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Keep both. Makes fault finding easier when one breaks.

Thank you for the replies. I'll try out the various DFSs at the weekend, when I get a bit more time. I assume the Solidisk and ACP versions are similar to the MRM version, and are using RAM that is directly mapped into a section of its own SWR bank?

Thanks for that. I'll try it out this evening. This has got me thinking / wondering if I could perhaps adapt one of the PALPROM based board designs, and use a 32k FRAM to store a modified 8271 DFS / 1770 DFS / DNFS / NFS / ADFS on one of the 16k banks, and use the other bank for workspace. The FRAM ...

For the 8271 there's the MRM E00 DFS, see https://stardot.org.uk/forums/viewtopic.php?f=4&t=11633&p=224870#p224870. Thanks for that info. Do you know if that DFS runs in a standard SWRam bank, or does it rely on its own special private RAM that gets switched in and out by the DFS? Edit: https://aco...

Does such a thing exist for the standard Acorn supplied 8271 / 1770 based controllers installed in a model B? Similar to the SWMMFS image?

Hi tucker,

I've still got a few left. If you're still interested, lets take it to PM, where we can sort out payment and delivery details.

Also, just double checking that it's a BBC B that you're wanting to install this into and not a Master?

If your beeb is working reliably after you hit the Break, then it's unlikely to be a RAM issue. As Kazzie has indicated, it might be better starting a new thread, but a couple of quick pointers: I'd definitely check that nRSTA and nRST lines are working as expected. If you've got a scope, then they ...

Please forgive my ignorance, but why would pressing break allow the beeb to continue booting normally if one of the ram chips is faulty? Boot up was a bit intermittent. Occasionally it would take more than one press of Break to get it to boot. Also, it would not always fail to boot on power up. Som...

Are you still looking for faulty DRAM? I've got a faulty Mostek MK4516N-10 that I pulled from my beeb yesterday if it's of any interest, otherwise it'll be going in the bin.

Final post, just to close out this thread. I tried just re-soldering the RAM first, but that didn't make any difference. In fact, I made things worse - I started to get strange sparkles in Mode 7. Turns out that was down to me not re-soldering one of the RAM pins properly. Panic over. Next, I remove...

Right. I think this might actually be a RAM issue. Moving S25 from North to South gets it booting reliably in 16k mode. Removing the jumper, boot up is still unreliable. All RAM is soldered in except IC53, which has been replaced at some point in the past (I think I did this). As a quick test, I pul...

If we're playing with interrupts, there's also the NMI to consider. At least that's just two sources to consider (IC27 pin 3 for the Econet, and IC27 in 8 for the FDC). The NMI line remains high at all times, so I don't think that's the issue. I've also swapped out the 6522s for known good ones, an...

Looking at the IRQ traces, I notice that on a good start the IRQ line is being held low by something. On a failed start, nothing is holding it low. Time to start swapping out some chips. A quick look at the circuit diagram I note the following all drive the nIRQ line: IC3 - 6522 IC4 - 6850 IC69 - 65...

We’ve see something similar before with a misbehaving Beeb, but nothing wrong in the reset circuits. Is the NMI line high (correct) or is something pulling it low? Also test the IRQ line with your scope, just to check that that is normal. Also check / search the hardware thread, as I say, this kind...

Could be global warming. I might have a play later, but might not have time. Not that it sounds an issue as meter giving expected result. So, the global warming issue was just in my house! 10x did work. I just didn't realise the scaling on the scope changed from 1v/division to 10v/division when I s...

X10 mode should have sorted it. Did you change to x10 on both probe and scope? I did, but the result was even odder, so I gave up on that for now. I'm fairly certain the measured voltage is fine. Here's a couple of screen captures from the scope. The yellow trace is nRSTA and the blue trace is nRST...

Thanks for the replies, guys. Board has been out, and everything around the Power Up reset circuit and the 555 timer circuit has been checked and re-soldered. If I measure nRSTA with a multimeter I get about 4.5v, so I'm pretty sure it's an impedance issue with the Scope. I get the same results on a...

Is it the case that a Ctrl-Break will usually bring it to life, but just pressing Break alone won't do it? Sorry. Just in the habit of pressing Ctrl Break all the time. A Break alone also brings it back to life. Edit: Another thing that initially confused me was that the scope was only measuring ab...

Hi, I've got a beeb that will not power up very reliably. 9 times out of 10 I will just get a low constant beep. Pressing Ctrl Break nearly always brings it to life. I've scoped the nRSTA and nRST lines (pins 34 on the 2 VIAs), and see nRSTA on IC3 rising first, followed by nRST on IC69 rising about...

Colday wrote: ↑

Sat Sep 14, 2019 8:09 am

I shall remove all the DFS ROMS shortly.

Which would you recommend I leave in?

You need to leave in the Watford DDFS ROM. You also need to provide version number of this ROM as previously requested by Hoglet (using *HELP).

Eventually regained access to my discord account and was able to see your photos. So, it looks like you've got a Watford Electronics 1770 based controller. I'm not familiar with the WE DDFS that you've got installed in the ROM expansion board, but I presume it's just a 1770 based DFS for use with th...

Indeed. I've just spent the last 5 mins trying to log in to an old account. I've given up!

The solution I've adopted is to replace the 6 pin RGB socket with an 8 pin version. The two 'extra' pins on the socket are then connected to the speaker header on the beeb motherboard. The RGB to SCART cables that I've bought from eBay sellers usually have extra cores in the cable, so I can then rem...

Thanks for the info. I'm guessing you tried the RS 146-3926 . Given that I don't need that quantity, I've just ordered up a pack of 10 RS 814-9440 for £1.70 (including VAT & postage). Ony real difference I can see between the two is load capacitance, and frequency tolerance / stability. Assuming th...

Thanks for the info. I'm guessing you tried the RS 146-3926 . Given that I don't need that quantity, I've just ordered up a pack of 10 RS 814-9440 for £1.70 (including VAT & postage). Ony real difference I can see between the two is load capacitance, and frequency tolerance / stability. Assuming the...

However, as everything original in Beebs are now 30-35 years old, I will replace them from now on for the sake of 30p. Out of interest what crystal will you be using? Have you tried any of the HC-49US (I assume the S stands for small) package devices in place of the original HC-49U? The US package ...

retroclinic wrote: ↑

Wed Sep 11, 2019 9:13 am

Closest I can find in an HC49 case is 30ppm

There's one seller quoting 20ppm:

https://www.ebay.co.uk/itm/IQD-16MHz-Cr ... Sw0JFbVeoM

Looking good .

Any suggestions on how to implement this? I have no idea :? I haven't read through the code to see what it's doing to determine 'Empty bank?', but I think it would be quite difficult for any code to reliably determine if a bank is empty. The data bus will not be getting driven during an attempted r...

Anyone any clue how it's detecting an empty socket? Not sure if it's related, but I had a similar issue with my IntegraB board, where Elite was incorrectly detecting empty ROM slots as RAM: https://stardot.org.uk/forums/viewtopic.php?f=1&t=17097&p=238345#p237713 The plausable explanation from 1024M...