Mk 012 with low signal

[gutimacuco]

Hello,



I have two Oktava Mk012 modded by Michael Joly.



One of them started to present low sensitivity, a very low signal compared to the other one. I opened them and the faulty one had much messier pcb.



I don't know a lot about eletronics and started to do continuity tests comparing the good and the bad one. Found some points that had continuity on the faulty that didn't on the good. The red lines on the second photo show these spots. I tried cleaning the pcb with isopropilic alcohol but it didn't change anything. This messiness made me think it was dirty/soldering problem.



Any thoughts?

 

[JohnRoberts]

A photo without the red scribbles might be easier to see... are those traces open/missing?

JR

 

[ccaudle]

Also interesting that one has a resistor on the backside which the other does not. There is an empty resistor location on the top side, so maybe one just had the resistor moved to the opposite side for some reason. Strange that both are not identical.

 

[Gus]

Did you try switching the capsules to find out if the low output follows the capsule or body?

 

[k brown]

Boy, have they changed - looks nothing like the ones I bought 20 years ago.

Are mica caps from the capsules?

 

[gutimacuco]

A photo without the red scribbles might be easier to see... are those traces open/missing?

JR

Here it is, sorry, thought i have posted it.

Also interesting that one has a resistor on the backside which the other does not. There is an empty resistor location on the top side, so maybe one just had the resistor moved to the opposite side for some reason. Strange that both are not identical.

Yeah, I found that strange too. But i counted the quantity and types and they match on both models. I think it is just a layout difference...

Did you try switching the capsules to find out if the low output follows the capsule or body?

Yeah, tried with the 6 capsules I have here..

Boy, have they changed - looks nothing like the ones I bought 20 years ago.

Are mica caps from the capsules?

The mica are the big brown ones covered with silicone? No, this is just the body pcb..

 

[k brown]

The capsule capacitors are on the body pcb; no components in the capsules.