Search found 646 matches

by KenLowe
Sun Sep 15, 2019 11:34 am
Forum: wanted
Topic: Faulty DRAM chips wanted!
Replies: 8
Views: 928

Re: Faulty DRAM chips wanted!

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.
by KenLowe
Sat Sep 14, 2019 10:17 pm
Forum: hardware
Topic: Beeb Power Up Issue
Replies: 21
Views: 226

Re: Beeb Power Up Issue

Final post, just to close this out. 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 removed RAM I...
by KenLowe
Sat Sep 14, 2019 7:00 pm
Forum: hardware
Topic: Beeb Power Up Issue
Replies: 21
Views: 226

Re: Beeb Power Up Issue

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...
by KenLowe
Sat Sep 14, 2019 6:25 pm
Forum: hardware
Topic: Beeb Power Up Issue
Replies: 21
Views: 226

Re: Beeb Power Up Issue

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...
by KenLowe
Sat Sep 14, 2019 5:00 pm
Forum: hardware
Topic: Beeb Power Up Issue
Replies: 21
Views: 226

Re: Beeb Power Up Issue

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...
by KenLowe
Sat Sep 14, 2019 4:09 pm
Forum: hardware
Topic: Beeb Power Up Issue
Replies: 21
Views: 226

Re: Beeb Power Up Issue

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...
by KenLowe
Sat Sep 14, 2019 3:33 pm
Forum: hardware
Topic: Beeb Power Up Issue
Replies: 21
Views: 226

Re: Beeb Power Up Issue

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...
by KenLowe
Sat Sep 14, 2019 3:09 pm
Forum: hardware
Topic: Beeb Power Up Issue
Replies: 21
Views: 226

Re: Beeb Power Up Issue

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...
by KenLowe
Sat Sep 14, 2019 2:37 pm
Forum: hardware
Topic: Beeb Power Up Issue
Replies: 21
Views: 226

Re: Beeb Power Up Issue

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...
by KenLowe
Sat Sep 14, 2019 2:02 pm
Forum: hardware
Topic: Beeb Power Up Issue
Replies: 21
Views: 226

Re: Beeb Power Up Issue

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...
by KenLowe
Sat Sep 14, 2019 1:39 pm
Forum: hardware
Topic: Beeb Power Up Issue
Replies: 21
Views: 226

Beeb Power Up Issue

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...
by KenLowe
Sat Sep 14, 2019 8:27 am
Forum: hardware
Topic: Epson SD-521 DD errors/fail
Replies: 32
Views: 239

Re: Epson SD-521 DD errors/fail

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).
by KenLowe
Fri Sep 13, 2019 10:11 pm
Forum: hardware
Topic: Epson SD-521 DD errors/fail
Replies: 32
Views: 239

Re: Epson SD-521 DD errors/fail

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...
by KenLowe
Fri Sep 13, 2019 9:11 pm
Forum: hardware
Topic: Epson SD-521 DD errors/fail
Replies: 32
Views: 239

Re: Epson SD-521 DD errors/fail

Indeed. I've just spent the last 5 mins trying to log in to an old account. I've given up!
by KenLowe
Fri Sep 13, 2019 2:13 pm
Forum: hardware
Topic: variable volume for the BBC
Replies: 18
Views: 2177

Re: variable volume for the BBC

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...
by KenLowe
Fri Sep 13, 2019 1:27 pm
Forum: hardware
Topic: Fixed: Mode 7 intermittent lines
Replies: 40
Views: 937

Re: Fixed: Mode 7 intermittent lines

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...
by KenLowe
Thu Sep 12, 2019 3:39 pm
Forum: hardware
Topic: Fixed: Mode 7 intermittent lines
Replies: 40
Views: 937

Re: Fixed: Mode 7 intermittent lines

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...
by KenLowe
Thu Sep 12, 2019 3:13 pm
Forum: hardware
Topic: Fixed: Mode 7 intermittent lines
Replies: 40
Views: 937

Re: Fixed: Mode 7 intermittent lines

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 ...
by KenLowe
Thu Sep 12, 2019 11:44 am
Forum: hardware
Topic: Fixed: Mode 7 intermittent lines
Replies: 40
Views: 937

Re: Fixed: Mode 7 intermittent lines

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
by KenLowe
Wed Sep 11, 2019 2:12 pm
Forum: emulators
Topic: MAME: Click (and other large ROMs)
Replies: 93
Views: 5090

Re: MAME: Click (and other large ROMs)

Looking good =D> =D> =D>.
by KenLowe
Wed Sep 11, 2019 7:44 am
Forum: emulators
Topic: MAME: Click (and other large ROMs)
Replies: 93
Views: 5090

Re: MAME: Click (and other large ROMs)

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...
by KenLowe
Tue Sep 10, 2019 11:36 pm
Forum: emulators
Topic: MAME: Click (and other large ROMs)
Replies: 93
Views: 5090

Re: MAME: Click (and other large ROMs)

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...
by KenLowe
Tue Sep 10, 2019 6:43 am
Forum: emulators
Topic: MAME: Click (and other large ROMs)
Replies: 93
Views: 5090

Re: MAME: Click (and other large ROMs)

daveejhitchins wrote:
Tue Sep 10, 2019 6:36 am
It was probably nothing more than a PCB layout issue. Swapping a few lines to ease the layout is common. It only shows up when you read the ROM off-board.
That's kinda what I was thinking when I edited my post :D.
by KenLowe
Tue Sep 10, 2019 6:30 am
Forum: emulators
Topic: MAME: Click (and other large ROMs)
Replies: 93
Views: 5090

Re: MAME: Click (and other large ROMs)

Nice detective work =D> =D> =D>

I guess it's relatively easy to obfuscate by jumbling up both the data and address lines!

Edit: I wonder if the swapping of D1 & D2 was deliberate, or perhaps a PCB routing error that was corrected in the ROM?
by KenLowe
Thu Sep 05, 2019 11:29 am
Forum: hardware
Topic: Spooling cats and Datacentres
Replies: 11
Views: 424

Re: Spooling cats and Datacentres

Looks very neat =D> =D>
by KenLowe
Tue Sep 03, 2019 1:36 pm
Forum: hardware
Topic: Last Gasp for the 8271
Replies: 24
Views: 1217

Re: Last Gasp for the 8271

Definitely interested in a couple of those. Full kits preferably, but I'll take the 8271 on it's own if that's all your offering initially, as I'm sure I'll be able to track down the other components.

Thanks
by KenLowe
Tue Sep 03, 2019 1:33 pm
Forum: hardware
Topic: Raspberry Pi to 1MHz bus interface
Replies: 110
Views: 5952

Re: Raspberry Pi to 1MHz bus interface

tricky wrote:
Tue Sep 03, 2019 11:23 am
I can't remember or find, did I ask about an audio in pin to pass through to the audo in?
This is shown on the schematic:
.
RPi_1MHz_Audio.PNG
RPi_1MHz_Audio.PNG (8.28 KiB) Viewed 205 times
.
Not sure if that answers your question?
by KenLowe
Wed Aug 28, 2019 1:13 pm
Forum: hardware
Topic: Raspberry Pi to 1MHz bus interface
Replies: 110
Views: 5952

Re: Raspberry Pi to 1MHz bus interface

It is clear to me that I'm a bit slow at ordering and sending out hardware kits . Does anyone want to support / take over that hardware supply? I still want to support this and future projects. If someone could take the load off me I can focus on development work. Not sure if anyone did get back to...
by KenLowe
Wed Aug 28, 2019 1:10 pm
Forum: hardware
Topic: Beeb to go... (Portable)
Replies: 5
Views: 292

Re: Beeb to go... (Portable)

At a guess, there was probably some flexibility built into the design of the case. Is it possible that some cases could have housed a Winchester drive and floppy drive, in which case an internal PSU would probably have been necessary? For dual floppy drives, the beeb supply would have been good enou...
by KenLowe
Wed Aug 28, 2019 1:04 pm
Forum: hardware
Topic: Femto Flash Floppy
Replies: 28
Views: 981

Re: Femto Flash Floppy

You could just add a pair of 2 pin headers (or a single 4 pin) to the board. Then attach a couple of wires with momentary contact switches on them? This would preserve real estate on the board and allow you to add the buttons as an option. Unfortunately, I'm not sure it would be as simple as that. ...