SLA1500 clone driver issue

[Leolabs]

Hi,anyone have a schematic of the SLA1500 driver card?I got a OEM clone here with intermittent issue on the High side drive.

For normal condition both High and Low output from the driver card is around 2.3V but once it got issue,the High side will output of around 4.4V something,which of course will turn on the 6N137(and proceeding BJT,which will turn on the MOSFET) and lead to high DC offset on the output.

All three 78M05 are working fine as measured,and also the symmetrical supply feeding the driver card OPAMP are fine too(got +11 something and -11 something all time).Swapping the driver card from a working unit WON'T help either.

Funny thing is the symptom is intermittent,sometimes is ok and sometimes is not.

Thanks in advance!

 

[Perry Babin]

Why do you need a diagram for the driver board if a known working board doesn't solve the problem?

The driver board voltage (2.3v) where are those taken?

Is that the voltage from a multimeter or the amplitude seen on a scope?

 

[Leolabs]

Why do you need a diagram for the driver board if a known working board doesn't solve the problem?

The driver board voltage (2.3v) where are those taken?

Is that the voltage from a multimeter or the amplitude seen on a scope?

The reason itself is simple,so that i can trace the pinout function of each,relevant to the driver card itself, and to the circuit surrounding the card.

2.3V is taken with a DMM,at pin 10 and pin 11 and will jump into 4.4V(only on pin 11) if there is issue.If u need a scope reading for advise,let me know if u need a waveform snapshot too.

 

[Perry Babin]

Are both pins 10 and 11 dropping the same?

And the voltages (all supply voltages and the mute) feeding the board are the same when the drive changes?

The sla1500 diagram should tell you what you need to know about the pin configuration.
http://www.bcae1.com/temp/SLA1500.pdf

 

[Leolabs]

Are both pins 10 and 11 dropping the same?

And the voltages (all supply voltages and the mute) feeding the board are the same when the drive changes?

The sla1500 diagram should tell you what you need to know about the pin configuration.
http://www.bcae1.com/temp/SLA1500.pdf

when issue is happening:
1)only pin 11 voltage is rising to 4.4V
2)pin 10 remain normal at 2.3V,which is matching the working unit.
3)all supply voltage reading normal as per first thread.

Mute voltage haven't check yet.What is the suitable reading range?

 

[Perry Babin]

Mute voltage should drop to ground and remain there.

Is the 4.4v from an increase in amplitude or is it that the voltage isn't being pulled pulled back to ground?

 

[Leolabs]

Is the 4.4v from an increase in amplitude or is it that the voltage isn't being pulled pulled back to ground?

Not really getting what u mean here on the 'voltage isn't being pulled pulled back to ground', but all I can tell it's measured with no audio signal applied and there is a resistor pull up to 5V.Continuity reading from pull up resistor to card's 74HC02 pin 4 is ok.

Any more inform u need? Kinda weird to me since first time encounter such issue.

 

[Perry Babin]

This is a power supply waveform but it's the same basic concept. You can see that the top waveform (good) has a falling edge that's very nearly vertical to near ground. The bottom waveform (bad) is falling much more slowly. The top waveform would read as a lower voltage on a multimeter.

 

[Leolabs]

Hi Perry,found the issue, it's from the active filter section.-V failed to supply the OPAMP due to faulty smd resistor thus creating a DC offset to the driver card.

Thanks for the advise anyway.