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I'd try a Schottky diode before giving up -- or a "zero drop" reverse polarity protection circuit. There's one which uses a MOSFET in the Discferret (www.discferret.com) schematics. Essentially it uses the body diode to provide initial current, then grounds the gate to turn the FET on (but only whe...

Okay, so this is looking promising. I've let this run for quite a few hours over the last two days, and test_memc_memory.py seems to be working well on the A3000, with a v2 board with only the 5V protection diode removed. (Which of course negates most of the reverse polarity protection, but previous...

What a frustrating project this has turned into! Of course the whole year has been frustrating, especially over here in California where we not only still have far too much COVID, but also air that's too smoky to venture outside about half the time... I thought I had something ready to go out to peo...

And on double checking the RISC OS 3.11 code, nope... the pattern is completely different. Starting at 0x38000ac, it alternates between the true and inverted versions, so you should see:

80000000
7fffffff
40000000
bfffffff

etc... so I have no good explanation for what's going on there!

I think this got lost in an edit, but you're quite right that you should be seeing instructions on the data bus as well as the pattern. That said, I think the pattern itself is executable because the flags are set to NV on every word, so you might be seeing the processor NOP'ing its way through the ...

That's interesting. If ts_rRomPatt is executing, even if you're seeing odd data on the top half of the bus, your ROMs are probably okay, as without a working data bus, the processor isn't going to make it anywhere near the code. About A3000 RAM... two out of my three boards had at least one bad RAM ...

I have a few of these boards sitting around; happy to post one to you if you want one: https://github.com/google/myelin-acorn-electron-hardware/tree/master/pcf8583_daughterboard/pcb You can solder four wires (cut off the bad CMOS chip and solder SCL and SDA to the vias under it, and pick up 5V and G...

I need to go watch more of the ABug videos really... so much condensed knowledge in there :) If D9 and up show nothing, I would double check that Romcs* is reaching all the ROM chips... with enough corrosion for the sockets to fall apart, I wouldn't be surprised if some of the vertical tracks connec...

Are interrupts enabled on boot? If the only hardware issue is that Irq*/Fiq* are stuck low, I would expect it to at least try to run the self-test. I've seen errors saying something like "unexpected IRQ" in the detailed self-test output, so I think this is accounted for. You can see if the self-test...

This feels like the kind of thing the detailed POST output might give you some hints on... no estimate on when I'll be done with the v2 post box boards unfortunately :( Trying to remember all the possibly related issues I've seen on A3000s... - stuck in reset - bad traces in address lines to IOC - b...

I wonder if there's some special magic on the A4 (something else on the I2C bus maybe?) that makes this work, or if you were just very lucky :) If anyone else out there has an A4 they wouldn't mind experimenting on, or perhaps one that probably needs its CMOS chip replacing anyway, it would be very ...

I wonder how that possibly worked! Was this with RISC OS 3.11? I just tried disabling CMOS access in Arculator (adding a "return;" at the start of i2c_change in cmos.c, which simulates getting no response at all from the chip), and doing a boot with DEL held down. This gave me a red screen to indica...

IanJeffray -- are you absolutely sure that you've been able to get to the desktop without a CMOS chip installed at all? That's not my experience (or danielj's or SarahWalker). When I was repairing my A5000, I found that it would boot to Supervisor without the CMOS chip installed (as in, literally cu...

Hah -- I was one of those kids who used to hang out at Fred Frampton's computer shop (I forget the name now). I was 12 at the time, so I guess I wasn't around when he came to visit... I'm guessing the 14 year olds would have been the "little'uns", Iain Brandram-Adams and Paul ?, who renamed themselv...

If the CMOS chip is not getting power because of a broken PCB connection then the machine will never work properly. When I started up my A5000 with no CMOS chip fitted, I got something similar -- Supervisor prompt but all modules unplugged. Buzz out the connections from the CMOS chip to the crystal...

The reason is simply that the code is not useful to those without a significant amount of knowledge at the moment. Totally understand if you'd rather keep it private, but you'd be surprised how many people with a significant amount of Econet knowledge are lurking here :) There's been quite a few at...

Boydie added :) Boards #6-#9 are all programmed but untested; I'll start pinging people from the list for address and PayPal details within the next week! Update : Testing not going well :( None of the v2 boards I've tested are able to access the A3000's ROM at full speed -- they need to have it slo...

So the &20000 bit comes from here in the test code: R_LINFAILBIT * &20000 ; Page zero RAM failure That's set either by failing the data line test or the address line tests , which could be: - jumpers set incorrectly for the amount of RAM in the system (I've seen this on an A3000) - gazzaD's IDE buff...

CJS added.

Some good results in testing tonight -- it works on my A3000, A5000, and A7000. Only the Bush IBX250 is problematic, but that's an odd machine anyway Next project night, I'll start making boards to post out to people on the list!

I love that we have the RISC OS 3.6 source. I wonder if it would be possible to build the actual ROM still. I have the ROOL DDE and an Acorn DDE from 1993 or so, so maybe one of them would work... Here's the code that prints SELFTEST . And here's the code that writes to the debug adapter and aborts ...

I’ll take it if it’s still available! Will email you.

Added Paul, DutchAcorn, 8271 :) You should indeed be able to use this for the A4, although there's no provision for handling the extra two signals, so just leave those unconnected. If anyone wants to dig up more info on what those are for, there's some room in the FPGA to possibly support talking to...

So here's something interesting. I built up the first r2 POST box board last night, and it exhibits a similar issue; I can read out a ROM just fine (at least I think I can -- I'm doing an 8MB read right now to check this) but the self-test output is garbled, whether I use `python3 show_self_test.py`...

That was a bit of a mission, but I finally have something that's able to mostly show me the waveform: https://github.com/michal-szkutnik/pyRigolWfm1000Z Running this gives me a plot of the waveforms: python3 pyRigolWfm1000Z/wfmutil.py plot TESTREQ_TESTACK_POST.wfm I also extracted it as a CSV then r...

Have been spending all my spare time prepping for the ABug presentation for this, but that's all done now, so I'll take a look at the captures tonight and see if anything comes to mind!

I'm working on my slides for my talk at the Virtual ABug this Saturday, and figured these scans might be helpful for anyone working on fixing an A5000's floppy drive connections.

(These are printouts of photos, which I've written on with my new favourite toy, a Uniball UM-153 gold gel pen.)

Finally I have got the Arcflash v2 board running in my A540 :D (thanks myelin for the help, and the Arcflash!) Yay! Really happy to see it working in the king of the RISC OS 2/3 machines :) Thanks also for finding the bug in the ROM builder where it was neglecting to byte-swap the bootloader area o...

One for me please!

I have one of the 0197,010/T REV 1 power supplies (which adds up to 102.3 W; 5.1V x 11A, 12V x 3.6A, -12V x -0.25A).

Arcflash v3 and POST box v2 boards (pictured against their earlier versions)...

Interesting! I had the same idea. Have you got a PCB design for an Econet module? I was going to design a Podule and a module. As the 26LS30 is obsolete, I was planning to "borrow" the line driver circuitry Myelin designed for his "Econet from scratch" project, and use the old Acorn opamp line rece...