Mac Plus screen repair

[mcmikey]

Another Mac Plus startup problem!

Hi,
I stumbled across this thread while I was trying to find a solution to my problem, and you guys seem quite knowledgable

When I switch it on it produces a continuous tone - slightly "rough" sounding - for 14 seconds. All I get on the screen is a single horizontal line in the middle. If I take out the RAM or unplug the logic board I get nothing. A friend has been over the analog board and can find nothing amiss (that's not necessarily a guarantee mind you...) and I have re soldered the usual connectors. I would like to know if it sounds like a logic board failure or an analog board failure.

Cheers,
Mike

 

[keysersoze]

Is it a bright horizontal line? That may indicate problem with the vertical sweep circuit.

"The major cause of this trouble is either of (1) connection failure due to ageing and/or cracks in the soldering of the P1 connector, or (2) troubles of the vertical sweep IC chip at reference U2 (12-pin TV, TDA1170A) on the analog board."

http://www.jagshouse.com/classicrepair.html

 

[mcmikey]

Thanks for the reply. I've been on that site before and done most of the things there. I haven't replaced the IC yet because I'm not entirely sure that is the problem. The fact that things change if the RAM is removed started me thinking in the direction of the logic board. If it is definitely this IC I'll certainly have a go at replacing it!

Cheers,
Mike

 

[MacTech68]

Just a sec - if this is a MacPlus, it doesn't yet use the TDA1170 vertical IC. - the SE, MacClassic and ClassicII use the TDA1170.

Instead it uses a bunch of discrete components to do the same job.

If you indeed have a MacPlus AND it is being used on 110-120Volts Mains power, AND is the 110Volt ONLY board, then these circuit references may catch the problem:

First, check the 4 pin yoke connector for bad solder joints or burnt pins.

check shorted CR15 zener diode = 1N4735 6.2V 1 Watt or 1N5234B 6.2V 1/2 Watt
check for shorted/fried Q4 = 2N4401
shorted Q2 = MPSU51
open resistor R3 = 1.5ohm 1/4 Watt
Also check Q5 = 2N5485

Check any components associated with these.

 

[mcmikey]

It is a Mac Plus - 240 volt model if that is any help. I've had it from new so I'm keen to keep
It going!

 

[MacTech68]

It is a Mac Plus - 240 volt model if that is any help. I've had it from new so I'm keen to keep
It going!

OK, if it is 240V model then those circuit references are wrong.

I'll see if i can convert them for you.


EDIT: Here it is:

check shorted CR15 zener diode = 1N4735 6.2V 1 Watt or 1N5234B 6.2V 1/2 Watt = SAME ON 240V
check for shorted/fried Q4 = 2N4401 = Q3 ON 240V
shorted Q2 = MPSU51 = Q1 ON 240V
open resistor R2 & R3 = 1.5ohm 1/4 Watt = SAME ON 240V
Also check Q5 = 2N5485 = SAME ON 240V

All these components are near the yoke connector.

 

[keysersoze]

Yikes, sorry for providing bad info. MacTech is here so you are in great hands!

 

[mcmikey]

EDIT: Here it is:

check shorted CR15 zener diode = 1N4735 6.2V 1 Watt or 1N5234B 6.2V 1/2 Watt = SAME ON 240V
check for shorted/fried Q4 = 2N4401 = Q3 ON 240V
shorted Q2 = MPSU51 = Q1 ON 240V
open resistor R2 & R3 = 1.5ohm 1/4 Watt = SAME ON 240V
Also check Q5 = 2N5485 = SAME ON 240V

All these components are near the yoke connector.

Great stuff - I'll have a look and report back!

Cheers,

Mike

 

[mcmikey]

OK I tested the Diodes and transistors as requested and they all apear to be functioning OK as far as I can tell. Below is a picture of the tracks on the logic board - I wonder if this might be the problem? I'm not sure whether to buy an anolog board or a logic board off ebay!



Cheer,
Mike

 

[MacTech68]

OK I tested the Diodes and transistors as requested and they all apear to be functioning OK as far as I can tell. Below is a picture of the tracks on the logic board - I wonder if this might be the problem? I'm not sure whether to buy an anolog board or a logic board off ebay!

Hmmm... on the face of it, you MIGHT have an etched/broken track there (or several). A quick test of suspect looking tracks with a mulimeter will quickly reveal if that is the case. Prototyping/WireWrap wire (for it's thin-ness) is ideal to jumper broken tracks.

I'll have a look at the vertical sync and see where it comes from.

 

[mcmikey]

I've since tested a few of the tracks and they all test OK. My problem with the diagnosis of faulty display circuitry is the strange beep emitted when the computer is switched on. Would the computer know the vertical sync is faulty? Quite often when you look at faulty vertical sync displays you can see some shading along the scan line that indicates an image is there, but not being displayed properly. I am just getting a bright line which would indicate the computer is not booting.

 

[MacTech68]

Unless it's connected to an external HD or floppy drive, or a floppy is inserted into the internal drive (in it's original configuration) it's not going to boot. And if the line is excessively bright, you might not see the blinking disk icon.

Have you checked the +5v and +12v ?

You should get continuity from pin 5 of the video/power connector on the logic board to:

Pin 13 of IC "LAG" at location U1E
and
Pin 40 of IC 6522 at location U11D

At least, that's where the Vsync comes from (directly). However, any other broken tracks could cause the Vsync to be inactive.

If you have access to a 128, 512, or 512ke you can swap logic boards to eliminate the logic board.

My experience is the most common cause is the 6.2volt Zener mentioned previously - but given that photo, I'm not too sure. I DO recall some tracks looking like that and still being intact.

I'd hate to purely take the 50/50 gamble on which is the culprit. Not good odds in this case.

 

[mcmikey]

I'd hate to purely take the 50/50 gamble on which is the culprit. Not good odds in this case.

The continuity is OK between those pins. Your comment about booting gave me an idea (which I may have tried before - it's been dead a couple of years) and I tried booting from a floppy. Nothing. The external drive powered up (the internal one needs some attention) but would not attempt to read the disk, which points in the direction of a logic board failure to my mind. Do you think that sounds logical?

 

[MacTech68]

The continuity is OK between those pins. Your comment about booting gave me an idea (which I may have tried before - it's been dead a couple of years) and I tried booting from a floppy. Nothing. The external drive powered up (the internal one needs some attention) but would not attempt to read the disk, which points in the direction of a logic board failure to my mind. Do you think that sounds logical?

Only IF the power to the logic board is good and within tolerance.

 

[mcmikey]

Power is OK - I've bought a new logic board off fleabay so once it arrives we'll know for sure...

 

[MacTech68]

Power is OK - I've bought a new logic board off fleabay so once it arrives we'll know for sure...

Crossing fingers - but it seems logical.

 

[mcmikey]

Crossing fingers - but it seems logical.

The Logic board arrived today. plugged it in and hey presto

 

[MacTech68]

The Logic board arrived today. plugged it in and hey presto

Phew! Glad to see it going.

 

[Renhor-Nibbor]

Hi, my name is Robbin, I'm a newbie here. I have a Mac Plus with the screen problem,
where it sometimes comes on, and other times will come on with a tap or two to the left side.
I have read this whole thread, and am still not certain of which solder joints may be responsible.
I took it out of the basement last week to check if it's still working, with intention to sell it.
I am so glad it came on the first time, or I never would have thought to check the Net for answers.
I have the mouse and keyboard with the numbers pad. I also have a Peak Systems 30 MB hard drive
in working condition. I have been able to load and use the files and apps that are on it.
I have the User Manual, and perhaps two hundred disks. Many games and applications with their manuals,
and some blank discs as well. I also have an Ergotron MacTilt mount. I'll be selling all of this,
in order to buy musical equipment for my song project (Link Below)

But all of this is useless, if I can't fix the screen problem.

I see MacTech68 is an ocean of knowledge, Hi, glad to meet you.

So, back to my issue. Can anyone give explicit instructions on how to recognize which solder joint/s
is/are the problem? Perhaps with a foto or graphic that points them out? It would be GREATLY appreciated!

Here's the project link --> http://robbin-rohners-forum.freeforums.net/thread/3/free

Me singing -->

[doublepost=1506365115][/doublepost]Oops, I didn't realize the song would appear automatically, the project link is above it.

 

[MacTech68]

Hi, my name is Robbin, I'm a newbie here. I have a Mac Plus with the screen problem,
where it sometimes comes on, and other times will come on with a tap or two to the left side...

Sorry for the late, late, late reply, Robbin. Welcome to the forum!

Intermittent faults that appear to come and go with a 'tap' to the casing are invariably these (Click for larger):





This is as the board would appear with the screen face down.

 

[Renhor-Nibbor]

Sorry for the late, late, late reply, Robbin. Welcome to the forum!

Intermittent faults that appear to come and go with a 'tap' to the casing are invariably these (Click for larger):


View attachment 731222


This is as the board would appear with the screen face down.

[doublepost=1509991835][/doublepost]Thank you so very much! The diagram is quite clear.
Do you ever do work on a Mac for hire?
If so, would you be interested in fixing my board?
International shipping for the whole Mac would be expensive,
but I could ship you just the board.

My email is robbrohn@aol.com

Robbin

 

[MacTech68]

[doublepost=1509991835][/doublepost]Thank you so very much! The diagram is quite clear.
Do you ever do work on a Mac for hire?
If so, would you be interested in fixing my board?
International shipping for the whole Mac would be expensive,
but I could ship you just the board.

My email is robbrohn@aol.com

Robbin

Shipping to Perth Australia from the US could still be more expensive, and what if it turns out to be a problem elsewhere? I appreciate your predicament, but if there is a place nearer to you that you can build a relationship with, more the better.

I have no idea about these guys - perhaps they can help:

http://noappleistoooldforus.com/

 

[Renhor-Nibbor]

Thank you for your fast reply,

I will look into that site, and evaluate it.


Now that I know where to look,

I will also look at my board again, and consider doing it myself.

I do have an excellent small point soldering iron,

and a fair amount of experience.


Thank you again, not only for myself,

but for all you have done for others.


Robbin

 

[Renhor-Nibbor]

Shipping to Perth Australia from the US could still be more expensive, and what if it turns out to be a problem elsewhere? I appreciate your predicament, but if there is a place nearer to you that you can build a relationship with, more the better.

I have no idea about these guys - perhaps they can help:

http://noappleistoooldforus.com/

[doublepost=1522435430][/doublepost]EUREKA!
After a long time since my last post, I finally made the effort to fix the screen problem.
With a magnifier, I examined all the solder joints that had been pointed out.
There were no apparent cracks, so I decided to melt the solder on them all.
I also lifted the connection to the tube several times, just in case there was any corrosion.
I actually thought it was all in vain, so when I turned it on, I was prepared for the worst.
So you can imagine my joy when it came on as it should. It has been turned on and off
quite a few times now, and I've even given it a few hard slaps to see if it would induce the problem.
I'm quite happy now

Thank you very very much!

Robbin Rohner

 

[Jose5019]

Hi! I´m Jose i have an old mac plus from my father, it was working until a summer day, the computer screen started to shake the image and suddenly turn off, when i tried to reboot, nothing works, only a repetitive sound came out. I haven´t found any solutions because here in spain, this computer is extremely rare because the majority of people had amstrad
or sinclair computers. anyone knows how to fix it