Repairs and stuff
Posted: Fri Dec 05, 2014 11:57 pm
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![Smile :-)](./images/smilies/icon_e_smile.gif)
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.
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
![Smile :-)](./images/smilies/icon_e_smile.gif)
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.