Dragon 32 Repair

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martinjharvey
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Dragon 32 Repair

Post by martinjharvey » Thu Oct 22, 2015 3:59 pm

I've got a Dragon 32 and Im in the process of trying to fix it. Powers on fine. I've got all the correct voltages at the 4116 RAM chips, which I've socketed and tested in a known working Speccy to worm out any that might be faulty. I've reseated the 40 pin IC's like the processor, SAM and the other one :lol:

I've knocked together a cable to connect to my TV using the monitor port but the display is all garbage. Columns the full width of the screen populated with @@@@@@ and a few other symbols. The columns containing the @'s start off a muddy red and the turn green after about 10 seconds.

I was just wondering if anyone has any experience in tinkering with the Dragon 32 and if so is the fault I describe a common one?

Im thinking that as the display is the same regardless of the CPU being plugged into the socket or not, would this point to the CPU being faulty?

Any help appreciated.

Thanks

Mart

Prime
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Re: Dragon 32 Repair

Post by Prime » Thu Oct 22, 2015 4:33 pm

Wit the CPU plugged in, if it is working bu there is a problem in the video side of things if you type 'MOTORON' and listen for the click of the tape relay, that will tell you if the machine is booting basic and getting to the point where the RAM is being correctly accessed (by the CPU).

Do you have a scope that you could use to test the data / address lines from the CPU?

Are the ROMS socketed? They are on some machines, but not on others.

Since you have put sockets in the RAM space it's also worth checking the continuity of the lines between them and of the Data lines.

Might also be worth asking for help on the Dragon archive here : http://www.archive.worldofdragon.org

Cheers.

Phill.

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Re: Dragon 32 Repair

Post by martinjharvey » Thu Oct 22, 2015 5:17 pm

Prime wrote:Wit the CPU plugged in, if it is working bu there is a problem in the video side of things if you type 'MOTORON' and listen for the click of the tape relay, that will tell you if the machine is booting basic and getting to the point where the RAM is being correctly accessed (by the CPU).
With the CPU plugged in I just get @ symbols on red and green columns. I've already tried typing 'MOTORON' and could hear no click from the relay when I did. The relay can be heard clicking when the power is turned on. As I'm getting the +5, -5 and 12v when testing the RAM and the ribbon from the PSU with multi-meter I'm assuming that the PSU is still good.
Prime wrote:Do you have a scope that you could use to test the data / address lines from the CPU?
Nope don't have a scope :(
Prime wrote:Are the ROMS socketed? They are on some machines, but not on others.
The ROM labelled Dragon Data 1-1 which I'm guessing is the BASIC rom is socketed. The ROM labelled 1-0 is soldered to the PCB.
Prime wrote:Since you have put sockets in the RAM space it's also worth checking the continuity of the lines between them and of the Data lines.
Yep checked for continuity before putting the sockets in and after to make sure the Data lines were still good. I've also removed and re-soldered the solder around the CPU and the other 40 pin IC's to hopefully get rid of any dry joints that I couldn't detect visually.

I'm guessing at the CPU being bad mainly based on an article I saw with a guy fixing up a D64 which has for the most part the same issue. The fault is there with CPU plugged in or not.

Tried to get on the WOD forums but cocked the registration up 3 times and got locked out. Will try again later :)

Thanks

Mart

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1024MAK
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Re: Dragon 32 Repair

Post by 1024MAK » Thu Oct 22, 2015 6:34 pm

If you don't have, or have access to a 'scope, do you have a logic probe?

If no, and the only test gear you have is your multimeter, you will be reduced to some limited voltage testing, resistance testing, and renewing/swapping parts (and hoping you will be lucky) in the hope of fixing it before you end up renewing everything!

It is worthwhile testing/checking the reset circuit. You can use your meter for this :D

Mark

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roland
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Re: Dragon 32 Repair

Post by roland » Thu Oct 22, 2015 9:58 pm

I'd advise Hoglet's magnificent debugger/ tracer in a godil :D from there you can "look" everywhere inside the Dragon. You can do memory tests, access I/O ports and step through the initialization routine.
256K + 6502 Inside
MAN WOMAN :shock:

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jonb
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Re: Dragon 32 Repair

Post by jonb » Fri Oct 23, 2015 6:05 am

roland wrote:I'd advise Hoglet's magnificent debugger/ tracer in a godil :D from there you can "look" everywhere inside the Dragon. You can do memory tests, access I/O ports and step through the initialization routine.
Does it handle the 6809 processor?

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hoglet
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Re: Dragon 32 Repair

Post by hoglet » Fri Oct 23, 2015 7:11 am

jonb wrote:
roland wrote:I'd advise Hoglet's magnificent debugger/ tracer in a godil :D from there you can "look" everywhere inside the Dragon. You can do memory tests, access I/O ports and step through the initialization routine.
Does it handle the 6809 processor?
Indeed it does, see:
http://www.stardot.org.uk/forums/viewto ... 90#p115756
and
http://www.stardot.org.uk/forums/viewto ... 20#p118351

Roland used it extensively in his Atom 6809 board debugging, see this thread:
http://www.stardot.org.uk/forums/viewto ... 8&start=30

GODILs can be bought here, for €73.71 (inc VAT and UK shipping, about £53)
http://shop.trenz-electronic.de/en/TE02 ... 40-pin-DIL

You will need a Xilinx programming cable as well, which can be had on eBay for about £25.

Dave

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Re: Dragon 32 Repair

Post by Prime » Fri Oct 23, 2015 9:04 am

A small point that might be significant.....

The Dragon and CoCo machine use the 6809E, which has an external clock generator...in those machines the E and Q clocks are generated by the SAM. There are also some other pinout differences between it and the non E version which i think Hoglet has tested with.

Cheers.

Phill.

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hoglet
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Re: Dragon 32 Repair

Post by hoglet » Fri Oct 23, 2015 10:12 am

Prime wrote: There are also some other pinout differences between it and the non E version which i think Hoglet has tested with.
Both the 6809 and 6809E should be supported (a "E mode" jumper allows the user to select between them, and this alters the clocking circuitry, and changed the functions of a few other pins). See the VHDL here if you are interested:
https://github.com/hoglet67/AtomBusMon/ ... CpuMon.vhd

The second link above shows it working on a Dragon motherboard. As I don't have a Dragon keyboard, I've been unable to test further than just seeing it boot.

This is still pretty experimental, but I think would be useful in this case.

Dave

martinjharvey
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Re: Dragon 32 Repair

Post by martinjharvey » Tue Oct 27, 2015 12:21 pm

1024MAK wrote:It is worthwhile testing/checking the reset circuit. You can use your meter for this
I've tested the reset switch and that is working fine. Other than that what would testing the reset circuit involve?

Tried a new processor in it to see if that would make a difference but it didn't :(

This is what I'm still getting when I turn the Dragon on....
WP_20151027_11_26_45_Pro.jpg
Might not be too clear from the photo but all of the screen is static apart from the 'A' characters that are scattered about the screen. These blink on and off constantly at a steady rate. Still no response from the keyboard, and the 'MOTORON' command as suggested isn't making the relay click either.

I'm now wondering if this could be the OS and BASIC roms that are faulty?

Mart

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1024MAK
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Re: Dragon 32 Repair

Post by 1024MAK » Tue Oct 27, 2015 3:27 pm

Have a look at a pin-out for the CPU (or data sheet) and find the reset pin. I don't know the 6809 as well as the 6502 or the Z80, so I forget it's exact name. Maybe "RES" or "RST". I would look it up, but I'm on a mobile...

Then with the black / negative meter lead connected to a 0V/Ground point on the PCB (modulator case, or power supply wiring pin), hold the red meter probe on the reset pin. See what voltage you get. Now press the reset button. Check that the voltage changes to the opposite logic level. Release the reset switch, and check that the voltage changes back to the original logic level.

By logic level, I mean 0.8V or less is logic zero / logic low. 2V or greater is logic one / logic high.

Mark

martinjharvey
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Re: Dragon 32 Repair

Post by martinjharvey » Tue Oct 27, 2015 3:47 pm

1024MAK wrote:Now press the reset button. Check that the voltage changes to the opposite logic level. Release the reset switch, and check that the voltage changes back to the original logic level.
I'm getting 4.91v at the reset pin, then when I press the reset button the voltage drops to 0.63v. When I release the reset, the voltage goes back to 4.91v again.

martinjharvey
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Re: Dragon 32 Repair

Post by martinjharvey » Mon Nov 02, 2015 7:06 pm

I've started a post on the Dragon Archive forum detailing a little bit more as to where I am with this. Still not got a working Dragon yet though :(

Here's the link to save me retyping :lol:
http://archive.worldofdragon.org/phpBB3 ... 5&start=10

Seems to be a missing or low -5v voltage problem now with the 4116 Ram IC's.

Anyone any ideas?

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apt-e
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Re: Dragon 32 Repair

Post by apt-e » Wed Jun 12, 2019 3:30 pm

I know this post if from a long time ago, but you never know.

I purchased a Dragon 32 with the same fault, turned out to be the Rom, fitted another rom and everything was fine.

interestingly, if you start most Dragon emulators without a rom image, you get the same thing, well in my experience anyway.

Regards

Paul

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