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Sorry, typo, RES (Reset) is on pin 40...

I should have realised. Yes, pin 40 does change state on <BREAK>

Your probe(?) is detecting the 2 and 1MHz clocks on pins 5 and 4, but not the 4 and 8MHz clocks they're generated from. Perhaps your probe isn't able to detect frequencies that high?

It is only a cheapo Laser probe.

Okay, assuming the remaining voltage tests are okay They did. can you test the various CPU pins using a logic probe or oscilloscope as follows: Can't access scope till morning, so, cpu pins; 1 low 2 high 3 low 4 high 5 nothing 6 high 7 high 8 high 9 low 10 high 11 low 12 high 13 nothing 14 high 15 ...

Can you check what you find on pins 7-4 of IC6?

7, Nothing
6, High
5, Pulsing
4, Pulsing

Can't get the scope till the morning. Pin 40 of IC1 is high until break is pressed.

Have you tested both the +5V supply at each connection where the wiring connects to the main board

+5V supply
VCC1=5.03v
VCC2=5.023v
VCC3=4.995v

0V/Gnd (using +5 by S38)
VCC1=5.001v
VCC2=5.001v
VCC3=4.990v

I'll get onto the ICs ......

You may also want to try running in in a minimal configuration.

Yes, I have tried all of that, except IC4 is not socketed (though I did try a piggy back at some point).

When you ran it with the test ROM in, was this EPROM in the OS socket? Were all the other ROM chips removed?

Yes.

You may also want to try running in in a minimal configuration.

Thanks, I'll take a look at that now.

Thread moved to the 8-bit hardware section. Thanks Mark. Has the machine had a disc interface or Econet fitted? I pulled the machine out of the loft to sell it so to be honest, I don't know much about it. It doesn't have econet and looks like it never has had. It doesn't have a disk interface thoug...

Over in the BBC Hardware Department thread ( https://stardot.org.uk/forums/viewtopic.php?f=3&t=17016 ) I attached that board to a BBC B that now no longer boots. Initially, I thought the board was the cause but now I suspect the Beeb was suffering anyway. Too long in the loft. Anyway, I've worked on...

Contact Dave H.

Thanks, I've sent him a pm.

As the subject says. Think one of mine in a BBC/B is fried.

'A' needs to be connected to the South East corner of S21 For some reason I remembered a lone piece of wire soldered to a jumper that came out of the same box of bits, way back. So thinking it probably became detatched from this board in the box, I connected (using similar) East/West to the two low...

‘A’ probably needs to be connected to one of the link / jumper shunt pins on the Beeb main board. That makes sense. Here is the other thread with what looks like same board installed. Thank you. So, progress. Armed with the above two comments and some guess work, 'A' needs to be connected to the So...

If you can connect A to ground (it's effectively an active-low signal) then that might be enough to get the board working. With A connected to ground the beeb fails to boot. I don't get the seccond 'beeeep' and there is a slight ticking noise from the speaker. No display. Disconnect from ground and...

Ok, thanks for that.

The TBP-24510N (5 rather than S) is a PROM (that's the non-erasable, pre-EPROM variety).

Having got up close with a magnifier, it still looks like TBP 24S10N
Editted to ask, probably a stupid question, would this be standard or programmed specifically for it's purpose?

Does your Beeb recognise ROMs on the mainboard with this expansion board fitted? Yes, ROMs on the mainboard are recognised. The "A" wire goes to a 'via' and then to the back of the board. A picture from the other side might show us where it goes, and what it might have done. Picture attached but it...

I have an Issue 4 Beeb which I intend to sell and it has had a mod done by a previous owner and I was wondering if anybody might know why. A schottky diode (lt1004) was soldered between D6 & D8, though the leg soldered to D6 was detached when I opened it up. Couple of not so good pics; mod1.jpg mod2...

Well, I didn't have any joy with this. Fitted it into IC76 & IC101 but it does not recognise any roms that are inserted into it. Not sure what ROM 0 is for or if it should be populated or what the solder point (marked 'A') below it is. 'A' appears to have had a wire soldered in it at some point. No ...

And sniffer, I'll see what I have. Definitely got one.

Cool. I'm happy to do some soldering.

I got mine from IFEL. It works a treat.

Are they still going?

I don't have a complete upgrade, but I've got a blank circuit board which you could get the bits for? Slight pain to solder as you need to get SOJ memory ICs onto it, but they do work. Yours for a quid plus postage. If the OP doesn't take you up on the offer, or if you have more than one, I'll take...

I have a spare one in need of a good home if you are interested.

Fantastic, thank you very much. I'll send you a PM.

As the title says

UN27/25: BBC Micro ROM Extension Unit. Allows up to 16 paged ROM's to be fitted into the BBC Microcomputer. Single plug-in printed board fitted inside the BBC Micro case. Takes power from the BBC micro. Power requirements from BBC Micro. ED 1983.

Ok, great. I'll have a play. Thanks all.

I thought I'd got an answer by downloading a excel sheet of BBC codes but it stops at UN27/24

Editted to say obviously I don't think it will be a BBC/A/B/B+ bit of kit, can't see how it would fit, but there is mention of a ZEUS system.

Found this board in a box of bits, no idea what it is, apart from some kind og rom expansion board.

Anybody any ideas?

Oooh, thanks for the offer but I've already ordered them from Mark at Retroclinic. Just waiting for them

No problem.

(and and the second processor!)

Got a few of those too, in cheese wedges. Must get them out and check them over.

If you get stuck I have both which I could flash for you for the cost of the eprom & postage.

Firstly, are you happy that your cable is in good condition? Yep, cable is good but _not_ the scart connector :oops: Been using composite until I didn't get any output from this machine. Odd thing is (or maybe not odd) that R118 which is a 3K9 is measuring at 280R. Really sorry about this noise.