Repairs and stuff

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

Repairs and stuff

Post by sorchard »

While in the mood for repairs I decided to go and raid the nest of Dragons hiding in my roof. The following observations/curiosities came up:

1.
This is more an observation on software compatibility: While looking at the MKII schematic I was reminded that some Dragons can only display a screen residing in the bottom 16K of memory. This affects machines with 16 x 2K DRAMs e.g. MKII D32s and ISS2 D32s with the memory daughterboard. Any part of the screen in the upper 16K will show garbage. (The reason is due to the latch between the memory and the VDG being driven by RAS0)

2.
Two D32s with the exact same fault: Smoke on power up. In both cases this was C11, a Tantalum capacitor on the 5V line near the power connector. Coincidence or weakness?

3.
Intermittent fault. Machine works for a while then crashes. Can be made to work or fail by bending the PCB slightly. This was due to a poorly soldered joint on the CPU socket. I've seen this type of fault a couple of times before over the years: once on my D64 (SAM socket) and on my first D32 (ROM socket). Always worth checking the joints when fault finding.

4.
Keyboard cables. These don't like being handled very much. I had a couple of these break and needed patching up.

5.
I found an ISS4 PSU board in a D32. I thought these were only found in D64s? It had a 7905 reg fitted instead of the 7912 required for the D64. I don't know if it was made like this or someone (not me!) converted it for use in a D32.

Oh, and I found this abomination :-)
IMG00082.jpg
IMG00082.jpg (175.42 KiB) Viewed 5691 times
IMG00083.jpg
IMG00083.jpg (171.28 KiB) Viewed 5691 times
IMG00085.jpg
IMG00085.jpg (239.92 KiB) Viewed 5691 times
It's a D32 upgraded to 64K, internal disk drive, serial port, switch mode PSU, TTL monitor output and built in speaker.

Sadly I no longer have a working TTL monitor. I'll have to convert the output to analogue one day.
Stew
User avatar
robcfg
Posts: 1529
Joined: Sat Apr 04, 2009 10:16 pm
Location: Stockholm, Sweden
Contact:

Re: Repairs and stuff

Post by robcfg »

Hi Stew,

If you take a look here, the Issue 4 power boards seem to have been 'fixed' to work with a D64, so it's perfectly normal. As we don't have pictures of an unmodified Issue 4 board, could you please take some pictures, or 300dpi scans for the wiki?

Regards,
Rob
sorchard
Posts: 530
Joined: Sat Jun 07, 2014 9:43 pm
Location: Norwich UK

Re: Repairs and stuff

Post by sorchard »

robcfg wrote:If you take a look here, the Issue 4 power boards seem to have been 'fixed' to work with a D64, so it's perfectly normal. As we don't have pictures of an unmodified Issue 4 board, could you please take some pictures, or 300dpi scans for the wiki?
No problem Rob. I've got some chores today so might not be this weekend. I'll also take a closer look at the ISS4 in my D64 to see if it matches the one in the wiki.
Stew
zephyr
Posts: 1474
Joined: Mon Jul 21, 2008 1:18 am

Re: Repairs and stuff

Post by zephyr »

sorchard wrote:While in the mood for repairs I decided to go and raid the nest of Dragons hiding in my roof. The following observations/curiosities came up:

1.
This is more an observation on software compatibility: While looking at the MKII schematic I was reminded that some Dragons can only display a screen residing in the bottom 16K of memory. This affects machines with 16 x 2K DRAMs e.g. MKII D32s and ISS2 D32s with the memory daughterboard. Any part of the screen in the upper 16K will show garbage. (The reason is due to the latch between the memory and the VDG being driven by RAS0)
I asked about this back in 2012.
viewtopic.php?f=8&t=1336
sorchard
Posts: 530
Joined: Sat Jun 07, 2014 9:43 pm
Location: Norwich UK

Re: Repairs and stuff

Post by sorchard »

zephyr wrote:I asked about this back in 2012.
I wasn't sure if you were interested in a more detailed answer or were just linking to the earlier post. I've replied to the old post anyway in case it's of interest.
Stew
sorchard
Posts: 530
Joined: Sat Jun 07, 2014 9:43 pm
Location: Norwich UK

Re: Repairs and stuff

Post by sorchard »

robcfg wrote:As we don't have pictures of an unmodified Issue 4 board, could you please take some pictures, or 300dpi scans for the wiki?
Photos of ISS4 PSU board in a D32:
Psu_iss4_d32_comp.jpg
Psu_iss4_d32_comp.jpg (997.42 KiB) Viewed 5619 times
Psu_iss4_d32_sold.jpg
Psu_iss4_d32_sold.jpg (1.15 MiB) Viewed 5619 times
I also checked the ISS4 board in my D64 and it has the same mod as the one in the wiki, other than the wire being black instead of green.

Edit:
I had a look at the mod to see what it does:
One of the connections to the RF circuit is to regulated +12V. The mod disconnects from 12V and connects to the unregulated feed to the 5V reg which I measured to be about 9.4V under load. I don't know what the effect of this mod is.
Stew
User avatar
robcfg
Posts: 1529
Joined: Sat Apr 04, 2009 10:16 pm
Location: Stockholm, Sweden
Contact:

Re: Repairs and stuff

Post by robcfg »

Thank you very much, Stew!

I edited your pictures a bit and uploaded them to the PSU Pictures page.
Post Reply