Quad 303 component query

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22-Oct-2017 11:42 AM

simes

simes

Posts: 4

Hi,
I could smell faint burning from my 303, and opening it up I found some blackening here:



https://imgur.com/a/ZMgF6

What should I be replacing please? Thanks!
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23-Oct-2017 01:30 AM

EJP

EJP

Posts: 1405

This is normal, and not the source of the burning smell. Have a good look on the amplifier boards, especially under the heatsink flange at the cable entry side of the boards.

EJP
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23-Oct-2017 10:56 AM

simes

simes

Posts: 4



Thanks for the reply, EJP...what should I be looking for please? Here are some more photos, if that helps.

https://imgur.com/a/BbF0t
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23-Oct-2017 11:34 AM

Joost Plugge

Joost Plugge

Posts: 938

Release the boards at one side, opposite to where the cables are connected, and swivel them downwards, remove all the dust with a brush and a Hoover, and make pictures, also make a picture of the big elco's looking from the underside of the chassis, my guess: the elco's ar very old and leaky.

Joost Plugge

DaDa Engineering

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23-Oct-2017 12:59 PM

simes

simes

Posts: 4

Thanks for your replies; here are those photos, Joost:


https://imgur.com/a/QSHHK
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23-Oct-2017 03:08 PM

Joost Plugge

Joost Plugge

Posts: 938

On the Psu board the resistor besides the heatsink is burned. It is difficult to predict what went wrong and what the resulting damage is. Looking at the pictures the 303 is partially upgraded/repaired. First repair the Psu with the two driver boards disconnect from the suply (remove the red wire from pin 1). Update the unit with our kit. Again, the results are unpredictable, worst case you also have to replace the output transistors, you could check those 5 transistors on the heatsink with a multiMeter with a Diode check.

Joost Plugge

DaDa Engineering 

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24-Oct-2017 12:35 AM

EJP

EJP

Posts: 1405

The burnt component is the 10R emitter resistor of the driver transistor. So probably that is gone and maybe its pre-driver transistor and probably the power transistor as well (centre one on the heatsink).
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01-Nov-2017 03:58 PM

simes

simes

Posts: 4

Thanks for all the replies, very helpful.
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