Resistor values (no schematic available)

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Hi guys , hoping you can help me establish the values of these 2 resistors please?
Burmester 785 preamp
 
It would be interesting if you can draw at hand a schematic of the components involved. It can give us an idea of its value.

In any case, consider that highly probably, those resistors are victims of any other part in the circuit became shortcircuited, semiconductors or the blue tantalum near them. So I suggest to search for components damaged in other part of the PCB.
 
My suspicion is that those R's are between 10 and 100R to decouple the Vcc and Vee pins of the opamp we can see close to them. If the chip became damaged by severe overload of their inputs, those resistors became smoke.

It would have to be sixty-something ohm then. As they look like ordinary 0.6 W, 1 %, 50 ppm/K metal film resistors, they probably had E96 values. That narrows it down to:

60.4 ohm
61.9 ohm
63.4 ohm
64.9 ohm
66.5 ohm
68.1 ohm
69.8 ohm

Chances are that all these values would work fine, once whatever made the resistors burn has been solved.
 
Thanks Marcel .
I can say that currently the volume pot does nothing.
I’m no expert by the way!
Should I replace the tantalum caps and those 1000uf electrolytics ?

There is also the possibility that the volume pot is faulty as it appears to be a common fault, it was seized until I used some contact cleaner on it .
 
Looking at the photo's, I would say the resistors are part of the psu and the chip in the metal can with heatsink is more than likely a dual voltage regulator - all located close to the transformer, caps and mini diode bridges.

Looks like the 2 burnt resistors are fed from the +/- voltage rail on the psu caps feeding the IC input. So maybe a dead IC regulator chip - if you take the heatsink off Andy, you should be able to read the chip type on the side of the metal can.

Yes, get rid of the tantalums.
 
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Quite easy to follow the tracks on the back of the board. You can see 2 secondary windings , each feeding a small round diode bridge, plus and minus on each are filtered by 1000uF caps and those 2 points feed the 2 burnt resistors which then feed the IC +/- input with each point having a tantalum to gnd. Then there are 2 more tantalum's probably on the IC regulated voltage output.

So, either the tantalum's are down to gnd, or the IC is cooked - or both maybe. I agree, these burnt resistors are likely 6R8 in value.

I would replace all tantalum's with electro's and also replace the 4 off 1000uF/40V axial electro caps, given the age of the preamp.

I suspect the diode bridges might be OK, but can be checked with a meter, these could also be replaced - they are still available in that style.

It will be interesting to see what type the IC is, there were not too many dual voltage regulator chips around in those days - 45+ years ago now.
 
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