New to the Board with a iic+ problem

[Pensa]

Hello folks, brand new to the board so saying hi to all and hoping some of you guy's can help with Mark iic+ problem. Picked up a non-simulclass 60w combo with reverb and graphic recently which has also just had a cap job with F&T replacements. Fired it up last night but when i hit the standby switch there was a series of about 5 or 6 popping sounds followed by some smoke. I flipped the standby to off very quickly and pulled the chassis, on inspection i noticed a fried resistor which i've circled on the pic. Can anyone tell me what this resistor is - it's value? and what may have caused it to blow?
Thanks in anticipation

 

[chipaudette]

Hi There,

I think that it's supposed to be a 2W 1K resistor.

Man, it looks kinda nasty in there. Why are all of your orange drop capacitors got that black tinge to them? Has this thing been gigged in smoky environments for most of its life?

Sorry, buddy. Good luck with the repair. Hopefully that one resistor is the only issue.

Chip

 

[Pensa]

Hi There,

I think that it's supposed to be a 2W 1K resistor.

Man, it looks kinda nasty in there. Why are all of your orange drop capacitors got that back tinge to them? Has this thing been gigged in smoky environments for most of its life?

Sorry, buddy. Good luck with the repair. Hopefully that one resistor is the only issue.

Chip

Thanks Chip, it does look a bit murky, not sure why those ODs are like that but the amp has been around Jazz club environments for most of its life with the previous owner so that could have someting to do with the way they are. Certainly needs a good clean up. I was thinking that resistors would blow as a result of another problem somewhere in the amp so am a bit cautious about just replacing it without finding out what could have caused it. Hopefully not too much damage though.

Pensa

 

[Boogiebabies]

Mesa used a .5W 1K in that spot. It's basically a jumper from the HV buss where the brown wire connects from the filter supply.
Before you replace the resistor, remove it and check the voltage at the buss with the brown wire. It should be no higher than
400-420V DC. If it's higher, you may have an issue with the 30uf/500V caps on the filter supply board or a dropper resistor.
If the voltage is around 400V-420V, replace the resistor and check the voltage drop at the filter cap on the main board.
If it's too high it will cook the resistor and may point to the 30uf cap on the main board as a possible culprit. Either that or
the vast amount of flux left at the bottom of that tie on cap job is conductive and it's shorting the preamp B+ to the ground plane.
All scenarios would cause enough heat from over voltage too cook that resistor. The last one is simply time. I have seen quite a few of those
resistors replaced simply because they were ready to quit.

Good Luck.

 

[Pensa]

Mesa used a .5W 1K in that spot. It's basically a jumper from the HV buss where the brown wire connects from the filter supply.
Before you replace the resistor, remove it and check the voltage at the buss with the brown wire. It should be no higher than
400-420V DC. If it's higher, you may have an issue with the 30uf/500V caps on the filter supply board or a dropper resistor.
If the voltage is around 400V-420V, replace the resistor and check the voltage drop at the filter cap on the main board.
If it's too high it will cook the resistor and may point to the 30uf cap on the main board as a possible culprit. Either that or
the vast amount of flux left at the bottom of that tie on cap job is conductive and it's shorting the preamp B+ to the ground plane.
All scenarios would cause enough heat from over voltage too cook that resistor. The last one is simply time. I have seen quite a few of those
resistors replaced simply because they were ready to quit.

Good Luck.

Boogiebabies, many thanks for your knowledgeable and detailed reply. I will run those checks, clean it up and post back with the results.

Cheers
Pensa

 

[Pensa]

Mesa used a .5W 1K in that spot. It's basically a jumper from the HV buss where the brown wire connects from the filter supply.
Before you replace the resistor, remove it and check the voltage at the buss with the brown wire. It should be no higher than
400-420V DC. If it's higher, you may have an issue with the 30uf/500V caps on the filter supply board or a dropper resistor.
If the voltage is around 400V-420V, replace the resistor and check the voltage drop at the filter cap on the main board.
If it's too high it will cook the resistor and may point to the 30uf cap on the main board as a possible culprit. Either that or
the vast amount of flux left at the bottom of that tie on cap job is conductive and it's shorting the preamp B+ to the ground plane.
All scenarios would cause enough heat from over voltage too cook that resistor. The last one is simply time. I have seen quite a few of those
resistors replaced simply because they were ready to quit.

Good Luck.

Boogiebabies, just a note to say thank you, followed your advice and found the culprit to be the 30uf F&T cap on the main board as you said. Replaced the cap and blown resistor and all working perfectly again.
Thanks again
Pensa