Search found 97 matches

by philb
Mon Oct 23, 2017 10:39 pm
Forum: hardware
Topic: Dead MDFS Resurrection
Replies: 212
Views: 8401

Re: Dead MDFS Resurrection

I think the ROM monitor does talk to the serial port but the way in which the monitor is entered is a bit inscrutable (to me). I'm fairly sure that in a stock ROM you can't get there until you've passed the hardware diagnostics, but obviously it wouldn't be very hard to make a version that bypassed ...
by philb
Mon Oct 23, 2017 10:21 pm
Forum: hardware
Topic: Dead MDFS Resurrection
Replies: 212
Views: 8401

Re: Dead MDFS Resurrection

I also see from the disassembly that SRL's Portable Monitor features in the ROM. I'm not quite sure how you invoke that though. I assume you talk to it through the serial port, and if it were possible to get the monitor running then this might give you a further route to debugging.
by philb
Mon Oct 23, 2017 7:39 pm
Forum: hardware
Topic: A5000 IDE interface just died... what to try next?
Replies: 18
Views: 503

Re: A5000 IDE interface just died... what to try next?

...but if you can't get floppy to work either, then the fault is possibly a dead controller and you can't get replacements of these :( (...even if you could, they are very fine pitch smd, so would need some serious expertise to replace) There seems to be a guy on ebay selling 82C711s at the moment....
by philb
Mon Oct 23, 2017 2:21 pm
Forum: hardware
Topic: Dead MDFS Resurrection
Replies: 212
Views: 8401

Re: Dead MDFS Resurrection

Here's the order of the checks it does, based on JGH's ROM disassembly: 1. ROM (7 flashes) 2. SIO (3 flashes) 3. FDC (4 flashes) 4.. SCSI (6 flashes) 5. CTC (5 flashes) 6. RAM (2 flashes) The RAM test involves writing to banked memory and if the address lines or page control were not working correct...
by philb
Mon Oct 23, 2017 11:54 am
Forum: hardware
Topic: Dead MDFS Resurrection
Replies: 212
Views: 8401

Re: Dead MDFS Resurrection

At what point does it do that? All lights come on, and then power & no clock stay on and the system LED starts flashing. Does that mean that by that point it has copied the ROM to RAM and is executing it? Yes. In what circumstances (if ever) would you get a RAM fault indicated? It does a more t...
by philb
Sun Oct 22, 2017 9:07 pm
Forum: hardware
Topic: Dead MDFS Resurrection
Replies: 212
Views: 8401

Re: Dead MDFS Resurrection

one minor thing - sometimes only no clock and power lights come on, but immediately switching it off and on again gets it going. Mine does that as well sometimes and the problem seems to be that the RESET generator circuit R49/C14 isn't working properly so the system gets stuck in reset. Sometimes ...
by philb
Sun Oct 22, 2017 8:08 pm
Forum: hardware
Topic: Dead MDFS Resurrection
Replies: 212
Views: 8401

Re: Dead MDFS Resurrection

I think Daniel had a self-built test ROM at one point but I don't know exactly what it did. What exactly are the symptoms of your unit at the moment, is it doing the "stuck with all LEDs on" thing? The way I identified the bad RAM on mine was to reboot it repeatedly (putting a squarewave a...
by philb
Sat Oct 21, 2017 8:18 pm
Forum: hardware
Topic: Broken MDFS
Replies: 19
Views: 651

Re: Broken MDFS

I guess I need to capture all the signals around IC43 and see if that part appears defective. I spent another half-hour in the lab today and it does seem that this chip is the culprit. Pins 10 and 11 are high, pin 9 pulses low in the same way as IC62 pin 12, but pins 5 and 12 are stuck high and low...
by philb
Sat Oct 21, 2017 8:07 pm
Forum: hardware
Topic: ST506 HDD woes
Replies: 31
Views: 1183

Re: ST506 HDD woes

It's odd that your drive's giving a "no index" error code, given that it's not even managing to spin the platter. You'd have thought it would give one of the motor errors in preference, as this is the more fundamental problem. I think that's exactly what "no index" means. The IN...
by philb
Tue Oct 17, 2017 10:19 pm
Forum: hardware
Topic: RISC-PC Not Working
Replies: 61
Views: 2236

Re: RISC-PC Not Working

If you moved the wires around a bit then that would probably have been enough to disturb the parasitic capacitances and change the frequency that the RTC counts at. 10pF isn't much!
by philb
Tue Oct 17, 2017 10:13 pm
Forum: hardware
Topic: RISC-PC Not Working
Replies: 61
Views: 2236

Re: RISC-PC Not Working

Jolly good. It sounds like you figured it out already, but the answer to your previous question is that the +ve end of the diode is the one away from the stripe. If your RTC is gaining time then that would suggest you don't have enough load capacitance on the crystal. You could try adding some small...
by philb
Mon Oct 16, 2017 7:37 pm
Forum: hardware
Topic: Fileserver reverse engineering
Replies: 0
Views: 90

Fileserver reverse engineering

Following the awesome work that was done to trace the MDFS circuit ( http://stardot.org.uk/forums/viewtopic.php?f=3&t=9407&p=182600 ) I was left wondering whether anybody had ever done this for the somewhat rarer FDFS and HDFS. Anyone know of any efforts in that direction? It'd be quite plea...
by philb
Mon Oct 16, 2017 6:50 pm
Forum: hardware
Topic: RISC-PC Not Working
Replies: 61
Views: 2236

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 11:59 am
Forum: hardware
Topic: BBC Model B takes up smoking
Replies: 39
Views: 945

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 6:44 pm
Forum: hardware
Topic: RISC-PC Not Working
Replies: 61
Views: 2236

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 5:20 pm
Forum: hardware
Topic: AKF12 display issues
Replies: 7
Views: 221

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 4:43 pm
Forum: general
Topic: Today I received.....
Replies: 4225
Views: 225838

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 4:36 pm
Forum: hardware
Topic: AKF12 display issues
Replies: 7
Views: 221

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 4:30 pm
Forum: hardware
Topic: Broken MDFS
Replies: 19
Views: 651

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 ...
by philb
Fri Oct 13, 2017 9:43 pm
Forum: software: other
Topic: Variants of ADFS
Replies: 16
Views: 414

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 8:13 am
Forum: hardware
Topic: SJ MDFS server circuit diagram/schematic
Replies: 32
Views: 2288

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 9:57 pm
Forum: for sale / freebies
Topic: SmallyMouse2 bare PCBs FTAGH
Replies: 7
Views: 209

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 9:17 pm
Forum: hardware
Topic: Broken MDFS
Replies: 19
Views: 651

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...
by philb
Thu Oct 12, 2017 7:04 pm
Forum: hardware
Topic: SJ MDFS server circuit diagram/schematic
Replies: 32
Views: 2288

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 6:40 pm
Forum: hardware
Topic: SJ MDFS server circuit diagram/schematic
Replies: 32
Views: 2288

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 5:42 pm
Forum: hardware
Topic: Broken MDFS
Replies: 19
Views: 651

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) ;...
by philb
Thu Oct 12, 2017 12:49 pm
Forum: hardware
Topic: Broken MDFS
Replies: 19
Views: 651

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 12:41 pm
Forum: hardware
Topic: Broken MDFS
Replies: 19
Views: 651

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 ...
by philb
Wed Oct 11, 2017 7:28 am
Forum: hardware
Topic: Broken MDFS
Replies: 19
Views: 651

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 6:47 pm
Forum: hardware
Topic: Broken MDFS
Replies: 19
Views: 651

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...

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