Bottlehead Forum
Bottlehead Kits => Moreplay => Topic started by: Galluch57 on December 12, 2024, 05:59:48 AM
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Hello -
I wanted to ask some advise as I find myself in a pickle. I built a Moreplay preamp a couple of years ago and it was a very successful build! Been sounding beautiful w/ my Dynaco ST-70. So as soon as I saw the upgrade kit, I jumped on it! I meticulously installed the upgrade over the course of a couple of nights, tested and when I put the Moreplay back in my system the improvement was SIGNIFICANT!!
NOW...here's the bummer part :( - the other night I fired up the system and the audio was low and distorted in both channels and seemed to get worse if I tried to turn it up louder. I tried both outputs from the Moreplay with my ST-70 as well as my headphone amp with every source input and it seems to come down to the Moreplay. My problem is that I AM mechanical, have soldering skills and was meticulous and extremely careful with the build but I don't possess the electrical knowledge or have the experience to troubleshoot the issue. Can you help me with that? I'd be so depressed if I had to put my Moreplay on a shelf as decoration (gorgeous as it may be!!Lol)...pride of building aside, it sounds incredible and I hope I can find the problem and repair it without spending a ton to involve a technician - thank you all for any help you can offer!!
Paul Gallucci
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There are voltage checks in the manual on pages 25 and 28, I would start by double checking that those are all correct, and posting what you find there.
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Will do tonight, thank you!
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I’m having trouble with my Moreplay a couple of weeks after installing the upgrade - was working beautifully for two weeks and now low volume distorted audio through both channels. I’m doing the voltage checks to begin troubleshooting but wanted to ask where I should clip the negative lead for the high voltage check now that the volume pot has been upgraded to the board mounted type?
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If it fits, you can clip it to either of the black wires where they connect to the input selector switch.
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Excellent, thank you - I was thinking that but wanted to be certain. I will post voltages in a few minutes.
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Here are my checks on the Moreplay w/ Upgrade:
Low Voltage Check:
A2 - A7 - 6.26v
B2 - B7 - 6.25 v
High Voltage Check:
6U/16U - 174.3v & 174.4v
B+ Reg TP on PC board - 177.5v
4U/14U - 10.85v & 10.69v
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Can you tell me about the 6V6 tubes you're using? You have the correct heater voltages to allow the tubes to work, the bias voltage isn't super far off, but the plates aren't pulling down. As you built the kit, were the voltages correct at that time? Do you have the ground jumpers on the volume/balance upgrade board?
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They are Marconi 6V6 G - they’ve worked beautifully for maybe a year + before the upgrade. All voltage checks were within spec when I built the upgrade and the ground jumpers are installed on the potentiometer board.
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I’d like to post pics but the jpeg’s from my phone aren’t an accepted file type
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Try this. Change the file name from .jpeg to .jpg.
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Can you put the stock tubes in just to double check?
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Yes, I'm going to. I had to go out of town for a couple of days.
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Here are the Morconi Tubes I've been using.
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...and thank you Paul, changing the file name worked.
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Moreplay Upgrade Pic 1
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Moreply Upgrade Pic 2
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Moreplay Upgrade Pic 3
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Can you measure 6 and 16 with the tubes we provided?
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6U - 172.6v
16U - 172.6v
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Can I see what the bottom of your upgrade board looks like? You should just be able to pop off the connections on the front of the board and bend it up.
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Here's the best I could do with the angle.
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Another
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I think you have some cold solder joints. You can leave the joints for the LEDs alone, but everything else should be reheated and flowed out.
https://www.youtube.com/watch?v=EN16Pi7pcfk (https://www.youtube.com/watch?v=EN16Pi7pcfk)
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Looks to me like the leads at the banded ends of the zener diodes (in the square pads) are not properly soldered on the underside of the board.
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Thank you - I will work on that tonight 🙏🏼
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I just wanted to show you this photo which was taken before installation of the board. Is it possible that those solder joints could have degraded in two weeks of use? (I used Kester "44" 63/37 rosin core solder)
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Yes, those haven't been heated enough and should be reflowed (excluding the LEDs, which take very little heat to solder properly).
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Paul, should I desolder and solder again or just heat the existing solder?
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Heat the existing solder, provided it has lead and is rosin core solder. Adding more solder will just add more metal that needs to be heated to flow out properly.
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Will do, thank you.
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I took the board off and reflowed everything except the LED’s.
6U - 173.4v
16U - 173.1v
Essentially the same as before 🤷🏽
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You will need to take the board out and show us a picture of the entire bottom of it.
You have excessive current flow where current should be regulated. If there were soldering issues present, it's possible that a transistor or two have shorted out from that fault, and you can check this by setting your meter to beep when you touch the leads together, then touch each pair of leads on each transistor (Q1/Q2-B &C) to see if there are shorts.
It's also possible that your main C4S board is working properly, but that there's a soldering issue related to the balance pot and the input/output wiring there, and the 6V6 grids are losing their ground reference and this is causing extremely screwy DC voltages. I would evaluate this by temporarily soldering one bare wire across the L-Out, R-Out, and ground lugs next to the balance pot. That will provide a DC short to ground, and if your voltages move dramatically, then you know the issues is in the input/balance pot wiring.
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Thank you. I’ll start with the transistors. They each have 3 legs correct? So I set my multimeter for continuity and try each combination of lead pairs on each transistor?
If there is a short I will get a beep?
I also have to remove the transistors to test them don’t I?
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That is all correct.
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One last question before I proceed. I labeled and desoldered all the leads running to the PC board to remove it so I could reflow the board on my work station. How many times can I remove the board without damaging the pads etc.? Seems to me I now have to remove the board again so I can desolder the transistors for testing
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Also, are the smaller PN2907 transistors more likely to have been damaged than the larger MJE5731A transistors? Should I test those also?
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The board can come on and off 5-10 times most likely. A lot of it depends on how gentle you are pulling the wires out.
Definitely test all the transistors, I've seen both the PN2907 and the MJE5731A transistors short previously.
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Can you give me the specs on both those transistor types and a source where I can order some spares? If I'm going to pull the board out again, I may as well just replace 5 transistors.
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I ordered replacement transistors - once they arrive and I replace them, I’ll give you an update. TY
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No, please don't randomly pull out all the transistors and attempt to replace them. The odds that you destroy the board in the process of doing this go up with every transistor you pull.
Please do the shorts test I asked you to do and report the results, then also do the second test I posted.
The diagnosis of the problem has to be completed before a remedy is attempted.
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Paul, just for clarity.
Can the shorts test be done with the transistor installed on the board?
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Yes, you should be doing that test with the transistors on the board.
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From a FAQ PB and I posted some time ago -
It takes some getting used to using meter probes in tight spots. Did you accidentally touched your meter probe to two terminals or leads at once? This can take out transistors. You can test transistors by unplugging the amp and measuring resistance across each of the three possible pairings of the three transistor leads. If any reading is very low, like under 100 ohms, the transistor is toast and will need to be replaced. It's usually the smaller 2N series transistors that fail.
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Sorry that I missed the last several entries everyone. I did already remove all 6 transistors and replaced them. Same voltages at the test points.
6U - 173.3v
16U - 173v
B+ Reg TP - 177v
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Were any of the transistors that you replaced shorted out?
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It's also possible that your main C4S board is working properly, but that there's a soldering issue related to the balance pot and the input/output wiring there, and the 6V6 grids are losing their ground reference and this is causing extremely screwy DC voltages. I would evaluate this by temporarily soldering one bare wire across the L-Out, R-Out, and ground lugs next to the balance pot. That will provide a DC short to ground, and if your voltages move dramatically, then you know the issues is in the input/balance pot wiring.
I won't be able to provide any more assistance on this until you complete this test.
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Is there any chance you can provide a diagram for this test? I’m not quite understanding .
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Temporarily soldering one bare wire across the L-Out, R-Out, and ground lugs next to the balance pot.
You are going to have to tell me what isn't clear about this instruction.
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Voltages after soldering bare wire across L-In, L-Out and ground lugs next to balance pot:
6U - 172.3v
16U - 172.3v
B+ Reg TP = 175.4
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Excuse the typo -- that should be:
L-Out
R-Out
Ground L
Ground R
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I wanted to mention that it appears that 2 of the LED's light but two do not. Photo attached
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When I completed the initial build these LED's did not illuminate but I read in the manual that some illuminate and some are dimmer, so since the voltage checks were within parameters when I completed the upgrade, I never thought much of it. Can you provide further troubleshooting advise?
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It would be helpful to go back to the plate loading resistors. The white wires need to be slipped out of the front plate solder eyelets on the PC board, then connect each wire to one each of the removed 10K plate loading resistors. Temporarily solder the other ends of those 10K resistors together and to a jumper wire, then run that jumper wire to Reg+ TP. This will be kind of a hodge podge of wiring floating in the air, but it's useful to see if your plate voltages pull down to the correct value under these conditions.
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I apologize - I’m trying to follow but it’s a bit confusing. I completely remove the two 10k resistors first?
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You already removed the 10K resistors in the process of installing the large C4S board.
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Understand now - the white wires you mention are soldered to the board at the ”Plate C” and “Plate B” locations?
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Yes, those are the soldered eyelets labeled as plate connections.
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New voltage test:
6U - 90v
16U - 90.1v
Image attached (Please note that I used leftover wire from original Moreplay build so what’s going to Plate B eyelet was supposed to be white but I used red because I didn’t have enough white wire to make that connection)
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There's going to be a soldering issue or a failed component in the B/C area of that main green PC board.
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Since I have replaced the 4 transistors in that B/C section of the board, I am suspicious about the 2 LED’s that don’t illuminate. I will check the soldering joints. TY
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The LEDs are sensitive to excessive heat, so you could try replacing them for the sake of thoroughness.
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I will. The two on that section of the board don’t glow. Could they possibly be the cause of my issue?
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It's very rare for one of our LEDs just just randomly stop working. Maybe I've seen that 1-2 times in 20 years. Generally there would be some other issue that takes them out as part of the failure process.
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Paul -
Very happy to report that after replacing the 2 LED’s that weren’t glowing on the B/C area of the board, the voltages tested in spec and the preamp sounds brilliant again!! Thank you for all your help & patience!!