SCSIless LCIII - Help!

[VMSZealot]

I'm very attached to my LCIII.  It was the first Mac that I purchased brand new, back when I was at Uni.  I bought it to 'replace' my SE/30 (it didn't replace the SE/30 - I still have my SE/30.  But I fancied a spot of colour.)  The LC475 had just been launched and Computer Warehouse (ol' CW) had a spread in MacUser advertising LCs at £250.  Oooh, I thought.  I can afford that.  It might be slower than the SE/30 - but colour.  I'll have a punt.  But wait!  How much for an LCII?  £350.  Hey - I can afford that too.  I'll buy…  No wait.  What about an LCIII?  £500 - but for £700, we'll throw in a trinitron Apple monitor - and for £800 you can have a special bundle with a Stylewriter II.  £800?  Shite.  That busts my budget…  But I want.  Badly.  One loan later, and I had my Mac.  And I still have it - except that it doesn't seem to work at the moment.

The LCIII does boot.  From the floppy disks that it came with. It refuses to believe that there might be a hard drive connected though.  Troubleshooting time.

1. Try another hard drive (no dice on any of the four I tried)

2. Plug hard drive into my Quadra (works - all four do).  So the hard disks aren't at fault.

3. Try a different logic board.  Yes, I have a spare LCIII logic board.  Same result.

4. Try a different PSU (in case the PSU isn't producing enough current to power logic board and hard disk - still no luck)

The caps on both boards are immaculate.  No sign of bulging, no sign of 'oiliness' on or around the caps.

The batteries are dead - but would that cause a problem on a restart (even after restarting the hard disk won't come to life)?  I haven't tried anything on the external port yet, mainly because I can't find the PSU for my zip drive.

I'm keen to get my old pal up and running again.  Has anyone seen anything similar or got any cunning plans?

The SE/30?  That works just fine (but I have recapped it).

 

[TheWhiteFalcon]

Did you replace the cable?

 

[uniserver]

there is a cap right next to the scsi chip, and that cap leaks into the scsi chip as well.

its a problem with the LC-III there is also a spot where the solder mask was not good for some boards and a trace gets eaten through that you can check.  if you have not changed all the caps, regardless of how well you think they look need to be changed.

and that is a fact.

 

[VMSZealot]

@uniserver - Two logic boards, both of which were working a couple of months ago, now display the same fault at the same time?  Is that not a bit of a coincidence?

 

[uniserver]

sure maybe you have bad luck.  or maybe you need to recap them... that sounds like a good idea.

 

[VMSZealot]

Damn.  Recap then.  I suppose I should do my Q650 at the same time - even though it works perfectly.

Could a flat battery cause a problem like this too?

I will test with the Zip drive first though.

 

[olePigeon]

Can you test the voltage?  It's possible the power supply could be going bad and the HDDs aren't getting enough power.

 

[uniserver]

yeah cap that 650 too.  it needs is. for sure.  the only machines that ( need ) a pram battery is the quadra/LC 475/605 and the Powermac 6100. you will get no video.       Well the Mac II and IIx and IIfx as well, they need the batt to kick on the psu.   otherwise most all the other 68k vintage mac's will run with out a pram battery installed.

 

[uniserver]

oh and what Doug said too... those TDK LC power supplies are known for not working,  they need all the filter caps changed. but in my experience if the psu is no good, the computer won't even turn on,  never had one where it would power up the main board but not the hard drive.

 

[madmax_2069]

I dont run a pram battery in my 475, I just use the double flip of the power switch method which bypasses that issue.

 

[Cory5412]

Although the "PizzaBox PowerToggle™" works, it's a bad idea if you plan on running the machine frequently, because what you're essentially doing is intentionally creating a power surge.

What I did last time I ran my 475 with any amount of frequency was built it a 3.0-volt battery using two AAs and just wired the whole thing in. Somebody with more patience and resources than fourteen-year-old-Cory could buy or build an AA holder for two batteries and wire it up to work well. As far as I've ever been able to tell, using 3.0V instead of 3V in that situation works well, but somebody else with some more EE credentials than I've got might have more information on why that's a bad idea.