Recapped Macintosh Classic with checkered screen

[falen6]

Just to chime in ......... I have exact same problem ........same low 5 volt at power up , slowly climbing to 5 volt then booting

I recapped the board ( well , the caps recommended to replace anyway )

I have the same ( but not as bad) area of protective layer been eaten by leaking electrolite . Looking at xeiters photos above , i thought i was looking at my own a/b board !!



will start changing the chips and diodes mentioned in this thread

Im fiddeling with macs for about 8 years or so now , and I have never seen this before on a classic ....... and after reading this thread it seems this might be an age thing , as in , these classic a/b's have reached the age where they start to spill their insides ....... this problem might become more and more evident with time


great work people ...... I have many things to change thanks to all your work.

 

[alexGS]

Welcome, falen6
Yes, I still have several machines with the identical symptom, I haven’t got around to fixing them yet. I’m really not clear which part actually fixes these - it sounded like resoldering the wires was part of the final solution. I have one that I’ve thrown many parts at, including optocoupler and diodes, and I’ve now ordered the TDA4605 (switchmode power supply controller) - maybe that is important. Good luck and let us know what works for you

 

[alexGS]

Do you have another classic that you recapped with jaycar caps that works ok and isnt suffering from cold start?

Sorry I missed this question - No, I don’t have any recapped Classics that are working properly.

Also your other three classics that have the same issue did you recap them with the same jaycar caps?

Yes. Only one machine turned on at all before the recap (with a checkerboard display), the other three would not turn on (just ‘dead’). After replacing the caps with Jaycar caps in all four, and one of the optocouplers, they all turn on.

All four wobble, two have the checkerboard, one goes away/boots when it warms up and the voltage reaches about 4.6V (starts at about 4.2V) and the other doesn’t really warm up at all, just a wobbly checkerboard.

I then did the optocouplers in the three I hadn’t done - no difference.

Focussing on one machine, I replaced the IRFBC40, the 200-ohm voltage adjuster trimpot, and the small 4148 diodes with no improvements.

I’ve ordered a set of low-ESR caps from Mouser to try. I’ll advise if it makes any difference. Have also ordered the Zener diodes, the MBR1045 rectifier diode, and the TDA4605 (I’m pinning my hopes on the latter). Logically, the Zener diode should affect the regulation if everything else is working, but it seems like we all get multiple faults at once with these.

 

[falen6]

Has Techknight gone on holiday , or retired ?? - hes the man that would figure this out in no time

I went back at my machine - i swapped the 1uf 50v cap in mine with a tant when i recapped the machine as i didnt have a radial - i found one today so put that in .......... machine is better !!!! - it gets up to 5 volts in half the time !! - I really dont get this at all

 

[alexGS]

I went back at my machine - i swapped the 1uf 50v cap in mine with a tant when i recapped the machine as i didnt have a radial - i found one today so put that in .......... machine is better !!!! - it gets up to 5 volts in half the time !! - I really dont get this at all

Ah, you mean the one near the optocoupler?

Many people fix the problem by replacing the optocoupler, or the signal diodes connected with the optocoupler (and the cap you mentioned). Nothing has been a complete fix for me, but certainly it’s worth a try.

I tend to think of the Classic analog board as a chain of weak parts, and improving any link in the chain can make just enough of a difference. The optocoupler is part of a feedback control loop, so the better it is working, the tighter the voltage regulation should be.

I’ve ordered a few replacement LM431 ‘transistors’ (actually shunt regulators) which are, again, connected to the optocoupler.

Meanwhile, we have 12 Mac SEs in the museum collection with no analog board faults at all…

 

[falen6]

Just goes to show the greed......... they made the machines with cheaper and cheaper parts ,,,,,,, look at apple today - they were proven to be sending commands to peoples devices to slow them down to make them buy new ones,,,,,,,,,, i used to love apple back in the day but what they are today is a joke .......... safety nets around foxcon buildings to catch workers trying to commit suicide !!! - apple has become utter hypocrites and i wouldnt buy anything they sell today

 

[falen6]

Happy to report I finally got my machine working 100%

Turns out it was the 470uf 50 volt that i didnt replace when i did the recap ( didn thave one )

a few arrived today and i changed it - hit the power switch and weh hey , beeeeeep ..........

so my recap was off this picture - i only replaced the caps in the box's ( EXCEPT THAT 470UF 50 V UNTIL TODAY)

swap them all people - I even measured that cap before i changed it and it 'appeared' to be good

Another Classic back in action

 

[falen6]

dont believe this

i put the machine all back together and got ready to play loom for the night , connected keyboard / mouse and hit the power

the dam problem is back

sickened to say the least

 

[falen6]

The machine is allot better
When i powered it up after changing the 470us 50 volt is was perfect

Now it starts everytime , beep , boot , no 'wavy' screen

but i am getting jittering on the screen all the time that wont go away plus it just resets a random times

all the voltages are good

and the mouse does not work


Im not far from hopping this dam machine off the wall

im gonna change every dam cap on this analog board

 

[alexGS]

I’ve already replaced all caps, so it’s not that for me but thanks for your report anyway. The biggest 400V cap seemed to solve a brightness-flickering problem; I haven’t found any specific capacitor that makes a difference to the voltage and wobble.

‘Jitters’ can be caused by a poor connection at the four-pin yoke connector (particularly if these are horizontal jitters) - resolder, and wirebrush the pins

 

[falen6]

reflowed all the usual culprits when i first recapped it - washed the board in acetone - cleaned both sides over and over looking for anything
there is nothing visibly wrong
have now reflowed prbably half the board ....... no change

i thought i was lucky earlier but im in the same boat as everyone else

it seems as these caps started going out of spec over the years they put a bad load on some important high tech component on the board - the very chips you were all discussing

on most of the caps ( 2200 , 1000, 470 uf ) that i replaced the magic goo was under them , on the board

the fella i bought it from ( and i know him ) said it was running up to a few months ago - i asked him this again and he insists it was booting up 6 months ago - he tried it a month ago , it didnt boot so he put it up for sale - i got it

when i saw all the goo under the caps i replaced i was thinking no way this booted 6 months ago - thats why i asked him a 2nd time

some kinda cascade failure of dying caps taking out one of the chips !!!

this A/B is really getting me down

back up on the shelf for a month !!!!

 

[dochilli]

To see if the voltages are stable, you need an oscilloscope. The rebooting can be a sign of changing voltages.
Did you change any of the following parts: DP3 and DP4 (1N4148), TDA4605, CNY17G, IRFBC40?

 

[alexGS]

To see if the voltages are stable, you need an oscilloscope. The rebooting can be a sign of changing voltages.
Did you change any of the following parts: DP3 and DP4 (1N4148), TDA4605, CNY17G, IRFBC40?

Thanks - did you mean me?
I’ve replaced all those except the TDA4605 (which is on order along with Zener diodes).
In the Classics I was working on, the 5V slowly increases rather than oscillating. When it hits 4.7V, the machine boots, and I don’t have any rebooting after that. I do have a handheld oscilloscope, but I didn’t see a noticeable ripple.

 

[falen6]

i only changed caps - dont have a scope - wouldnt know how to use it if i did

but i do have a doner board so will change DP3 and DP4 (1N4148), TDA4605, CNY17G, IRFBC40 1 by 1 and see if it makes any difference

just need to take a week time out otherwise the machine will become a UFO from my window !!!

 

[xeiter]

i only changed caps - dont have a scope - wouldnt know how to use it if i did

but i do have a doner board so will change DP3 and DP4 (1N4148), TDA4605, CNY17G, IRFBC40 1 by 1 and see if it makes any difference

just need to take a week time out otherwise the machine will become a UFO from my window !!!

Sorry to hear you are going through what I just went thought. I changed so many components in my Classic (please see my posts above for full list and order of when and what I did).

The last changes that seemed to have done it were:

1) installed socket for QP1(CNY17G) and replaced for another new one (I had soldered another new one in before this)
2) installed socket for IP1 (TDA4605) and replaces for another new one (I had soldered another new one in before this)
3) replaced QP2 (IRBC40) for another new one (I had soldered another new one in before this)
4) removed all power cables connections to AB board, cleaned everything and soldered them in with new solder
5) removed IP3 (in the area where most caps are), cleaned everything and soldered them in with new solder

So for points 1), 2) and 3) I had actually replaced the components twice (second time using sockets for 1) and 2))

I have a strong suspicion that what did it for me was actually 4) and 5) and my Classic 5v was VERY sensitive to temperature change so cracked cold joints could be the culpit.

Please do share your journey here as sharing my journey here helped me alot - many people offered their very good advices.

An please do not send your classic flying out of the window - I know how you are feeling as I went through the same: just walk away from your mac and come here to this thread instead of killing your Classic. There always is a logical resolution - we just need to find it.

 

[falen6]

i hear ya xeiter

mac wont go out the window ......... not until i find and fix this problem !!!! haha

like you i just put it away for a while , calm down and try again.

I have a vintage Casio 1000 synth here for over a year - power supply board problems ( low voltages) ive taken that thing down from the attic so many times , tried , gave up and put it back - ive changed so many components and it still wont work properly

but its always worth the wait when the dam thing finally works

 

[mrkrsl]

I realise this is an old thread, but it is one of few with good details that covers the exact Classic II power supply issue I was experiencing and fixed. So I thought I’d add my experience in case someone else reads through.

tl;dr: A careful, full soap/water wash + dry of the Analog Board solved the cold boot slow voltage ramp-up issue for my Classic II.

My issue was the same as described in this thread:

• Full re-cap of both boards the power would come up low (roughly 4.1v and 10.2v)
• Voltages would then slowly rise over two or three minutes, eventually powering the Logic Board which would boot at around 4.6v and then later allow the HDD to start spinning at 12v. Exaggerated screen wobble from the beginning.
• For about 5 or so minutes the screen image would keep wobbling, then gradually settle.
• This was an issue from a cold (temp) boot. When already stabilised and warm, the machine would restart as if there wasn’t a problem.

History:

When I recapped the board there was cap leakage, which I had thoroughly cleaned with IPA. The board looked old, but there wasn’t much visible evidence of electrolyte. I also cleaned the area with the octocoupler with IPA. I re-soldered around 50 or so joints on the board. No difference. I read all the threads about this issue, including this one, and was about to order a replacement optocoupler and DP3 and DP4 diodes.

Washing:

I had read elsewhere that washing the board with water is good. Apparently capacitor electrolyte is water soluble. Presumably it’s not alcohol soluble, though IPA does look like it cleans it up. It may also be the case that leaked electrolyte spreads insidiously, so even though it looks like the leakage is limited to the grey/purple pools under the old capacitors, it may migrate over the whole board and remain largely invisible.

I washed it thinking it was all I could try while I waited for replacement components. I masked off the speaker with some film and used a medium soft kids paintbrush with warm water and a little dish soap in a cup. I worked the octocoupler area in particular and went over the whole board other than the speaker and the raised parts of the transformers, on both the component and trace sides. After that, I rinsed it off under the tap and thoroughly dried it with a hairdryer on low heat. (20 mins +) I intended to do a final rinse with deionised water, but forgot in the end.

I made sure the board was completely cold before testing. It booted and the disk spun immediately. No screen wobble. 5.1v and 12.2v from power-on. Subsequent tests over 1+ week and 10+ cold boot cycles have been solid. Immediate bong at power-on, disk spins. Voltages stable from the first second. The issue seems 100% solved for this Classic II with this issue by water/soap cleaning and drying.