Burning R206 resistor in 303

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06-Mar-2019 03:30 PM

bluegrass

bluegrass

Posts: 77

I have an issue with a rebuilt 303. It is burning out the r206 10r resistor on the power supply board. Any ideas on where to start much appreciated.
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07-Mar-2019 05:55 AM

EJP

EJP

Posts: 1589

This means overcurrent in the driver transistor, which means the centre power transistor won't turn on, which means it is faulty or misconnected.
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07-Mar-2019 08:09 AM

bluegrass

bluegrass

Posts: 77

Brilliant, thanks for that. I'll replace them all with MJ15003's and see how that goes. I'll check everything on the boards to make sure there is no other damage done.

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07-Mar-2019 10:47 AM

EJP

EJP

Posts: 1589

The PSU power transistor needs to be MJ802.
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07-Mar-2019 11:08 AM

bluegrass

bluegrass

Posts: 77

Ok,  thanks. The FAQ transister alternative page seems to suggest the MJ15003 for all.

 The MJ802 is not available on the site, i'll try and source one from somewhere else but use the MJ15003 for the other 4.


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07-Mar-2019 11:29 AM

bluegrass

bluegrass

Posts: 77

Apparently the MJ802 is no longer in production. Is there an alternative? Thanks
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07-Mar-2019 08:16 PM

Ton

Ton

Posts: 54

Perhaps the MJ802G ?


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08-Mar-2019 12:39 AM

EJP

EJP

Posts: 1589

That's what is meant. G is just a suffix indicating higher gain. It is customary to use just the part number proper, i.e. MJ802. Otherwise for example in another thread I would have to be talking about the LME49710ANPB, when LME49710 is already quite long enough thanks. And you yourself talked about MJ15003 rather than MJ15003G, which is all you can actually find.

Last time I looked, Farnell had about 1,300 MJ802G in stock.

MJ15003 is not an acceptable substitute for Tr3. The MJ802 has maximum Ia of 30A as against 20A for MJ15003. More current capability is required as it has to pass current for both channels. (It looks like a shunt regulator in the schematic, but it isn't, it is in series).

But I would check the connections first. The usual Tr3 fault is a c/e short, not an open circuit.

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11-Mar-2019 09:34 AM

bluegrass

bluegrass

Posts: 77

Thanks for the advice.

I'll check the original connections etc, and then order an MJ802 if the original is faulty.


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