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MAC 4300V Service Manual Mystery

Ah jeez, that sucks.

Before you call it a day, check power supply voltages. One of those three-legged regulators coulda called it a day. If all sorts of stuff is messed up that's where I'd be looking first. Edit - don't neglect the 5V standby power supply that's in the right rear - as I recall that powers most of the logic board and the IR remote receiver.

I just got back from an overseas trip and haven't attacked my power amp boards again.
 
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Oh I didn't know that... I could always part it out, selling the HR-4300 remote, not to mention the knobs, dial glass, faceplate, and amp boards. Seems like the logical thing to do, if nothing else. These units don't seem to be that common, and I don't see them online often, in order to diagnose problems with them... Is it the 5.6V regulator in this diagram?5.6V.png
 
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I think it's worth a quick check of that main board to see if you have the +/-15V and 5V. The preamp and logic needs all three of those voltages. Upon further checking the 5.6V standby appears to power the power-up relay so if it turns on, chances are the 5.6V standby supply is good. It's unclear from the schematic but there appears to be a 5V supply rail that comes off the 5.6V, with D15 and C12 on that big power uspply/logic board. Not sure where that goes.

Anyhow, what is or is it not doing? Can you, for example, select FM and the frequency display comes up?
 
w3jn said:
I think it's worth a quick check of that main board to see if you have the +/-15V and 5V. The preamp and logic needs all three of those voltages. Upon further checking the 5.6V standby appears to power the power-up relay so if it turns on, chances are the 5.6V standby supply is good. It's unclear from the schematic but there appears to be a 5V supply rail that comes off the 5.6V, with D15 and C12 on that big power uspply/logic board. Not sure where that goes.

Anyhow, what is or is it not doing? Can you, for example, select FM and the frequency display comes up?
Click to expand...

I put it away before I got more pissed off lol. I’ll take it out and turn it on again later today to see what its doing. None of the inputs were working, if I remember correctly…
 
Yeah, quick checks of the 3 legs of each regulator on the big main board should give you the picture.

IC1: Pin 1 10V; pin 2 0V; pin 3 5V
IC2: Pin 1 0V; pin 2 -25V; pin 3 -15V
IC3: Pin 1 25V; pin 2 0V; pin 3 15V

upload_2023-3-31_14-24-45.png
 
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