Hi folks. I'm looking for some help on a Mark IV. It's lost it's output. I found a .02 poly Xicon cap near V1 that has one leg broken off. For the life of me I can't determine where the other leg goes. It doesn't show up on the schematic either. The one leg I know about is connected to R 201. It's the other leg I'm not sure of. I can't find the broken off end stuck in any of the nearby solder joints. I'm really stuck. Any help would be greatly appreciated! Many thanks.... RDKelley
Mark IV mystery cap
- Thread starter RDKelley
- Start date
Help Support The Boogie Board:
mejoshee
Well-known member
i don't know if you noticed but this is the mark v part of the forum 
that's ok. i'm taking your word for it that it's connected to r201 (can you ohm it out just in case?):
looking at the schematic that's floating around out there (like schematicheaven.com, etc.), you won't see the parts where the high voltage taps are coming from, but i would say that it's probably going wherever "D" is on the schematic, from v1. not sure why it's a poly if it's a dc bulk cap, but i personally don't have the amp disassembled right in front of me to say. if the poly cap is part of the high voltage part of the circuit, then losing that on v1 (the input stage) would definitely kill any further amplification. a .02 (uf) cap is in the range of an interstage coupling cap, though.
can you take a pic and post it of where it is? you might still need to take it in to a mesa tech simply because that portion of the circuit is not visible on a schematic, depending on how much damage has been done--hopefully none. if you're not in a hurry, i can disassemble my head and take a look inside that area, but that might not be in the next couple days. either way, having a picture of it will help a lot on pegging down where it actually goes.
do you have tools to fix this and were you intending to do it yourself? it can be done, probably pretty easily, but care needs to be taken depending on which part of the circuit the cap actually goes to. i will try to help you the best i can, but you might need to wait a little bit.
that's ok. i'm taking your word for it that it's connected to r201 (can you ohm it out just in case?):looking at the schematic that's floating around out there (like schematicheaven.com, etc.), you won't see the parts where the high voltage taps are coming from, but i would say that it's probably going wherever "D" is on the schematic, from v1. not sure why it's a poly if it's a dc bulk cap, but i personally don't have the amp disassembled right in front of me to say. if the poly cap is part of the high voltage part of the circuit, then losing that on v1 (the input stage) would definitely kill any further amplification. a .02 (uf) cap is in the range of an interstage coupling cap, though.
can you take a pic and post it of where it is? you might still need to take it in to a mesa tech simply because that portion of the circuit is not visible on a schematic, depending on how much damage has been done--hopefully none. if you're not in a hurry, i can disassemble my head and take a look inside that area, but that might not be in the next couple days. either way, having a picture of it will help a lot on pegging down where it actually goes.
do you have tools to fix this and were you intending to do it yourself? it can be done, probably pretty easily, but care needs to be taken depending on which part of the circuit the cap actually goes to. i will try to help you the best i can, but you might need to wait a little bit.
mejoshee
Well-known member
mejoshee said:i don't know if you noticed but this is the mark v part of the forum
looking at the schematic that's floating around out there (like schematicheaven.com, etc.), you won't see the parts where the high voltage taps are coming from, but i would say that it's probably going wherever "D" is on the schematic, from v1. not sure why it's a poly if it's a dc bulk cap, but i personally don't have the amp disassembled right in front of me to say. if the poly cap is part of the high voltage part of the circuit, then losing that on v1 (the input stage) would definitely kill any further amplification. a .02 (uf) cap is in the range of an interstage coupling cap, though.
can you take a pic and post it of where it is? you might still need to take it in to a mesa tech simply because that portion of the circuit is not visible on a schematic, depending on how much damage has been done--hopefully none. if you're not in a hurry, i can disassemble my head and take a look inside that area, but that might not be in the next couple days. either way, having a picture of it will help a lot on pegging down where it actually goes.
do you have tools to fix this and were you intending to do it yourself? it can be done, probably pretty easily, but care needs to be taken depending on which part of the circuit the cap actually goes to. i will try to help you the best i can, but you might need to wait a little bit.
did you mean this cap?
i don't think this is the culprit. my iv is still working and that's also disconnected in mine.
Hi. Yes! That is indeed the culprit. I'm sorry to hear that your's is missing and the amp is still working fine. Well, not sorry your amp is working....you know. It just means I still have more work to do to hunt down what is causing the lack of output in my amp. I know that all volts are correct. I did check that much before I found the mysterious one-legged cap.
I can't tell you how much I appreciate your help. I do wonder, however, what that silly thing is for. Anyway, back to the drawing board. If you have any other ideas on the no output problem, I'd sure love to hear them. Thanks again! RDK
I can't tell you how much I appreciate your help. I do wonder, however, what that silly thing is for. Anyway, back to the drawing board. If you have any other ideas on the no output problem, I'd sure love to hear them. Thanks again! RDK
mejoshee
Well-known member
RDKelley said:
glad to know i could help! i bet it's from whenever they switched from a to b version.
