Bottlehead Forum
Bottlehead Kits => Eros Phono => Topic started by: Lowercase on February 23, 2021, 10:23:39 AM
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Just completed my Eros. Passed resistance checks without issue. But my readings starting with OA/OB to OkC/OkD are quiet high:
IA 210-230V 216V
IB 210-230V 217V
OA 155-185V 214V
OB 155-185V 214V
OC 95-100V 193V
OD 95-100V 192V
OkA 95-105V 204V
OkB 95-105V 204V
OkC 0.7-2V 6.7V
OkD 0.7-2V 6.5V
Can upload photos of the board shortly.
Thanks as always!
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Stupid mistake found. I swapped a pair of resistors from the power supply to the C4S board. They were swapped back in to the right place. They were the 270k bleed on the power supply and 27k on the C4S. Orange and yellow are the same color right? ;D
New voltages below which are still high, starting at OC/OD now, but a step in the right direction. So I guess it’s a game of what did I fry now? All LEDS are lit too and no burnt or funky looking parts.
IA 210-230V 217V
IB 210-230V 217V
OA 155-185V 145V
OB 155-185V 145V
OC 95-100V 141V
OD 95-100V 140V
OkA 95-105V 140V
OkB 95-105V 140V
OkC 0.7-2V 4V
OkD 0.7-2V 4V
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I just did the same thing today putting 330K resistors in place of 22K resistors, it's not all that easy to find.
Can you check your R1 values on the PC board up front? The servo circuit is nearly turning off the EF86 and still the OkA/B and OC/OD voltages are pretty close together. I would check for continuity between each pair of legs on the 2N2222 transistors as well. How do the caps that hang off the edges of that board look?
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R1A/B are both reading 113
Caps look just fine. No bulging or anything amiss.
Q3D/C is 174 base to emitter, no beeping, and readings that start at 400 and rise when on collector, no beeping on either side. Don’t know if I measured the right way, but hopefully pinpoint in right direction.
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You want to check for shorts between base and collector, base and emitter, and emitter and collector. I've also found that if you take the board off up front, it's pretty common to swap a few wires on accident when putting it back, so definitely double check that as well.
If all else fails, build photos are often helpful as well.
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I was able to replace the resistors on the power supply without having to remove it thankfully. So nothing was removed around up front.
Just tested and no beeping on any three combinations. So is it safe to assume they are shorted and in need of replacing?
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Beeping means they are shorted, no beeping means they are OK.
I would post some build photos, especially of the 6922 socket.
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Of course. So good there. Images below in gallery.
https://imgur.com/a/PANgrsL
Sorry, I’m never able to upload to the site directly.
Of note. Just flipped the top over and the 12au7 has a darker than what appears normal spot at the top near the getter.
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One 27K resistor looks pretty mangled, does it still measure well?
Are 9 and 10 connected together? How about 14 and 15? That shouldn't cause the problem you have, but it's something I noticed.
Maybe also post some photos of the EF86 sockets and the bottom of that front C4S board.
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Yeah.chipped when removing. I get 26.6/26.7, kinda takes awhile though to get there and settle.
Both 9/10 and 14/15 are connected. Adding photos to gallery now.
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The time to settle is from cap charging.
Hopefully PJ can look over those voltages and come up with a plausible reason that they are so whacky.
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One thing I noticed while building that differed from the manual were the resistors I got for the R2 spots on the shunt regulator. They measured 100KΩ so figured it was just a different brand.
Thanks for the help. Super excited to get this up and running!
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Yes, those higher power 100K resistors tend to go in and out of stock fairly regularly.
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The bias servo is not working. You checked the 2N2222 transistors. indicating they are OK, so there's something else not right in that area. The output of the servo transistor is 4v which is too high, meaning the input to the 2N2222 is too low. Can you measure DC voltage at each end of the 27K resistors? This will tell us whether the input to the servo transistor is all right, and if it isn't then we have a better idea where to look for a broken wire or bad solder joint
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Measurements below with front facing the text at the top of the board:
RKA
Front 139.7
Back .90
RKB
Front 139.7
Back .90
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Yeah, they are in the right proportion and both are too high.
I think the 2N2222 collector is not connected to the EF86 cathode (pin 3 on the tube socket).
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Just taking a look and the connections from the EF86 pin 3 to the C4S board all look solid, I have some close ups in the gallery below too. The 2N2222 appears to have good joints too including the collector, but will reflow tomorrow just to be sure. Will also take another test just to be sure I didn't mess that up the first time. Since the RKA/B are correct ratio does that point to the transistors being the most likely culprit or some other connection in the line?
https://imgur.com/a/PANgrsL
Thanks again for all the help!
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Try measuring the resistance between tube pin 3 and the 2N2222 collector - and any points in between that might be accessible. A joint that looks good is not always a joint that conducts electricity ...
I assume the EF86s have glowing cathodes, by the way - if the tube is not functioning you'll have the same symptoms.
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Will do tomorrow and report back.
The EF86s are super faint, a small red dot in the middle. More than I would have expected them to be honestly. Would the prior resistor mess up have caused them to go bad? Especially since both sides are practically mirrored readings? When I did the initial glow test though they also looked about the same.
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Yes, the cathodes are so well shielded they are pretty dim: that's normal. As long as the C4S is working, the EF86 currents are too small to do any damage.
I expect the same problems could be caused by installing the 2N2222's backwards - I think you had checked that already, but it might be worth confirming.
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Measured both sides and at all points from 3 to collector had 0. Reflowed joints in the area and retested, same results.
Retested the 2N222, base to emitter is 174, base to collector starts at 400 and rises. Collector to emitter starts at 300 rises.
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Running low on things to check :^) is the emitter grounded? Is the transistor correctly oriented? Somehow the EF86 cathode current needs to get to ground, and it isn't.
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Getting 0 when ground to emitter is tested. Yeah it’s oriented correctly. Tabs match up to the PCB, both to the left when looking above.
Since the circuit checks does that possibly mean tubes since you mentioned it earlier?
Noticed couple minutes after unplug OkC has 4.3, but OkD has .7 volts. Anything there?
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Re-Soldered the a/b pins and the C4S board. Plugged it in and same voltages again. Checked the ef86 tubes. Very very faint glow, but are warm to the touch. Photo below of tubes on:
https://i.imgur.com/my5FexG.jpg
Also, the getter has a more opaque ring around it unlike the 6922. They were like that when I got them though. Image below:
https://i.imgur.com/SZ7UCXJ.jpg
Keep looking over and rewarming anything that doesn’t look 100% perfect. Also retesting after doing a round and keep getting the same results without anything budging, same voltages in the second post.
If you need more images let me know.
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I'm not sure what you mean by "opaque" - the getter flash is usually silvery but you can't see through it. The nearest EF86 does appear to have a whitish getter deposit at the top of the tube - unless that's a reflection? That would be a sign of a bad tube that has leaked air. I'm skeptical abput that being the problem though. I'll keep thinking about it.
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Pale silver/white would probably be the better description. I know that all white no silver is bad, seems like a portion is halfway there. And nope, no reflections, the other EF86 looks about the same as the closet one too. Can get some better photos from above if you want. Wish I had an easy way to test them, but no tube tester! Does the photo with power on look correct? I guess the manual wasn't joking when it said dim!
Appreciate all the help, really looking forward to installing it in my system!
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I have seen many EF86s with getters that look like that and worked just fine. I would guess it's something specific to that particular production line.
It is a bit of a stab in the dark, but it may not hurt to replace the 2N2222A transistors. In order to do this, you should get a spring loaded solder sucker (the blue/yellow one that's $20 will work fine).
Cut the transistors off from the board with side cutters, then heat the bottom of a joint with the soldering iron and use the spring loaded sucker to suck out the solder and the lead.
I have on a few occasions seen those transistors fail when I've made a wiring error here and there.
-PB
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Yeah I took a closer look at them this morning and they do look fine. Comparing too much to the other two which are uniformly silver and a bit darker.
Ordered two of the 2N2222A and will swap them out. Hopefully the fix all along!
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Replaced the 2N2222A transistors and some exciting results to report!
IA 210-230V 217V
IB 210-230V 217V
OA 155-185V 153V
OB 155-185V 151V
OC 95-100V 100V
OD 95-100V 101V
OkA 95-105V 101V
OkB 95-105V 103V
OkC 0.7-2V 1V
OkD 0.7-2V 1V
Still some slightly under and over optimum, but within 10%! Can’t wait to hook it up. Thanks to both Pauls for helping diagnose!