Mac 512ke questions

[Surfheart]

I recently bought a Mac 512k with the 800K disk drive upgrade from Ebay and I had a few questions for the fine folks here.

I thought at first it had some bad joints because the raster would sometimes go to a thin vertical line until I slapped the side.

I took the back off to find one of the legs of C1 had pushed right out of the underside of the board and was quite loose. It had also lifted the pad and bit of the track!

I replaced it and left one of the legs long so I could bypass the lifted track. That solved the main issue with the unit, but there are a number of small things still occurring and I'm not sure where I should be looking to resolve them.

When the Mac is cold, whenever there is floppy disk access, the bottom of the raster will jump a tiny bit. There are also very faint horizontal bands moving through the raster.

Both these things go away once the Mac has warmed up, but then the other issue begins, a very very high frequency whine or whistle will start. This will last maybe 10 or 15 minutes then stops and usually doesn't return.

Anyone have any ideas on where the problem might lie? I'm worried that these are symptoms of a failing flyback transformer, but I'm yet to replace any other caps or freshen up the solder on L1 or the Flyback. I'm not very experienced with a soldering iron yet

 

[Mac128]

Have you adjusted the voltages? The floppy drive problem is directly related to out-of-whack voltages in compacts I have seen with this issue. Otherwise, without consulting my Pina Books, I would say this unit is in need of a complete recap. Considering it's age, that is most definitely a contributing problem here. Either way, even if you track this down to a specific cap, merely refreshing the solder joints is not going to cut it.

 

[Surfheart]

Thanks mac128. Guess I just have to practice my soldering skills on some scrap boards and do the recap.

I'm relieved that you don't seem to think this is a problem related to the flyback transformer.

 

[Mac128]

Haha, did not say it couldn't be the flyback ... Just several other things to check first. I don't have my reference books handy, or I would go into more detail. Of the dozen or so M0001 compacts I have had, none have ever had the flyback fail, but a few have exhibited the symptoms you describe, usually resolved by adjusting voltages or replacing caps.

 

[H3NRY]

SOunds like the power supply voltage is fluctuating with load, as in floppy running or not. Caps are likely culprits, and the whistle may be from the flyback. Most usual problem there is cracked solder due to heat cycling. Reflow the solder on all the transformer joints and other hot parts in any case. If you don't run the machine with loose flyback connections, the transformer will last just about forever. Horizontal retrace lines on the screen may be due to the internal brightness control turned up too far. Proper setting is to turn the user brightness all the way up, then set the internal control just below the point where retrace is visible (or in some Macs where focus goes to heck). Retrace lines could also be due to voltage setting being off, so a voltmeter check is in order. Good luck, and learn to solder. It's a very useful skill.