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Macintosh Classic issue

demonlg

Member
Hi to all, again with a questions and sorry for my english.

I have buyed a Mac Classic computer (probably 2mb because it have a little ram board connected on the logic board but without sim inserted and jumper setted on SIM NOT INSTALLED). The system not boot up and the screen turn on with a garbage static image and square have a fast flickering, nothing bong!
I have disassembled all because logic board have capacitor leaking (little but present) and very poor state, battery is without leak but 0 volt, i have removed this and at this moment the system don't have a battery.
Then i washed the logic board and recapped it with new capacitor.
Then i have reassembled all and turned on, the screen appear with full horizontal lines but after 2 minutes the system bong and boot up from SCSI hdd (OS7.1) . After 10 minutes of working the system going to continuosly resetting, infinite, and in any case it try to boot then reset again or screen stays with garbage image or freezed.
I have measured 5v rail and 12v rail, and with multimeter i have an oscillation from 4.5v to 5.1v on 5 volt rail and 11.5v to 12,7v on 12 volt rail. At this point i have decided to check the analog board in switching power supply section.
At first look all of output electrolytic capacitor have a leaking and it have corroded part of bottom wiring side, i have replaced only all output capacitors and cleaned board and all damaged solder point, and cleaned all connectors.
Try to turn on, system boot up normally, load OS from disk, and...... again after any minutes the system going to reset continuosly!
On the service manual i have readed section of votlage regulator trimmer resistor, i have turned on system and regulated it to have stable 5,1volt and 12,5 volt on output, the computer seems to work...........but..........after one day i have returned on it and again horizontal lines and same issue!
Now if i measure 5v lines and 12v lines after 2-3 hour of stop i have noted a time increasing voltage, when the system is cold, and stabilize it when hot, the system try to boot up when i have 4,9volt on multimeter, if it is down of this value the system is hanged, or resetting continue. Also i have noted the SCSI disk not spin every time computer turned on, seems spin when the voltage is ok and, i have noted also the voltage drop down when system going to continuosly reset, both 5 volt drop rapidly from 5 to 2 volt and 12 volt drop rapidly from 12 to 9 volt.
Finally, in any case the systen boots up and working for about 10 minutes, or other case i have the issue at first boot time.
I think so the voltage regulation and checnking circuit have a problem, or other capacitor need to be replace on analog board.
Can any one help me?

Thanks

Emanuel
 

imactheknife

Well-known member
Sounds like power on analog if hard disk isn’t always powering on. Post a picture of display so we can see if you can.
 

bibilit

Well-known member
A lot of posts concerning this issue, try googling for Optoisolator Macintosh Classic and 68kmla
 

demonlg

Member
ok i try to replace optocupler cny17, in the same area of this i have two little electrolityc capacitors, i don't have replaced it! Try to replace it before optocupler because i don't have it's now, i need to order.

Then, the screen verbation, tipically vertical vibration, is possible a non fully functional of big capacitor 220uF 400volt on the first line input line area?

In fact, i have replaced only the capacitors in the output wire area, have to replace all other, two or three in the flyback area.

And, i have a bridge rectfier without serigraph type on top, can anyone have a good replacement parts to buy?
finally, the leakage of utput capacitor have attacked two big diode but serigraph model on top is the same of bridge rectifier, not readable.
 

demonlg

Member
Hi to all, thanks for support, the mac now is perfectly working, i have replaced capacitor C40 (.022uF) with wrong value when hot, then i have replaced all electrolityc capacitors on analog board. For my prevent, i have replaced LM317T and TDA4605 and zener DP3 1n4148 (in the vicinity of the C40) and then big input capacitor 220uF 400v + bridge rectifier (this one with a little corrosion).

Now the screen not flickering and i have very stable image, hdd spin up, and both line 5v and 12v don't have a slow fluctuation from 4.6 to 5.2 volt or from 11,5 to 12,5 volt, but start immediatly to 5,2 and 12,5 volt stable, finally i have startup bong after 1 second of poweron system and the horizontals lines on screen not appear when booting.

Note: the C40 capacitor is connected to CNY17 but in my case the value of its capacity changed holding it between two fingers while I measured it, the value dropped drastically when it warmed up.

Nice job.

Thanks at all.

Emanuel
 

demonlg

Member
Hummmm..... false alarm!
After changing the components that I described in the previous post, I kept the mac on for some time without any problems, I also turned it off and on several times without encountering problems on the 5v and 12v voltages, it was always perfect, stable and when turned on it was always between 5.2 and 5.3 volts or between 12 and 12.5 volts, without any oscillation of the voltage or of the monitor. The night has passed, I am in Italy, this morning happy with the result obtained yesterday by turning the mac back on but ... I notice the 5v voltage which is at 4.7 volts and gradually increases, the display shows the horizontal lines again and vibrates, does not bong and does not boot. I keep it on for about 15 minutes noticing that the voltage gradually increases until it reaches 5.15 volts, at this point a series of resets begins, then here is the bong, I hear the hdd start and it starts loading the operating system. Now the voltage measured continuously while it is on has oscillations ranging from 5.15 to 5.22 volts, but it seems as if once it reaches 5.22 volts it starts to go down and then rises again to 5.22 and then again back down, it has this oscillation of about 0.1-0.15 volts continuously, but the system does not reset and starts stable, only the vibration of the screen remains. The 5v never hit yesterday's 5.3 volts, and the monitor never stopped vibrating. At this point I think, either I really have to change the CNY17 (i have found 1 on ebay with code CNY17-2) or the capacitors I used on the outputs are not of excellent quality, in reality they are part of a purchased kit on Amazon probably of Chinese origin. At the same time the computer works regularly, without any reset. I'm really exhausted from this.
 

demonlg

Member
I kept the mac on for 1 hour, the voltage on 5 volts stabilized on 5.19 5.22 volts without ever resetting, but screen remained to vibrate. Then I switched it off and on again after 1 minute, the 5 volt spike marked 5.34 volts for the first 10 seconds and the screen was stable, then the voltage dropped slowely to around 5.2 volts and the screen started to vibrate again, there is something that generates this loss of voltage, but I don't understand what!
 

demonlg

Member
OK i try this, i have replacement for DP4, on schematic is an 1n4148 zener diode, then i have buyed CNY17-2, it's ok this or is wrong code? Schematic says only CNY17.

Thanks
 

demonlg

Member
In the meantime I tried to turn on the mac without the logic board, and it seems that without the voltages they are ok. This is really very strange, yet the logic board works and it is with new capacitors!
 

demonlg

Member
Another check, i have readed in other similar post with similar problem, i have disconnected ground from my line cord, and the voltage measured on hdd connector now start at high value, but, on 5v rail i measure 5,00 volt, and in a 12v rail i have measuerd 12,8 volt, i thinks so this 12v,8 volt is to high! But in this case test the hdd won't spin, in precedence it spin when 5volt is at 5,19volt. Screen not weavy, little flickering is percepible, but not boot. Damn!
 
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demonlg

Member
Ok, the hdd not spin if i power it with another power supply, is this a not correlated problem, some case spin, in other case not spin, this is not a mac problem, but i have booted mac with inside rom system, and it's ok without line ground! Very strange fact!
 

AwkwardPotato

Well-known member
Do not, under any circumstances, interrupt the safety ground on the line cord! The fact that the Classic seems to work better without it connected is a fluke.

As bibilit said, replace the optoisolator. CNY17-2 may be suitable. If the Amazon capacitor kit is particularly crappy, it may also be causing problems. In the future, try getting the parts from an electronic components distributor (e.g. Farnell) where you'll also be able to find the CNY17-3.
 

demonlg

Member
Yes it's definitely not a good thing but I was curious to see if it did the same thing to me too, and in fact now it always works when I turn it on even after hours! The HDD has its own problem, I don't know if it's always due to exhausted capacitors, I have had to change them in some MFMs, I'll try. Meanwhile, I'm also dedicating myself to the mouse and keyboard, the mouse works regularly, the keyboard seems not to, at least I can't start the system by pressing the necessary keys. Actually this keyboard comes from a Macintosh LC II, but it is identical to many online views, while the one they sold me with the computer is still an Apple but 101 keys, it looks like a standard PC, and this works perfectly. I remember that the keyboard was working when I bought the LC II, I cleaned it and I checked the membrane and it seems ok to me, but not even the reset button seems to work, at least the classic does not reset if I press it. The mouse connected directly to the classic or pass-through in the keyboard works regularly, but the keyboard does not seem to show signs of life at least during the boot phase, if the disk starts I could try to open a text file and check if not all the keys go , from the rom boot I can not do anything, I just managed to format a floppy without problems. I will have to wait a few days for the ordered components to arrive, I will change both the zener 1n4148 in DP4 (DP3 I have already changed it) and the optocoupler, I also bought the IRFBC40 (which I do not understand why it is not equipped with cooling fin. For the rest I repeat, I would like to understand what is throwing in the ground and determines the loss of power.
 

demonlg

Member
What is the largest hdd supported for Mac Classic? My model is Conner CP3040A, 40mb disc. Unfortunately is dead after 3 days of working, motor not spin, try to spin 6-8 times then stop.
 

bibilit

Well-known member
but not even the reset button seems to work

The reset is not used in the Classic, used for soft-start on several units but unused on the MC.

the loss of power.

If your hard drive is bad, maybe the source of your issue, draining power from the PSU side.
 

demonlg

Member
Yes, but i have same problem with hdd disconnected from power supply and scsi connector, mac classic working only with power cord ground disconnected, without problem.

Now, ok the disk is faulty, tested out of mac, but i have to replace with another one, and i have ordered zener diode and optoisolator for replacing.

Keyboard question: the mini din connector is compatible with ps2 pc connector or not? Because i have to test keyboard in other computer but i don't have another mac with this connector, i have an LC 2 but i have to restore it after classic.
 

demonlg

Member
Hello, parts arrived today, i have replaced cny17-3, two 1n4148 in the vicinance, and again all output capacitor with a more good parts. I have buyed a new capacimeter with esr and the value of the capacitor parts aquired on Amazon have very wrong value, example 2200uF capacitor measuring 1780uF, the new one value is ok.

Then, i have found a replacement of two output diode for 5 and 12 volt output, not for the heatsinked one, and i have removed all component affected with electrolite and cleaned all and again the board, then resoldered all.
Have tested the voltage regulator trimmer (200ohm) and it's ok, and i have rotate it to 50% (in precedence i have rotate it clockwise for compensate 5 volt output)
Finally i have removed and tested the two rifa filter caps and our value result wrong and replaced with other one i have with correct value, and the two big filter capacitor on the 220v line input area, c16 and c28.

Ok, power on mac with ground on power cord connected......wow, perfect voltage 4,9 volt and 12,2 volt, monitor image perfect without any flickering and very clare and stable. Turned off mac for 1 minute, then again turned on, all ok for about 50 seconds, then fuse blowned up!

I have checked with multimeter on power bridge rectifier (new) output (+ and -) and i have a short, then after a full check in the area i have found the mosfet IRFBC40 with all pin shorted! After remove it from board the short on rectifier is going out, but now i have to replace the mosfet! Tomorrow arrive one buyed!

I don't know because the mosfet is deaded when the mac results working perfect and in precedence, last week, i have turned on mac continuosly for 2 hour without problem! Is possible now with all charge and good output voltage the old mosfet have signed our end of life? -:)

Emanuel
 
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