Extended FP III resistance issue [resolved]
- Thread starter Neuronal
- Start date
Progress - thankfully! - but not quite there yet. I put in new LEDs (I've left the old transistors in), and now everything lights up nicely. But...
Left
IA - 150
OA - 69
IB - 0
OB - 71.5
Right
IA - 150
OA - 0
IB - 0
OB - 6.4
Of note the moment I turn on the unit the top lights on the right board (both of them) go on; then after a few seconds the whole center board and then the whole left board and the bottom (B side) of the right board lights up. The delay for the center and left boards feels like what I am used to with my paramounts. I feel like the fact that there is no delay at all for the top right lights must mean something (current leaking somehow?). Of note, those same upper right lights stay lit up for many more seconds after the other lights have all gone off when I turn the power off.
Anyways, getting closer. I didn't replace any of the transistors, but I have replacements for all of them and can swap them out if you think that is what is going on. I am quite certain at this point everything is oriented correctly and in the correct position, etc....
Left
IA - 150
OA - 69
IB - 0
OB - 71.5
Right
IA - 150
OA - 0
IB - 0
OB - 6.4
Of note the moment I turn on the unit the top lights on the right board (both of them) go on; then after a few seconds the whole center board and then the whole left board and the bottom (B side) of the right board lights up. The delay for the center and left boards feels like what I am used to with my paramounts. I feel like the fact that there is no delay at all for the top right lights must mean something (current leaking somehow?). Of note, those same upper right lights stay lit up for many more seconds after the other lights have all gone off when I turn the power off.
Anyways, getting closer. I didn't replace any of the transistors, but I have replacements for all of them and can swap them out if you think that is what is going on. I am quite certain at this point everything is oriented correctly and in the correct position, etc....
You can swap the outside pair of boards from side to side to see if the 0V at OA follows a board or stays on one side of the preamp.
That's certainly an option, as well as double checking the LEDs.
One step forward....two steps?
So I rebuilt that board completely and reinstalled it. When I powered up, the LEDs were perfect (they all lit up across all three boards at about the same time after a delay). As I was taking voltages, I noticed smoke and immediately shut it down.
Turns out, in my excitement, I forgot to add the black wire that interconnects the A and B side of the board, and the two 270 ohm resistors (that interconnect 7-9 and 9-10) on the power supply on just that side burned out.
My question (for now) is: should I just replace those two resistors, or are there other parts I likely damaged? Should I rebuild the entire power supply on that side? At least it looks like I fixed the board....
Sorry for all the low-level screwing up and then asking for help. I apparently can record electrical transients from living neurons, but am incapable of following instructions carefully
So I rebuilt that board completely and reinstalled it. When I powered up, the LEDs were perfect (they all lit up across all three boards at about the same time after a delay). As I was taking voltages, I noticed smoke and immediately shut it down.
Turns out, in my excitement, I forgot to add the black wire that interconnects the A and B side of the board, and the two 270 ohm resistors (that interconnect 7-9 and 9-10) on the power supply on just that side burned out.
My question (for now) is: should I just replace those two resistors, or are there other parts I likely damaged? Should I rebuild the entire power supply on that side? At least it looks like I fixed the board....
Sorry for all the low-level screwing up and then asking for help. I apparently can record electrical transients from living neurons, but am incapable of following instructions carefully
I have absolutely no idea. You'd kind of need to start over on that side. At least replace those resistors and run the preamp without the outer 12AU7 on that side, then check Kreg and O voltages on the small PC board to be sure it's regulating to 150V, then go back through the small outer board and rebuild it. You shouldn't have to pull out the black jumper wire to rebuild the board.
OK, I think I'm good here, but just want to check to make sure I haven't missed anything. THANK YOU so much for your generosity and patience in walking me through this, Paul! You are the best!
I replaced the blown resistors on the left power supply, all of the transistors on the left side board, and both the transistors on the shunt reg board on the A side. I deduced that I had taken out the A side of the shunt reg board in addition to the left board during my little smoke event because there were some asymmetrical resistances when I compared the A and B sides of the shunt reg board (and hence asymmetrical resistances when I compared the left and right C4S boards relative to the bus ground). These became more normal when I replaced the Shunt reg A side transistors (but not identical - if I ground at the ground bus, on the shunt reg OA reads 80 kOhms, while OB reads 147kOhms; all other readings were identical across the boards).
I figured this was close enough to start measuring voltages - the shunt reg board read exactly what it read when it was working before (Krega 1.9, IA 213, OA 154, KRegB 1.8, IB 212, OB 150); there is some minor variance in the left and right boards that I (hope) is just variance:
left -
IA - 150
OA - 75
IB - 0
OB 75
right-
IA - 150
OA - 71.5
IB - 0
OB - 71.5
I took all the other voltages in the manual, and they are dead on. I am TERRIFIED of smoking this again, but I think I am ready to go? Thanks again for your help with this Paul - and I wish you and yours a very happy Thanksgiving!
I replaced the blown resistors on the left power supply, all of the transistors on the left side board, and both the transistors on the shunt reg board on the A side. I deduced that I had taken out the A side of the shunt reg board in addition to the left board during my little smoke event because there were some asymmetrical resistances when I compared the A and B sides of the shunt reg board (and hence asymmetrical resistances when I compared the left and right C4S boards relative to the bus ground). These became more normal when I replaced the Shunt reg A side transistors (but not identical - if I ground at the ground bus, on the shunt reg OA reads 80 kOhms, while OB reads 147kOhms; all other readings were identical across the boards).
I figured this was close enough to start measuring voltages - the shunt reg board read exactly what it read when it was working before (Krega 1.9, IA 213, OA 154, KRegB 1.8, IB 212, OB 150); there is some minor variance in the left and right boards that I (hope) is just variance:
left -
IA - 150
OA - 75
IB - 0
OB 75
right-
IA - 150
OA - 71.5
IB - 0
OB - 71.5
I took all the other voltages in the manual, and they are dead on. I am TERRIFIED of smoking this again, but I think I am ready to go? Thanks again for your help with this Paul - and I wish you and yours a very happy Thanksgiving!
Your left and right C4S boards have the voltages you want.
1.8V or 1.9V at the K terminals on the middle board still indicates an issue there, most likely something like a solder bridge on the bottom side of that PC board or you have the input and output red wires swapped possibly.
1.8V or 1.9V at the K terminals on the middle board still indicates an issue there, most likely something like a solder bridge on the bottom side of that PC board or you have the input and output red wires swapped possibly.
I can't remember exactly and the manual isn't specific, but I would imagine a reasonable range would be 4-12V.
I rewarmed all the joints in the shunt reg board, and the KReg popped up to 4.1 V on both sides - plugged it in and tried it out. First record was the Whatnauts 12" of Help Is On The Way, and it sounded AMAZING (to my ears, more lower noise and more bass extension for sure).
Thanks again for everything, and a happy thanksgiving to all!
Thanks again for everything, and a happy thanksgiving to all!
PB - thanks again for your help with this fix. I definitely learned a lot! Two quick questions - the C4S boards got pretty banged up with all the soldering/desoldering I did, and now that I have a much better understanding of what is going on I was thinking of building some clean C4S boards that will hopefully last forever. The ones used for the EFPIII upgrade are no longer made, but there are these little mini boards for the Sex 3.0 upgrade that should mount on the stand-offs alright (I think). Could these be used for the outer C4S boards in a EFPIII? Would these be basically drop-ins? Related to this - is the MJE5731A a drop-in replacement for the MJE340?
thanks again for all the advice -
Bob
thanks again for all the advice -
Bob
The small C4S boards we sell can be substituted for the outer boards without a ton of difficulty. An MJE5731A and an MJE340 are not at all compatible. The 340 is an NPN and the 5731A is a PNP.
The MJE350 can be substituted with an MJE5731A for better thermal capabilities. A tip50 can be substituted for the MJE340, though that's severely overkill in a Foreplay.
The MJE350 can be substituted with an MJE5731A for better thermal capabilities. A tip50 can be substituted for the MJE340, though that's severely overkill in a Foreplay.
OK, I got the Sex 3.0 C4S boards - just to verify, the underlying circuit on the board is the same as on the boards that came with the EFPIII, right? So if I just take the components/values that are supposed to go on the EFPIII boards and stuff them into the correctly marked spots on the SEX3.0 board (i.e., position R1 on one board is wired up the same as position R1 on the other board) I should be good to go?
Quick related question - I was reading on another thread that people like tantalum resistors for R1, but these come in limited values. How far off can I be and feel ok about it (as these control the current, right?) I'm building the paramount soft start boards now, for example - cool to sub a 220 for the specified 215? in the EFPIII circuit, can a 250 be subbed for the 237?
thanks as always!
Quick related question - I was reading on another thread that people like tantalum resistors for R1, but these come in limited values. How far off can I be and feel ok about it (as these control the current, right?) I'm building the paramount soft start boards now, for example - cool to sub a 220 for the specified 215? in the EFPIII circuit, can a 250 be subbed for the 237?
thanks as always!
I wouldn't go for the tantalum resistors, they don't really fit the boards all that well.
What I would suggest is putting the parts into the boards but not soldering them, then posting photos.
You will not need the black jumper.
What I would suggest is putting the parts into the boards but not soldering them, then posting photos.
You will not need the black jumper.
