Semi-broken STE - Help!

Semi-broken STE - Help!

Post by badactres » Tue, 18 Mar 2003 06:47:47



Hi,

I just picked up a 520STE at carboot sale for 1!

Just the 'puter.. no leads or anything. I didn't really expect it to work,
but surprisingly it is showing signs of life.. I could do with some help to
nurse it back to full health though.

It powers up and checks floppy drive ok.. then maybe 50% of the time, the
GEM desktop appears, and for a few minutes I can move mouse pointer, access
menus etc.. Then the screen goes black, and the floppy disk will click and
whirr... If I leave it, the screen seems to alternate between white, fading
to black.. then suddenly white again. The change from white to black seems
to coincide with the floppy drive being accesssed.

If I switch off, then back on it will usually be ok again.. for a while..

I've opened it up and pressed down on all the socketed chips I could see (2
under floppy drive and 1 square chip in big big recessed socket to the right
under the keyboard), removed & refitted the memory simms, which seems to
have made it run a little longer before dying, but it still isn't very
happy.

I'd love to get it working so if anybody could suggest anything I'd really
appreciate any help.

Cheers!
Norm

 
 
 

Semi-broken STE - Help!

Post by Jim DeClerc » Tue, 18 Mar 2003 07:34:35


That is a good mystery. First, check the power supply voltage with a
digital voltmeter. Low voltages can cause some really strange things. If
the power supply works at all, which it does, there is a capacitor that
looks like it has had to much to eat on it, and is probably leaking, if
not dripping its insides out. If a capacitor does not look pretty, for a
first cut, replace it.

The floppy runs off 12 VDC, and that load should not cause anything else
to happen, unless the power supply is defective, and the 12 v load pulls
down the 5 v line.

From the symptoms and the power supply circuit diagram (typical) you need
to replace two 470 uF capacitors.

Check the voltages first.

Jim

: Hi,

: I just picked up a 520STE at carboot sale for 1!

: Just the 'puter.. no leads or anything. I didn't really expect it to work,
: but surprisingly it is showing signs of life.. I could do with some help to
: nurse it back to full health though.

: It powers up and checks floppy drive ok.. then maybe 50% of the time, the
: GEM desktop appears, and for a few minutes I can move mouse pointer, access
: menus etc.. Then the screen goes black, and the floppy disk will click and
: whirr... If I leave it, the screen seems to alternate between white, fading
: to black.. then suddenly white again. The change from white to black seems
: to coincide with the floppy drive being accesssed.

: If I switch off, then back on it will usually be ok again.. for a while..

: I've opened it up and pressed down on all the socketed chips I could see (2
: under floppy drive and 1 square chip in big big recessed socket to the right
: under the keyboard), removed & refitted the memory simms, which seems to
: have made it run a little longer before dying, but it still isn't very
: happy.

: I'd love to get it working so if anybody could suggest anything I'd really
: appreciate any help.

: Cheers!
: Norm

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Semi-broken STE - Help!

Post by DJPsymile » Tue, 18 Mar 2003 11:29:09


Quote:> It powers up and checks floppy drive ok.. then maybe 50% of the time, the
> GEM desktop appears, and for a few minutes I can move mouse pointer,
access
> menus etc.. Then the screen goes black, and the floppy disk will click and
> whirr... If I leave it, the screen seems to alternate between white,
fading
> to black.. then suddenly white again. The change from white to black seems
> to coincide with the floppy drive being accesssed.

> I've opened it up and pressed down on all the socketed chips I could see
(2
> under floppy drive and 1 square chip in big big recessed socket to the
right
> under the keyboard), removed & refitted the memory simms, which seems to
> have made it run a little longer before dying, but it still isn't very
> happy.

I had a similar problem when I soldered a 4MB stick of ram in my ST. (I
labled the data lines wrong, which meant the system couldnt access the
memory banks).

In your case, if its not the power supply, I reckon the memory connectors
have a bad contact, which get worse as the system expands to heat.

Try diff sticks, swap the order or just abraise (sp?) the contact pads on
the ram with a little wire wool.

Dan.

 
 
 

Semi-broken STE - Help!

Post by Frederic Pecour » Tue, 18 Mar 2003 18:07:38


Hi

I got the exact same problem some 10 years ago, but due to the pin of
the mfp68901 used for monochrome detection. It had most probably been
electronicaly damaged after many hot pluging-unpluging sequences on my
TV. After some minutes, when the chip got warm enough, it started
switching by itself from colour to mono indefinitely.....which drove the
ST into a reset loop where the screen turns to black during reset, while
white a few seconds later, til the next reset ! I had to have the chip
replaced.......

I would bet on that reason in your case !

Fred


> Hi,

> I just picked up a 520STE at carboot sale for 1!

> Just the 'puter.. no leads or anything. I didn't really expect it to work,
> but surprisingly it is showing signs of life.. I could do with some help to
> nurse it back to full health though.

> It powers up and checks floppy drive ok.. then maybe 50% of the time, the
> GEM desktop appears, and for a few minutes I can move mouse pointer, access
> menus etc.. Then the screen goes black, and the floppy disk will click and
> whirr... If I leave it, the screen seems to alternate between white, fading
> to black.. then suddenly white again. The change from white to black seems
> to coincide with the floppy drive being accesssed.

> If I switch off, then back on it will usually be ok again.. for a while..

> I've opened it up and pressed down on all the socketed chips I could see (2
> under floppy drive and 1 square chip in big big recessed socket to the right
> under the keyboard), removed & refitted the memory simms, which seems to
> have made it run a little longer before dying, but it still isn't very
> happy.

> I'd love to get it working so if anybody could suggest anything I'd really
> appreciate any help.

> Cheers!
> Norm

 
 
 

Semi-broken STE - Help!

Post by badactres » Tue, 18 Mar 2003 19:34:39



Quote:> Hi

> I got the exact same problem some 10 years ago, but due to the pin of
> the mfp68901 used for monochrome detection. It had most probably been
> electronicaly damaged after many hot pluging-unpluging sequences on my
> TV. After some minutes, when the chip got warm enough, it started
> switching by itself from colour to mono indefinitely.....which drove the
> ST into a reset loop where the screen turns to black during reset, while
> white a few seconds later, til the next reset ! I had to have the chip
> replaced.......

> I would bet on that reason in your case !

> Fred

Thanks! I'm going to try everything that everyone has suggested. I'm not any
kind of electronics expert, but somehow your description seems to match very
closely what is happening with my STe. Especially as I've discovered another
problem connected with screen resolution.. If I switch from low to medium
res, the ST often (not always) freezes for 5-10 seconds while floppy drive
whirrs and clicks.. Then it will either switch to med res, or will go into
the black -> white screen reset loop.

Maybe a coincidence..?

Do ST's usually access the floppy-drive during a change of screen
resolution? I don't remember mine doing this (though was long time ago).

Thanks!
Norm

 
 
 

Semi-broken STE - Help!

Post by badactres » Tue, 18 Mar 2003 19:38:10



Quote:> I had a similar problem when I soldered a 4MB stick of ram in my ST. (I
> labled the data lines wrong, which meant the system couldnt access the
> memory banks).

> In your case, if its not the power supply, I reckon the memory connectors
> have a bad contact, which get worse as the system expands to heat.

> Try diff sticks, swap the order or just abraise (sp?) the contact pads on
> the ram with a little wire wool.

Thanks.. I'll try this.. I think I've even got some spare Atari Simms
somewhere so will try different ones in case the memory chips might be bad.

Really want to get this working.. I'm quite e*d to have an ST again! I
Always regretted selling mine.

Thanks,
Norm

 
 
 

Semi-broken STE - Help!

Post by badactres » Tue, 18 Mar 2003 19:44:55



Quote:> That is a good mystery. First, check the power supply voltage with a
> digital voltmeter. Low voltages can cause some really strange things. If
> the power supply works at all, which it does, there is a capacitor that
> looks like it has had to much to eat on it, and is probably leaking, if
> not dripping its insides out. If a capacitor does not look pretty, for a
> first cut, replace it.

> The floppy runs off 12 VDC, and that load should not cause anything else
> to happen, unless the power supply is defective, and the 12 v load pulls
> down the 5 v line.

> From the symptoms and the power supply circuit diagram (typical) you need
> to replace two 470 uF capacitors.

> Check the voltages first.

> Jim

Thanks Jim, Just looking under the sheilding, the capacitors look ok.. None
of the leaking and dripping that you described. I'm going to check the
voltages tonight after work. From what you say, I think you're right that
the floppy shouldn't drain enough power to crash the system.. I guess it's a
symptom rather than the cause of the problem.

I have to admit I'm a bit nervous about replacing anything that involves
soldering, but I might have to get my hands dirty this time! I don't want
this ST to end up stuck in the back of a cupboard.. Really want to get it
working!

No doubt I'll be back with more questions after I've tried everybody's
suggestions!

Thanks for quick response!
Norm

 
 
 

Semi-broken STE - Help!

Post by Tom McEwa » Wed, 19 Mar 2003 03:28:13


Quote:

> Do ST's usually access the floppy-drive during a change of screen
> resolution? I don't remember mine doing this (though was long time ago).

A change in resolution (whether between mono and RGB monitors, thus changing
the state of the monitor detect pin, or between medium and low res using the
options menu) always causes a full reset of the machine, and this of course
includes checking to see if there's a disk in the floppy drive.

So, if you've got a res-changer button on your monitor lead (and no sensible
ST owner shouldn't, or you'll wear out the socket in no time at all) make
sure you've saved anything you've been doing before pushing it!

Tom

 
 
 

Semi-broken STE - Help!

Post by David Bol » Thu, 20 Mar 2003 03:10:39



>A change in resolution (whether between mono and RGB monitors, thus changing
>the state of the monitor detect pin, or between medium and low res using the
>options menu) always causes a full reset of the machine,

Fortunately this isn't the case when switching between low and medium
res. A low/medium <-> high res change will perform a warm boot so
everything gets reloaded.

When changing between low and medium res, GEM is re-initialised and this
means reloading any desk accessories and the desktop.inf/newdesk.inf
file. Any auto-folder programs that remain in memory are still there
after a low <-> medium res change.

Quote:>and this of course includes checking to see if there's a disk in the
>floppy drive.

My experience was that the floppy was read only if the ST didn't have a
hard drive, or the desktop was saved with an open window for A: or B:

Regards,
  David Bolt

--
A3010 4Mb, A4000 4Mb RiscOS 3.11        |Member of the OGR Team Acorn
AMD 1800+ 512Mb WinXP                   |checking nodes at 47Mnodes/sec
AMD Duron/1100 256Mb SuSE 7.3           |
AMD Duron/950 64Mb SuSE 7.0             |http://www.distributed.net/
Intel Celeron/400 256Mb SuSE 7.3

 
 
 

Semi-broken STE - Help!

Post by Johann-Wilhelm Arn » Fri, 21 Mar 2003 06:01:00


Hi David,

DB>My experience was that the floppy was read only if the ST didn't have
DB>a hard drive, or the desktop was saved with an open window for A: or B:

With standard TOS the check for the floppy is always before the check for
harddisk and before running the auto folder programms. Also if there is an
executable programm in the bootsector, it is executed before the harddisk
is read.

Johann

 
 
 

Semi-broken STE - Help!

Post by David Bol » Fri, 21 Mar 2003 08:15:12



>Hi David,

>DB>My experience was that the floppy was read only if the ST didn't have
>DB>a hard drive, or the desktop was saved with an open window for A: or B:

>With standard TOS the check for the floppy is always before the check for
>harddisk and before running the auto folder programms. Also if there is an
>executable programm in the bootsector, it is executed before the harddisk
>is read.

This only occurs when there is a reset. When changing between low and
medium resolution, there is no reset and so this check doesn't occur.
Changing between low/medium and high resolution will cause a warm reset
to occur and so the executable-floppy-in-drive-A: check occurs.

Regards,
  David Bolt

--
A3010 4Mb, A4000 4Mb RiscOS 3.11        |Member of the OGR Team Acorn
AMD 1800+ 512Mb WinXP                   |checking nodes at 47Mnodes/sec
AMD Duron/1100 256Mb SuSE 7.3           |
AMD Duron/950 64Mb SuSE 7.0             |http://www.distributed.net/
Intel Celeron/400 256Mb SuSE 7.3

 
 
 

Semi-broken STE - Help!

Post by Johann-Wilhelm Arn » Tue, 25 Mar 2003 08:00:00


Hi David,

Quote:>This only occurs when there is a reset. When changing between low and
>medium resolution, there is no reset and so this check doesn't occur.
>Changing between low/medium and high resolution will cause a warm reset
>to occur and so the executable-floppy-in-drive-A: check occurs.

That's true, but it's important that the floppy is allways tested if there
is a harddrive or not.

Johann

 
 
 

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