G'day everyone,
I obtained this "dead" amp for some hobby fault finding and to test some speakers once it's hopefully fixed. I'm keen for any expert advice having had an initial look and to focus on next suggested checks. My take so far:
Re p9/44 SCHEMATIC DIAGRAM 1, the 5.6v supply to Q7502 is good.
Put simply: the standby LED is not lit because p17 is LOW thus not turning on Q7506. One thought is that the chip has an incoming fault condition causing this, but how to figure what & where is my current challenge. The spec sheet for Q7502 isn't of great help (to me) and the chip is reasonably complex but pins 8 to p22 seem to be where all the i/o is happening. There is surprisingly little on the internet to tap into from others (I would have hoped) with a similar problem esp as the amp is ~20yrs old and looks in OK condition.
All input very welcome. And, I'm a tech so I'm OK working on this.
Thanks.
I obtained this "dead" amp for some hobby fault finding and to test some speakers once it's hopefully fixed. I'm keen for any expert advice having had an initial look and to focus on next suggested checks. My take so far:
Re p9/44 SCHEMATIC DIAGRAM 1, the 5.6v supply to Q7502 is good.
Put simply: the standby LED is not lit because p17 is LOW thus not turning on Q7506. One thought is that the chip has an incoming fault condition causing this, but how to figure what & where is my current challenge. The spec sheet for Q7502 isn't of great help (to me) and the chip is reasonably complex but pins 8 to p22 seem to be where all the i/o is happening. There is surprisingly little on the internet to tap into from others (I would have hoped) with a similar problem esp as the amp is ~20yrs old and looks in OK condition.
All input very welcome. And, I'm a tech so I'm OK working on this.
Thanks.
Attachments
For anyone interested, it looks like I have an issue here due to long-term corrosion. The air slots on the top of the cover have allowed dust and the environment to contaminate the inside, so I'm in clean-up mode and working through the electrical connections of everything. Having done some cleaning up and then jumpering across the standby transistor Q7506 to switch on the LED - I just wanted to see that LED lit! - I noticed it's input was high, when previously it was low so there may be a bad connection/dry joint somewhere to find. It's an interesting one to work through but it's not seeming to be a power component failure as I'd originally anticipated.