls the amp's protections : DC, overheating, and so on.
The amp does actually work. I've got about 4 mV offset before the relay and nothing overheats. It even makes nice sounds! Nothing crackles or distorts.
But the damn relay won't trigger.
I can force it to do so by bringing about 2 V on pin 8 of the TA chip, then the relay engages after about 30 seconds (all I need to do is short the - good - 100k resistor between pin 8 and 9 with a low value resistor). So basically, the chip seems to work, right?
Otherwise, voltage on pin 8 is too low, but why? 😕
I checked everything around the protection circuit. I can'f find anything odd. Just the bloody pin 8 low voltage. Oh, the cap is new (the old one was fine anyway).
I also tried to lift R8325 (1k) but that didn't make any difference.
Do you have any clues please?
Thank you.
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Thanks Mooly.
Mmm... that cap is a tantalum. No, I haven't checked it.
Edit: checked OK but replaced by a normal electrolytic. No difference.
Mmm... that cap is a tantalum. No, I haven't checked it.
Edit: checked OK but replaced by a normal electrolytic. No difference.
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chartz,
Check the voltages for the other protection detection pins. Luxman utilized them all and added additional muting, thermal protection circuits around the TA7137.
There is no way around this. You have to check ALL the TA7137 pins and work your way back.
Check the voltages for the other protection detection pins. Luxman utilized them all and added additional muting, thermal protection circuits around the TA7137.
There is no way around this. You have to check ALL the TA7137 pins and work your way back.
Thank you both.
All good except for pin 8, that's the problem! Forcing voltage to pin 8 makes it work normally.
There is some failure somewhere within the Luxman application, but where?
Anyway, the service sheet doesn't give those values. They are all over the web, but what do they mean?
I mean this:
I get what Q8305 & 8305 should do in case there's a problem, but lifting the 1k is not restoring normal operation (I thought it would, actually).
All good except for pin 8, that's the problem! Forcing voltage to pin 8 makes it work normally.
There is some failure somewhere within the Luxman application, but where?
Anyway, the service sheet doesn't give those values. They are all over the web, but what do they mean?
I mean this:
I get what Q8305 & 8305 should do in case there's a problem, but lifting the 1k is not restoring normal operation (I thought it would, actually).
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According to the block diagram pin 9 -constant voltage power supply circuit feeds pin 8 muting circuit-- even in the test circuit 50 volts Vcc is fed to pin 9 via a 220Kohm resistor giving a very small current draw .
Check that out.
Check that out.
It had to be tried. Surprised to see a tant for that but any way 🙂
That would have my next line of attack, to see if the transistor was shunting anything away.
Are the two series resistors to pin 9 OK (shown as R8312 and 8313)?
Yes, they are fine. I get about 3 V on pin 9 as expected.
Here it’s 100k. All in good order.
Here it’s 100k. All in good order.
If it comes down to it this chip is cheap and was fitted to a whole load of different makes of audio amplifiers in the past.
Its no "big deal " changing it .
Its no "big deal " changing it .
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You’re right of course but I really want to understand why I should have to do it in the first place. Blindly replacing things is something I don’t like!
What you said is perfectly logical and understandable but faults in digital chips can be queer --only one section of the chip non functional there have been several in the past month here that required replacement after a whole regiment of posts advising to try this or that.
I helped a guy a week or so ago which boiled down to replacing the chip which again was cheap and --bingo ! it worked.
I helped a guy a week or so ago which boiled down to replacing the chip which again was cheap and --bingo ! it worked.
Ordered just now. I will let you know the outcome – I always do.
Unless someone comes up with a genius idea!
Cheers
Unless someone comes up with a genius idea!
Cheers
Pix from a NAD3150 showing pin 8 current draw in microamps so 2.5mA(above) probably suggests internal IC damage. External 2V supply at pin 8 overcomes this voltage "sag".
The number of posts here ending up with faulty digital chips is mounting up MBZ is right I missed that.