Amp4 debugging ... no output chip, relay is shorting?

[krilli]

Hi,

An Amp4 doesn't want to play nice. I'm powering it with a Mean-Well HRPG-200 which has short-circuit protection built in. When I connect the power, the supply goes into protection. (The supply is otherwise functioning correctly.)

I inspected the board, and found three bad joints, which I corrected. It still shorted out.

As the bad joints were around the power stage, suspected I had blown the power chip and tried removing it (an STA517B), and still the amp shorts out. I disconnected the J10 jumper; No love.

However, I tried disconnecting the relay by lifting one leg of R100, the through-hole relay resistor. Then the board powers up nicely.

My questions:
- Through where could the short circuit be?
- Is it OK to power on the amp without the output chip?: Does the power chip control the relay in a meaningful way, causing the relay to somehow short out if it isn't under proper control? And will it damage other components like the TC2000 for instance?
- Could the relay itself be the culprit? (E.g. melted relay coil ...)
- What about the SOT-23 transistors that control the relay?

Thanks in advance for any hints you could give.

[krilli]

Never mind, it's something else

[V-bro]

For the sake of others then perhaps, this relay coil should measure about 1.4Kohms...