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1N4001 (in fact 1N4001 through to 1N4007) are silicon rectifier diodes. They work fine in mains frequency applications, but are not very fast. 1N5819 diodes are fast, low voltage Schottky diodes. As such they are better suited to use in the output sections of switch mode power supply units. If you d...

You may want to replace C17 (2200uF 16V) as well, as this is the main smoothing capacitor for the +5V rail. I recommend a low ESR 105 o C type. [Although a normal electrolytic will work fine, low ESR types did not exist when these PSU were made...] Also while there, you may as well replace that last...

I’ve added you Gordon.

Mark

Voltages on the auxiliary power port of three of my Beebs: Model Serial number +12V -5V +5V —————— ———————————————— —————— —————— —————— BBC B 03-ANB01-3088426 14.21V -5.31V 5.03V BBC B 01-ANB04-6011871 14.1V -5.21V 5.001V BBC B+ 01-ANB51-3504713 13.86V -5.21V 5.02V Mark

The 'horrendously loud crackling noise' sounds like (sorry) you have a poor connection, or dry solder joint in part of the audio sound circuitry. Or maybe a component is breaking down, or there is contamination on the PCB in the area of the audio sound circuitry. Do you have, or have access to an os...

The +12V output is not regulated, so if there is no load on the +12V (nothing internally uses this supply voltage in an unexpanded machine) but the +5V supply is heavily loaded (normal machine) then a higher voltage on the +12V is normal. If more current (than that used by an unexpanded machine) is ...

Are you keeping note of all the addresses that the memory test program shows as failures? If yes, please post them here. If not, please start taking notes. It certainly is a good idea to swap the DRAM chip for IC64. It’s possible that you have multiple issues with this machine. However, the normal w...

Hi Robert I’ve updated the list to reflect your upgrade to a full table. We all would be very grateful for a supply of snacks and soft-drinks. But as always with these things, it may be a good idea to check with the museum (or Jason may know) just to check that they are okay with this (I have forgot...

OK still none the wiser. I ran Martins test program and that sometimes passes and sometimes fails but does not return an IC! It returns the address buy no IC number.....? Part of the test is the displayed image during testing. Is the pattern drawn consistent? If it shows anything odd, take a photo....

...the leftmost microswitch (although they also seem to be called "tactile push buttons" or "tactile momentary switches")... Yeah, those switches/buttons are tactile momentary push button switches, not microswitches. Microswitches are more complex and hence last longer, have a greater voltage and c...

I should add that the connections may be different at each end. For example one device may use RTS/CTS, while the other device may use DSR/DTR.

There is a reason why RS232 break-out boxes with signal LEDs and patch panels / DIP switches used to be popular...

Mark

Please note that there never was a universal standard for connecting two computers together using a RS232 serial connection. The RS232 standards are mostly concerned with connecting Data Terminal Equipment (teletypewriters and later computers and other equipment) and Data Communications Equipment (M...

As this Beeb is on the dark side, is it Kylo Ren’s Beeb? And is it more kryoflux compatible than a standard Beeb?

Mark

Mark, I was just running the 3 line bit of code which reads and writes to ?$4000. 10 A=0 (or 255) 20 ?&4000=A: IF ?&4000<>A THEN PRINT ?&4000 30 GOTO 20 This type of short test program is designed only to pick up the simple most common faults with DRAM chips. That is where the suspected DRAM chip a...

Hi James

I’ve sent you a private message (PM).

Mark

I suggest you contact the person who posted it via private message (PM)

Mark

smokey wrote: ↑

Sat Apr 20, 2019 9:16 pm

CMcDougall wrote: ↑

Sat Apr 20, 2019 9:07 pm

probably the chip LM324N (Quad OPAMP) at IC13, but they are soldered in

Are you local to Gloucestershire or Worcestershire

James

Colin lives in Scotland.

Mark

Hi Mark I do not have another working computer currently (8 bit) I bought the electron as untested. It turns on and displays Acorn Electron > Iam not electronicly wise Can i send this to you for testing ? James Hi James Whereabouts are you? I’m located just south of Bristol. I can take a look at yo...

From inside the case, unless someone left a note (maybe in marker pen), there is no easy way to know. If you disconnect the BBC micro from the mains, and then remove the PSU section from the main case, you can then see capacitors C1 and C2 (the two X2 type suppression capacitors, originally Rifa bra...

I've made some updates. I haven't implemented interrupts or a FAT32 driver as yet, but I've added in 4 sideways RAM slots (4, 5, 6 and 7) alongside the 4 ROM slots that were already implemented (12, 13, 14 and 15). This way I can load the Electron Sideways RAM version of MMFS (ESWMMFS) into slot 4 ...

RIFA cap looks to be exactly the same as one of the ones in the BBC Micro so getting one should be no problem - unless there is a better quality part anyone can suggest. Any good quality (meaning a brand name type sold by proper electronic suppliers) class X2 capacitor that has the same value, the ...

Normal Acorn BBC B boot screen: BBC Computer 32K Acorn DFS BASIC > Your Acorn BBC B boot screen: BBC Koeputer 3:K Acgrf DFS BA←IC > So the characters that are different are: K instead of C. K in binary is 01001011 and C in binary is 01000011. Bit 3 is 1 instead of 0. e instead of m. e in binary is 0...

Welcome on board marra!



Welcome to the world of Acorn machines

Enjoy the forum

You can make your confession here
Put yourself on the map by sticking a pin in it at this link
You can list your Acorn machines vitals here

Mark

If you compare the characters displayed in the MODE 7 ‘boot up’ screen with the characters that should be displayed, you can work out which bit or bits are incorrect. In the back of the manual there is a chart of the MODE 7 / teletext character set. Which memory test program are you using? How long ...

There are still full tables available if you do want more room. The tables are fairly large, but I don’t have actual dimensions to hand. If you look back at photos of previous events at Cambridge, that may help you. The previous events end up in this sub-forum . Last year Jason posted about table si...

*waves* There's been two "list updated" posts since my request to come along, so I think you've overlooked me! :( :oops: Oops :oops: Sorry about that Bryan. I’ve added you now. Not sure how I missed you the first time #-o If I have missed anyone else out, or have any other details wrong or incorrec...

Well, that’s the problem with pigeonholing... there’s always something that doesn’t fit...

Mark

Do you have any of the following:

• Another 8 bit computer such as another Acorn, or Sinclair?
• Any test gear, such as a multimeter or oscilloscope?

Is this a failure of a previously working computer, or have you never had this one working for loading?

Mark

Hi, presumably if you just want to attend for a look around and a chat, no need to book, even as a "no kitter"?? If you wish to attend to visit and look around the museum and chat in the common area, yes no need to book. If you do wish to spend any length of time in the room that we (ABUG) are usin...

anightin wrote: ↑

Thu Apr 18, 2019 11:22 am

... permission to attend ABUG in Cambridge in June

Best go and post in the relevant booking thread super quick, as it’s filling up fast...

Mark