Dragon 64 with a couple of issues

Hardware Hacking, Programming and Game Solutions/Cheats
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schombi
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Dragon 64 with a couple of issues

Post by schombi »

I got hold of a Dragon 64, which optically appeared to be in good condition. However, I found a couple of issues:

- First there was no reaction at all when the power button was pressed. The PSU was known to be good. I suspected the brown PSU board (with UM 1287) and luckily I had a blue issue 3 with UM 128? on the shelf (last number is unreadable) and with this board installed the Dragon powered up. If this was also an UM 1287, I believe no changes need to be made, but all documents on PSU board replacement talk about the Dragon 32 only where the Dragon 64 does not get mentioned. Should I worry?

- The Video output is crap on both the RF and the monitor connector. The picture is mainly B&W, but text seems to have traces of green/red/blue colors? I tried to tweak the potentiometer VR1 (there does not seem to be a VR2 on this board, as I had on my Dragon 32???), but I can only get a slightly better B&W picture.

- All keys seem to work, but "e" doesn´t. Is there anything I could do to overcome this? Removing the key and spraying Servisol did not help. What else can be done? What is best practice to dismantle the keyboard?

- Is there a service manual for the Dragon 32 and/or 64?


Thanks!
RWAP
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Re: Dragon 64 with a couple of issues

Post by RWAP »

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CaptainNemo
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Re: Dragon 64 with a couple of issues

Post by CaptainNemo »

If a contact cleaner doesn't work, then it's probably a broken/cracked soldering joint. Take out the Keyboard and inspect the pins/connectors underneath that key. Use a screwdriver to push and verify that all the joints are solid.

I had the same problem with the Q key in my Dragon 64 -- when I pushed one of the joints it fell off.

Finally, Clean the area and re-solder.
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schombi
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Re: Dragon 64 with a couple of issues

Post by schombi »

Will do. Thanks to you both.

Any advice on the video? Beside from VR2, is there any other place to tweak the signal? The problem with missing colors resp. characters being partially green, blue etc. is present on the monitor and the TV signal.

Update: Solder joints looked normal. Nothing found with the screwdriver. Re-soldered (I7, isn´t it?), but no change. Apart from pulling the caps, the keyboard cannot be dismantled any further? I just compared the D64 keyboard with one from the D32. The D32 one has screws on the rear side, but the D64 keyboard doesn´t. Using the D32 keyboard (screwed differently and does not fit perfectly) on the D64 leads to a working "e", so it confirms it´s not the computer, but the keyboard itself.

For the video, I think the partially colored characters are just kind of a distortion. Tweaking VR2 almost lead to a "perfect" B&W.

What component normally fails on the PSU board? I´d like to revive the faulty one. I inspected it and on its back you can see "ISS 4", while on the heat sink someone wrote 64K. So is the one I used not suitable for a Dragon 64?
sorchard
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Re: Dragon 64 with a couple of issues

Post by sorchard »

I've just been looking at the schematics and photos and it seems to me that issue 3 PSU boards are for D32s and issue 4 boards are for D64s

A key difference is the PSU voltage on pin 3. D32s have -5V here and D64s have -12V.

Putting the issue 3 board in a D64 shouldn't do any damage but there isn't sufficient voltage to run the -5V reg on the D64 main board. This will affect the video and probably explains what you are seeing.

Putting an issue 4 board in a D32 will supply -12V instead of -5V to the memory chips and it could be bad news. Not all memory chips use this supply but I wouldn't want to try my luck.

The faulty board will almost certainly have a simple fault. I would power it up and check the voltages on pins 1-4 on the output connector.

A dodgy power switch seems most likely to me, followed by shorted electrolytics and/or open diodes and least likely blown regulators. It might be worth reflowing the soldered joints just in case there were any marginal ones from manufacture that have now failed.
Stew
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schombi
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Re: Dragon 64 with a couple of issues

Post by schombi »

Hmm, that´s very interesting, Sorchard. Thanks!

I found these photos
http://archive.worldofdragon.org/index. ... U_Pictures

Has someone ever tried a D32 to D64 PSU board upgrade? What exactly needs to be done?
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schombi
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Re: Dragon 64 with a couple of issues

Post by schombi »

Another update: All components on the faulty PSU board (ISS4) looked okay to me, but there were no voltages on the connector to the main board and not even on the voltage regulators. I inspected the rear of the PSU board and found that (due to jiggling?) some solder joints of the power connector were without solder. However, the board is not very forgiving and by removing remaining solder, some of the tracks already came off. I then re-soldered the power connector and measured again at the front voltage regulator and all for a sudden I saw around 18V. I quickly replaced the ISS3 in my Dragon 64 with the "repaired" ISS4 and, guess what, I had a signal with green colors! Sorchard, you hit the nail on the head! However, I have my doubts on the reliability of my repair. This 9 pin connector together with the sensible tracks on the board maybe wasn´t the best idea Dragon ever had. I also doubt that one can get hold of a replacement ISS4 these days?

Now I need to work on a solution for the broken keyboard. It´s a pity that the D64 board doesn´t have screws on the rear side.
RWAP
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Re: Dragon 64 with a couple of issues

Post by RWAP »

Glad to hear you fixed the Iss4 PSU board - it should be fairly easy to replicate the PCB if there was enough interest.

As for the keyboard, there must surely be some way of removing the back plate - is it held by small plastic tabs, or riveted?
sorchard
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Re: Dragon 64 with a couple of issues

Post by sorchard »

Great to hear you've got it working and as RWAP also said, it wouldn't be hard to reproduce the PSU board. Though there are alternatives... One of my Dragons, hidden in my attic somewhere, doesn't have a PSU board at all. It's got a switch mode PSU, built in speaker and 3.5" disk drive, but that's another story :-)

Getting the 'E' key working again could be a pain. On a D32 keyboard it might be possible to swap the key with one of the shift keys, but a D64 keyboard seems to have all the keys trapped under a metal plate. I hope I'm wrong but it may be that the only way to dismantle the keyboard is by desoldering all of the keys.
Stew
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robcfg
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Re: Dragon 64 with a couple of issues

Post by robcfg »

It would be lovely to have pictures of your modded Dragon!

Maybe we could add an article on the subject. I've thought a couple of times on modding a dragon with an HxC floppy emulator or two 3.5" drives like the Alpha.

It may also be a good idea to have a list of components of the PSU boards (like the one in the DragonDOS cartridge page), so people can mod a D32 PSU to a D64 one, for example.
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