Search found 205 matches

by philb
Mon Oct 16, 2017 7:50 pm
Forum: 32-bit acorn hardware
Topic: RISC-PC Not Working
Replies: 61
Views: 6967

Re: RISC-PC Not Working

No resistor, is that vital? What value should I use? They are 2150mAh (mAH? MaH? MAH? Mah?) batteries. It's fairly vital to restrict the charging current into the battery, yes. Otherwise the batteries will overheat and may start venting. The fact that you currently have a diode in series will be he...
by philb
Mon Oct 16, 2017 12:59 pm
Forum: 8-bit acorn hardware
Topic: BBC Model B takes up smoking
Replies: 39
Views: 3891

Re: BBC Model B takes up smoking

KayjayUK wrote:That is so true. I stripped and repaired 6 psu's at one time about 2 years ago, every one of them has now popped. Oh and I used RS parts, I have always believed in their quality but I assume this isn't a quality issue.
That is a bit strange. Do you remember exactly what part you used?
by philb
Sun Oct 15, 2017 7:44 pm
Forum: 32-bit acorn hardware
Topic: RISC-PC Not Working
Replies: 61
Views: 6967

Re: RISC-PC Not Working

Do I need 2 diodes? A300 picture shows two, but the RISC PC technical drawing battery/RTC page only shows one. You need 2 diodes if you are using a non-rechargeable battery: the second diode blocks the reverse current which would otherwise try to charge the battery when main power is on. If you are...
by philb
Sat Oct 14, 2017 6:20 pm
Forum: 32-bit acorn hardware
Topic: AKF12 display issues
Replies: 7
Views: 1043

Re: AKF12 display issues

Thanks. it was set to 2. I changed it to some other random number and it did seem to remember it over a power cycle.

I'll try configuring it to 10 and see what happens, though I'm a bit puzzled that delete-power-on didn't put it back to the right value at least transiently.
by philb
Sat Oct 14, 2017 5:43 pm
Forum: general
Topic: Today I received.....
Replies: 5988
Views: 609055

Re: Today I received.....

Most of the parts to build an MFM disk reader board... https://lh3.googleusercontent.com/Yi8ecaCMCjOdt--E0mtD7tEKNTQrGdmFKpcUInPpE1-K06Of2OrzVOVBmC8DpAg2MVlAhga7VA8D7uLHzJlX7-6YfHMrZF67qeX__q7GiFuhGV8mwvZhT2InrrfDbCFsKqikfV-2e38wm5k8hzZU75XbmvDHywk3XFsBzSaKfwht9sUcfd-UOQ_Z1I8IeqMMFHbBj84EkFIvj2xoPt4...
by philb
Sat Oct 14, 2017 5:36 pm
Forum: 32-bit acorn hardware
Topic: AKF12 display issues
Replies: 7
Views: 1043

Re: AKF12 display issues

I soldered a wire to reconnect SK7 pin 5 to IC4 (having belatedly realised that both these parts are through-hole so soldering them on the back is much easier than doing it on the front!) and that does seem to have fixed my missing yellow column. I'm still missing ctrl and left shift which suggests ...
by philb
Sat Oct 14, 2017 5:30 pm
Forum: 8-bit acorn hardware
Topic: Broken MDFS
Replies: 30
Views: 3196

Re: Broken MDFS

ISo if I'm reading that correctly, it fails if bit 7 reads back as a 1 through IC53. I put my scope on that chip and this does indeed seem to be what's happening. I am sort of assuming that this is the SCSI RST# signal and is supposed to have gone low as a result of the write to &4D. I'll have to s...
by philb
Fri Oct 13, 2017 10:43 pm
Forum: 8-bit acorn software: other
Topic: Variants of ADFS
Replies: 16
Views: 2670

Re: Variants of ADFS

One of the major obstacles many of us are finding is being able to archive real SCSI/ST506 Winchester discs. Being able to do a direct sector copy from proper ADFS to IDE/CF/SD etc. ADFS would be very helpful, but as others have already said, having two versions of ADFS live at the same time doesn'...
by philb
Fri Oct 13, 2017 9:13 am
Forum: 8-bit acorn hardware
Topic: SJ MDFS server circuit diagram/schematic
Replies: 32
Views: 4667

Re: SJ MDFS server circuit diagram/schematic

Thanks, I found that the other day and it does help. (Though I am a bit colourblind so it possibly doesn't help me as much as some... #-o)
by philb
Thu Oct 12, 2017 10:57 pm
Forum: for sale / freebies
Topic: SmallyMouse2 bare PCBs FTAGH
Replies: 7
Views: 1116

Re: SmallyMouse2 bare PCBs FTAGH

I'd be interested in one. I will try to get along to the "London" show to pick it up.
by philb
Thu Oct 12, 2017 10:17 pm
Forum: 8-bit acorn hardware
Topic: Broken MDFS
Replies: 30
Views: 3196

Re: Broken MDFS

I am sort of assuming that this is the SCSI RST# signal and is supposed to have gone low as a result of the write to &4D. I'll have to see if I can figure out from the schematics which latch is supposed to be driving that net. Memo to self, yes it's RST# and it comes from pin 10 of IC26 via pin 12 ...
by philb
Thu Oct 12, 2017 8:04 pm
Forum: 8-bit acorn hardware
Topic: SJ MDFS server circuit diagram/schematic
Replies: 32
Views: 4667

Re: SJ MDFS server circuit diagram/schematic

Doh, right, I see.

It seems that JSchem can read ExpressSCH files and write them out in its own xml format. Which is pretty grim, but I suppose I could implement a netlister from that...

Or I could adopt your strategy and cover the wall of my office in printouts :)
by philb
Thu Oct 12, 2017 7:40 pm
Forum: 8-bit acorn hardware
Topic: SJ MDFS server circuit diagram/schematic
Replies: 32
Views: 4667

Re: SJ MDFS server circuit diagram/schematic

Would someone with ExpressSCH installed be able to generate a netlist and post it here? Following the wires in the PDF schematic is a bit of an eye test, particularly where they get bunched tightly together.
by philb
Thu Oct 12, 2017 6:42 pm
Forum: 8-bit acorn hardware
Topic: Broken MDFS
Replies: 30
Views: 3196

Re: Broken MDFS

I've taken the parity mod back off and, as I sort of expected, it didn't make any difference. The first check that the ROM seems to be doing (edit, thanks JGH for the disassembly!) is: XOR A OUT (&00),A ; SCSI DATA = 0 OUT (&0C),A ; SCSI REQ OFF OUT (&4D),A ; SCSI RST ON IN A,(&01) ; SCSI COMMAND BI...
by philb
Thu Oct 12, 2017 1:49 pm
Forum: 8-bit acorn hardware
Topic: Broken MDFS
Replies: 30
Views: 3196

Re: Broken MDFS

Hm, right, that's sort of as I feared/suspected. Mine does have a hand-hacked parity mod on the SCSI bus which might possibly be upsetting it, I might see about removing that and see if the situation improves. Otherwise I suppose I'll have to (a) learn Z80 assembler; and (b) disassemble the ROM to f...
by philb
Thu Oct 12, 2017 1:41 pm
Forum: 8-bit acorn hardware
Topic: Broken MDFS
Replies: 30
Views: 3196

Re: Broken MDFS

I just whipped out IC15 from the MDFS and replaced it with a DRAM "borrowed" from my 80286 copro and that does seem to have done the trick. At least, it now boots as far as giving me six flashes on "system failure", which seems to indicate a SCSI bus error. Would I expect to get that if I don't have...
by philb
Wed Oct 11, 2017 8:28 am
Forum: 8-bit acorn hardware
Topic: Broken MDFS
Replies: 30
Views: 3196

Re: Broken MDFS

Right, cool. I guess I can scavenge one out of another machine and confirm that it really does fix the problem to begin with. I have a feeling the 80286 copro uses the same parts.
by philb
Tue Oct 10, 2017 7:47 pm
Forum: 8-bit acorn hardware
Topic: Broken MDFS
Replies: 30
Views: 3196

Re: Broken MDFS

Replaced C3 and I now have a plausible-looking MUX drive but the unit still doesn't boot. After a bit of poking around at data signals I think I have a faulty DRAM. Everything looks OK while it's reading from ROM, then I get: https://lh3.googleusercontent.com/YKFflURMMJA4ogAt5Aw-NAYLp8i-718WCVcLRCOO...
by philb
Mon Oct 09, 2017 9:34 pm
Forum: 8-bit acorn hardware
Topic: Video ULA/proc VC2023 in an Iss3 beeb weirdness..
Replies: 8
Views: 1271

Re: Video ULA/proc VC2023 in an Iss3 beeb weirdness..

does a extra wire jumper needed somewhere on an Issue3 board by any chance :-k Don't think so. The service manual contains a list of all the changes between issue 3 and issue 7 and the only video-related mod is the one you already did. If you swap the upper and lower RAMs around, does the behaviour...
by philb
Sun Oct 08, 2017 9:33 pm
Forum: for sale / freebies
Topic: BeebSCSI mini
Replies: 168
Views: 24778

Re: BeebSCSI mini

Sorry for the delay, I've now made them available on my store webpage. Your T&C's are still silly. http://www.xeropage.co.uk/shop/index.php?id_cms=3&controller=cms&content_only=1 It's true that "consectetur" seems to have gained a spurious space, but I think we should be able to forgive the odd typo.
by philb
Sun Oct 08, 2017 3:12 pm
Forum: 32-bit acorn hardware
Topic: Acorn 3000 4mb Ram Expansion
Replies: 49
Views: 5583

Re: Acorn 3000 4mb Ram Expansion

I finally got my A3000 working well enough to try out the two 4MB boards that I received from Dave. Am I safe to assume that if the machine POSTs correctly with the expansion in place and reports 4096MB then the RAM is good? I don't remember exactly how thorough a RAM test it does at POST time. If n...
by philb
Sun Oct 08, 2017 3:09 pm
Forum: 32-bit acorn hardware
Topic: AKF12 display issues
Replies: 7
Views: 1043

Re: AKF12 display issues

Oh right, perfect. So it looks as though the "yellow column" on pin5 is my problem. I also seem to still have some sort of CMOS RAM difficulties since the machine only boots to the Supervisor prompt today (although last week it was happily starting the desktop) and delete-power-on doesn't seem to he...
by philb
Sun Oct 08, 2017 2:20 pm
Forum: 32-bit acorn hardware
Topic: AKF12 display issues
Replies: 7
Views: 1043

Re: AKF12 display issues

I'm pleased to report that replacing the four big electrolytic caps on the AKF12 power supply board seems to have cured the display issues and the picture now looks pretty good. Here's the PCB in question. It comes out of the monitor easily, no need to remove the chassis or mess with any of the conn...
by philb
Thu Oct 05, 2017 10:32 pm
Forum: 32-bit acorn hardware
Topic: ST506 HDD woes
Replies: 37
Views: 4895

Re: ST506 HDD woes

This page: http://stason.org/TULARC/pc/hard-drives-hdd/rodime/RO3065-53MB-3-5-HH-MFM-ST506.html has some interesting info about the RO3065. In particular, it seems that it does have embedded servo data so what I said earlier about the positioner is probably not relevant. For some reason I had been v...
by philb
Thu Oct 05, 2017 9:33 pm
Forum: 8-bit acorn hardware
Topic: MDFS PSU capacitor polarity
Replies: 4
Views: 772

Re: MDFS PSU capacitor polarity

jgharston wrote:Are any of these of any use?
I think the full-res versions of those might have been, but the thumbnails (which seem to be all that was available) didn't have enough detail. Thanks anyway though, I got it figured out.
by philb
Thu Oct 05, 2017 11:41 am
Forum: 32-bit acorn hardware
Topic: ST506 HDD woes
Replies: 37
Views: 4895

Re: ST506 HDD woes

Is there data on the disk that you want to retrieve, or are you just interested in making it work again? It's possible that the head alignment has drifted a bit, in which case reformatting it might improve the situation. Some disks of that vintage needed to be reformatted if, for example, their orie...
by philb
Wed Oct 04, 2017 9:55 pm
Forum: 32-bit acorn hardware
Topic: ST506 HDD woes
Replies: 37
Views: 4895

Re: ST506 HDD woes

It's a shame there's no ST506 to CF Card converter out there, breath new life into those factory fit ST506 controllers in the A4x0's :mrgreen: There is, sort of. http://www.pdp8.net/mfm/mfm.shtml Emulating an ST506 disk is harder than you might think (and somewhat harder than replacing an IDE or SC...
by philb
Wed Oct 04, 2017 11:00 am
Forum: 32-bit acorn hardware
Topic: ST506 HDD woes
Replies: 37
Views: 4895

Re: ST506 HDD woes

from the sounds of it, there are relays and/or solenoids involved - and it's the solenoid type click' which appears to be associated with the previously working A420's drive now failing. Could be the same fault for the never-working A410's drive... I don't think I've ever seen a hard disk with rela...
by philb
Tue Oct 03, 2017 6:41 pm
Forum: 8-bit acorn hardware
Topic: MDFS PSU capacitor polarity
Replies: 4
Views: 772

Re: MDFS PSU capacitor polarity

Nevermind, I traced out the connections and it is indeed just that one capacitor that's wrong on the silkscreen. So now I have a full set of new PSU caps in there. Just need to figure out why the machine won't boot now!
by philb
Mon Oct 02, 2017 5:19 pm
Forum: 8-bit acorn hardware
Topic: MDFS PSU capacitor polarity
Replies: 4
Views: 772

MDFS PSU capacitor polarity

Could someone with an MDFS do me a favour and post a photo of the PSU circuit showing which way around the electrolytics are fitted? On my board I have discovered that at least one of the originals was fitted the opposite way round to the markings on the PCB. I assume this is a PCB artwork error but...

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