Search found 202 matches

by mw0uzo
Sat Jan 14, 2017 5:25 pm
Forum: hardware
Topic: Dead BBC Masters - ROM screwup leading to main system damage
Replies: 234
Views: 10601

Re: Dead BBC Masters - ROM screwup leading to main system damage

That's pretty crazy! I wonder if some other chip on the BD data bus is dragging everything down (or up)? Do you have an oscilloscope? It might be worth going back to the original chips and checking levels on the BD data bus. The following chips share the BD data bus: - IC3 (WD1770 floppy controller...
by mw0uzo
Sat Jan 14, 2017 4:39 pm
Forum: hardware
Topic: Dead BBC Masters - ROM screwup leading to main system damage
Replies: 234
Views: 10601

Re: Dead BBC Masters - ROM screwup leading to main system damage

lol no. Forum rules do not allow what i want to type.
by mw0uzo
Sat Jan 14, 2017 4:25 pm
Forum: hardware
Topic: Dead BBC Masters - ROM screwup leading to main system damage
Replies: 234
Views: 10601

Re: Dead BBC Masters - ROM screwup leading to main system damage

Ok new brain installed. Sometimes I wish mine could be replaced too.
SV204759.JPG
SV204763.JPG
SV204764.JPG
So new CPU, put the new mem back in, user VIA in system VIA position. user VIA not installed. Will it boot? Will it blend? Will it get frizbeed out of the window in disgust?
by mw0uzo
Sat Jan 14, 2017 2:17 pm
Forum: hardware
Topic: Dead BBC Masters - ROM screwup leading to main system damage
Replies: 234
Views: 10601

Re: Dead BBC Masters - ROM screwup leading to main system damage

BigEd wrote:You've done a great job of desoldering and socketing though! I'm sure you'll get there...
One socketed System VIA, swapped with the user.
SV204754.JPG
SV204755.JPG
Got to look after the kids for a bit, then i'll scoop out the brain :twisted:
by mw0uzo
Sat Jan 14, 2017 1:01 pm
Forum: hardware
Topic: Dead BBC Masters - ROM screwup leading to main system damage
Replies: 234
Views: 10601

Re: Dead BBC Masters - ROM screwup leading to main system damage

No. So, what's left. The System VIA and the CPU. :roll:
by mw0uzo
Sat Jan 14, 2017 12:49 pm
Forum: hardware
Topic: Dead BBC Masters - ROM screwup leading to main system damage
Replies: 234
Views: 10601

Re: Dead BBC Masters - ROM screwup leading to main system damage

Damn. No init. :(
I will try the old RAM.
by mw0uzo
Sat Jan 14, 2017 12:38 pm
Forum: hardware
Topic: Dead BBC Masters - ROM screwup leading to main system damage
Replies: 234
Views: 10601

Re: Dead BBC Masters - ROM screwup leading to main system damage

ICs installed. Put original user VIA back in and new PBC. I'm scared.
SV204742.JPG
SV204745.JPG
SV204748.JPG
by mw0uzo
Sat Jan 14, 2017 11:51 am
Forum: hardware
Topic: Dead BBC Masters - ROM screwup leading to main system damage
Replies: 234
Views: 10601

Re: Dead BBC Masters - ROM screwup leading to main system damage

Good luck with the repair! [-o< While I have a break, I have a question. Do I desolder the other VIA, replace both and the PBC then test? My thinking is I want to be absolutely sure that the new PBC isn't damaged by anything particularly annoying. Or, just replace the user VIA with what came out an...
by mw0uzo
Sat Jan 14, 2017 11:47 am
Forum: hardware
Topic: Dead BBC Masters - ROM screwup leading to main system damage
Replies: 234
Views: 10601

Re: Dead BBC Masters - ROM screwup leading to main system damage

PBC removed! That wasn't easy. RAM chip socket was in the way of quite a few pins, as were the resistor packs on the other side. To make it even worse. on the same side was a very heavy double sided GND trace on one of the pins. Had to be as sure as i could all the pins were desoldered and broken aw...
by mw0uzo
Sat Jan 14, 2017 10:03 am
Forum: hardware
Topic: Dead BBC Masters - ROM screwup leading to main system damage
Replies: 234
Views: 10601

Re: Dead BBC Masters - ROM screwup leading to main system damage

Ah, it's like Christmas when the post comes, sans socks and slippers
by mw0uzo
Fri Jan 13, 2017 1:06 pm
Forum: hardware
Topic: Dead BBC Masters - ROM screwup leading to main system damage
Replies: 234
Views: 10601

Re: Dead BBC Masters - ROM screwup leading to main system damage

I found a source for 2xPBCs! Last 2 remaining. \:D/
Thank you CJE micros! http://www.cjemicros.co.uk/micros/products/index.shtml
by mw0uzo
Thu Jan 12, 2017 7:54 pm
Forum: hardware
Topic: Dead BBC Masters - ROM screwup leading to main system damage
Replies: 234
Views: 10601

Re: Dead BBC Masters - ROM screwup leading to main system damage

Powered up the board with the user VIA removed. No init, so that is the user VIA damage from short/static/badMMC preventing boot theory eliminated.
by mw0uzo
Thu Jan 12, 2017 7:42 pm
Forum: hardware
Topic: Dead BBC Masters - ROM screwup leading to main system damage
Replies: 234
Views: 10601

Re: Dead BBC Masters - ROM screwup leading to main system damage

tricky wrote:I am truly envious of your desoldering and your burn rate is no worse than mine ;)
:D Preheating the board with hot air station helped desoldering the few stubborn holes. That's enough for tonight. Hopefully my new iron will arrive tomorrow.
by mw0uzo
Thu Jan 12, 2017 7:27 pm
Forum: hardware
Topic: Dead BBC Masters - ROM screwup leading to main system damage
Replies: 234
Views: 10601

Re: Dead BBC Masters - ROM screwup leading to main system damage

I soldiered on with the broken iron, fixed with epoxy and gaffer tape. (Unfortunately the epoxy was not high temp type so it softened and came apart again. burned my fingers for about 1/3rd of the job :/ ) Got the user VIA out without any damage to the through holes! SV204728.JPG SV204731.JPG Discov...
by mw0uzo
Wed Jan 11, 2017 6:12 pm
Forum: hardware
Topic: Dead BBC Masters - ROM screwup leading to main system damage
Replies: 234
Views: 10601

Re: Dead BBC Masters - ROM screwup leading to main system damage

Started to desolder the VIAs, but then my soldering iron broke at the handle! This resulted in a scrape on the board, annoyingly. More worryingly it exposed the mains wiring inside that had two nicks in the insulation exposing bare wire, worryingly close to the metal sleeve of the iron. It is earthe...
by mw0uzo
Tue Jan 10, 2017 8:58 pm
Forum: hardware
Topic: Dead BBC Masters - ROM screwup leading to main system damage
Replies: 234
Views: 10601

Re: Dead BBC Masters - ROM screwup leading to main system damage

Capture
CaptureE.zip
(4.93 MiB) Downloaded 14 times
by mw0uzo
Tue Jan 10, 2017 8:55 pm
Forum: hardware
Topic: Dead BBC Masters - ROM screwup leading to main system damage
Replies: 234
Views: 10601

Re: Dead BBC Masters - ROM screwup leading to main system damage

I have changed the RAM to eliminate the possibility of damaged RAM weirdness. Just solder wick used, was extra careful, zero PCB damage! :D SV204714.JPG SV204717.JPG SV204719.JPG SV204723.JPG Still no init, but from Dave's work to be expected. Dave, I'll post another capture of the data bus, it seem...
by mw0uzo
Tue Jan 10, 2017 2:32 pm
Forum: hardware
Topic: BBC Micro US Model UNB09 Board Layout
Replies: 5
Views: 635

Re: BBC Micro US Model UNB09 Board Layout

I've got a very poor condition B+ with the same fault. It's an ongoing project, the first thing I found that was dead was the 555 timer power on reset circuit. It charges a small cap through 1Mohm resistors. I had to replace the 555, capacitors and 1Mohm resistors before the signal would work proper...
by mw0uzo
Tue Jan 10, 2017 9:40 am
Forum: hardware
Topic: Dead BBC Masters - ROM screwup leading to main system damage
Replies: 234
Views: 10601

Re: Dead BBC Masters - ROM screwup leading to main system damage

Ha, damn. Clearly I can't count and got over excited :oops: :lol: It was the first clear read I could see, the rest seemed to be writes. I'm out this eve till ~11pm Actually, it does look like your screen shots show the first read of the system VIA. And it's preceded in the traces by 27 writes to t...
by mw0uzo
Mon Jan 09, 2017 6:50 pm
Forum: hardware
Topic: Dead BBC Masters - ROM screwup leading to main system damage
Replies: 234
Views: 10601

Re: Dead BBC Masters - ROM screwup leading to main system damage

Dave, please double check in case I have misread the capture :) Just looking at those two screen shots, a few things don't seem right: 1. The value on the BD data bus is 0x40, where as the 6522 should be outputting 0x80 from &FE4E after a power-up reset. 2. The BD data bus doesn't actually seem to ...
by mw0uzo
Mon Jan 09, 2017 6:29 pm
Forum: hardware
Topic: Dead BBC Masters - ROM screwup leading to main system damage
Replies: 234
Views: 10601

Re: Dead BBC Masters - ROM screwup leading to main system damage

Ok I think i've found the read from the VIA in both captures
The read is the correct value 0100 0000
The value returned by the PBC was 1101 1111
So the bad IC is the PBC!!!!
VIAreadD3-D0.JPG
* ^ D3-D0 = D7-D4
VIAreadD7-D4.JPG
Dave, please double check in case I have misread the capture :)
by mw0uzo
Mon Jan 09, 2017 11:14 am
Forum: hardware
Topic: Dead BBC Masters - ROM screwup leading to main system damage
Replies: 234
Views: 10601

Re: Dead BBC Masters - ROM screwup leading to main system damage

danielj wrote:Mark Hayesman of Retroclinic would be my first port of call if you can tie it to the PBC. He's likely to have some.
Brilliant, thank you.

I couldn't resist - here are the captures for BD7-BD0, two captures of each nibble.
CaptureD.zip
(3.96 MiB) Downloaded 14 times
by mw0uzo
Mon Jan 09, 2017 10:35 am
Forum: hardware
Topic: Dead BBC Masters - ROM screwup leading to main system damage
Replies: 234
Views: 10601

Re: Dead BBC Masters - ROM screwup leading to main system damage

hoglet wrote: The pinout looks pretty compatible with a 27C256 EPROM; you would just need to bend pin 1 (VPP) out and connect it to +5V.

Am I missing something subtle here?
Yeah, that should work, after all we only need one rom mapped into 0000-3FFF!
by mw0uzo
Mon Jan 09, 2017 10:14 am
Forum: hardware
Topic: Dead BBC Masters - ROM screwup leading to main system damage
Replies: 234
Views: 10601

Re: Dead BBC Masters - ROM screwup leading to main system damage

Also just had a look at the technicalities of making the test ROM, it looks like it's not possible to fit a standard EPROM to the OS ROM socket. http://www.adsb.co.uk/bbc/bbc_master.html It would require an adaptor board that may be available, or make one. I might consider this for getting a bugfixe...
by mw0uzo
Mon Jan 09, 2017 9:47 am
Forum: hardware
Topic: Dead BBC Masters - ROM screwup leading to main system damage
Replies: 234
Views: 10601

Re: Dead BBC Masters - ROM screwup leading to main system damage

The one other case I remember of a Master spontaneously dying turned out to be the PBC (IC21): http://www.stardot.org.uk/forums/viewtopic.php?f=3&t=8698 Dave Very interesting. Obtaining potentially two spare PBCs may be difficult, I haven't found a known good source for it yet. My two masters are i...
by mw0uzo
Sun Jan 08, 2017 9:15 pm
Forum: hardware
Topic: Dead BBC Masters - ROM screwup leading to main system damage
Replies: 234
Views: 10601

Re: Dead BBC Masters - ROM screwup leading to main system damage

Do you think it's possible you inserted the ROM backwards? I'm sceptical about this, as it's next to other ROMs and would be really obvious. I don't think so, it's not the sort of mistake I have made, not for a long, long time. But I can't discount it completely, stupid things sometimes happen. If ...
by mw0uzo
Sun Jan 08, 2017 9:05 pm
Forum: hardware
Topic: Dead BBC Masters - ROM screwup leading to main system damage
Replies: 234
Views: 10601

Re: Dead BBC Masters - ROM screwup leading to main system damage

/PRST is held low and goes high at exactly the same time as /RST. There are two tiny blips, one at immediate switch on and one about halfway along before it goes high. Otherwise, this signal looks good. It resets the VIA until the CPU starts, allowing it to later read the interrupt register to detec...
by mw0uzo
Sun Jan 08, 2017 8:19 pm
Forum: hardware
Topic: Dead BBC Masters - ROM screwup leading to main system damage
Replies: 234
Views: 10601

Re: Dead BBC Masters - ROM screwup leading to main system damage

Pretty much nothing is socketed in a Master :( Dan, can you confirmed that PRST is low for some time after the clock starts on power up? Do you think it's possible you inserted the ROM backwards? I'm sceptical about this, as it's next to other ROMs and would be really obvious. Dave I'll check this ...
by mw0uzo
Sun Jan 08, 2017 7:29 pm
Forum: hardware
Topic: Dead BBC Masters - ROM screwup leading to main system damage
Replies: 234
Views: 10601

Re: Dead BBC Masters - ROM screwup leading to main system damage

Ok, it look like /PRST is the power on reset signal, derived from a tant capacitor and 27k resistor. This goes into IC8, 6522, controlling the keyboard, sound and disc interface... and the battery backed SRAM. Faulty reads from this IC explain the possible bad reads from the SRAM and the bad read fo...
by mw0uzo
Sun Jan 08, 2017 6:27 pm
Forum: hardware
Topic: Dead BBC Masters - ROM screwup leading to main system damage
Replies: 234
Views: 10601

Re: Dead BBC Masters - ROM screwup leading to main system damage

It might be a good idea to capture BD0-BD7 and see what's on there (although it might only be one read that we can compare)