Bottlehead Forum

Bottlehead Kits => Legacy Kit Products => Foreplay III => Topic started by: Neuronal on October 31, 2020, 10:56:07 AM

Title: Extended FP III resistance issue [resolved]
Post by: Neuronal on October 31, 2020, 10:56:07 AM
Hi - after burning in my (newly built after all these years) FPIII for a few months I decided to install the extended upgrade. When I took resistances at the terminals, everything was normal. To be extra careful, I also read across all of the accessible resistors to make sure they were still reading correctly. Everything looks fine except for the B side 127 kOhm resistor on the shunt regulator board (light blue, on the lower left when looking at the flipped chassis with the volume pot towards me), which reads 82.3 kOhms, as opposed to the A side equivalent resistor, which reads correctly at 148 kOhms. When I read across the + and - terminals on the A side, I get 148 kOms, and when I do the same on the B side I again get 82.3 kOhms.

Is this a problem, and if so is it limited to that one resistor (or instead maybe I've messed up something that lives in parallel to that resistor)?; I haven't yet fired it up to take voltages, as I'm afraid of smoke given the strangeness.

thanks in advance for any advice or help- it is really appreciated!
Title: Re: Extended FP III resistance issue
Post by: Paul Birkeland on October 31, 2020, 01:12:08 PM
The voltage divider that biases up the heaters sits across one of the regulated B+ rails and will throw off one of those resistances.  I would bet if you heat up and lift out one end of the resistor in question, it will measure perfectly.

Having said all that, if you have had this kit sitting around for 10 years, the probability that the included LEDs have absorbed too much moisture to be soldered is somewhat high. 
Title: Re: Extended FP III resistance /voltage issue
Post by: Neuronal on November 01, 2020, 11:03:05 AM
Thanks Paul - I remembered your advice from before about old LEDs, and before the build I went ahead and bought 20 from the Queen.

I fired it up, and the tubes lit up. But now a new set of problems:

1. On the left, the A side C4S board LEDs light up; the B side does not light, but the LED soldered into the tube holder does light. On the right, no LEDS on either the A or B side, and the LED in the tube holder does not light either

2. Voltages (VDC) are really off. Power supply voltages (strips 1-10) are normal. But:

H1 - 4.5 V
H2 - 11.4 V
12 - 25 V
15 - 15 V
21 - 25 V
22 - 4.5 V
21 - 208 V
21 - 156 V

Any advice? I'm not sure where to start with this....
Title: Re: Extended FP III resistance issue
Post by: Neuronal on November 01, 2020, 11:03:46 AM
Oh, and since I forgot to mention it, all the shunt reg LEDs light up fine
Title: Re: Extended FP III resistance issue
Post by: Paul Birkeland on November 01, 2020, 02:55:41 PM
It would be far, far easier if I could have:

IA, OA, and OB for the two outside boards.

IA, IB, OA, OB, and Kreg for the middle board.

Title: Re: Extended FP III resistance issue
Post by: Neuronal on November 01, 2020, 03:51:57 PM
on it, will send ASAP
Title: Re: Extended FP III resistance issue
Post by: Neuronal on November 04, 2020, 02:27:35 AM
Total newbie ? - just to verify, KReg is the K lead on the regulator chip, not the pad marked K that sits near it. Thanks - b
Title: Re: Extended FP III resistance issue
Post by: Paul Birkeland on November 04, 2020, 04:49:44 AM
The pad marked K.
Title: Re: Extended FP III resistance issue
Post by: Neuronal on November 04, 2020, 02:41:04 PM
quick update - I went back and realized that made some JV errors here - on the A side I flipped the MJE350 and MJE340 transitors, and on the B side I made some simple wiring errors. I cut the leads really short on those transistors on the A side when I first installed them, so unless you have some advice as to how to get a three lead transistor out of the board without clipping the leads, I'm going to clip them out and write the Queen for replacements, then reinstall on that side. More to follow....
Title: Re: Extended FP III resistance issue
Post by: Paul Birkeland on November 04, 2020, 03:10:55 PM
If you have an electrically powered solder vacuum pump, this can all be pulled apart in a few minutes.

Beyond that, trying to use solder braid or a manual pump will destroy the boards most likely, so I would clip them and just replace the parts.

The MJE340 is no longer in our inventory, but Mouser and Digikey should still have them.
Title: Re: Extended FP III resistance issue
Post by: Neuronal on November 04, 2020, 03:20:44 PM
now you've got me trying to justify spending $250 on one of those nice Hakko jobs, as opposed to $2.00 on new transistors. I'll wrestle with my conscience and we will see how this goes. I mean, I'm definitely going to need to desolder more in the future, right? :)
Title: Re: Extended FP III resistance issue
Post by: Paul Birkeland on November 04, 2020, 03:41:07 PM
Yeah, I bought one of the $200 Hakko pumps not that long ago, I don't know why I waited so long to do that.
Title: Re: Extended FP III resistance issue
Post by: Neuronal on November 10, 2020, 01:48:45 PM
OK, I bought one of those Hakko desolder guns (totally awesome!) and replaced the regulators on the A board, and went through and verified the wiring is correct throughout. Voltages seem off:

LAI - 44
LAO - 41
LBI - 0
LBO - 34.5

RAI 34
RAO - 21
RBI - 0
RBO - 16.8

center
AKreg - 4.1
AI - 217
AO - 44
BKReg - 4.4
BI - 216
BO - 40.1

All the LEDs on the center light up fine. Only on the left board, only A left lights. On the right board there is a flash from the top two leds and then they both go out.
Also -
H1 - 8
H2 14
H4 7.8
H5 14

Thanks for any help you can provide - I will not be defeated! :)
Title: Re: Extended FP III resistance issue
Post by: Paul Birkeland on November 10, 2020, 03:21:07 PM
What did you replace with what? New photos?

The lettering is "IA" for input A, "IB" for input b, "OA" for output A, "OB" for output B, etc.

Your raw power supply is working, your K voltages show that the regulators have enough voltage to operate, but you only have 40V on each rail.  Whatever issue is present must be present on both sides.

If you remove the two outer 12AU7s and leave the center one in the socket, what voltages do you see on the center PC board?
Title: Re: Extended FP III resistance issue
Post by: Neuronal on November 10, 2020, 04:03:21 PM
In the initial build on the left C4S board I had put the MJE350 where the 340 was supposed to go. Those are corrected now. I had also made a silly wiring error connecting the right board, which I've now fixed.

With the right and left tubes out, but center 12AU7 in:

KRegA - 1.9
IA - 219
OA - 152.8

KRegB - 1.93
IA - 219
OA- 150

Pics of boards attached; I solder on the bottom per the instructions so only solder on the top of the board is for the wiring. Oh, and the H1-2 voltages are also lower than in the manual if that means anything. - thanks again!
Title: Re: Extended FP III resistance issue
Post by: Paul Birkeland on November 11, 2020, 06:19:37 AM
Well, your center board appears to be OK.  I would imagine you still have issues on the outside boards such as backwards LEDs or possibly 2N2222/2N2907s swapped.
Title: Re: Extended FP III resistance issue
Post by: Neuronal on November 11, 2020, 10:43:09 AM
you were right - transistors were flipped. It is a miracle I can put my shoes on by myself. The only upside of my stupidity is that I get to use my Hakko one more time, thereby proving its value to my wife. Fixing now, more to follow....
Title: Re: Extended FP III resistance issue
Post by: Paul Birkeland on November 11, 2020, 12:49:15 PM
There are reasons that we no longer have the MJE340 nor the 2N2907 in our inventory anymore ;)
Title: Re: Extended FP III resistance issue
Post by: Neuronal on November 11, 2020, 02:58:25 PM
OK, I flipped the transitors. They looked kinda crappy coming out - that could either be aesthetics or I smooshed them. In any case, I reinstalled and got this:

left
IA - 159
0A - -.1
IB - 0
OB - 10.3

right
1A - 48.2
OA- 28.3
IB - 0
OB - 23.3

On the left board the top two LEDs now light up; in the right both top two light up, but they are really dim.

Getting closer?
Title: Re: Extended FP III resistance issue
Post by: Paul Birkeland on November 11, 2020, 04:27:30 PM
Is it possible that you have some backwards LEDs on those outer boards?  Did any of the transistors measure shorted when you pulled them out?
Title: Re: Extended FP III resistance issue
Post by: Neuronal on November 11, 2020, 04:45:59 PM
I ordered new transistors from Mouser and have a bunch of new LEDs; updates when the parts arrive....
Title: Re: Extended FP III resistance issue
Post by: Neuronal on November 14, 2020, 08:57:51 AM
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....
Title: Re: Extended FP III resistance issue
Post by: Paul Birkeland on November 14, 2020, 09:00:28 AM
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.

Title: Re: Extended FP III resistance issue
Post by: Neuronal on November 14, 2020, 09:00:50 AM
OK, will do now. I will say, when I bought that Hakko I thought it was an indulgence, and now it is my best friend!
Title: Re: Extended FP III resistance issue
Post by: Neuronal on November 14, 2020, 10:11:38 AM
OK, did the swap - the voltages and the behavior follow the board, which (I think) is all and all good news. Is the right next move to swap out all the A side transistors?
Title: Re: Extended FP III resistance issue
Post by: Paul Birkeland on November 14, 2020, 10:12:44 AM
That's certainly an option, as well as double checking the LEDs.
Title: Re: Extended FP III resistance issue
Post by: Neuronal on November 16, 2020, 02:06:15 PM
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 :)
Title: Re: Extended FP III resistance issue
Post by: Paul Birkeland on November 16, 2020, 03:06:53 PM
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.
Title: Re: Extended FP III resistance issue
Post by: Neuronal on November 24, 2020, 03:31:37 PM
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!
Title: Re: Extended FP III resistance issue
Post by: Paul Birkeland on November 24, 2020, 04:01:15 PM
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.
Title: Re: Extended FP III resistance issue
Post by: Neuronal on November 24, 2020, 04:31:53 PM
what is the target I am shooting for for KReg?
Title: Re: Extended FP III resistance issue
Post by: Paul Birkeland on November 24, 2020, 04:43:20 PM
I can't remember exactly and the manual isn't specific, but I would imagine a reasonable range would be 4-12V.
Title: Re: Extended FP III resistance issue
Post by: Neuronal on November 25, 2020, 05:00:07 PM
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!
Title: Re: Extended FP III resistance issue [resolved]
Post by: Neuronal on January 18, 2021, 06:50:10 AM
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
Title: Re: Extended FP III resistance issue [resolved]
Post by: Paul Birkeland on January 18, 2021, 07:02:19 AM
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.
Title: Re: Extended FP III resistance issue [resolved]
Post by: Doc B. on January 18, 2021, 07:16:54 AM
Also bear in mind that the orientation of the different transistors can be reversed (e.g. MJE350 and MJE5731A are reversed), so you want to check the pinout before you install a different type.
Title: Re: Extended FP III resistance issue [resolved]
Post by: Neuronal on January 23, 2021, 04:19:16 PM
thanks PB and Doc!
Title: Re: Extended FP III resistance issue [resolved]
Post by: Neuronal on February 21, 2021, 05:06:11 PM
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!
Title: Re: Extended FP III resistance issue [resolved]
Post by: Paul Birkeland on February 22, 2021, 05:37:26 AM
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.
Title: Re: Extended FP III resistance issue [resolved]
Post by: Neuronal on February 22, 2021, 06:26:17 AM
will do!