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Pororo

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    ChicagoLand
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  • Headphones
    O2 Mk1, SRX-MK3, HE-4
  • Headphone Amps
    717, 007T (modded)
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    Paradigm Atom v6, Pioneer HPM 700

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  1. Movin' on to the other amp board now.
  2. Problem solved. I started testing resistors and found 2 bad ones R35 and R37 both 100R, measured 140K and 450K. Considering these 2 probably saw 450V, I also pulled the adjacent Q13 and Q14. One tested bad; replaced them both. This is in the vicinity of the 1000V film cap that shorted to ground. Both balance and offset now set near zero. Thanks for all the tips guys!
  3. Yes, all shorts isolated and cleaned. I have not measured any resistors out of circuit, except for the 2k one in series with the pot. There doesn't seem to be any damage to the topside of the PCB; haven't checked the bottom too closely due to the angle bracket.
  4. I had some time, so I swapped the offset pot and the problem remains... -38VDC that doesn't budge. All 4 LEDs are still lit. Is the next step pulling the 1968A and testing them? Any other ideas?
  5. Thanks Kevin. Now that I think about it, it seems unlikely that both 1968A would fail and give the same measurement. Yes, all 4 LEDs are still lit. I'll try swapping out the pot when I have time on Monday.
  6. Here's the C - E measurements: 2.04 OL OL OL OL OL OL OL OL OL OL OL OL OL 2.04 OL Are both 1968A bad? EDIT: I checked 4 new and uninstalled 1968A and they all measure OL OL for C-E... so I guess that means I've got 2 bad 1968A? Does it make sense that that would cause -41V offset that doesn't budge? The pot I checked before installing. It was centered so I put it at max resistance. I guess it's possible it failed under load or got zapped either directly or indirectly from the arcing.
  7. Thanks for the response Spritzer. Here's the results of the diode test. They're all good, right? 0.689 OL 0.607 OL OL 0.661 OL 0.625 OL 0.658 OL 0.623 OL 0.651 OL 0.620 OL 0.650 OL 0.618 OL 0.658 OL 0.619 OL 0.658 OL 0.618 0.688 OL 0.606 OL
  8. I'm trouble shooting some more on the amp board. Right now, all 4 LEDs are lit, and the balance is adjusted to zero. But the the offset is stuck at -41V. The pot is set to maximum resistance. Lowering the resistance gives slightly more negative offset like around -43V. So I tried increasing the value of the 2K resistor in series with the pot and it helps a small amount, maybe getting to around -38V then if I bump up the resistance above a certain threshold the offset climbs sky high to 452VDC! The heatsink is warm, but not hot. The PS is putting out +/- 455V and +/- 15V. Before I could even adjust the balance and offset though, I had problems with arcing and LOUD popping. Once there was a short underneath one of the 0.1uf 1000V caps and the other 3 or 4 times I assumed the solder joints of the outputs were shorting. I cleaned them all top and bottom and there is no trace of flux and no more arcing. My assumption is that the outputs were shorting because there was no apparent damage anywhere else and the arcing/popping stopped after cleaning the flux. I've got 1968A and 4686A installed. EDIT: I forgot to mention: the output current is set at 10mA with 100ohm resistors. Do you guys think one or more of the outputs are damaged? Any other ideas?
  9. ^^^ Yeah, that's what I should have done from the beginning; getting the fets from Bdent instead of ordering everything from Mouser. I'll troubleshoot these later when I have time and just stuff 2 new boards.
  10. John, I double checked the datasheets and you're right top/bottom was misread and as Inu noted, 2sc2705 and 2SC1815 are both ECB. So these 2 were initailly in the correct orientation and I still had the problem. Thanks guys, I'll start testing transistors and resistors.
  11. A short was my first thought... But the fuse didn't blow, so I thought the fets might be the problem. I'll have to take the bracket and heatsink off again, a major PITA. In retrospect I should have picked the onboard version for my first build.
  12. I checked the datasheets for the transistors and this is what I've come up with for the original part and the sub. Reading L to R with the front (flat side) facing you: 2SA1486 ECB STN9360 BCE 2SC2705 BCE MPSW42 EBC 2SC2240 ECB MPSW06 EBC 2SA970 ECB MPSW56 EBC 2SC1815 BCE MPSW06 EBC BUT, I've noticed that the silk screening on the board shows both 2SC1815 and 2SC2705 as ECB and this was the reference I used to originally rewire. I removed the angle bracket and heatsink and pulled the 3 transistors and changed the pin orientation using the BCE reference. Put the whole thing back together, connected the wires to the PS board and fired it up. I had the exact same problem with the big PS heatsinks shooting up to high temps in under 5 seconds. Immediately turned it off. Is it possible that the 3 originally mis-wired(?) transistors were damaged the first time it was turned on and putting them in the right(?) orientation was pointless? Would damaged transistors in the right orientation cause exactly the same problem though? I double-checked the pin-outs above and they look right to me, but I'm not 100% sure that the datasheets are accurate. Anyone see an error there?
  13. Guys, I need some help with troubleshooting. I've got the compact PS and off-board Rev 0.6 amp boards. A1968, 450V. The PS looks good. I get: +15.1V/-14.9V +455V/-455V, bias is 585V. Without the amp boards wired I'm seeing 475VAC and 18.5VAC from the toroid. After I wired it up and turned it on, only 1 LED lit up, the one marked with a yellow arrow in the photo below. The 3.15A slow blo fuse did not blow. In less than 5 seconds the big heatsinks on the PS board got VERY hot and I had to turn it off. There was no arcing or smoke in the 5 seconds that it was on. I see no burnt resistors or bulging caps. I disconnected the wires and turned on just the PS and everything was fine, heatsinks were cool. I'm using all of the new Fets: STN9360, MPSW42, MPSW06, MPSW56. I know the pinouts of these are different from the old Japanese ones. You can see in the photos that I've crossed the legs (used 600V heatshrink). Can I assume that the PS board is good? Or is it possible that adding a load is causing something strange? Any ideas?
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