Beomaster 4500 no standby light.

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Hi all, I’ve recently acquired a Beomaster 4500 and discovered it was missing the EPROM (IC3) and AM/FM board. I’ve flashed a M27C512-12C1 with SW 1.6 from a bin file on this forum and replaced IC3. The relay clicks when plugged in but the panel doesn’t light up at all (no standby light). If I remove the EPROM the panel lights up randomly. Shorting the test pins while powering on also does nothing. Any insight as to what the issue could be would be much appreciated, many thanks.

[Rose Black]

@Retro Bowl From what you’re describing, it doesn’t really sound like a bad EPROM on its own — the random panel lighting when IC3 is removed points more toward a power, reset, or bus issue. I’d start by carefully checking the 5V rail at the CPU/EPROM, the reset line on power-up, and continuity around the EPROM socket, as a missing or unstable reset or supply can stop the system from ever properly starting even though the relay clicks.

[ad1111]

Thanks for the advice, the CPU, EPROM, and RAM chip are all receiving 5.18V. On power up the reset line goes high then drops to 0v as expected, power fail is high and the pins from the EPROM are continuous with where they need to go (multimeter beeps) according to the service manual. Could the RAM chip (tmp8155) have gone bad?

[ad1111]

Now that I look at it again, the relays seem to click twice, on and then instantly off again. I don’t know whether this is normal behaviour. The amplifier chip was also internally shorted so I’ve removed it but still nothing, and the power fail line isn’t tied to GND either.

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