AMB-5 Problem

4 posts in this topic

HI all, new here, just registered.

I'm the audio (and everything-else-tech) guy at my church. We have a BSS PS-8810 (no Cobranet card) in the amp rack, driving some old Micros for the main PA and CTSes for monitors and other stuff.

I picked up an old AMB-5 on Ebay on a whim the other week, the idea being to add a "lecture" automatic mixer for those times where there's a simple event and no engineer can make it. Great idea (the AMB-5 should talk to the 8810 over IQ bus), except it's an Ebay find, which is the source of my problem. A note on top "needs to be checked with laptop" is a big red flag that it's a tech special.

The AMB-5 powers up as best I can tell (the three PS heatsinks are warm and the power LED lights, but I haven't taken a voltmeter to it yet). The backup battery is toast, and there's a fair bit of green corrosion in the microprocessor section of the board, including chip pins. Doesn't respond to RS-232 or IQ. Checking the RS-232 connection in more detail, it's holding CTS low and won't connect even with RTS-CTS looped back to the host computer.

Any pointers on where to look? I'm hoping it's just a power supply problem, which is relatively easy to fix. I'll check the power supply with a VTVM when I get back to it later this evening. If the power supply is good, where should I look next?


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Power supplies check out good.

My gut feeling is the microcontroller is shot. Since the IQ-Bus comes straight from the chip (through buffers) and the RS-232 from the UART (through bus drivers) that's fed from the chip, and both are kaput, the common point of failure would be the 68HC05.

Next step is to get the scope out, verify the oscillator is running, and look between the HC05 and the UART, but I'm guessing it's the HC05, which means it's time for a call to the parts department.

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