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| Macintosh Classic, no power at all |
Posted by: amedeo_68k on 2024-07-02 09:02:31
Hi, I have an issue with a Macintosh Classic, Early analog board, fully recapped, no power at all, Fuse is good, RP2 is good, any ideas ? |
Posted by: dochilli on 2024-07-02 12:45:06
Broken solderjoint at the power connector?
There are a lot of parts on classic AB that can be defect. Most often: DP3 and DP4 (1N4148), TDA4605, CNY17G, IRFBC40. |
Posted by: amedeo_68k on 2024-07-02 13:12:24
All solderjoints are perfect, I'm going to check the components you mentioned. Another issue is that I find a no easy way to test the analog board without the CRT, While on Mac SE / SE30 the PSU is a separate box, on Classic there is the Flyback HV; Working with detached anode cap would be insane, is there a way to disconnect the HV section ? |
Posted by: emuboy on 2024-07-03 07:32:03
Check the voltages to the TEA2037A |
Posted by: amedeo_68k on 2024-07-05 03:44:36
Thank you, I'll do shortly, meanwhile I tried with another Analog Board (V2) (already fully recapped), with its own CRT, it is easier to say I swapped thr Logic board to another Mac Classic ( that was battery bombed ), I now get this, ideas? |
Posted by: emuboy on 2024-07-05 07:10:48
it might be the logic board? is it recapped? |
Posted by: LaPorta on 2024-07-05 07:14:56
Is this second analog board powering another machine correctly, or you just happen to have this AB and don't know if it works for sure? |
Posted by: amedeo_68k on 2024-07-05 08:21:25
I have two analog board, both fully recapped and one logic board (recapped as well)
- First analog board (rev A), no power at all
- Second analog board (rev B), weird vide and stripes, no sound
- Logic board alone with external power and headphones, I can hear chime |
Posted by: emuboy on 2024-07-06 02:59:52
I would say, the second analog board seem to have voltage issues, I would test the 5v and 12v on the hard drive molex as a starter, then take it from there. |
Posted by: amedeo_68k on 2024-07-06 07:14:10
Hi everyone, on the fully dead analog board I replaced the components as suggested by @dochilli and we are back to life !! Thank you !
There is a little issue. I have some little flickering on screen but only if the internal hard drive is attached. May be some interference.
About the second analog board do you have any ideas ? Thank you. Amedeo |
Posted by: emuboy on 2024-07-06 07:17:50
No power could be anything, from a fuse to a dead transformer, I would check what voltages do I have and follow the schematics for starter. |
Posted by: amedeo_68k on 2024-07-06 09:50:52
@emuboy hi. The no power at all analog board has been fixed. I’m talking about the other one. Heavily distorted video. No chime |
Posted by: dochilli on 2024-07-07 08:52:03
Did you check the voltages of the repaired board? 5 V should be between 4.85 and 5.15V. |
Posted by: just.in.time on 2024-07-07 19:33:16
I agree on checking voltages. Both without hard drive and again with hard drive connected. Sounds like hard drive is pulling just enough current to pull down the voltage. |
Posted by: just.in.time on 2024-07-07 19:48:52
@amedeo_68k there is a similar thread talking about unstable voltages here https://68kmla.org/bb/index.php?threads/se-30-sony-cr-44-psu-unstable-voltage-output.33182/
They are discussing SE/SE30 Sony PSU, so definitely different than your Classic but perhaps there are similar parts on your board that perform similar functions. |
Posted by: amedeo_68k on 2024-07-07 23:52:08
I think the issue is more on the 12V side. Btw now I no longer have the logic board. I had two Analog and one Logic board ( one Classic were battery bombed ). Btw I think I can measure voltages on logic board connector without the logic board |
Posted by: dochilli on 2024-07-08 04:04:48
- I think you can not measure the voltages when the LB is not connected. The results may be others.
- The 12 V side is also changing, if you change the 5 V side with the potentionmeter. You have to measure both when you turn the potentionmeter. |
Posted by: amedeo_68k on 2024-07-08 04:36:35
I could put a dummy load and check voltages with oscilloscope. I’ll let you know. The frustrating thing is that you cannot test analog board without CRT |
Posted by: kupouzar on 2024-07-08 04:38:08
Hey, if the screen is flickering with HDD attached, try measuring the 5V line and adjusting the voltage using the trimmer on the analog board (use a plastic tool). If this doesn't help, I'd try replacing the optocoupler again. There are many kinds and the quality is not always the best. I suggest using a CNY75GB. In case it still doesn't help, it could be the flyback transformer as well - but they're hard to obtain.
edit: I believe the trimmer is for the 12V as well but the 5V line is always measured. |
Posted by: amedeo_68k on 2024-07-12 08:04:58
ok, cool, I'm going to try next week, Thank you |
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