Re: RME Octamic II input circuit anyone
Hi. On my desk there's an Octamic with a PCB severely damaged by a shorted diode. The device turns on, but there's no dual voltage on pins 4 and 8 of the 4580 op-amps. Andrealikescaps, would you be so kind to take a snapshot of the PS input section and post it here? If you still need information about the mic input circuit, just let me know (although there are probably many differences from Octamic I and II).
PS Please note that, as you can see in the attached picture, I removed the transformer to clean and repair the PCB....
jantoman
Member
Last Activity: 10-19-2022, 01:11 AM
Joined: 07-11-2013
Location: Monza Brianza
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Re: iMac A1311 PSU 614-0444
Hi. I found out that in my power supply one of two MOSFETs near the output plug was shorted... That's why I couldn't get a correct 12v rail for the inverter. I replaced both MOSFETs and now everything works fine.Leave a comment:
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Re: iMac A1311 PSU 614-0444
Same iMac, 21,5" Mid-2011. I'm trying to fix an issue with an on/off flashing backlight, everything else seems to work.
These are the voltages I measured on the PS 14-pins connector:
pins 1, 3, 5, 7, 8, 14: ground
pin 2: +3,3 volts
pin 4: +12 volts
pin 6: nothing
pin 9: +3,3 volts
pin 10, 11, 12, 13: +10,50 volts
Pin 13 is connected to the inverter input, that is marked 12 volts: there's definitely something wrong.Leave a comment:
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Re: iMac G3 Lime Green (M5521) power supply
This morning I found the spare KA5S12656 in the mailbox: the measure readings matched with the good IC, so I soldered it, reassembled the iMac and turned it on keeping my fingers crossed... Well, it finally works. Hooray!
Thanks for your assistance and support, guys. I don't think I'd have any chance to get it working without your help. Respect!Leave a comment:
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Re: iMac G3 Lime Green (M5521) power supply
Hi: here I am again, I've been busy for a while and I had to put the iMac on a shelf. A couple of weeks ago a friend of mine came visiting my lab, saw it and told me "I've got one of those, but I don't remember if it's still working: I can give it to you, if you like". Of course I said "YES!"
He brought it here yesterday: as I inserted the plug I heard a relay click that was missing on my "patient"... first thing to check. Then I pushed the start button and it booted right at once... great! I turned...Leave a comment:
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Re: iMac G3 Lime Green (M5521) power supply
Yes, there's a jumper to the +B line heading to the flyback transformer. Tomorrow I'll be busy, but Friday I'll try to check the PS again.
Thanks guys for your help: it's about 40 years I'm messing up with electronics, but I always tried to stay away from CRT devices and I don't know much about them.Leave a comment:
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Re: iMac G3 Lime Green (M5521) power supply
Right. Maybe it's a better idea to remove the flyback transformer to work safely on the boards, do you agree? Maybe it's defective as well, like another iMac 233 I have on a shelf waiting for the spare transformer... (different kind, of course)Leave a comment:
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Re: iMac G3 Lime Green (M5521) power supply
I replaced all three el-caps, C906 - C918 (47 mF) and C916 (1 mF). Then I mounted the analog board on the chassis, connected the CRT tube and plugged the iMac through a 70w lamp, an useful trick against short circuits. In fact, when I switched it on, the lamp flashed quickly then went off...
The fuse didn't blow, though. I'll check the rest tomorrow: here it's past midnight and I better go to sleep.
Just a question: do you think I could check the analog board without connecting the CRT?Leave a comment:
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Re: iMac G3 Lime Green (M5521) power supply
Good news. I removed the transformer from the PCB and guess what? look at the 49v pin...
I fixed it with a short wire and soldered the transformer back in its place. Next thing to do is to check the other components of the startup circuit, then I'll try to turn on the iMac and see what happens, keeping fingers crossed....Leave a comment:
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Re: iMac G3 Lime Green (M5521) power supply
Of course: look at the short wire soldered on the main cap's negative pin.
15 ohms.
No continuity with ground, neither one of them. I guess you nailed it. I'll check the other components you mentioned, but the transformer seems definitely faulty...
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Re: iMac G3 Lime Green (M5521) power supply
The IC and some capacitors. The contacts are good, anyway, no matter how they look (the crappy neon light doesn't help).Leave a comment:
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Re: iMac G3 Lime Green (M5521) power supply
Thanks a lot for your support, RJ.
- on pin 1 (drain) there's the same voltage I find on the main capacitor: they're connected by a transformer winding, pin 2 and 3 (1 is ground). About 335 volts rising to 360... then I turned it off
- pin 2 is connected straight to ground
- on pin 3 (VCC) about 43 volts
- pin 4 (feedback) is connected to the optoisolator's pin 4 through R904 (15 ohms), there's 1,0-1,2 volts on it. Pin 3 is connected to ground and pin 1 and 2 are connected...Leave a comment:
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iMac G3 Lime Green (M5521) power supply
Hi. A friend asked me to fix his old iMac that stopped working. I opened it up and found out that the SMPS IC was burned so badly that it was impossible to identify the type. After a lot of research I discovered it was a KA5S12656: I bought some of them from AliExpress, keeping my fingers crossed. Now I get the correct voltage on the main cap and on pin 3, but nothing happens when I push the front switch: I guess there should be a control voltage sent from the logic board to pin 5 (soft-start) but I can't see nothing there. Following the service guide's Troubleshooting suggestions, I checked the... -
Re: AcBel 9841 problems
Just finished to fix a faulty AcBel 9841 PSU... I followed the suggestions on the first post replacing the small caps on the daughter boards, along with some others on the main board. One of the fastest fix I ever done: I reconnected the PSU to the main board and got the Apple chime at once. I LOVE this forum. Thank you so muchLeave a comment:
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Re: Apple imac A1418 820-3302A
Hi. Me and a friend spent part of the afternoon trying to fix his iMac with the same problem of yours. I replaced L9100 with a fuse holder and connected the LCD: the 1,6A fuse blew at once. I thought it was a lamp fault and I tried to connect just the data plug, with the same result. Guess he'll have to buy a new display...
BTW, where did you find the L9100 coil-resistor or whatever it is?
Thanks in advance.Leave a comment:
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Re: Apple MDD G4 PSU (AcBel API1PC36) - Recap question
Same symptoms here. The funny thing is that I replaced the original PSU with a brand new one... Apple had a "quiet fans" program for the MMD and his owner bought the whole set (PSU + fans) sometime ago "just in case". Last week his G4 stopped booting; we replaced the PSU with the new one, but the computer refuses to boot almost always. Maybe a cap was DOA.
I checked the original PSU but I didn't notice any bulged cap: I'll give it a closer look with the help of your picture...Leave a comment:
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Re: New Members - please post your introductions here
Hello from Italy. When I read the forum's name I thought "This is genius!"
I'm a musician with a passion for electronics. I started playing piano at six and dismantled my first radio at fourteen
I got a proper musical training, but I never studied electronics (except for some basic physics notions). That never stopped my curiosity, anyway: sometimes I don't even check the warranty dates (I'm not very proud of it, to be honest...) I work as a professional musician, electronics is just my hobby......
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