Apple IIe (clone) problems

13 posts / 0 new
Last post
Offline
Last seen: 1 month 4 weeks ago
Joined: Oct 4 2018 - 09:15
Posts: 4
Apple IIe (clone) problems

Hello there, this is my first post.

 

I have a Brazilian Apple IIe clone, named Tk-3000. It was produced in 1986 and worked fine for many years, up to a few years ago. The first problem was that the disk drives began to fail, but I could still boot to AppleSoft Basic (but that is not the topic for today). Then it started to show memory corruption and loss of video signal. I have been trying to troubleshoot it for a long time now, with no success, so I found this forum hoping someone could offer some advice.

 

My setup:
I have removed all addon boards, leaving only keyboard and display attached to the motherboard (pic0).
The video connector is a RCA composite video which I plug into a modern flat TV (more on this later).

 

The problem:

  1. The computer boots ok, everything seem to be fine, I can run some simple BASIC programs (pic1 & pic2).
  2. After a few minutes, though, the video signal starts to flicker (pic3).
  3. It gets worse and sometimes the TV can not recognize the signal anymore (pic4).
  4. Sometimes the signal comes back to normal on its own, sometimes it comes back after a full reset (Ctrl-Apple-Reset), only to start flickering again.
  5. Sometimes, during the flickering, some garbage characters appear on the screen and/or the computer freezes (pic5).
  6. Booting into self test mode sometimes it works (pic6), sometimes not (pic7).
  7. After some point, the computer is no longer usable. If I turn it off for a looong time, it usually goes back to the begining (boots ok).

 

What I have tried:

  1. Measured the voltages with a multimeter while computer was on (all voltages seemed ok, even during the flickering).
  2. Visually inspected the capacitors on the motherboard, none showed obvious signs of leaks.
  3. Reseated all ICs (all of them are socketed), problem persisted.
  4. Tried three different display setups, all giving the same problem:

  Computer -> RCA cable -> LCD TV with composite Input
  Computer -> RCA cable -> RCA2HDMI adapter -> LCD TV with HDMI input
  Computer -> RCA cable -> RCA2VGA adapter -> Monitor with VGA input
  * I do not have an old tube TV to test with.

 

Does anyone recognize these simptoms ? What should I try next ?
(I have a bunch of spare 74XXX logic ICs, and have also ordered some 4164 RAM ICs)
(I do not have an oscilloscope)

Best regards,
migueletto.

 

 

AttachmentSize
Image icon Boot ok1.31 MB
Image icon Program running1.59 MB
Image icon Flickering1.84 MB
Image icon Very bad flickering1.73 MB
Image icon Garbage / freezing1.47 MB
Image icon Self test OK1.17 MB
Image icon Self test not OK1.38 MB
Image icon Motherboard 1.69 MB
Image icon Black pins64.76 KB
Image icon Measuring voltages on the board1.43 MB
Image icon VIA pads468.78 KB
macnoyd's picture
Online
Last seen: 58 min 31 sec ago
Joined: Oct 15 2012 - 08:59
Posts: 361
I've seen this before but

I can't give you a specific answer, only things to look for.

My first thought is "corrosion on the motherboard".  Looking at your photo, I can't really tell of you have corrosion on the board or not.  But you have enough VIA's exposed on the top that makes me think you have corrosion on the board.  Look at the solder over the VIA pads and see if the solder is gray and oxydized.  Also look around the base of the IC sockets for any white film-like substance.  If you see  any, it's likely you have corrosion underneath the sockets that can only be addressed by socket removel/cleaning/new socket replacement.  If you see corrosion on the legs of IC's, you can clean them as a temporary measure, but chances are that the occurrence will happen again with humidity and time.

It's a good idea to carefully extract each IC and re-insert upon inspection.  This will take some time to do.

 

Some have taken a chance to "radically" clean their motherboards by removing all chips, running the motherboard through a dish wash cycle, then rincing the board thoroughly with a final rince in distilled (or D-I) water, then using dry shop air to blow the chip sockets dry, then leaving out in the sun for a complete dry before repopulating the board again.  A double-edged sword using this method because it can make a corroded trace worse if there is any moisture left on it over time.  You have to be really careful to dry the board completely using this method.

 

I had a motherboard with an issue similar to yours and I ended up replacing ALL the sockets, but this isn't something most folks would do to save a motherboard.

 

One final thought... It's possible that the power supply is failing, particularly on the +12V side.  You might want to keep that in mind before digging too deep into the motherboard.  If you have a good spare supply you can swap, that would eliminate the supply one way or the other.

 

There are folks here (like SpeedyG and others) that have really good info posted on-line regarding troubleshooting the motherboard.  I'm sure they'll chime in at some stage to point you in a proper direction should you decide to dig deeper beyond cleaning.  Good luck in your quest!

 

 

Online
Last seen: 22 min 51 sec ago
Joined: Jul 5 2018 - 09:44
Posts: 165
Have you metered the power

Have you metered the power supply?  Especially when it is going flaky?  Maybe your voltages are off.  Power supplies can be heat sensitive.  They can work fine when cool but then start to drift as they heat up.  Bad voltage levels can cause all sorts of weird and anomolous behavior.

 

Offline
Last seen: 7 hours 52 min ago
Joined: Aug 4 2018 - 21:59
Posts: 94
When you checked your power

When you checked your power supply, did you check AC readings or just DC?

Your symptoms sound like failing output filter capacitors in your power supply.

Online
Last seen: 22 min 51 sec ago
Joined: Jul 5 2018 - 09:44
Posts: 165
I agree with David.  Bad

I agree with David.  Bad voltages, especially on the 12V supplies can also cause disk failures, because the drive motors and steppers use a lot of 12V juice.

 

Offline
Last seen: 1 month 4 weeks ago
Joined: Oct 4 2018 - 09:15
Posts: 4
Update

Thanks for all replies. Here are some updates.

The solder points on top of VIA pads vary in aspect, ranging from shiny to dark gray. I have uploaded a picture showing some of them, although the quality is not great.

Another thing I have not mentioned: the back of the motherboard has some jump wires and a couple of discrete componeted added, but they appear to be fine. I guess it was the common practice of hiding last minute fixes under the hood.

Upon close examination, I have found that two 74LS74 ICs had blackened pins (see picture). The sockets did not appear to be damaged though. I have replaced the 7474s, but nothing changed.

Regarding the power source, I have only the original one. To measure the voltages, I raised the power source connector a little bit and placed alligator clips on the male pins on the motherboard (see picture). Today I measured it again, this time leaving the computer on for several minutes. Here is what I got:

  •     +12V: +11.48 to +11.60
  •     -12V: -11.27 to -11.32
  •     +5V: 5.02 to 5.03
  •     -5V: -5.04

None of the voltages were fluctuating beyound those values, even during the bad flickering. Maybe I should measure the voltages elsewhere on the board ?

Another observation: some of the ICs got really hot, especially a 74LS245 (enought to hurt if I leave my finger for just 2 seconds). Since I had a spare, I swaped it, but the new one still got hot. I also measured the voltage between VCC and GND of this and other ICs, always gettimg a consistent +4.98V.

 

Best regards,

migueletto.

 

Online
Last seen: 22 min 51 sec ago
Joined: Jul 5 2018 - 09:44
Posts: 165
Your 12V and -12V are a

Your 12V and -12V are a little weak, like your +5V and -5V they should be if anything just slightly above spec on an unloaded system.  That may or may not be the problem, but it would certainly be interesting to try a known good power supply.

 

 

 

Offline
Last seen: 7 hours 52 min ago
Joined: Aug 4 2018 - 21:59
Posts: 94
The DC level is only part of

The DC level is only part of the picture, AC ripple is critical unless you check that on an old power supply you are just wasting your time.

Offline
Last seen: 1 month 4 weeks ago
Joined: Oct 4 2018 - 09:15
Posts: 4
Just a quick update

There was definitely an issue with the power source, so until I can figure out what to do with it, I tried something else to continue testing the system. I took a modern ATX power source and made connectors to plug +5V, +12V, -12V and GND into the motherboard. For -5V the solution was to use a 7905 regulator (-12V -> -5V). The ratings on the ATX PSU are more than enough to handle the load on the Apple II/e board. So far the system has been running for four straight hours without a single glitch. Even the RAMWorks clone card works, memory test is OK, 80 columns is also working. Unfortunately, the DiskII clone card still refuses to work. Drive head makes that characteristic sound on boot, disk spins, but that is all. It looks like nothing is beeing read from the disk. Anyway, I wil post an update if I make any progress.

 

Online
Last seen: 22 min 51 sec ago
Joined: Jul 5 2018 - 09:44
Posts: 165
Have you tried replacing the

Have you tried replacing the 74LS125 on the Disk II analog card?  That chip often blows.  It is known as the "fuse chip".

 

Online
Last seen: 22 min 51 sec ago
Joined: Jul 5 2018 - 09:44
Posts: 165
One easy way to get a good

One easy way to get a good power supply for your //e clone is just to buy a new one:

 

https://www.reactivemicro.com/product/ultimate-universal-power-supply/

 

You can also replace the board in your original with one like this:

 

https://www.reactivemicro.com/product/universal-psu-kit/

 

The DIY option is slightly cheaper.

 

The even more DIY option is to rebuild your existing power supply board.  Since it is a clone there is a lot less info on what would need to be replaced than if it were an Apple branded power supply.

 

Other options would be to try to find another Apple II power supply used, like off eBay, etc.

 

Offline
Last seen: 1 month 4 weeks ago
Joined: Oct 4 2018 - 09:15
Posts: 4
I came across that Universal

I came across that Universal Power Supply site some time ago. The unfortunate reality is that, because of indecent import rates down here, buying a $100 product from the US would cost me the equivalent of probably $400 (plus shipping). About rebuilding it, you are right. It is different from Apple branded power sources I have seen on the net. For now the franken-power-source is good for testing. When it comes the time to assemble everything, however, I guess I will have to source all those components.

Online
Last seen: 22 min 51 sec ago
Joined: Jul 5 2018 - 09:44
Posts: 165
I hate the way some countries

I hate the way some countries really rip off their citizens on import/exports, it really sucks.  Shipping internationally is a huge hassle and expensive in general, even to places that don't have obscene import duties.

 

 

Log in or register to post comments