Need assistance from someone familiar or has Crown DC300A

[saabracer23]

I have this Crown DC300A that I’m rebuilding in the hope it will be used in an active 3 way setup. I noticed that a single red wire has come undone from its home. It’s the last thing stopping me from reassembling this thing and starting adjustments. It goes from wherever on the board to the small board mounted on the face just below the channel one gain pot(lower wire on right hand side of pic below). Can anyone help me out on figuring out where this wire needs to go? I’ve scoured the board lookin for a break point with no luck.

Dan

 

[llwhtt]

Where does the RED wire go on that board? It's the IOC PCB correct?

Craig

 

[elnaldo]

I've fixed 2 DC300A but I don't remember or kept picts of that detail. But with schematic (what I have) and knowing where the other end of that wire goes (what you can check) we can connect that wire in the right place.

 

[dshoaf]

My first guess is that it is the power supply connection that powers the single chip - looks like an LM339 - on the IO board. IIRC, Crown was pretty consistent with its color coding of wires.

Cheers,

David

 

[saabracer23]

Where does the RED wire go on that board? It's the IOC PCB correct?

Craig

I've fixed 2 DC300A but I don't remember or kept picts of that detail. But with schematic (what I have) and knowing where the other end of that wire goes (what you can check) we can connect that wire in the right place.

My first guess is that it is the power supply connection that powers the single chip - looks like an LM339 - on the IO board. IIRC, Crown was pretty consistent with its color coding of wires.

Cheers,

David

Yes, it does in fact lead to the IOC board with the LEDs. It attaches to the back of this board, but I can’t figure out where.


Dan

 

[llwhtt]

Where does it go on the IOC board, if we know that we can figure out where it goes on the main board. The red wire maybe the +10VDC supply for the comparator IC just like David said.

Craig

 

[saabracer23]

Where does it go on the IOC board, if we know that we can figure out where it goes on the main board. The red wire maybe the +10VDC supply for the comparator IC just like David said.

Craig

So there is a photo of it in my first post, it’s the wire on the very bottom. Here is a pic of the back of the board and it’s the trace with the red line under it. There are four resistors that come off the trace and the other side of those resistors are the red dots.

Dan

 

[elnaldo]

Which DC300A version is yours? I don't see that board or that IC in my DC300A schematics.

 

[llwhtt]

You are not making this easy, what resistors are those? Does it also go off board to the LEDs? Looks like there's a orange band on one of the resistors, probably R140 and R240, if so that's the +45VDC line. Now we need to find +45VDC on the main board.

Craig

 

[llwhtt]

I can't find +45VDC anywhere. However on the DC-300A II J0124-8 schematic it shows the IOC circuit uses +60VDC at W31 terminal.

Craig

 

[saabracer23]

Which DC300A version is yours? I don't see that board or that IC in my DC300A schematics.

You are not making this easy, what resistors are those? Does it also go off board to the LEDs? Looks like there's a orange band on one of the resistors, probably R140 and R240, if so that's the +45VDC line. Now we need to find +45VDC on the main board.

Craig

I can't find +45VDC anywhere. However on the DC-300A II J0124-8 schematic it shows the IOC circuit uses +60VDC at W31 terminal.

Craig

I apologize all, not trying to make this hard lol. I really do appreciate the help. I believe this is the first version, it doesn’t say mk. II or anything like that. Serial number is 32472 if that does anything for you. The small board that this wire goes to and that is attached to the face does indeed go to the led board. It has the number 9794 printed on it. Of the four resistors that come off that trace two are 33k and the other two are 2m. The chip on the board is an LM339N. Maybe another chip was used at another time? Anything else you need let me know.



Dan

 

[llwhtt]

OK, that IS the +45 or +60 VDC wire. I have a DC-300A but no IOC. Your main board has the dreaded UA739/749 opamp in the middle?

 

[saabracer23]

OK, that IS the +45 or +60 VDC wire. I have a DC-300A but no IOC. Your main board has the dreaded UA739/749 opamp in the middle?

It certainly does, did you mean beloved or dreaded? Not sure if your phone autocorrected there or not. Is there something to be done with the UA739PC?

Dan

 

[ConradH]

The uA739PC is a weird-ass chip, not easily replaceable by anything. Some say it's part of the reason the DC300 is claimed to be slightly harsh. If it is, it's pretty slight. I don't know if the available 739s are fakes, but you want OEM if you ever have to replace it. Apparently there's a zener or two that, if they fail, can take the chip along for the ride. If you replace outputs, be sure to match them using the Vbe method from Crown, not the usual Ib method usually used. If you can wait a day or two, I can open mine up and see if the wire is visible without major disassembly.

 

[saabracer23]

The uA739PC is a weird-ass chip, not easily replaceable by anything. Some say it's part of the reason the DC300 is claimed to be slightly harsh. If it is, it's pretty slight. I don't know if the available 739s are fakes, but you want OEM if you ever have to replace it. Apparently there's a zener or two that, if they fail, can take the chip along for the ride. If you replace outputs, be sure to match them using the Vbe method from Crown, not the usual Ib method usually used. If you can wait a day or two, I can open mine up and see if the wire is visible without major disassembly.

Thank you very much. Good info to know. From what I read, the 300As with the IOC board is supposed to be better sounding than the ones without. I replaced every diode in the amp so I should be good to go on that front. Thanks again!

Dan

 

[llwhtt]

No phone here, I know how to spell! Dreaded is what I said and meant, zero replacements or upgrades there. The later DC 300A II got rid of that particular opamp and used a more common opamp and that's the one with IOC that supposedly sounds better. If you were to replace a few resistors on that IOC board you can connect that RED wire straight to the +60VDC power supply. That's how the later versions did it.

Craig

 

[ConradH]

I had a look in mine, not knowing what version I've got. No IOC board, so no red wire. Sorry, but llwhtt seems to have it covered for you.

 

[saabracer23]

No phone here, I know how to spell! Dreaded is what I said and meant, zero replacements or upgrades there. The later DC 300A II got rid of that particular opamp and used a more common opamp and that's the one with IOC that supposedly sounds better. If you were to replace a few resistors on that IOC board you can connect that RED wire straight to the +60VDC power supply. That's how the later versions did it.

Craig

Great, that’s an option for sure. I was just joking about the autocorrect. Is there any instruction on how to do that as far as resistor values and such? If they use the same board and traces maybe update the board fo the better opamp! I at least want to get this thing going. I put too much work into it just to be stopped by one measly wire haha.

Dan

 

[llwhtt]

Upon closer inspection the IOC circuit is different between the two versions of the DC300A II. The main boards are different as the later board incorporates the IOC circuitry on it. The amp will run fine without the IOC circuit. We just need to find the +45VDC source on the board you have OR is the +45VDC a mistake on the schematic?!

Craig

 

[saabracer23]

Upon closer inspection the IOC circuit is different between the two versions of the DC300A II. The main boards are different as the later board incorporates the IOC circuitry on it. The amp will run fine without the IOC circuit. We just need to find the +45VDC source on the board you have OR is the +45VDC a mistake on the schematic?!

Craig

I’m not having any luck with a schematic with the IOC board. Would you be able to share. This is a real bummer, to be halted by a single wire lol.

Dan