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Post by svart on Feb 27, 2023 18:22:44 GMT -6
Have you checked the solder joints around that area?
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Post by mcirish on Feb 27, 2023 19:52:49 GMT -6
Have you checked the solder joints around that area? Yep. That's the first thing I did even before swapping out the relays. |
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Post by mcirish on Feb 28, 2023 20:04:33 GMT -6
Ordered all the polystyrene caps and transistors. Unfortunately, this is a fairly shotgun approach as the problem is so intermittent. Hopefully, this will solve it and I can move on to other things.
I will write back in a week or so when the parts arrive.
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Post by svart on Mar 1, 2023 7:54:53 GMT -6
Ordered all the polystyrene caps and transistors. Unfortunately, this is a fairly shotgun approach as the problem is so intermittent. Hopefully, this will solve it and I can move on to other things. I will write back in a week or so when the parts arrive. Unfortunately that's sometimes the fastest way to fix something. Single-point failure troubleshooting is more for education and morbid curiosity if you have the time. Most techs would just shotgun a section because parts costs are a lot cheaper than bench time. |
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Post by hadaja on Mar 2, 2023 23:12:05 GMT -6
So if stam offered to assist a few posts back why not take him up on the offer?
and / or what was the outcome from his assitance?
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Post by mcirish on Mar 4, 2023 23:50:59 GMT -6
Joshua's offer of assistance was to send it somewhere to be fixed. I had asked for schematics but I understand why he didn't want to send them. I found some Neve schematics for the two stages used in this preamp. It's pretty close. The problem is so intermittent that it may not show itself for the next repair guy. No sense in having it sit on someone else's bench for a month. Anyway, I'm more than capable of repairing this.
Most parts are here and I will install this next week.
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Post by mcirish on Mar 9, 2023 9:30:55 GMT -6
Installed all new caps and transistors in channel one. Been burning in since Monday. Found some cold solder joints on the gain switch for channel two, causing some intermittent issues as well (only at the 55dB setting). I think I will burn it in until next Monday and call it done. Thanks to everyone for comments and help.
At least now, I have a fairly accurate schematic to use next time.
Adding more to it. Found a bad cap in channel two now. After running for hours, we noticed an oscillation in the output. Traced back to a 220pf (C12) cap in the feedback loop right after the output trim. We were pretty sure that was the culprit in channel one as well but it was very intermittent. Must have been a bad run of those caps. Fortunately, I had bought (2), figuring something would go wrong with the second channel as well. I have never seen a bad run of polystyrene caps, but this was definitely the cause in channel two.
I think it's going to have to run on the bench another week before I will say it's working again.
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Post by miadaudio on Mar 9, 2023 16:42:05 GMT -6
Installed all new caps and transistors in channel one. Been burning in since Monday. Found some cold solder joints on the gain switch for channel two, causing some intermittent issues as well (only at the 55dB setting). I think I will burn it in until next Monday and call it done. Thanks to everyone for comments and help. At least now, I have a fairly accurate schematic to use next time. Adding more to it. Found a bad cap in channel two now. After running for hours, we noticed an oscillation in the output. Traced back to a 220pf (C12) cap in the feedback loop right after the output trim. We were pretty sure that was the culprit in channel one as well but it was very intermittent. Must have been a bad run of those caps. Fortunately, I had bought (2), figuring something would go wrong with the second channel as well. I have never seen a bad run of polystyrene caps, but this was definitely the cause in channel two. I think it's going to have to run on the bench another week before I will say it's working again. Be gentle with the polystyrene caps while soldering them on the board. They are very sensitive to soldering temperatures and can easily be damaged by heat. More than other film caps. It's not a bad idea to use some sort of a heatsink on the lead while you solder the cap. Something like an alligator clip for example. |
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Post by mcirish on Mar 16, 2023 15:19:29 GMT -6
After touching up a few more solder connections and replacing a bad cap in channel two, it's now run for four days without the odd oscillation on either channel. Maybe the caps were damaged when it was first assembled. Who knows. I will put it back in the rack and burn it in another few days before putting it on a session.
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Post by svart on Mar 16, 2023 16:03:56 GMT -6
After touching up a few more solder connections and replacing a bad cap in channel two, it's now run for four days without the odd oscillation on either channel. Maybe the caps were damaged when it was first assembled. Who knows. I will put it back in the rack and burn it in another few days before putting it on a session. Nothing finds a problem like trying to use something you think is fixed.. |
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Post by mcirish on Mar 16, 2023 16:13:57 GMT -6
No truer words were ever said.
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Post by mcirish on Mar 31, 2023 8:22:09 GMT -6
No issues have reappeared. I think its all good now....
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Post by matt@IAA on Mar 31, 2023 19:10:46 GMT -6
Good news. Man I’m sorry.
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Post by jcoutu1 on Apr 16, 2023 17:32:04 GMT -6
No issues have reappeared. I think its all good now.... I think mine has intermittent issues as well. Haven’t had enough free time to really dig in and figure it out. I may hit you up for advice once I do some more testing. |
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Post by mcirish on Apr 16, 2023 17:37:50 GMT -6
Glad to help. It was a tough one.
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