Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: goldencalves on October 14, 2021, 02:47:06 PM
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Hi, I put together the speedball upgrade and was very much enjoying it for a month or two (all of the voltage and resistance readings checked pre and post upgrade), when all of a sudden one channel started popping and gave out. Popping was able to be manipulated by touching/slightly shifting the large tube.
I smelled some burning plastic and noticed the sheathing on the black wire running from U14 to U20 melting to the 270 ohm 5W resistor connected to 15U and 21U, so I pulled it off (still maintained its sheathing) and put some space between the wire and resistor.
When I tested it out a month or so later (when I had a few minutes), I got it turned on again it appeared to have fixed itself and worked very well for a couple of weeks until the same thing happened, one channel giving out entirely and the other one extremely quiet.
Voltages:
OA - erratic, will be 0, sometimes climb slowly to 140-160, then drop back down to around 0 and stay there mostly
OB - 40-42
G - 0.0-3.0
B+ -48-51
Two LEDs are out, pictured below along with some general pictures of the surrounding build. Please let me know if any other pictures would be helpful from anywhere I didn't get.
Thanks,
Chris
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Can you post a picture of the solder and/or flux that you used to complete this build?
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Paul, thank you so much for the quick response.
Below are the pics, in order of the soldier, the flux that I definitely used (Sterling), and the flux that I may have used on just a couple of spots (Oatey).
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The solder you have is fine.
The fluxes you have used are for plumbing. They are both conductive and corrosive. I could tell that you used these because of the corrosion that's already started on your bottom panel.
I would remove the tubes from your kit and pop it out of the base, then run it through your dishwasher with no detergent. This will discolor the plate a little bit, but it's the only way I've ever recovered kits that have ended up in this situation.
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OH JEEZ. I had no idea I have been using plumbing flux for years!
So run the whole thing through the wash, circuits and everything? Will I have to re-do any of the soldiering or anything like that, or the wash should fix it?
And should I run with extra heat? Or just a normal cycle?
Thanks again,
Chris
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Hot water and the top dish rack. It may fix the kit, or you may have to bin it. Plumbling flux is really, really harmful to this stuff. Since you used rosin core solder, you shouldn't have to redo any of the solder joints.
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Thanks again, I appreciate the instruction. Will run tonight and test it again tomorrow after it dries.
...you may have to bin it. Plumbling flux is really, really harmful to this stuff.
However, I don't understand why, especially as this issue has apparently come up before in other people's builds, that this isn't mentioned in the manuals. I read both very closely, line by line repeatedly during fabrication, and checking back the Crack Manual I have (from 2015 or so) doesn't say anything about plumbers flux (or soldier for that matter). The Speedball Manual mentions to not use plumber's soldier but makes no mention of flux-types to use or not use. I personally, as a very casual hobbyist, had no idea that there was any real differences between fluxes, and had no idea that the use of the wrong kind of flux could potentially destroy my kit.
I also double-checked the packaging on both fluxes and neither make any specifications on their use, not even oblique inferences for plumbing. They are just "flux". I have also seen other, more invested, hobbyists (and professionals) use these same types of flux on electronics.
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Yes, this has happened before, maybe once every 2-3 years. The solder you used has the correct flux in it. The manual never mentions anything about using extra flux as it's completely unnecessary. We are happy to answer questions like these as they come up in the future, but do be aware that we do call out in the manual not to use plumbing solder to build electronics.
You might also take note that the flux containers say not to use them with leaded solder, so that should also have raised some questions.
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One of those cases references ASTM B813 on the front.
ASTM B813: Standard Specification for Liquid and Paste Fluxes for Soldering of Copper and Copper Alloy Tube
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Ran unit through the dishwasher. Brought it into the shop to scrub some of the residual rust/corrosion spots off of some terminals with a tooth brush and 99% isopropyl and noticed this 5w resistor (attached picture) had cracked.
I am assuming I should not test this out without replacing this? What is the best resource to find a replacement? This is the same resistor that was melting some of the sheathing on a wire that was touching it, not sure if that is relevant info or not.
Re: Non-leaded flux, neither of these flux containers say to not use them with leaded solder, just that they work with non-leaded solder. I originally used non-leaded solder when I bought all of this kit for craft projects, and switched to leaded when I started messing with more electronics. The flux seemed to work just as well getting the leaded solder to stick to metal just as well as it did with the unleaded solder.
Re: unnecessary flux, I recently did a job soldering PCBs and the client required flux to be used even though we were using rosin-core solder (and flux was actually necessary on a laser-etched board, the solder would absolutely not stick anywhere without it). The instructional videos I watched to catch-up on electronics soldering also universally suggested flux in combination with rosin-core solder. I was not aware the rosin core would work just as well or better without flux, and neither is this delineated in either of these manuals.
@ scblock Re: ASTM B813, good to know for the future, but I did not even realize that this was a standards code as opposed to just a product or batch code.
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Yes, replace that resistor. You can e-mail replacementparts(at)bottlehead(dot)com to inquire about this.
The flux you used is like running a wire between everything it touches, and it likes to spread around as heat is applied to it, so you'll have to fire the amp back up and see what the voltages look like once that resistor is replaced.
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Thanks Paul.
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I really hope everything works out. Posted that just in case it helps anyone else in the future.
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@scblock Thank you. It is useful information.
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OK, so:
1) Unit went through dishwasher
2) isopropyl/toothbrush scrub of most reachable solder joints
3) replaced cracked 270 ohm resistor b/w U15 and U21
Large speedball readings basically the same:
OA : 0
OB : 44.5
G : 3.0
B+ : 50
And the 2 LEDs on the large board in front of Q2A are out (rest of LEDs are working).
Anything else I can do? Would it be worth it to do a full resistance/voltage check?
Should I replace the other 270 ohm resistor as well (does not appear damaged from the exterior)?
Thanks,
Chris
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What are the DC voltages on each side of each 270 ohm resistor in the power supply?
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U15 - 124v
U21 - 187v
U13 - 50v
Are these the correct locations?
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Can you try again with no tubes?
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W/ no tubes:
U13 - 237
U15 - 241
U21 - 246
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Now try just the 12AU7 and post voltages on terminals 1-5.
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W/ 12AU7 only:
1 - 73
2 - 231
3 - 0
4 - 231
5 - 74
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This is major progress!
Can you post some photos of the wiring around the octal socket that you have currently?
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I'm just glad that its looking like the whole thing isn't toast!
Also: there is only one LED on the octal. I had some short/issue a little while back and I followed the advice on a post in this forum that swapped out a jumper for the 2nd LED (which worked).
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PB is looking for pics of the other socket. Octal= 8 pins, Noval= 9 pins.
Sometimes photos can be deceptive but check that the jumper you put in on the Noval socket is not shorted to pin 7.
That will give you all sorts of grief. In general you should not have that much uninsulated wire exposed. pin a2 is the way they should be.
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Of course, thank you, that socket does have 9 pins not 8!
The jumper is currently not shorting to the 7th pin. I went ahead and wiggled the tube all around the noval and it doesn't appear that any wire is touching nor able to touch its neighbor.
I will pick up some liquid insulator and shore up those exposed bits asap though, thanks for the tip.
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The wire that's oddly routed at B8 is going to cause problems eventually.
The upper wire on B2 doesn't look to be well captured by solder.
You may find at this point that it's just easier to order a replacement big board + parts.
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Thanks Paul, I am about to resolder those two wires on the oct.
Are there any other readings I can take to narrow down the issue on the big board?
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It's totally possible that the big board just didn't survive the flux event. What is the DC resistance to ground that you get from OA and OB on the big PC board?
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Resistance to ground from:
OA - 0
OB - 124.7
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OK, can you post some photos of how the TIP50 is mounted on the A side?
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These?
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Yeah, I would double check that the mounting hardware is properly installed. If the metal tab of the TIP50 is allowed to contact the heatsink, you will get the issue you're having.
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The solder on the TIP connections looks rather crystalline but that might be due to the trip through the washer. Do they need reflowing?
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Thanks PB and Deluk.
I checked the TIP50 assembly, took it apart and reassembled; it had been assembled correctly. The insulator looks pretty beat up, probably from the wash, with some dents but looks intact (pic attached).
I went ahead and reflowed the TIP connections, then reflowed everything I could reasonably reach on the big board.
After the reflow, the DC resistance readings:
OA : 60
OB : 126
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60 ohms? 60K? 60M?
You could carefully power it up and see if the rail voltage stays up above 150 or tanks down like it has been. That issue that only comes up with the 6080 installed and a 0 ohm resistance at OA or OB on the PC board does point to a transistor installation problem or another slight possibility is a shorted or backwards 100uF cap.
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Where do I check the rail voltage?
I had it set to DCV, so I believe 60 volts, but I don’t have it in front of me, will have to double check tomorrow.
I did double check the transistors and they appeared to be correctly oriented.
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The rail voltage is on terminals 2, 4, 13, B+ on the big PC board, and IA/IB on the small PC board.
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Success! Thanks so much for bearing with a novice.
All the rail readings were 182v.
The 60 and 124 OA and OB resistance readings from yesterday were in mV (if I am reading my multimeter correctly).
As the OA resistance is still low at 60, should I be attentive to anything in particular going forward?
And would the flux that I used periodically need to be scrubbed from the connections (IE does it continue to sweat out from the solder points as the points are exposed to heat over time?).
Many thanks again for the assistance.
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Resistance will be in Ohms, not volts.
Can you double check the DC voltages at terminals 7 and 9? With 182V of B+, the voltages at 7 and 9 are likely either correct or one of them is now 0.
If the flux returns, another round through the dishwasher would be called for, though I can't recall ever having to perform that task twice on the same kit.
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Oops, I didn’t mean to jump to a premature resolution! The LEDS were all lit up and I listened to a record without problem before seeing your last response.
DC voltages:
7: regular bounce between 105 and 111v
9: regular bounce between 102 and 108v
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Those are good working voltages.
-PB
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Oh excellent! Thanks again so much. So glad that I didn't have to save up for a whole new kit!
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Glad to hear your amp is functioning well now, goldencalves. Enjoy some weekend listening! :)