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I have a vox cambridge 30 reverb i got from a friend. I know he replaced the speaker, why im not sure. It has weak sound, no bass unless you play at max volume. I checked the board and it burnt resistor R84. If what ive read online is true i think its a 10 ohm resistor. But does anyone know of any common issues i should check up on that would have caused the resistor to burn out originally? Also does anyone the specs on C47, i would like to replace it as it was on top of R84 and got a little burned as well. Thanks
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According to my schematic/parts list R84 is 10 ohms, 1/2 W. C47 is .02uf, 50V. I have replaced the TDA2050 output IC (IC7) in one of these amps with no notes about any other components damaged. A shorted TDA, previously replaced, could have caused too much current thru R84. It may not be open, even though it looks burned. R84 and C47 are in series and across the output of the TDA to ground.
The LDR for the trem circuit (LT9914) is a problem I have seen in these amps, along with flakey normaling contacts on the headphone and external speaker jacks. These can cause a variety of level, tone and distortion problems. I have only repaired 3 of these amps. I have substituted a 1M ohm resistor for the resistor part of the LDR to be able to check the rest of the amp. An authorized Vox amp guy suggested a generic replacement for the expensive LDR replacement from Korg, which I used successfullly. This requires adjustment of the 2 pots (VR11,12) in the tremolo control circuit.
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