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In Reply to: RE: Help request for BMC MCCI phono stage posted by katylied on March 02, 2025 at 02:30:37
They are clearly marked as 15K. So the question is, was the original value 7.5K and if so, why did they fail and/or get so hot?? Design issue or component failure?
Follow Ups:
Ralph: I've unsoldered the resistors and the one on the bottom and take a measure: they are 150 ohm as can see from the very good picture I've found but don't know why somebody added a 200 ohm resistor on top of each one...
I will install new resistors of the same value as I found it but doing a better job for the soldering to avoid problems
As I stated in my original post, one possible answer is that the 200 ohm resistors were added to lower the overall value of the 150 ohm resistors, as shown above. In other words, rather than going to the trouble of removing the 150 ohm resistors, they added a 200 ohm in parallel to create the equivalent of an 86 (rounded up) ohm resistor.If this is in the power supply, this was likely done to raise the B+ voltage. It would be nice to know what that target is, but apparently BMC isn't talking.
Edits: 03/06/25
I would expect that would have been a bit neater. The photo shows parts that could flop around during shipping.
Two things are sticking out here. The first is that the resistors are getting far too hot. If it were me I'd figure out why- is the circuit drawing too much current or are the resistors underrated. If the latter, why are there not also holes under them to promote cooling?
...because you're right about the method and appearance. When the original poster wrote, "I've just bought a BMC MCCI phono stage" I assumed they meant that they bought it used. Although I do find it curious that the tacked on parallel resistors appear to be the same type (i.e. brand) as the originals, which makes me wonder if it were half-assed that way at the factory. I hope not.
You are right, I've bought it used and the seller did not know about any repair because was not the original owner and probably did not care to look inside. Now I replaced the two 150 ohm with new one but leaving more space from the circuit board and soldered the 200 ohm on top of them (with some space in between). I've also replaced all the electrolytic caps in that area (one was "pregnant" as a technician friend told me) and the unit is working. I've ordered some 150, 200 and 120 ohm (the third one) same kind of resistor and when will arrive I will pass the unit to my technician in order to understand why was "modified".I amd also looking to find someone else who own the same phono stage in order to get some other inside pictures...
Thanks and yes, I agree. I will reinstall the resistors as I found it for now. Let's hope to get an official answer from BMC...
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