You are not logged in.

#1 2014-11-08 14:11:09

iMic
Administrator
From: Adelaide, Australia
Registered: 2014-05-12
Posts: 891
Website

Europlus Power & Floppy Drive Issues

We had a brief demonstration of vintage computers here a couple of nights back. For the most part it went well, other than a small mishap we had with the Apple II. Because I rushed through setting up the machines, it seems I connected the 5.25" floppy drive to the controller card one row of pins over. Presumably this shorted the system, because the PSU started to crackle and squeal, followed by the smell of burning electronics.


After I disconnected the card and drive, the machine started up into AppleSoft BASIC without any issues, but it didn't sound too healthy. The PSU was still making a faint hissing sound (mind you, it did this before the incident as well). I shut it off and haven't powered it up since.


I removed the PSU covers and noticed that the board does still have some residue left over from when the EMI Suppression Caps blew open last year. Presumably the other capacitors, being 32 years old, aren't that healthy either. If I smell around the PSU, there's a strong smell where the residue remains, but nothing that smells like burning electronics, as would likely be expected after a component has fried.


I'm thinking of recapping the PSU then re-testing the system. Considering it still boots into AppleSoft BASIC, the machine should still be repairable. If it doesn't start up into ProDOS from the FDD, chances are the drive electronics or controller card has burned out.


Just curious to see if anyone has anything else in mind that I should check before I perform any repairs.


Thanks,

iMic.


Resident Professor of Alternative Methodology
Faculty of Macintosh Restorations & Modifications - "It works, let's fix it!"

Offline

#2 2014-11-08 16:55:24

ClassicHasClass
Member
From: Electron Alley
Registered: 2014-05-26
Posts: 1,106
Website

Re: Europlus Power & Floppy Drive Issues

You probably killed the controller, not the PSU. And believe me, you weren't the only person who ever did that.

Offline

#3 2014-11-08 18:11:18

iMic
Administrator
From: Adelaide, Australia
Registered: 2014-05-12
Posts: 891
Website

Re: Europlus Power & Floppy Drive Issues

Well the PSU needs work anyway, since the capacitors in there are 32 years old (it's a 1982 ASTEC). The noises it was producing when powered up were definitely coming out of the power supply, but I wouldn't be surprised if that was a case of an already degraded unit trying to handle an overload.

The controller card is some kind of no-name thing. Not sure if I'll bother fixing it or whether I should find a genuine Apple card. See post below.

IMG_4974.jpg

IMG_4975.jpg


Resident Professor of Alternative Methodology
Faculty of Macintosh Restorations & Modifications - "It works, let's fix it!"

Offline

#4 2014-11-08 18:35:15

iMic
Administrator
From: Adelaide, Australia
Registered: 2014-05-12
Posts: 891
Website

Re: Europlus Power & Floppy Drive Issues

The PSU is now running happily, so chances are the squealing was one of the capacitors. The machine still recognises the presence of the drive controller card (I need to hit RESET to enter AppleSoft BASIC with the card installed), which is a positive sign.

It could be the drive itself, according to this AppleFritter thread. It does smell a bit crispy, although that could be the fumes from the fresh grease in there. It powers up and initialises correctly, but no data is requested from the disk. I'll take the covers off and see what the chips look like.


Also, another small issue, but I noticed the POWER light on the Apple II's keyboard no longer lights up. It's always had issues, but in the past I've been able to lightly tap it to make it work. Now it doesn't work at all. Does anyone know what kind of LED or bulb these take?



UPDATE: After reading this article, I inspected the drive electronics and sure enough, I found the source of the burning silicon smell - the 74LS125 chip. Looks like I found the cause of the problem. The part number of this chip is 201 T HD74LS125AP, looks like a Renesas (Datasheet Here).

Interestingly, both Jaycar Electronics and Element14 appear to have 74LS125 chips in stock. Looking at the Jaycar datasheet for the Texas Intruments chip, this look to be the correct part.

Element14 - TEXAS INSTRUMENTS - SN74LS125AN - IC, BUS BUFFER
Jaycar - 74LS125 Quad Tri-State Buffer IC

I need to place an order to Element14 soon anyway, and Jaycar is only a short drive from here, so if either of them can be used then I should be set to make this drive work again.


IMG_7335.jpg

Last edited by iMic (2014-11-08 19:13:04)


Resident Professor of Alternative Methodology
Faculty of Macintosh Restorations & Modifications - "It works, let's fix it!"

Offline

#5 2014-11-09 00:43:11

mcdermd
Member
From: Corvallis, OR
Registered: 2014-05-12
Posts: 970
Website

Re: Europlus Power & Floppy Drive Issues

I have the bulb type written down someplace at work. I had a somewhat difficult time attacking them down but eventually found them at a somewhat local electronic supply company. I made sure to pick up half a dozen.


Daily Drivers: 27" iMac 2.8 GHz Quad-Core i7 (Late 2009), 21.5" iMac 2.7GHz Quad-Core i5 (Late 2013), 11" Macbook Air 1.6 GHz i5 (Mid-2011)
See the restored heroes here.

Offline

#6 2014-11-09 02:34:20

techknight
Member
Registered: 2014-05-22
Posts: 449

Re: Europlus Power & Floppy Drive Issues

Hey, i think that 74LS125 is broken... lol Cant quite put my finger on it, but i think its dead jim.

Last edited by techknight (2014-11-09 02:34:45)

Offline

#7 2014-11-09 07:17:15

iMic
Administrator
From: Adelaide, Australia
Registered: 2014-05-12
Posts: 891
Website

Re: Europlus Power & Floppy Drive Issues

techknight wrote:

Hey, i think that 74LS125 is broken... lol Cant quite put my finger on it, but i think its dead jim.

I couldn't see it from a visual inspection, but it does look a little char-grilled underneath in that photo. Looks like the camera flash may have uncovered something that I didn't. I'll remove the chip soon and take another look.


Resident Professor of Alternative Methodology
Faculty of Macintosh Restorations & Modifications - "It works, let's fix it!"

Offline

#8 2014-11-09 12:10:47

volvo242gt
Member
From: Duvall, WA
Registered: 2014-05-22
Posts: 409
Website

Re: Europlus Power & Floppy Drive Issues

You may want to go ahead and replace the MC3470P amplifier chip as well.  They also tend to get cooked when the disk ][ connector is off one pair of pins.  Seems about 50% of the time it's only the 125, and the rest of the time it's both that have popped.

-J


modern: Mac Pro 2.8GHz 8-core 6GB/500G/DVD-RW, A1150 MBP 2GHz CD, 2GB/80G/DVD-RW
Pre-Mac: ][+, //e
other: iPhone 6s 128GB Space Gray

Offline

#9 2014-11-09 14:42:54

iMic
Administrator
From: Adelaide, Australia
Registered: 2014-05-12
Posts: 891
Website

Re: Europlus Power & Floppy Drive Issues

I'll have to inspect it and take my chances. The MC3470P isn't anywhere near as common - as a matter of fact none of my suppliers have anything close to it.


Resident Professor of Alternative Methodology
Faculty of Macintosh Restorations & Modifications - "It works, let's fix it!"

Offline

#10 2015-02-13 15:14:45

iMic
Administrator
From: Adelaide, Australia
Registered: 2014-05-12
Posts: 891
Website

Re: Europlus Power & Floppy Drive Issues

I replaced the 74LS125. It didn't work at first immediately after installing the chip, but after leaving it for a few hours, it had no problems starting the machine up from an ADTPro boot disk.

I thought it was about time those old capacitors were replaced as well.


A2_PSU.jpg


It's working alright so far. The repair was somewhat tedious since some of the solder pads in the PSU were only held down by the soldered component leads themselves, but since these tracks were rather large, it was easy enough to just stick the traces back down and solder to them to brace them up.


Resident Professor of Alternative Methodology
Faculty of Macintosh Restorations & Modifications - "It works, let's fix it!"

Offline

#11 2015-02-14 15:21:50

iMic
Administrator
From: Adelaide, Australia
Registered: 2014-05-12
Posts: 891
Website

Re: Europlus Power & Floppy Drive Issues

She good.

IMG_7933.jpg


Resident Professor of Alternative Methodology
Faculty of Macintosh Restorations & Modifications - "It works, let's fix it!"

Offline

#12 2015-07-08 03:43:45

Elfen
Member
From: NYC, NY
Registered: 2015-07-07
Posts: 20

Re: Europlus Power & Floppy Drive Issues

The Disk Card is a cloned card, not of Apple's originals unless it an older Apple I/II card. The II/II+ cards have 2 PALs on it with 4 other chips, two are 74XX/X series. Depending on how off you were when you inserted the cable one of the two blows along with the 74LS125 in the drive. In this case you got lucky that the chips on the card didn't blow.

Depending on which of the two are blown on the card, the symptoms are as follows, though I forget which chip causes the symptoms:

- if one blows, the disk drive acts normally but does not read. The head goes into a magnetic high and erases the disk in the drive. After replacing the chips, you need to demagnetize the drive's head.

- if the other fails, the 74LS125 in the drive goes with it, making it a killer card as it kills any drive you attach to it. It may also blow the 2003A (the chip by the edge connector) as well. 50% of the time the 2003A goes in this case but I replace it anyway as a "wounded" 2003A will not show symptoms of failure until months later, leaving you scratch you head as to what is going on.

Offline

Board footer

About ThinkClassic

ThinkClassic specialises in the maintenance, repair, restoration and modification of Vintage Apple and Macintosh computers. Ask questions and find answers about classic Apple desktops, laptops, accessories and peripherals.