Bottlehead Forum
Bottlehead Kits => Eros Phono => Topic started by: onion_breath on May 12, 2017, 07:10:30 PM
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I've been putting together my Eros kit over the past few days and have now reached the Shunt Regulator Voltage test. So far kit has been going fine, but I am getting measurements that are far from what is expected.
All four of my LEDs on the Shunt Regulator are lighting up and the tube is currently glowing. I'm not sure if the tube could be the problem - all of the tubes I've received have very faint lettering on them so it's hard to determine which is which. I put what I thought was the 12bh7 in the socket (tallest tube out of the lot assigned to this kit), but maybe thats the 6DJ8 (i don't think it's the EF86 tubes since those are the only ones that match).
My measurements for the D1 teflon wire is 4.873 V DC. The D6 teflon wire read 3.3356 V DC.
Any insight would be greatly appreciated. Also, if there's any other measurements needed or even photos to add in aiding me I am all for it.
Thanks,
Greg
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The 12bh7 is the tallest tube in the kit.
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So since I am using the correct tube is there any insight as to why my readings are so low?
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The best way to get help from the Bottlehead team is to post all out of spec voltages with the terminal number and value. Post pictures too since that's helpful for troubleshooting remotely.
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No problem. Individual triode variations will make the hybrid regulator tube cathodes (pins 3 and 8 of the 12BH7) vary quite a bit. The voltage must be at least 2.5v for the 431 chip to work properly, and a voltage over 36v will damage the chip. As long as the other voltages are within spec, you should have no problems.
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Hi Paul,
Just so I'm understanding correctly - the Shunt Regulator Voltage test is expecting the readings on D1 and D6 to peak above 300 VDC and drop to about 225 VDC, but the readings I received on D1 ( 4.873 VDC) and D6 (3.3356 VDC) are seemingly lower than what's expected. So these readings aren't an issue? I just want to know before moving forward with the next set of instructions, since there's nothing on page 58 of the manual mentioning readings this low.
Thanks again,
Greg
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Bump
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I'm guessing PJ misread your post and thought you were listing cathode voltages rather than plate voltages. You are correct that those plate pins D1 and D6 should read 225V volts. Check your PC board over for missed solder joints and misplaced components. Posting a good closeup picture of the board here will give us an opportunity to help try to spot any errors.
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Doc B is correct, my error.
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Thanks for for response. I went ahead and reheated a solder point on one of the 1N5820 rectifiers that looked liked it needed a touch up. Attached are the best photos I could take at the moment. Let me know if there's any other photos I can take to make troubleshooting easier.
Thanks in advance
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Since the problem is associated with the shunt reg PC board that is installed on the D socket, close up photos of that board were actually what I was asking for, rather than the power supply board.
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If you have adequate voltage at IA and IB (In other words, measure the high voltage output of your power supply board in addition to what you're measuring now), and almost no voltage at OA and OB (which go to D1 and D6), then you very likely have inadequately soldered the center legs of the MJE5731 transistors. I am guessing this is at the heart of your problem since the LED's are lit up.
If you measure the output of the power supply board and it's very low, then there's likely a short that's dragging everything down.
A bad tube at the D socket will generally give very high voltage at D1 and D6.
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I was finally able to get some time to go through your suggestions and here's what I was able to measure.
IA 336.3
IB 337.1
OA 3.18
OB 4.87
output power supply board 6.31
I reheated and re-soldered all the legs of both MJE5731 transistors and checked for any other bad solder joints while I had the iron hot. I'll also attach a few photos of the shut reg PC board.
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Here are the photos. If you need more detail I can try and post with some better lighting.
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Pull the 12BH7 and remeasure IA and OA.
You don't appear to have a short behind the C4S, which is a good thing, but something at the output of the C4S is yanking down your regulated voltage. Do also check that you have LM431's or TL431's in the 431 slot, as sometimes MPS4250's can be installed accidentally since they look the same (though this usually produces a different set of symptoms).
-PB
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Checked the 431 slot which had 431's installed properly. Pulled the 12BH7 and measured IA and OA. IA read: 352.2 VDC ; OA read: 4.78 VDC.
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If there are any other measurements needed to help troubleshoot, or anything else recommended please let me know.
I'll just be putting the build on hold in the meantime.
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Are all of the jumpers on the board showing good continuity from pad to pad?
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Remove the red wire from OA that connects to the tube socket. Also remove the red wire from OB that connects to the tube socket.
Now recheck OA and OB.
-PB
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I removed the red cable from both OA and OB.
OA : 4.79 VDC
OB : 4.89 VDC
I also remeasured IA and IB.
IA : 360 VDC
IB : 360 VDC
I'll see what recommendations you have, and will try to work on more troubleshooting tonight.
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Remove the other red jumpers on OA and OB, then remeasure OA and OB.
-PB
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Finally got a chance to remove the other OA and OB jumpers.
OA : 219.8 VDC
OB : 222.3 VDC
I'm getting nervous this troubleshooting will never end :'(
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Well, this tells us that the C4S bits of the PC board are OK (the center bits with the MJE5731A/2N2907 and LED's).
When you have the OA/OB bits jumpered to the outsides of the board, your voltages are sinking like crazy. You've checked the placement of the individual parts, but I'd wonder if there's an issue with the way the board is wired to the tube socket. If the OA and OB pads aren't connected to D1 and D6, but rather to D3 and D8, I could see you getting this problem.
-PB
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I double checked the OA and OB pads, which were properly connected to D1 and D6. I am tempted to just reattach the pads to OA and OB, but before doing so should I check for anything else? Otherwise I can reattach and send you measurements of the results.
BTW - as I was assembling and now disassembling, I've noticed that the wires (specifically the red wire used for this kit) seem to be breaking, like they're somewhat brittle. Is this a normality I should be seeing with cable that have a relatively small gauge?
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If the wires are breaking right at the insulation it is an indication that your stripper is set too tight and nicking the wire itself, creating a stress point. If it's just breaking in random places it's because its getting work hardened from too much bending and flexing.
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Well Doc & PB - any more input on possible next steps?
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Have you checked all the wires connecting to the board for continuity?
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I have not. What's your best recommendation for checking continuity? And just to be clear - are you referring to just the Shunt Regulator board, or both Shunt Regulator board and PSU board?
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You want to be sure to put the probes 'outside' of the wire connections so you don't accidentally test in such a way that you are leaving out a broken part of the wire or a cold joint within the span of the ohmmeter probes. In the case of a PC board attached to a tube socket you want one test lead on the pad the wire is attached to on the board rather than touching the end of the wire itself, and at the other end you want the other probe touching the tube socket terminal rather than the wire end attached to it.
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So this project has been on the back burner for some time and I'm just getting some time now to get back into it. I was checking some wires on the Shunt Regulator board and noticed the wire that connects from D3 to the Kerg B pad was broken. In the process of replacing that I noticed that the drain wire on the 6" STP cable that connects from the C socket to the D socket was never soldered in the center pin of D. I reread the directions and there is no comment on having that soldered between attaching the cable and conducting the Shunt Regulator Voltage test. Do you think this could have caused the problem for the readings? And if so is there an issue if I solder that wire now? I was working through the manual and see no more connections going to the center pin of D.
Thanks!
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Yes, I would go ahead and solder that connection.
-PB
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Okay. Well I soldered the drain wire at center pin on D and also replaced the broken cable and checked all the other cables for cold joints. I also did as Doc B suggested and checked for continuity on the tube socket terminals at D1 and D6. My results are still very low readings - comparable to my first measurements on D1 and D6. This time around my results were 4.8 VDC on D1 and 3.2 VDC on D6.
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What voltages do you see at OA and OB now?
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OA - 3.02 VDC
OB - 4.81 VDC
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I think at this point that your best bet is to send your Eros in for repair and we can figure out what's going on for you.
-PB