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Not another "330c Blowing Fuses" thread! Yes, I'm afraid so...

JB8

JB8

Well-Known Member
I'll do my best to state the facts, just the facts:

  1. Came across a decent looking 330c, cleaned the pots and interior dust, had to install new speaker terminals as previous owner had hacked them out of the unit
  2. After new terminals installed, tested the unit and found left channel good and clear, right channel was sizzling bacon
  3. Having read the amazing "Noisy Transistor" thread I decided to replace the 1344's on the EQ amp with 1845's, but, and here's the fun part, they were KSC1845Y, not F. Needless to say, nothing got better after the installation, so I moved to the other 1344's, assuming they must be the culprits. At this point I'm still thinking the 1845Y is the right move, so I replace the two 1344's located on the amp board (Q421/Q422). Not good, fuses burnt out immediately.... fudge, only I didn't say fudge
  4. I then go on a transistor rampage research junket which schooled me on the difference between the Y and the F, so I found some F's and ordered em up!
  5. The arrived, I installed the two in the amp board first, figuring I could at least get back to the sizzle stage maybe, but no sir, blew two more fuses
  6. I then replaced the two KSC1845Y's on the EQ amp with 1845F's, and watched the fuses get close to burning out but turned off the unit before they could blow
So now I'm thinking I've shorted something out, which is my fault because I'm mucking around in here and likely have no business doing so, but I shall continue because it's fun to learn, right?

I'm also wondering if it's essential to be replacing these transistors in pairs - if I replace 1344's with the proper 1845's, should I also be replacing the 2SA844s with KSA992F's, or whatever the complimentary pair is?

I've been reading in several threads not to just jump around changing stuff out so I'm trying to put on the brakes a bit before I further mess this thing up. My skill level is mediocre at best, I can sort of read a schematic, I'm ok with a DMM, and I'm down with soldering and some solder sucking when needed.

Lastly, I know many of you are going to shy away from this rats nest, but if anyone has a "here are the next 3 things I'd eliminate" (one of the three can't involve my love for vintage gear), I'm game to get after this and keep poking around, so to speak!
 
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letter will be gain ranking .. doubt very much that would cause blown fuses . most likely you fitted them wrong way round or caused some other short circuit .
 
Thank you, @petehall347, appreciate the reply. I fitted them facing the same way the previous transistors were installed and thought my research was sound regarding the pin out, but I'll double check them. It's the "caused some other short circuit" bit that makes me nervous. Simply not sure where to start, but based on the other 7 page thread I read earlier today, where you walked another enthusiast through this process, it can certainly be a needle in the haystack unless you're savvy and know you're way around diagnostics.

I need to better understand the signal flow and what could have happened to create a short circuit along with who the usual suspects are, but in a nutshell. Again, not looking for an extensive tutorial, just a few clues on next steps. If I can't figure it out I'll need to determine if it's out of my league and just sell it on as is, but at some point I'd love to be able to challenge this scenario, and win, or at least better understand next steps.

Thanks again, any advice is sincerely appreciated!

IMG_8384.jpg IMG_8385.jpg
 
JB8 said:
I'll do my best to state the facts, just the facts:

  1. Came across a decent looking 330c, cleaned the pots and interior dust, had to install new speaker terminals as previous owner had hacked them out of the unit
  2. After new terminals installed, tested the unit and found left channel good and clear, right channel was sizzling bacon
  3. Having read the amazing "Noisy Transistor" thread I decided to replace the 1344's on the EQ amp with 1845's, but, and here's the fun part, they were KSC1845Y, not F. Needless to say, nothing got better after the installation, so I moved to the other 1344's, assuming they must be the culprits. At this point I'm still thinking the 1845Y is the right move, so I replace the two 1344's located on the amp board (Q421/Q422). Not good, fuses burnt out immediately.... fudge, only I didn't say fudge
  4. I then go on a transistor rampage research junket which schooled me on the difference between the Y and the F, so I found some F's and ordered em up!
  5. The arrived, I installed the two in the amp board first, figuring I could at least get back to the sizzle stage maybe, but no sir, blew two more fuses
  6. I then replaced the two KSC1845Y's on the EQ amp with 1845F's, and watched the fuses get close to burning out but turned off the unit before they could blow
So now I'm thinking I've shorted something out, which is my fault because I'm mucking around in here and likely have no business doing so, but I shall continue because it's fun to learn, right?

I'm also wondering if it's essential to be replacing these transistors in pairs - if I replace 1344's with the proper 1845's, should I also be replacing the 2SA844s with KSA992F's, or whatever the complimentary pair is?

I've been reading in several threads not to just jump around changing stuff out so I'm trying to put on the brakes a bit before I further mess this thing up. My skill level is mediocre at best, I can sort of read a schematic, I'm ok with a DMM, and I'm down with soldering and some solder sucking when needed.

Lastly, I know many of you are going to shy away from this rats nest, but if anyone has a "here are the next 3 things I'd eliminate" (one of the three can't involve my love for vintage gear), I'm game to get after this and keep poking around, so to speak!
Click to expand...
Keep at it! I'm new to this as well, I got into it because I couldn't find anyone in the Memphis area to work on my reel to reel, the first two years were spent fixing my own mistakes, but low and behold I've got the best running tape machines in town after an electronics guy told me the damage I inflicted on those machines made them too far gone... Electronics is cheaper than ladies and alot more rewarding
 
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Were the 2SC1344's retangular shaped like Q103, for these, the bevel face is the front face, not the face with printing.
Q101(ecb) orientation does not match the artwork,
upload_2021-6-8_20-0-22.png

upload_2021-6-8_20-0-56.png

possible sm error?

EDIT: Q102 also appears wrongly orientated.
 
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Fantastic! This is exactly what I was hoping for, only wish I wasn't working this morning so I could dig in immediately... I'll let you know how it goes and thank you again, this forum is gold!
 
JB8 said:
Thank you, @petehall347, appreciate the reply. I fitted them facing the same way the previous transistors were installed and thought my research was sound regarding the pin out, but I'll double check them. It's the "caused some other short circuit" bit that makes me nervous. Simply not sure where to start, but based on the other 7 page thread I read earlier today, where you walked another enthusiast through this process, it can certainly be a needle in the haystack unless you're savvy and know you're way around diagnostics.

I need to better understand the signal flow and what could have happened to create a short circuit along with who the usual suspects are, but in a nutshell. Again, not looking for an extensive tutorial, just a few clues on next steps. If I can't figure it out I'll need to determine if it's out of my league and just sell it on as is, but at some point I'd love to be able to challenge this scenario, and win, or at least better understand next steps.

Thanks again, any advice is sincerely appreciated!

View attachment 2251899 View attachment 2251900
Click to expand...
A,m in the same boat.
 
Update for the crew.

I had installed the KCS1845F's backwards at both at Q101 & Q102 as well as on the amp board, Q421 and Q422, thanks @mbz! The info around the pin out was very helpful, I didn't realize the 1344's orientation was a bad reference and have learned to really study the pinout more closely, thanks @CT Jim, appreciate the reminder. And welcome to the thread, @Reliving., the more the merrier.

I flipped the two on the board, then flipped and replaced the two on the EQ amp and BINGO! No more fuse blowing and I'm learning, which is a huge bonus.

Still getting the snap crackle pop, frying bacon from the left channel but I'm making progress. Ok, and you knew this was coming, are there more usual suspects to replace at this point? I'm still assuming it's transistor based and yes, I may have just swapped out pairs that were fine in the first place, but I'm good with that, the new parts certainly won't hurt now that they're in properly.

I've got a 430 that has a "distant sound of the ocean" on one channel, so I'm assuming that's filter caps, but on this 330c, should I be concerned about caps at this point or stay the course and replace more transistors until I conquer it? I have some freeze spray, should I just start targeting transistors and see what comes from the search?

Thanks again, these little milestones are actually huge lessons to learn if I want to continue this home schooling for vintage solid state gear, really appreciate the assists!
 
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Noise is present with volume at zero across all functions - AM, FM, FM Stereo, Phono and Aux
 
I would start checking voltages at the power supply. Compare to schematic
Or do you still have a good left channel??
 
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The Fuxtor said:
Or do you still have a good left channel??
Click to expand...

Left channel sounds clear and strong, will that change my approach?

I'll do some checking for voltages and track down the 2SC458's as well and provide an update when I know more. I'm optimistic, thanks, all!
 
JB8 said:
Left channel sounds clear and strong, will that change my approach?

I'll do some checking for voltages and track down the 2SC458's as well and provide an update when I know more. I'm optimistic, thanks, all!
Click to expand...
Very probable the 2sc458 transistors are the cause.
 
I'd replaced Q421 and Q422 on the main amp board (both with KSC1845Fs) and the issue has persisted, so I'm thinking I should replace the 1344's on the pre amp since they can be notoriously noisy as well? Couldn't find any other 458's listed, am I missing any?

IMG_8393.jpg
 
Welp, I fixed it! I'm actually pretty surprised it didn't take more, but thanks to you all helping to narrow down where the issue was, it's now good to go!

I ditched the idea of replacing the 1344's on the pre amp and decided to just focus on the left side of the main amp. I hit Q402 with freeze spray and it spazzed out pretty good, so I replaced the 2CS1345F with another 1845 (thankful to have a nice grip of them, so versatile). I hooked up one of my test speakers, crossed my fingers (not literally) and pushed the power switch, then pushed the speakers 1 button and.... Still static, damn. So, I replaced Q404 and bingo bango bongo, no static! Whew, man does that feel good, and the sound is exactly what I expected.

Success!! Thanks all, really appreciate your support and I'll be back with more questions!

IMG_8396.jpg
 
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