Who else is building a Beeb from scratch?

[!FOZ!]

I've got no serial ULAs left, I was hoping for a CPLD replacement, I guess sacrificing the cassette function and replacing the ULA with a few wire links would allow the RS423 to work.

I got mine by contacting CJE, http://www.cjemicros.co.uk/micros/indiv ... -SERIALULA - this was circa just under a year ago though.

[maniacminer]

I've got no serial ULAs left, I was hoping for a CPLD replacement, I guess sacrificing the cassette function and replacing the ULA with a few wire links would allow the RS423 to work.

I got mine by contacting CJE, http://www.cjemicros.co.uk/micros/indiv ... -SERIALULA - this was circa just under a year ago though.

Yeah, I've seen those. £26+£3 P&P isn't worth it to me. I guess I'd rather put money into getting a replacement ULA made for when CJE doesn't have any ULAs at any price. At least that way Beebs of the future may have a opportunity to have good old cassette input. Children I've spoken to recently have never used a dial up modem, a compact disc or a tape, let alone a 40+ year old 8 bit micro. We need to keep the system alive through obsolescence and have ready logic diagrams for the impossible to replace parts in the Beeb - video ULA and serial ULA - made with simple logic that can be fabricated with whatever technology is available at the time.

[maniacminer]

Okey its like this mostly i look at the legs. Longer is positief + short -
Thats for most parts.
En de diodes have a mark like a wite line or black line. so you cant mis .

R8 is wrong way around.
Black tip is +

Yeah I am confident knowing the correct end. However I am unsure what direction to place the component on the board given all the examples seem to place the negative (cathode end) to the positive + marker on the pcb - see the differences in my pictures in the last post. How have you placed your D2?

I've no idea why the silkscreen shows the cathode of the diode as the anode. Oh well, I've got a rope of 5,000 1N4148's in an ammo box, so I'd better get snipping. It would have been useful for the board creator to not repeat the mistakes of the original.

[!FOZ!]

At least that way Beebs of the future may have a opportunity to have good old cassette input.

Totally agree. Though, I've been hard pushed to find a decent tape player on eBay to go back down memory lane myself these days. Most of the acorn ones look very tired - I guess its a refurb project in the wait on the flip side!

[thedark]

This is mode 6
I dont have mode 7 any ideas?
Whe gonna replace a saa5050 or is it something else where we have to look.
This is from a beeeeeb to beeeeb beeb
It starts to pay off but there was a lot going on in my beeb but my electronic guru got it almost working. I am so happy

[chrissawer]

I dont have mode 7 any ideas?
Whe gonna replace a saa5050 or is it something else where we have to look.

It might be the SAA5050, if you have a spare it is worth swapping it out. If not there are some further ideas in this thread: viewtopic.php?p=393588

[BeebMaster]

IMG-20240203-WA0005.jpg

This is mode 6
I dont have mode 7 any ideas?

Could it be that you have built an Electron....?

Is mode 7 not available at all, or is it that the Beeb starts up in mode 6?

Default mode is set using the keyboard DIP switches or links, so maybe something is wrong there, and it's not setting bit 0 of the mode number, or something is wrong where that is fed back to the motherboard (via the keyboard ribbon I expect).

[thedark]

I got one spare SAA5050 here.
And its best to change the ic54 to New one.

Whe express change to mode 6 to see of rest works so far. If not than back to drawing board.

[!FOZ!]

IMG-20240203-WA0005.jpg

This is mode 6
I dont have mode 7 any ideas?
Whe gonna replace a saa5050 or is it something else where we have to look.
This is from a beeeeeb to beeeeb beeb
It starts to pay off but there was a lot going on in my beeb but my electronic guru got it almost working. I am so happy

Congratulations on this milestone in your build - keep going!

I am not sure its the same issue for you - but note that I had some issues with my MODE7 display earlier in the thread.

[1024MAK]

IMG-20240203-WA0005.jpg

Mark

[thedark]

An other saa5050 dit not work
Any ideas where to look further ?

[maniacminer]

An other saa5050 dit not work
Any ideas where to look further ?

By changing modes from MODE4 to MODE7 for example, you can exercise the TTXVDU switch from the 6845.

Check and see if there is a valid enable/latch signal on pin#1 of IC15 (74LS273) - it comes from pin #17 on IC2 (6845) if that isn't present, check continuity between those points.

If that signal is working, then check the outputs of IC15 and make sure that there is valid data on the other side of its pins - D0 -> pin#9, D1 -> pin#12, D2 -> pin#6, D3 -> pin#15, D4 -> pin#5, D5 -> pin#16, pin #19 -> D6 and pin#2 that controls the "LOSE" Load Output Shift Register Enable - that tells the IC to start displaying the character that is provided on the D0-D6 pins.

If there are signals here, check if there is HS on pin #12 of the SAA5050/IC5 and VS on pin #13.

Also worth checking if there is any video signal on pins #22,#23 & #24 - if there are, then you'll need to go through the circuitry to the video ULA (pins #9, #11 & #13) and see if the video arrives there.

From what I remember the video ULA has a register to select "Teletext" mode and all it does is to connect the RGB input to the RGB output and overlay the cursor on top.

[1024MAK]

Which VideoProc (Video ULA) chip are you using?

Mark

[thedark]

The fault on the mode 7 issue whas 3 wrong resistors. The board is fully working now after a view weekse testen and reparen.
Thanks go's to roland leurs for testen and solving the problems.

Tonny

[!FOZ!]

IMG-20240213-WA0004.jpg
IMG-20240213-WA0003.jpg
IMG-20240213-WA0002.jpg
IMG-20240213-WA0001.jpg

The fault on the mode 7 issue whas 3 wrong resistors. The board is fully working now after a view weekse testen and reparen.
Thanks go's to roland leurs for testen and solving the problems.

Tonny

Fantastic news!! Very happy for you.

[thedark]

Nou whe can test it l8er on.
And then to my next project

[maniacminer]

Looks like 200kR got into where 1kR was supposed to go I'm glad you've got it running

I spent a couple of hours today fitting all the sockets to the three boards I'm building, I've still got quite a few bits to get, a variable capacitor, RF modulator, DIN sockets, IDC sockets and some tall pin headers for connecting the keyboard. On the IC side of things, I've got one mostly working video ULA (it has some duff SRAM in the palette register) and I'll use that for testing.

[thedark]

I have used the wrong resitors but its working so far. Nou if i got it here i have to test the ports. And disk interface and build the econet. Then i can say its finished.

[maniacminer]

I've got a question. Is it worth using the 5 pin "domino" or just a regular 5 pin DIN for the serial port? I find the serial port connector annoying because it can be put in either way around and that is just useless (what was Acorn thinking?). I don't have anything invested in serial that I can't make up another cable for.

Smiles or dominoes?

[hoglet]

I've got a question. Is it worth using the 5 pin "domino" or just a regular 5 pin DIN for the serial port? I find the serial port connector annoying because it can be put in either way around and that is just useless (what was Acorn thinking?). I don't have anything invested in serial that I can't make up another cable for.PXL_20240222_103317118~2.jpg

Acorn chose a pin assignment that meant no damage would occur when inserted upside down. I just stick a "TOP" label on mine. I think the different shape was to prevent a serial cable being plugged into the cassette interface, or visa versa.

Dave

[thedark]

In this forum whe talked about that.
Just make a cable with a 5 din to domino female.
So you can plug the axorn stuf in there like a transfer cable or find a donor board for a spare.
Conclusies
Use the 5 din chasispart
Make a cable 5 din to domino female and youre done. For youre own serial stuf you can use the 5 din directly

[maniacminer]

I've got a question. Is it worth using the 5 pin "domino" or just a regular 5 pin DIN for the serial port? I find the serial port connector annoying because it can be put in either way around and that is just useless (what was Acorn thinking?). I don't have anything invested in serial that I can't make up another cable for.PXL_20240222_103317118~2.jpg

Acorn chose a pin assignment that meant no damage would occur when inserted upside down. I just stick a "TOP" label on mine. I think the different shape was to prevent a serial cable being plugged into the cassette interface, or visa versa.

Dave

Oh, I thought they'd do the same as the Einstein where rotating the plug switches between TX/RX and CTS/RTS?

BBC vs Einstein

[markusher]

I remember that story from BITD too, but someone messed up with the RTS and RxD so it didn't work.

[maniacminer]

I remember that story from BITD too, but someone messed up with the RTS and RxD so it didn't work.

I think that would make more sense as the plug was designed to be rotated. In the very distant past, I remember an old B&O thing that you could put the headphones jack in one way around and it would still output sound through the speakers and if rotated it would only output sound via headphones. Still, I don't find it particularly useful to connect the outputs to outputs and the inputs to inputs when thinking about a serial connection

[thedark]

Its a bit silent in here. Is everyting going as planned?. Its time for me to get modern hardware in there like speech a video nula got already a copro pi and a emulator on the 1 mhz bus. And a beeb wifi to play games. I am trying to get a zi-modem to work with starcom2 but so far no Lucky.
And how are you been doing?

[MarcRetro]

For a long time (past 5 years) I have been working on my own project to make a BBC pcb. The idea started maybe 25-30 years ago. A year ago I finished my first prototype of my efford. Some pictures where presented here.... (not with my explicit consent!!!) from the red board. The board worked, but some things where not right.... Some holes where to small and other things.

I think it was my 3th or 4th BBC I got from a friend. It didn't do anything...
I tried many things and with the lack of tools I couldn't get it fixed.
I desoldered the board (Issue 4) and reapplied all of the components new.
A real disappointment occurred and it still didn't work.
Then I removed all all components again and the board layed on my attic for many years.

About 5 years ago I went to my attic and watched all the things I liked.
With nothing to do during Covid I started with scanning the board on a MFP at work. It was my wish from that time.
Very detailed scans and setting up the first outlines.
It was a issue 4 so I was wondering what the difference would be with a issue 7.
That would be very disappointing with the knowledge I have now.

Last week I received my second revision of my board.
It is based on a issue 7 board. Witch I totally dissected. I turned on my autistic mode and made a real 1 on 1 copy of the original board! The Red one is discarded by this.
And yes it has some flaws. Even the issue 7 is not perfect.
Funny flaws are here...
Should I tell you?

The initial board (issue 4) has cost me more than a thousand hours I think.
The check with the issue 7 board was less but still 1 or 2 hundreds of hours. I can show you the pictures!
My last Christmas vacation went up on it (sure I don't care...)

Greeting,

Marc

[1024MAK]

Oh, do tell

Mark

[maniacminer]

Its a bit silent in here. Is everyting going as planned?. Its time for me to get modern hardware in there like speech a video nula got already a copro pi and a emulator on the 1 mhz bus. And a beeb wifi to play games. I am trying to get a zi-modem to work with starcom2 but so far no Lucky.
And how are you been doing?

Mine work, but I haven't soldered any of the connectors on yet, all the ones along the top edge (Econet and Analogue In are done) the RGB, RS423, Cassette are yet to do, then all the IDC connectors on the bottom need soldering and then I've got to find some video ULAs as I'm using a video ULA pinched from another Beeb. It's a back-burner project, so it might be done before summer...

[maniacminer]

Oh, do tell

Mark

Please, please, please fingersX all that shitty DRAM is gone, all those vertical antennas - um - cough - resistors, are now laid flat...

[MarcRetro]

One of the flaws is that there are two of the 47nf (A) capacitors are only connected to one of the power rails.
Many of the millions capacitors out there never have seen power....