52 replies to this topic

[russg]

Hello. Was responding to a post about copying a Express! cart and had my RT8 in the slot, working fine when I plugged the Maxflash cart into the passthru port of the RT8.
It could be a coincidence, but seems it might be related, the RT8 stopped working. At first the computers wouldn't boot with the RT8 inserted, then I opened the RT8 up
and turned the little pot in it and now the computer would boot, but the RT8 won't keep time. I will try to fix it. The RT8 has two chips, a capacitor 104/I5Z, a small can
labeled Y1, the pot labeled YC1. I'm sure there was 2.95 volts to it, measured. The two chips are as follows:

SPI
SP74HCT138N
8430

and

M3002-16Pi
D7064100
R-(mu)EM87-14C

Are those chips available at Jameco? Which chip or other part might have gotten shorted when I plugged the Maxflash in? Can I measure something to tell what
is wrong? I have an oscilloscope and VOM. Has anyone heard about plugging a Maxflash into a pass thru? I might think this is a warning not to do that.

Edited by russg, Fri Jan 20, 2012 2:38 PM.

[sloopy]

2.95v maybe border line, IIRC they use 2032's which is nominal 3.6v

the 138 is common, the clock chip is difficult to find...

and that pot you turned? that is what is used to adj the clock, so you will have to play with it for a while to get the time to not drift...

sloopy.

[Fox-1 / mnx]

At first: note that the RT-8 and 8Mbit MaxFlash can't be used at the same time. The RT-8 sits at $D5B8-D5BF which the MaxFlash 8Mbit also seems to use. A 1mbit MaxFlash should work with it.


One of my RT-8's started to act up a while ago. It simply stopped running sometimes. Everything worked, like setting T/D, reading T/D no problem, except the clock didn't count. Couldn't find anything wrong but removed the crystal to solder it back on later and it worked again.

2 Weeks later... same started to happen. Clock didn't run anymore but after some hours it suddenly started to run all by itself to stop with it later again, purely at random.

Seached for an old digital watch, took it's 32.768MHz crystal out and put it on the RT-8 and the thing started to run again.

Some weeks later.... same is happening. Sometimes it runs, sometimes it stops for hours to run again some later.

Changed the trim pot for another one I had laying around. Worked for some weeks without problems, then same problems again. Bought another RT-8 cause I more or less really need one to keep the BBS running.

At the meanwhile I've put in another (new) trim pot that is physically too large to close the shells but it's running now without problems for several weeks. Maybe it's solved but I'm not sure yet.

All above was not related to battery issues. Exchanged the 2032 (3V) several times for a new one.


As for the M3002-16PI... It's a 4 bit RTC (BCD format) with 16 x 8 RAM but not available anywhere and no suitable replacement either.

[russg]

Thanks for those.
Now, it gives a green screen and no boot. If I plug it in with no battery it boots fine, as if it isn't there.

[Fox-1 / mnx]

Try the RT-8 on another Atari if you can. just to rule out one factor. With and without a know good battery. If it shows the same behavior take out the 74xx138 and try again.




edit: assuming that the IC's are socketed as in the ones I have.

Edited by Fox-1 / mnx, Sat Jan 21, 2012 2:57 AM.

[guus.assmann]

Caution!
The schematic diagram is not correct.
There should be a diode to prevent the battery from feeding the complete computer.
And also one to prevent the computer from charging the battery.
Of course these parts are present in the device, but only missing in the diagram.

BR/
Guus

P.S. The part that can be adjusted is a capacitor.
And the crystals may also be found on a PC-MB. (Small cylindrycal shape near battery)

[russg]

Now it boots fine in both computers with the battery in, doesn't keep time. My chips aren't socketed. I guess I'll by some sockets and a 138N. I realize the 'can' is the crystal and the 'pot' is a capacitor. I have a test motherboard I can
plug it in and get at it opened up and the computer powered on.

[russg]

It will not boot with battery connected now. I guess I'll buy some sockets and a 138N. The 'can' is a crystal and the 'pot' is a capacitor. I don't think there are any protective diodes guus mentions.
I have a test board I can plug it into.
Here's my RT8.

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[russg]

well, the 138N is out. Ordered 138N, correct mhz crystal in a can, .01 pf ceramic I think, a 20 pf cap to replace the variable cap, some 16 pin sockets from Jameco.

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[bbking67]

I may be stating the obvious, but have you checked the contacts on the edge connector? In the pic it looks particularly nasty...

[sloopy]

And lifted two solder pads...

sloopy.

[guus.assmann]

Hello all,

I just had a look at the schematics that I have for this RTC.
There must be some provision that prevents the battery from powering the computer, that's obvious.
And there are no diodes on the outside of the battery or RTC-chip. That much is certain.
So the chip has the circuits inside.
But the capacitor and timer-crystal are also connected to pin 1, just as the battery minus.
For this reason I come to the conclusion that this chip will not function properly when there's no battery connected.
Maybe a resistor (10K or so?) will also do.
And if you'd like to use a goldcap, that can also work fine.
In such case, place the charging resistor and a diode between the minus of the cap and GND. (e.g. pin 8 of the LS138)
The cathode of the diode (Ring on housing) to the GND.
Charching resistor has to limit the current into tha cap, as this would be much too high for cap and supply. about 100 Ohm is fine.

The fact that te computer hangs when the clock is present can also mean that the oscillator is not runing. (as expected)
In such case, it will not be possible to read the clock registers.
But if the LS138 is functioning, the clock will appear to be present.
So the program will keep trying to read the clock.

BR/
Guus

[russg]

bbking67, on Sat Jan 21, 2012 7:20 PM, said:

I may be stating the obvious, but have you checked the contacts on the edge connector? In the pic it looks particularly nasty...

Those contacts I put solder on. Yes, they look nasty, I don't think they are the problem tho. I think the contacts are gold and they wear off. I know of no other way I could repair those than put the solder on them.

[russg]

sloopy, on Sun Jan 22, 2012 1:02 AM, said:

And lifted two solder pads...

sloopy.

Those two have the pads on the other side where the printed circuit connects to them are intact. I have trouble desoldering and the cart traces and solder pads are delicate. I would guess
I'm not going to succeed in reviving this cart, all I can do is try. Thanks for the interest.

Edited by russg, Sun Jan 22, 2012 9:09 AM.

[Fox-1 / mnx]

guus.assmann, on Sat Jan 21, 2012 3:52 AM, said:

Caution!
The schematic diagram is not correct.
There should be a diode to prevent the battery from feeding the complete computer.

The schematic is correct and matches both my original RT-8's. No diode's in there.

Note that the battery is connected to the main +5V but not to the main ground.

[Fox-1 / mnx]

guus.assmann, on Sun Jan 22, 2012 5:21 AM, said:

The fact that te computer hangs when the clock is present can also mean that the oscillator is not runing. (as expected)
In such case, it will not be possible to read the clock registers.

If the oscillator doesn't run all it does is not "counting". You're still able to read and set Time/Date. It just won't be updated.

[russg]

bbking67, on Sat Jan 21, 2012 7:20 PM, said:

I may be stating the obvious, but have you checked the contacts on the edge connector? In the pic it looks particularly nasty...

I put solder on some edge traces, as they were worn off and the cart didn't work, the solder did make it work. I got out my magnifying spectacle and followed the traces
from solder to points on the cart and all were beeping the continuity horn. It had been working for a long time after the solder had been put on. Thanks. I looked for
obvious things, voltage where the schematic showed it should be, negative where should be.

Edited by russg, Sun Jan 22, 2012 10:14 PM.

[bbking67]

I hadn't seen that it was solder... in the pic it just looked worn out. I guess the only other way would be to use a circuit pen (I just bought one for my 800xl keyboard mylar actually). Back in the 80's I had some stuff that I think was called "Nickel Print". If the continuity is good everything should be okay...

[russg]

My parts came from Jameco yesterday (Jan. 25, 2012). Today I worked on it (the RT-. My poor RT-8. I soldered a 16 pin socket where the 138 was. Checked connections, voltage, continuity. Put two AAA bateries
in my battery holder I have connected to the RT-8. Fired up the 64K 600XL. Ran TDLINE and date in June 6, 1994 comes up. Turned off, plugged in RT-8. Ran DATE and set for Dec. 20, 2011. Ran
TDLINE and it shows Mon Dec 20, 2011. I also set the time when I did DATE. Turned off the computer unplugged the RT-8, plugged it back in, fired it up, ran TDLINE and walla! Mon. Dec. 20, 2011! It actually works.
It is pretty beat up and old, I'd never sell it in its condition. BUT I FIXED IT! Still wonder if plugging the 1 mb Maxflash killed the 138. Thanks for listening. Now I have 20 caps, a crystal can, another 16 pin socket and
another 138.

[Fox-1 / mnx]

russg, on Thu Jan 26, 2012 5:51 PM, said:

It is pretty beat up and old, I'd never sell it in its condition.

The key part on it is the M3002 and as long this one is working the condition doesn't matter. When dropping the pass-thru part it isn't difficult to make one yourself from the ground up.

russg, on Thu Jan 26, 2012 5:51 PM, said:

Now I have 20 caps, a crystal can, another 16 pin socket and another 138.

Now try to locate some M3002's and start making a new batch :-)


edit: sp.

Edited by Fox-1 / mnx, Fri Jan 27, 2012 6:17 AM.

[russg]

Fox-1 / mnx, on Fri Jan 27, 2012 6:16 AM, said:

russg, on Thu Jan 26, 2012 5:51 PM, said:

It is pretty beat up and old, I'd never sell it in its condition.

The key part on it is the M3002 and as long this one is working the condition doesn't matter. When dropping the pass-thru part it isn't difficult to make one yourself from the ground up.

russg, on Thu Jan 26, 2012 5:51 PM, said:

Now I have 20 caps, a crystal can, another 16 pin socket and another 138.

Now try to locate some M3002's and start making a new batch :-)


edit: sp.

I don't know how to make the printed circuit board. Heh.

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[Fox-1 / mnx]

russg, on Fri Jan 27, 2012 6:56 AM, said:

I don't know how to make the printed circuit board. Heh.

No need for that. It can be done on a small vero board and build it into the XL/XE. Sure, not as nice as a real PCB but it's not too bad.

[Mathy]

Hello Russ

If you can find enough M3002-16PI's, we'll find somebody who can make PCB's.

Mathy

[sloopy]

no doubt... find the chips, PCB's are easy ;')

sloopy.

[Larry]

So what do you think actually "fixed" it?

I'm particularly interested because mine has much the same behavior. (Although it looks a bit better than yours... ) Mine will work for a while then won't come up, etc. I touched up all the solder joints and that fixed it for a time, then same thing all over again.

-Larry