Repairing an early Apple ][+ [message #369186] |
Wed, 20 June 2018 20:48 |
|
Originally posted by: frank_o_rama
Hello All!
I recently picked up a super-clean, low serial (12xxx), late 1979 dated, Apple ][+ which is unfortunately riddled with problems. I was hoping to get some advice on how to repair this machine.
When I started off, it had a couple loose chips (555 - no cursor) and was crashing to monitor on startup which I traced to a bad D0 ROM chip. Luckily the '79 dated 6502 works, as does all 48k of the RAM. Fixed those pretty easily and then ran into some video glitching issues. Video output is pretty bright (background is grey rather than black), and suffers from vertical bars with graphics modes on (green vertical stripe on the far left edge). Sometimes it leaves the color on when going back to text mode, as well. Additionally, once it heats up there are some intermittent sync issues with horizontal and vertical. Some fringing on the upper-right side of the screen when this happens as well (the image "slides" off the sides of the screen). Do I need to check the master clock to see if it's off? Or maybe the video counters? I swapped a couple chips in the video circuit with working ones which didn't change anything.
The keyboard is a Datanetics with what I believe to be a dead MM5740AAE encoder. I can only see about 2 volts on the outputs that are on. Some are always off. The outputs do not change when I hit the keys. I think I have a line on a replacement chip, but wanted to know if there was a better way to test these encoder chips.
Lastly, testing the power supply, there's no -12 volts present. It's the earlier Astec style used on the ][ (Astec AA11040 - non "B" version). The top model number has been hand-overwritten with a "30" at the end. Is this worth keeping original and doing a re-cap, or should I just remove the interior and replace it with a ReactiveMicro Universal PSU? I have a spare working unit that I can use in the interim for testing, etc.
Thanks for any thoughts.
Frank
|
|
|
Re: Repairing an early Apple ][+ [message #369211 is a reply to message #369186] |
Thu, 21 June 2018 10:19 |
|
Originally posted by: Mark D. Overholser
On 20-Jun-18 17:48, frank_o_rama@hotmail.com wrote:
>
> Hello All!
>
> I recently picked up a super-clean, low serial (12xxx), late 1979
> dated, Apple ][+ which is unfortunately riddled with problems. I was
> hoping to get some advice on how to repair this machine.
>
Congratulations on you find...
> When I started off, it had a couple loose chips (555 - no cursor) and
> was crashing to monitor on startup which I traced to a bad D0 ROM
> chip. Luckily the '79 dated 6502 works, as does all 48k of the RAM.
> Fixed those pretty easily and then ran into some video glitching
> issues. Video output is pretty bright (background is grey rather than
> black), and suffers from vertical bars with graphics modes on (green
> vertical stripe on the far left edge). Sometimes it leaves the color
> on when going back to text mode, as well. Additionally, once it heats
> up there are some intermittent sync issues with horizontal and
> vertical. Some fringing on the upper-right side of the screen when
> this happens as well (the image "slides" off the sides of the
> screen). Do I need to check the master clock to see if it's off? Or
> maybe the video counters? I swapped a couple chips in the video
> circuit with working ones which didn't change anything.
>
Sounds like it might be a Capacitor Issue...
> The keyboard is a Datanetics with what I believe to be a dead
> MM5740AAE encoder. I can only see about 2 volts on the outputs that
> are on. Some are always off. The outputs do not change when I hit the
> keys. I think I have a line on a replacement chip, but wanted to know
> if there was a better way to test these encoder chips.
>
I don't know the Normal Behavior here, so I have nothing to add..
> Lastly, testing the power supply, there's no -12 volts present. It's
> the earlier Astec style used on the ][ (Astec AA11040 - non "B"
> version). The top model number has been hand-overwritten with a "30"
> at the end. Is this worth keeping original and doing a re-cap, or
> should I just remove the interior and replace it with a ReactiveMicro
> Universal PSU? I have a spare working unit that I can use in the
> interim for testing, etc.
>
Probably Capacitors too... I have a Power Supply with the Hand Written
30 too, that makes it a 115/230 VAC Switchable Power Supply, verses the
more common 115 VAC ..
> Thanks for any thoughts.
>
> Frank
>
>
MarkO
|
|
|
|
Re: Repairing an early Apple ][+ [message #369224 is a reply to message #369212] |
Thu, 21 June 2018 14:09 |
|
Originally posted by: frank_o_rama
My power supply is serial 20547 and has the same "030" handwritten model number. There's a gold "115V ONLY" sticker where your voltage select switch is, and the power switch is "ON at top" unlike yours which looks upside down.. The switch has an bit of a flange on the top and bottom of the rocker, unlike the newer switches. It's dated April 23, 1979 (motherboard is late '79). Haven't popped the rivets yet but guessing all electrolytics are bad.
Sorry, not seeing any capacitors in the video circuitry besides the normal bypass caps, which I don't think dry out.
F
|
|
|
Re: Repairing an early Apple ][+ [message #369225 is a reply to message #369186] |
Thu, 21 June 2018 15:22 |
|
Originally posted by: James Davis
On Wednesday, June 20, 2018 at 5:48:08 PM UTC-7, frank_...@hotmail.com wrote:
> Hello All!
>
> I recently picked up a super-clean, low serial (12xxx), late 1979 dated, Apple ][+ which is unfortunately riddled with problems. I was hoping to get some advice on how to repair this machine.
>
> When I started off, it had a couple loose chips (555 - no cursor) and was crashing to monitor on startup which I traced to a bad D0 ROM chip. Luckily the '79 dated 6502 works, as does all 48k of the RAM. Fixed those pretty easily and then ran into some video glitching issues. Video output is pretty bright (background is grey rather than black), and suffers from vertical bars with graphics modes on (green vertical stripe on the far left edge). Sometimes it leaves the color on when going back to text mode, as well. Additionally, once it heats up there are some intermittent sync issues with horizontal and vertical. Some fringing on the upper-right side of the screen when this happens as well (the image "slides" off the sides of the screen). Do I need to check the master clock to see if it's off? Or maybe the video counters? I swapped a couple chips in the video circuit with working ones which didn't change anything.
>
> The keyboard is a Datanetics with what I believe to be a dead MM5740AAE encoder. I can only see about 2 volts on the outputs that are on. Some are always off. The outputs do not change when I hit the keys. I think I have a line on a replacement chip, but wanted to know if there was a better way to test these encoder chips.
>
> Lastly, testing the power supply, there's no -12 volts present. It's the earlier Astec style used on the ][ (Astec AA11040 - non "B" version). The top model number has been hand-overwritten with a "30" at the end. Is this worth keeping original and doing a re-cap, or should I just remove the interior and replace it with a ReactiveMicro Universal PSU? I have a spare working unit that I can use in the interim for testing, etc.
>
> Thanks for any thoughts.
>
> Frank
Call (or Send it to) an "Apple Authorized Sales & Service" Center, like this one:
Computer Center of Hayward
23951 Mission Blvd.
Hayward, CA 94544, U.S.A.
www.ccoh.com
Showroom # 1-510-733-1843
Service # 1-510-733-1846
Fax # 1-510-733-1855
Mon.-Fri. 10am-6pm (Pacific Time)
Sat. 10am-3pm
Closed Sundays
|
|
|
Re: Repairing an early Apple ][+ [message #369247 is a reply to message #369186] |
Thu, 21 June 2018 18:37 |
Michael J. Mahon
Messages: 1767 Registered: October 2012
Karma: 0
|
Senior Member |
|
|
<frank_o_rama@hotmail.com> wrote:
>
> Hello All!
>
> I recently picked up a super-clean, low serial (12xxx), late 1979 dated,
> Apple ][+ which is unfortunately riddled with problems. I was hoping to
> get some advice on how to repair this machine.
>
> When I started off, it had a couple loose chips (555 - no cursor) and was
> crashing to monitor on startup which I traced to a bad D0 ROM chip.
> Luckily the '79 dated 6502 works, as does all 48k of the RAM. Fixed those
> pretty easily and then ran into some video glitching issues. Video output
> is pretty bright (background is grey rather than black), and suffers from
> vertical bars with graphics modes on (green vertical stripe on the far
> left edge). Sometimes it leaves the color on when going back to text
> mode, as well. Additionally, once it heats up there are some intermittent
> sync issues with horizontal and vertical. Some fringing on the
> upper-right side of the screen when this happens as well (the image
> "slides" off the sides of the screen). Do I need to check the master
> clock to see if it's off? Or maybe the video counters? I swapped a couple
> chips in the video circuit with working ones which didn't change anything.
The sync issues are not the result of anything in the digital logic.
Assuming that the monitor is properly adjusted, the black level and sync
instability are the result of improper voltages powering the video output
mixer. When the -12v is fixed, those problems will be fixed.
> The keyboard is a Datanetics with what I believe to be a dead MM5740AAE
> encoder. I can only see about 2 volts on the outputs that are on. Some
> are always off. The outputs do not change when I hit the keys. I think I
> have a line on a replacement chip, but wanted to know if there was a
> better way to test these encoder chips.
Without referring to the schematic, I’d bet that power supply voltages are
the problem here, too.
Don’t attempt to do troubleshooting on a system that does not have proper
voltages applied. Missing or improper voltages can result in almost any
kind of consequent misbehavior!
> Lastly, testing the power supply, there's no -12 volts present. It's the
> earlier Astec style used on the ][ (Astec AA11040 - non "B" version). The
> top model number has been hand-overwritten with a "30" at the end. Is
> this worth keeping original and doing a re-cap, or should I just remove
> the interior and replace it with a ReactiveMicro Universal PSU? I have a
> spare working unit that I can use in the interim for testing, etc.
If the +5v is good, most of the power supply is working properly. The other
three voltages are simple transformer windings, diodes, and filter
networks. A *very* leaky electrolytic could load a secondary output,
lowering its voltage, but this seems unlikely (since a little more
electrical leakage, bordering on a short, would cause the power supply to
shut down cyclically).
I expect the -12v is missing because of: 1) a faulty connector, 2) a broken
printed circuit trace (possibly inside the power supply), or 3) an open
Schottky diode in the -12v power supply circuit.
I’d recommend (temporarily) substituting a known-good power supply before
doing any further system testing.
> Thanks for any thoughts.
>
> Frank
>
>
>
--
-michael - NadaNet 3.1 and AppleCrate II: http://michaeljmahon.com
|
|
|
Re: Repairing an early Apple ][+ [message #369322 is a reply to message #369225] |
Fri, 22 June 2018 11:30 |
|
Originally posted by: frank_o_rama
They'll just swap my Rev 4 board for a newer revision one without the authentic vertical black line on the left hand side of the image.
Also, I'm in Portland, Oregon.
f
On Thursday, June 21, 2018 at 12:22:11 PM UTC-7, James Davis wrote:
>
> Call (or Send it to) an "Apple Authorized Sales & Service" Center, like this one:
>
> Computer Center of Hayward
|
|
|
Re: Repairing an early Apple ][+ [message #369323 is a reply to message #369247] |
Fri, 22 June 2018 11:34 |
|
Originally posted by: frank_o_rama
On Thursday, June 21, 2018 at 3:37:40 PM UTC-7, Michael J. Mahon wrote:
>
> The sync issues are not the result of anything in the digital logic.
>
> Assuming that the monitor is properly adjusted, the black level and sync
> instability are the result of improper voltages powering the video output
> mixer. When the -12v is fixed, those problems will be fixed.
>
I'm not seeing a video mixer in the schematic. There's just a 2N3904 after the 3 video lines tie together. Whatever component is bad, it gets worse and more frequent as it warms up.
> Don’t attempt to do troubleshooting on a system that does not have proper
> voltages applied. Missing or improper voltages can result in almost any
> kind of consequent misbehavior!
My guess is that when the original power supply failed, it took out a bunch of other chips on the -12v line.
>
> I’d recommend (temporarily) substituting a known-good power supply before
> doing any further system testing.
>
Have that one covered! Still doesn't work.
f
|
|
|
Re: Repairing an early Apple ][+ [message #369335 is a reply to message #369323] |
Fri, 22 June 2018 14:26 |
Michael J. Mahon
Messages: 1767 Registered: October 2012
Karma: 0
|
Senior Member |
|
|
<frank_o_rama@hotmail.com> wrote:
> On Thursday, June 21, 2018 at 3:37:40 PM UTC-7, Michael J. Mahon wrote:
>>
>> The sync issues are not the result of anything in the digital logic.
>>
>> Assuming that the monitor is properly adjusted, the black level and sync
>> instability are the result of improper voltages powering the video output
>> mixer. When the -12v is fixed, those problems will be fixed.
>>
>
> I'm not seeing a video mixer in the schematic. There's just a 2N3904
> after the 3 video lines tie together. Whatever component is bad, it gets
> worse and more frequent as it warms up.
Yep, it’s the 3904 and surrounding circuitry. That’s what mixes the video,
blanking, and sync pulses.
Do you have access to an oscilloscope? A look at the composite output and
any changes with time would simplify diagnosis.
There are a few resistors that establish the relative levels of the signals
in the composite output and their DC levels. It could be a problem with any
of the resistors or the transistor.
The leakage of some color burst when in text mode was a well known problem
with early ][‘s and ][+’s. Apple fixed it by adding another gate in the
“prototyping area” of the board. The problem is that some color
monitors/TVs were very sensitive to even a very low amplitude color burst,
and stayed in color mode.
The sync changes associated with warmup are much more typical of monitor
drift, not system drift. But if sync levels are marginal, monitor drift
that is insignificant with normal sync levels could show up.
Have you tried leaving the monitor on with system cooling down, then
turning on? Or vice versa. That would localize the warmup phenomena to the
monitor or the system.
>
>> Don’t attempt to do troubleshooting on a system that does not have proper
>> voltages applied. Missing or improper voltages can result in almost any
>> kind of consequent misbehavior!
>
> My guess is that when the original power supply failed, it took out a
> bunch of other chips on the -12v line.
There’s not much connected to -12v, but a power supply spike can be
damaging. Still, don’t assume the worst. Most of your system is working
fine. ;-)
>>
>> I’d recommend (temporarily) substituting a known-good power supply before
>> doing any further system testing.
>>
>
> Have that one covered! Still doesn't work.
OK.
> f
>
>
--
-michael - NadaNet 3.1 and AppleCrate II: http://michaeljmahon.com
|
|
|
Re: Repairing an early Apple ][+ [message #369375 is a reply to message #369322] |
Fri, 22 June 2018 20:21 |
|
Originally posted by: James Davis
On Friday, June 22, 2018 at 8:30:28 AM UTC-7, frank_...@hotmail.com wrote:
> They'll just swap my Rev 4 board for a newer revision one without the authentic vertical black line on the left hand side of the image.
>
> Also, I'm in Portland, Oregon.
>
> f
>
>
>
> On Thursday, June 21, 2018 at 12:22:11 PM UTC-7, James Davis wrote:
>>
>> Call (or Send it to) an "Apple Authorized Sales & Service" Center, like this one:
>>
>> Computer Center of Hayward
They probably would if they could, but probably would not have one to swap in.
But they might have some good advise (like MJM's) for you if you call them.
Aren't there any Apple repair places in Portland, Oregon, to ask at? MJM lives up that way, I think. You two should get together and form an Apple II repair association.
|
|
|
Re: Repairing an early Apple ][+ [message #369526 is a reply to message #369335] |
Mon, 25 June 2018 01:18 |
|
Originally posted by: frank_o_rama
the prototype area on this board is empty. Haven't pulled the CPU to check the revision but it can't be later than 4 based on what components it has. I guess I've only known "RFI" boards so I was unaware of those issues. This is the oldest apple I've had.
Monitor is a new-ish HDTV which works fine with my others.
I'll check those parts on my scope and hope it's an easy fix. Also going to check the datanetics key switches to see if any are stuck on. could be a reason the encoder isn't changing values.
f
|
|
|
Re: Repairing an early Apple ][+ [message #369580 is a reply to message #369526] |
Mon, 25 June 2018 16:52 |
|
Originally posted by: frank_o_rama
Looks like it's a bad 200 ohm "video level" potentiometer after the transistor. Was reading 130 ohms or so. Everything else seems fine so hoping that's the end of that once I get parts. (SurplusGizmos.com on Cornelius Pass Road is closed Mondays ;) --FYI awesome electronic parts and surplus store for anyone local to Portland)
Thanks for the advice Michael.
f
|
|
|
Re: Repairing an early Apple ][+ [message #369625 is a reply to message #369580] |
Tue, 26 June 2018 12:50 |
Michael J. Mahon
Messages: 1767 Registered: October 2012
Karma: 0
|
Senior Member |
|
|
<frank_o_rama@hotmail.com> wrote:
>
> Looks like it's a bad 200 ohm "video level" potentiometer after the
> transistor. Was reading 130 ohms or so. Everything else seems fine so
> hoping that's the end of that once I get parts. (SurplusGizmos.com on
> Cornelius Pass Road is closed Mondays ;) --FYI awesome electronic parts
> and surplus store for anyone local to Portland)
>
> Thanks for the advice Michael.
>
> f
>
You’re very welcome, Frank—and thanks for the pointer to SurplusGizmos!
--
-michael - NadaNet 3.1 and AppleCrate II: http://michaeljmahon.com
|
|
|