Bottlehead Forum
Bottlehead Kits => Eros Phono => Topic started by: Dhouse7516 on March 12, 2023, 11:27:25 AM
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Hi Paul and Doc, I'm in a predicament and hope you might have some advice.
After building and installing the shunt board, I did the voltage check and passed (I don't recall the actual measurements, it's been a while). I then proceeded through the rest of the build, passed final the resistance test, but failed the final voltage check on the C4S board. The B side of the board was fine, but all the values on the A side were off (If I recall correctly, they were low - apologies, but I did not write the actual values down at the time). I double-checked all the solder joints and connections on the C4S and A,B, and C sockets and they looked solid to me.
I found a couple of posts here where users had similar issues and Paul's advice was to remove the blue wires from IA and IB on the C4S and re-check the shunt board. I did that and got the following readings on the shunt board:
OA: 283
OB: 210
BREG A: 283
BREG B: 210
KREG A: 6.42
KREG B: 2.83
I was confused that I now had higher values on the A side, but went back and reflowed the solder joints on the D Socket and some that I thought might be problematic on the shunt board and terminal lugs, measured again and got the following values:
OA: 273
OB: 207
BREG A: 273
BREG B: 207
KREG A: 6.5
KREG B: 2.84
I read another post where Paul or Doc advised someone whose measurements were off to try going through the rest of the build to see if they evened out after doing the C4S Board. This obviously differs from my scenario but I tried hooking up the blue wire to IA and IB on the C4S again (hoping this wasn't a mistake), tested and passed the resistance test, and tried the voltage check again:
IA: 140
IB: 159
OA: 138
OB: 157
OC: 97
OD: 96
OKA: 97
OKB: 97
OKC: 1.76
OKD: 1.61
With the C4S connected, the measurements on the shunt board were:
OA: 161
OB: 140
BREG A: 161
BREG B: 140
KREG A: 3.73
KREG B: 2.63
I am assuming that the issue is with the shunt board or D socket, but would appreciate your thoughts. I walked away from the project for a couple of months and got the Eros back out today to take some pictures, which I will post shortly.
Thanks much,
Darren
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Here are the pics. The D socket joints look a little funky in these post-reflow pics, but I double-checked and none are shorting. Also, that's dust you're seeing, not debris from the build - I didn't notice it until I started uploading the pictures. It has now been cleaned up :).
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It would be a good idea to try to get the board above the D socket working properly first. Based on the information provided, I would expect there to be flaky solder joints at work that are preventing that C4S board from operating properly.
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Okay, thanks. I will go back and look again. Do you see anything obvious in the pics of the shunt board or the D socket that I might be missing?
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Are Breg and +reg connected on the D socket C4S board? It looks like they might be, but it's tough to tell.
Typically when I get these for repair, I will find a lot of soldering issues, and sometimes builders will focus on one spot and damage traces on the front C4S board by focusing their soldering efforts on a few specific parts. I'd say in the last year I have dealt with that exact set of circumstances on Eros 2 kits at least four times.
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That makes sense. I am fairly certain that BREG and +reg are connected via the 220 resistor lead on both sides, but I will confirm later tonight or tomorrow. I think that I will go ahead and disconnect that board and send you a picture of the underside.
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Paul, I desoldered the shunt board and will post some images later. A question in the meantime: if the D5 and D6 terminals were shorting/touching, could that be the culprit behind the high voltage readings on side A of the board? Once I removed the board, I noticed that my re-soldering work was a bit sloppy on those two pins, and it’s conceivable that D6 could have touched the stripped wire going into D5 when the tube was inserted. Thanks.
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That would drag either OA or OB on that D socket C4S down to about 56V. It wouldn't hurt anything in the process.
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Thanks. I think I found the problem. See the pics of the underside of the board below. I think that the red wire that connects OA to +reg was shorting against the middle pin of the MJE5731G. It's also possible that the red wire on OB was shorting against the middle pin on that side. See the red circles in the pics. Sloppy solder bulbs on my part! Would either of those scenarios explain the voltage issues? Regardless, please let me know if you see any other problems with the board. I'm also including a better pic of the D socket.
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OA and OB connect to the middle leg of each of the MJE5731As anyway, so that wouldn't be a huge concern.
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Ah, of course they do. Thanks. Do you see any obvious issues with the board (top or bottom) or the D socket? I'm attaching another picture from the top of the board. Thanks much.
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You can get weird readings like what you got if the blue and white wires on the D socket get switched by accident when connecting to the C4S board above the D socket.
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Not sure I am following. There are no blue wires connecting to the D socket, correct? Do you mean black wires? Sorry if I’m being dense.
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Sorry, the red wires leaving OA/OB and the white wires leaving KregA/B. Having one pair of those wires swapped will result in odd regulator behavior.
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Got it. All four of those were properly wired. I'm kind of at a loss. I think all the solder joints look fine.
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With the front C4S board disconnected, can you recheck the IA, IB, OA, OB, KRegA, and KregB voltages so we know where things stand at the moment?
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After reconnecting the board, with the blue wires disconnected from the front board, these are my voltage readings.
IA: 288
IB: 288
OA: 285
OB: 228
KregA: 6.36
KregB: 2.5
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The B side R4 seems like it may not be well soldered on both ends.
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That's what I was thinking. B side breg pads look like they could use a reheat.
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Okay, thanks. I'll give it a shot.
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I reflowed all of the Breg pads, the +reg pad, and the pad at the other end of the R4 on the B side, and I am still getting the same voltage readings as posted above.
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I also tested at the R4 pads, and they are good at 219K ohms.
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Is the jumper leaving OB well soldered on both ends?
The 6V cathode 288V on the plate to me seems like the regulator on that side just isn't connected somehow. Also be sure the 431 regulator is there and not an MPS4250.
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The 431 regulators are both in the right place. I will double-check the OB jumper tonight. Thanks.
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Well, I stepped away for a bit and then took another shot at this. I reflowed all the D-Socket and shunt board joints and reconnected the board above the D socket. My measurements are below. I suspect that I may have damaged one of the traces on the shunt board. I hate to admit defeat, but I might need to send it in to y'all. Let me know if you have additional suggestions. Thanks much.
IA: 290
IB: 289
OA: 282
OB: 155
KregA: 6.41
KregB: 4.5
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Typically that set of voltages would have me double checking that the wiring going to the 9 pin socket is all routed properly. If you swap a pair of the wires going between that board and tube socket, you can end up with wonky voltages like this.
If you are unable to remedy this issue, you can contact queen(at)bottlehead(dot)com about ordering a repair service. Be sure to send her a link to this thread so she knows we have worked on the problem here.
-PB
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Yep, I triple checked all of those wires, and reflowed the solder for all of them. It's all good. Are there any issues on the board that you can think of that might cause these voltages? Anything I should focus on in particular? I've confirmed that the regulators are in the right place, reflowed the solder to the R4, and confirmed that BREG is connected to +Reg. Is it possible I have a defective or damaged regulator? I tested the resistor and it measured fine.
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A defective regulator will typically short out and you'll see 1.8V or so on Kreg and low OA or OB voltage.
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Got it. When you said above that the cathode and plate voltages caused you to think the regulator wasn't there, it made me think that a defective regulator could also cause the voltages. Anything else I should focus on?
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So the red wire connecting the B side of the shunt regulator to 28L just snapped off at the BReg joint as I was lifting the board to re-check my wiring. I'm guessing that it got damaged with all the fiddling I've been doing. Would that cause the voltage readings I was getting (if it wasn't properly connected to the board)? In any event, I will replace it and see what that does, once I can find some wire. It's 22AWG, correct?
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A broken wire could cause some issues, though one wire is unlikely to cause all of what you're seeing.
-PB
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Okay, thanks. I am at a loss. I went back over the board and the tube terminals again, re-flowed a couple of additional joints, replaced the shunt board wires and am still getting very similar readings:
IA: 284
IB: 285
OA: 280
OB: 152
KREG A: 6.38
KREG B: .45
Unless you have any additional thoughts, I will reach out to the address you provided earlier and request a repair. Please keep me in the loop as I really want to know what the issue is here and learn from this! Thanks for all of your help.
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Paul, as I was going back over the board just now, I noticed that the R3 resistor on the B side has a large crack in the end. I tested it and it's bad (no resistance). If you think that this might explain the issues I'm having, I'll order another one and replace before sending in for repair. Thanks.
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It certainly wouldn't hurt to give that a try.
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Thanks, I assume this is a suitable replacement?
https://www.digikey.com/en/products/detail/stackpole-electronics-inc/RNF14FTD2K49/1706690
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Sure, that will work nicely.
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Thanks, Paul. I need to order some additional single-core wire as well. It’s 26awg, correct?
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22 AWG solid is recommended. The kit should have come with some extra wire.
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Thanks, I used up the extra when I was re-wiring the D socket and the board
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I received the replacement R3 resistor today that we discussed above. It's physically smaller than the one supplied with the kit (see picture). I assume that's because it has a different tolerance or wattage. Maybe a dumb question, but do I need to be concerned about this? Do I need to replace the A side R3 with a matching resistor (I bought two) as well as the B side, which is the one that is damaged? Thanks.
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Just replace the one that needs to be replaced. They function indentically.
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Excellent. Thanks, and will do.
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So this is strange. I tested the new resistor before installing and it passed at 2.49k ohms. After I installed and soldered it to the board, the resistance check at the leads (on both sides of the board) is failing. I’m getting readings of 10-11 ohms (not K ohms). When I test the R3 on the A side at the leads I am getting 2.49k ohms. Does this suggest any obvious issues to you?
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The most obvious issue to me is that I might suck at soldering PCB boards.
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That would most likely be a shorted 431 regulator.
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Okay, thanks. Does that mean I should replace the regulator, or could it be a soldering issue?
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I would plan on replacing the regulator.
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Okay, thanks Paul.
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And, you are correct. I tested and it’s shorted.
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Okay, so I replaced the LM431 and the blown R3, and I'm still failing the shunt test. OB and Kreg B are now back in range, but everything else is high. Any thoughts?
IA: 290
IB: 289
OA: 281
OB: 220
KregA: 6.38
KregB: 3.49
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everything else is high
IA: 290
IB: 289
OA: 281
OB: 220
KregA: 6.38
KregB: 3.49
The B side of the board is working properly. The A side likely has a broken wire or poor solder joint that isn't allowing the regulator to function properly. The pairing of 281V on the 12AU7 plate and 6.38V on the cathode indicates that the current source half on the A side (Q1/Q2, R1, R2, and the LEDs) is working properly, but the 431 regulator half of the board isn't functioning. Is the Breg to +reg jumper installed?
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This is very helpful, Paul. Thanks. I will go back and look at all of the joints and connections on the 431 half and report back.
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Christ, the RC resistor on the A side just caught fire as I was doing a voltage check. I guess it's time to admit that I am out of my depth and send this in. I will reach out to queen tomorrow to request a repair package.
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Paul, being a glutton for punishment, I am thinking that I might make one more run at this before sending it in. I looked through my spare resistors and I have both 220 ohm 1 watt and 220 ohm 1/2 watt. Which is more appropriate for the RC position on the C4S board? Thanks.
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If Rc blew up, then Cc must have been shorted.
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Thanks! Excellent call. CC is definitely shorted.
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I am assuming that the shorted capacitor is a symptom of the larger issue of excessive voltage on the A side of the board, rather than the cause of the issue. Do you agree?
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The cap is a 400V rated cap and the Eros doesn't make 400V anywhere in the circuit. I would expect that cap to still last a few thousand hours at 600V, so excessive voltage seems very unlikely to be an issue.
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Okay, thanks. That makes sense. I will replace it and the RC resistor (assuming a 1 watt 220ohm is in spec?) and see where I’m at.
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Sorry, my mistake. The 220ohm I have is half watt. The 1 watt was 220k.
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The wattage of the 220 ohm resistor is not particularly important.
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Hi all,
A follow-up. I basically re-soldered and rebuilt the A regulator side of the shunt board (new RC, R3 and R4, new capacitor, and new regulator - which was shorted), and am now getting the following readings:
IA: 267
IB: 267
OA: 267
OB: 220
KregA: 1.88
KregB: 3.5
Any thoughts? Thanks much.
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I think I would just send this in for repair. There is likely something else at work here that's causing all these problems that will probably be rather difficult for me to track down, but nearly impossible to detect over the forum. You can contact queen(at)bottlehead(dot)com to request a repair box, and be sure to post a link to this thread and let her know that we have worked on this for a bit.
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Okay. Thanks, Paul. I will reach out to Eileen.
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One final question before I send this in. I noticed that the 220K ohm resistor at R4 on the A side was only measuring at 69K ohms, so I replaced it with a new one. The new one measured fine at the lower R4 and Breg pads, but as soon as I connected it to the +Reg pad, it dropped to 69K ohms. I then checked the resistance of the 225K poly capacitor, and it was also 69K ohms, so obviously bad. Do you think it's worth it for me to try replacing the cap before sending this in, or is the failed cap most likely a symptom of a larger problem? If there's a chance this might solve the problem, I would like to try before paying for repair, but not if you don't think it lead anywhere. Thanks again for all of your help and patience. This is my third BH kit, and the only one I've had trouble with!
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There's something else going on. You'd be the only person in the history of the company to have a cap short like that, so I would suspect something else is at work.
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Haha. Well, I would hate to hold that ignominious title. In any event, the solder pad at +Reg for the R4 resistor just came off, so it's clear I'm just doing more damage at this point. I have connected with Eileen and will send this in. I am not going to bother soldering the new R4 back in, but will include it in the box. Thanks much, Paul.
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Well, I should have checked this earlier, but I just tested the MJE5731 on Side A, and it's shorted. I am guessing that this is the problem. Unless, you disagree, I am going to swap in a new one and re-test everything.
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That will certainly cause some problems. Usually those short from excessive voltage, and there isn't enough voltage in an Eros to do that, but it's worth a shot.