π¬π§ BBC Master Compact: Part 3 (Motherboard Fault) [TCE #0553]
32Thanks to #PCBWAY for sponsoring this video!
My BBC Master Compact has a weird fault where it won't work when in its case, even just resting without any screws. Remove it from the case and place the bare motherboard on my bench ... works perfectly!
00:00 ... Intro
01:09 ... Examining the board
02:20 ... Examining the bottom case
03:50 ... Faulty when in the case
06:45 ... Fine when out of the case
07:20 ... Expansion ports?
10:30 ... Removed dodgy composite video RCA jack ... weird video output
11:43 ... A few days later
13:05 ... Looks suspicious
15:50 ... Moment of truth ...
17:37 ... Channel outro & thanks
Turns out that the right-hand stand-off in the bottom case had damaged two pins of IC22, the CF30050 I/O controller. When I re-flowed the solder on these and put it back into its case ... booted straight away! Finally.
Next, I'm going to try loading some DFS software using my simple disk interface adaptor board.
My Github page:
https://github.com/0ddjob/BBC_Micros
My Master Compact has these ROMs installed:
MOS 5.10
UTILS 1.10
ADFS 2.10
The Master Compact is a cutdown version of the Master 128 that had the computer contained within the keyboard and a separate unit containing the 3Β½" drive and power supply. The keyboard was connected to the unit by a 5V power cable and a DB25 cable for the disk drive.
Some further info here:
https://chrisacorns.computinghistory.org.uk/Computers/MasterCompact.html
You can run the machine with just a +5VDC power supply with 2.1mm plug (centre positive) - probably a modern USB charger is enough.
The major chips on the board:
6522: Versatile Interface Adaptor (VIA)
VC2069: Video ULA (or VIDPROC)
HD6845: CRT controller (CRTC)
SAA5050: Teletext character generator
CF30048: CRTC Multiplexer
CF30049: Peripheral Bus Controller
CF30050: I/O Controller
CF30058: Memory Controller (socketed)
WD1772: Floppy Drive Controller (FDC)
65C12: CPU
PCD8572: 1Kbit (128x8bit) EEPROM (socketed)
There are some empty sockets for the RS232 serial support. ECONET support comes via a daughterboard that plugs into the motherboard.
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