Dragon 64 with a couple of issues

Hardware Hacking, Programming and Game Solutions/Cheats
sorchard
Posts: 530
Joined: Sat Jun 07, 2014 9:43 pm
Location: Norwich UK

Re: Dragon 64 with a couple of issues

Post by sorchard »

Converting from Issue 3 to Issue 4 could be as simple as swapping the 7905 reg for a 7912, if you don't mind losing the TV output. An issue 3 schematic would be useful to confirm this. There is some video level shift circuitry on the issue 4 that seems to be absent on the issue 3.

I remember doing the internal drive conversion the hard way and removing and refitting the cartridge connector to insert an adaptor for the DOS card. The drive was mounted in the side of the top cover above the cartridge port. I'll have to go on an expedition into the roof in the not too distant future to see what I can dig up. I've been putting it off as I know I've got boxes of tapes, books and cartridges and once it's all located I've got the large task of figuring out what needs scanning/dumping/uploading.
Stew
User avatar
schombi
Posts: 18
Joined: Sat Jul 19, 2014 6:32 am
Location: Karlsruhe, Germany

Re: Dragon 64 with a couple of issues

Post by schombi »

Would that be REG3 (the top one) on my blue Iss3 board?
IMG_1071s.jpg
IMG_1071s.jpg (65.16 KiB) Viewed 5782 times
sorchard
Posts: 530
Joined: Sat Jun 07, 2014 9:43 pm
Location: Norwich UK

Re: Dragon 64 with a couple of issues

Post by sorchard »

schombi wrote:Would that be REG3 (the top one) on my blue Iss3 board?
Yes, that's the one. If you decide to have a go at this then you may wish to check the value of R2 which is a load resistor for REG3. It's 10K on an issue 4, but I can't see what it is in the issue 3 photo.

Resist the temptation to attach REG3 to the heatsink. The metal tab has a different voltage to the other components and things will be very unhappy without an insulating kit.

It would be wise to do a final check of the voltages on the connector before attaching to the D64 main board, and remember to mark the board as modified otherwise it might end up in a D32 in future and damage it.
Stew
User avatar
schombi
Posts: 18
Joined: Sat Jul 19, 2014 6:32 am
Location: Karlsruhe, Germany

Re: Dragon 64 with a couple of issues

Post by schombi »

Thanks for mentioning not to attach REG3 to the heatsink. I was almost tempted to do that. :oops:

How do I check the value of REG2?
sorchard
Posts: 530
Joined: Sat Jun 07, 2014 9:43 pm
Location: Norwich UK

Re: Dragon 64 with a couple of issues

Post by sorchard »

I could have been a bit more clear: I was worried about R2 the resistor, not REG2 the regulator. R2 is located above the ribbon cable. It's 10K (brown-black-orange) on the issue 4 board.

I've just noticed R2 is clearly visible in the other issue 3 photo and is 10K there too, so no problem.

I'm a little worried that I might be leading you along a path towards disaster so I feel that I should give you a friendly warning... Only attempt this if you understand what the modification is doing and you are confident doing it. If something goes wrong then it could damage your D64. For example if you get a short between input and output on REG3 then this will send a high voltage to the rest of the system. Also, as you've discovered, these boards are not the highest quality and it is very easy to delaminate the copper tracks if you don't have a temperature controlled soldering iron.
Stew
User avatar
schombi
Posts: 18
Joined: Sat Jul 19, 2014 6:32 am
Location: Karlsruhe, Germany

Re: Dragon 64 with a couple of issues

Post by schombi »

Thanks for clarifying. You´re right, there is a good chance to damage precious hardware, so I better refrain from converting an ISS3 to ISS4. I just wanted to be on the safe side, if my "repaired" ISS4 PSU board should break. I doubt I will be able to find a replacement as I did for the D32.

By the way, which temperature would you recommend for such sensitive boards? 350°C is too high, I reckon?
sorchard
Posts: 530
Joined: Sat Jun 07, 2014 9:43 pm
Location: Norwich UK

Re: Dragon 64 with a couple of issues

Post by sorchard »

Actually, 350°C is not a bad temperature if you're reasonably confident at soldering. It's about picking the temperature that works best for the speed you work at. The key is to maintain a consistent temperature.

The biggest problems are encountered when de-soldering. The solder reflows at a higher temperature due to impurities and it's very easy to keep the heat on too long resulting in the pad becoming detached from the board (The glue melts). If I'm more interested in preserving the board than the component then I will cut the legs of the component so they can be removed one at a time, but even then care is required because side cutters can apply a large force and break the pad off the board.

Just to make things worse, the PSU boards seem to be generally made of paper. These are lower cost but are much more fragile than glass boards. (The main board, for example, is made of glass)

At least you have a 'Plan B' if your issue 4 board does fail. You also have the option of running a wire from each pin of the connector to the correct destination on the board, bypassing the damaged tracks.
Stew
Post Reply