Macintosh Classic II with no sound. Analog board issue?

[Mr_formal]

Thanks, I tested it this morning and the speaker works, this is Mac classic II though, and not SE 30. Just wanted to mention that, but now I can cancel new speaker order since it works.
I also want to mention that I have to keep the 5v and 12v rail low or else it won't boot. 5v is at 5.91 right now but it's usually stable around 5.8 12v is usually between 11.5 and 11.9 If I go to exact 5v and 12v it shows garbage on the screen. I did recap all capacitors on analog and logic boards, but I looked through some more Posts about it and it might be two diodes that are the culprit of all my problems. It said dp3 and dp4 on analog board usually go bad, so I'll replace those. If you have any other tips, I'd be happy to hear them, I managed to get everything working except the speaker and it really bugs me.

 

[zigzagjoe]

Thanks, I tested it this morning and the speaker works, this is Mac classic II though, and not SE 30. Just wanted to mention that, but now I can cancel new speaker order since it works.
I also want to mention that I have to keep the 5v and 12v rail low or else it won't boot. 5v is at 5.91 right now but it's usually stable around 5.8 12v is usually between 11.5 and 11.9 If I go to exact 5v and 12v it shows garbage on the screen. I did recap all capacitors on analog and logic boards, but I looked through some more Posts about it and it might be two diodes that are the culprit of all my problems. It said dp3 and dp4 on analog board usually go bad, so I'll replace those. If you have any other tips, I'd be happy to hear them, I managed to get everything working except the speaker and it really bugs me.

That is very weird. Do you trust your multimeter/positive it has a good battery? I'd suggest most likely your meter is reading incorrectly as system insanity would be expected when voltage is too low (<4.5v) not greater than 5v. Also, where are you measuring?

The analog board has no electronics on it that pertain to the speaker. Just a straight connection from LB audio circuit to speaker via AB. So other components shouldn't change anything, that's why I suggest checking the -12v line as is used for audio in related designs. Just a guess though. I haven't looked in detail at the classic/classic II audio section.

 

[Mr_formal]

I tested multimeter on a battery and it read 1.6v, tested 12v barrel jack and it reads 14v, yeah thanks for pointing that out. This is a brand new multi meter, so I figured it would be correct, but I guess it reads a little high on the dc side. Testing it on an outlet reads a perfect 120v, so ac reading looks like the only correct one. I've been testing the voltage on the Mac through logic board cable, since floppy port read a different voltage than logic board, and thought the power cable for logic board would be more accurate.

The -12v is the same as 12v, but I'll try to get different multimeter or find out what's wrong with mine.

 

[Mr_formal]

I tested multimeter on a battery and it read 1.6v, tested 12v barrel jack and it reads 14v, yeah thanks for pointing that out. This is a brand new multi meter, so I figured it would be correct, but I guess it reads a little high on the dc side. Testing it on an outlet reads a perfect 120v, so ac reading looks like the only correct one. I've been testing the voltage on the Mac through logic board cable, since floppy port read a different voltage than logic board, and thought the power cable for logic board would be more accurate.

The -12v is the same as 12v, but I'll try to get different multimeter or find out what's wrong with mine.

I just tested a laptop charger and USB port and they read correctly, so I'm getting mixed messages. I don't know if my multimeter is accurate, so I'll try and get one to compare to.

 

[Mr_formal]

That is very weird. Do you trust your multimeter/positive it has a good battery? I'd suggest most likely your meter is reading incorrectly as system insanity would be expected when voltage is too low (<4.5v) not greater than 5v. Also, where are you measuring?

The analog board has no electronics on it that pertain to the speaker. Just a straight connection from LB audio circuit to speaker via AB. So other components shouldn't change anything, that's why I suggest checking the -12v line as is used for audio in related designs. Just a guess though. I haven't looked in detail at the classic/classic II audio section.

I just realized I said 5.8v and not 4.8, I want to clarify that 5v is 4.8v not 5.8v. I have to keep both rails below their rated voltage.

 

[Mr_formal]

I had another question about classic II. It seems every time I adjust the voltage to a perfect 5v it freaks out. I'm attaching an image. I also noticed that it does this if I don't have the back cover on and I jiggle the logic board. Is the Mac classic II logic board sensitive to movement?

 

[zigzagjoe]

I had another question about classic II. It seems every time I adjust the voltage to a perfect 5v it freaks out. I'm attaching an image. I also noticed that it does this if I don't have the back cover on and I jiggle the logic board. Is the Mac classic II logic board sensitive to movement?

That is a dead giveaway for bad connections/broken solder joints. Nothing should be movement sensitive. That is probably your actual issue here. Analog board joint problems problems are also common (more common than LB actually) and generally the entire board should have all joints reflowed even if not obviously needed. If you have done that, then gentle slight flexing of the LB and tapping around with a plastic tool can help pinpoint where the issue may lay.

I just realized I said 5.8v and not 4.8, I want to clarify that 5v is 4.8v not 5.8v. I have to keep both rails below their rated voltage.

That's still odd, but less weird at least. Generally, you should be fine from about 4.75v to 5.25v, but in reality I wouldn't really expect a problem if they happened to be a bit high.

 

[Mr_formal]

Thanks, I'll try and reflow the solder on logic board. Another thing I did was check diodes dp3 and dp4, that I heard go bad. I desoldered them and checked them, and they were fine. Hopefully reflowing the joints will help.

 

[Mr_formal]

I can't exactly pinpoint where the cracked joints are, everywhere I tapped made it worse, but I got a bus error when I turned the Mac on its side, could that point toward the right direction? I don't really want to reflow all joints, but I'll start doing that now since there's probably no way to pinpoint it.

 

[zigzagjoe]

I'd check the big through-hole devices first on the LB. If you have macsbug installed, the address that it bus errored at (especially if consistent) may give a pointer to where problems lie. Re-seating the rom chips may also help.

 

[Mr_formal]

I'd check the big through-hole devices first on the LB. If you have macsbug installed, the address that it bus errored at (especially if consistent) may give a pointer to where problems lie. Re-seating the rom chips may also help.

I just finished running a heat gun across the entire back side. I'm going to reflow the solder on the chips on the front side as well. I noticed a crack near where the ram is while reflowing, I did have some issues with the ram, so I might have fixed it, but I'll reflow all the chips and whatnot to be safe.

 

[Mr_formal]

I finished reflowing the entire board and Mac logic board is no longer sensitive to movement, however I still can't raise the voltage above about 4.85v (read from floppy port) and 11.61v. If I raise voltage to 5v the Mac either freezes on startup, or gives random sad mac error code. The audio still doesn't work either, but that's probably a different problem.
Could the voltage problem be the new caps on analog board? This is where I sourced them:

Macintosh Classic and Classic II Analog PCB Cap Kit for p/n 630-0525

<p>High temp, electrolytic cap kit for the Macintosh Classic II (and some Mac Classic) analog PCB.</p> <p>Features correct specialized low-impedance capacitor types where appropriate.</p> <p><strong>Note: There are two versions of Analog boards found in

console5.com

 

[Mr_formal]

Another quick note, the system boots at 4.85v but is unstable, best I've found so far is 4.80v

 

[Mr_formal]

Another note is that 12v and -12v on logic board is different.I turned the Mac on its side to measure, and 12v is 11.47 and -12v is 11.74. the -12v is higher.

 

[Mr_formal]

Does anyone know where I might be able to source the dfac chip for the classic II, I've checked the audio amplifier IC and using the datasheet to test it it looks fine. I can't find a datasheet for the dfac chip, and I think it's bad. I want to replace it to see if the audio works.