How to Health Check My BBC Master (128/512)

[SteveLovell]

Hi there,

I recently inherited my father's old BBC Master. It was originally a 128, but was upgraded to a 512, I think. I played games on it as a kid, so it has some nostalgia factor for me, but I don't have the space keep it. As such I'm not looking to keep it, but would like to get it into full working order before selling it on. It may be fine as it is, but I'm seeing some odd behaviour when attempting to load some old games.

I've replaced the PSU, since the original one went pop (literally) when I turned it on for the first time a few weeks ago. Having sorted that ... it looks like I have problems with CMOS battery. That seems to be just a set of 3xAA batteries. I replaced them (although the sticker on that says not to, but to replace the whole unit), but I still seem to lose the config regularly. Once I've run all the config options (following this guide), things look reasonable, though I am having to regularly do "insert x" commands and/or resets with Power-On+R

I've little idea how to use the on-board utilities, so I'm mostly testing using game disks. In addition to the above, here's what I'm seeing so far ...

1. Some things load and play fine.
2. Some titles just hang.
3. Elite complains that I have missing ram in slot #6.
4. Some discs seem to be corrupted.

I've little to no idea of how much of this is due to the hardware and how much the software. If anyone can give me pointers of things I can do to check the state of the hardware, that'd be amazing. How would you check the state of a recently acquired machine like this? Happy to upload some photos to show you what I'm looking at if that will help.

Cheers, Steve

P.S. I'm new here, so please be gentle!

[1024MAK]

Hello and welcome to StarDot

Do you have a multimeter, or access to one, or know someone with one?

The “CMOS” chip is a combined Real Time Clock (RTC) and memory chip (low power CMOS static RAM) that (should) contain the current time and date, and various configuration settings.

To do this, it requires a continuous supply of power, hence the battery pack. The reasons for the warning about replacing the complete battery pack are twofold:- it contains a diode and a resistor to prevent the alkaline cells from being damaged by the main +5V supply in the computer. And Acorn wanted to make the operation as painless as possible, so sold the complete pack so that changing it was simple and there was (supposed to be) less chance of user error.

While the computer is powered and switched on, the internal PSU supplies power to the chip, so I presume that you are only having problems with the configuration being lost after it has been powered off for more than ten to twenty (or more) seconds.

With regards to tapes and disks, these can degrade. For the disks, look carefully at the surface of the actual disk (visible through the cut-out hole). Are there any ‘scratch’ marks? Is the surface clean, or can you see any mould?

If there is any mould, or the surface is degrading on a disk that you have used, the resulting muck and dirt can clog up the read head in the drive.

Mark

[SteveLovell]

Thanks Mark,

I do indeed have a multimeter. It doesn't get out much, but I know how to use it (that had been my father's too at one stage). What to test with it is another question altogether.

On using the multimeter to test my battery pack, it wasn't happy. The individual batteries are fine, but the connections are heavily corroded. And after a little (gentle) handling, bits fell off, so it's definitely going to need replacing/fixing. Any suggestions for sourcing one? I don't own a soldering iron, and don't especially want to.

Will physically inspect some of the discs. Looks like I've got issues with some of the keyboard keys too. I imagine it mostly needs a good clean as those keyboards are pretty robust.

Cheers,

Steve

[1024MAK]

If you don’t want, or are not able to make your own battery pack, Mark (not me!) at www.retroclinic.com can often supply them. He also sells on eBay.

In most cases, the keys just need use. Any that are stiff, or which don’t respond, press them around fifty times. The action of pressing them helps to clean the plastic mechanism and clean the contacts.

Mark

[sydney]

A good photo of the motherboard would be useful. The ram error reported by elite is probably a jumper which replaces ram with a ROM. A photo would confirm this.

[SteveLovell]

Thanks guys,

Two pics. One the main board (plus 512 board, I think), the other another expansion board (unless that's for the 512 but I think not).





If these aren't sufficiently clear to see what you need to see, let me know!

[RobC]

That extra board looks like a Morley AA ROM board. It allows you to switch between ROMs on the board and sideways RAM under software control. I can't remember the commands at the moment but think the manual is on the web. It probably accounts for Elite giving the "no ram in bank 6" error as it's probably configured to have a ROM paged in rather than RAM.

[SteveLovell]

Thanks RobC,

A quick Google revealed it is indeed a Morley AA Master ROM Expansion board.

With that identified, I found the instructions and properly installed it (it was previously sat loose instead of connecting with the ROM slots below), I was then able to use the boards *HI command to set slot 6 to ram. And then Elite seems to load successfully.

I'll have a play with some of the other discs tomorrow. It's too noisy for me to continue while my daughter is in bed!

Things are looking promising!

Cheers,

Steve

[RobC]

was then able to use the boards *HI command to set slot 6 to ram. And then Elite seems to load successfully.

Glad that you sorted it - I now remember the *HI and *LO commands! There's also a command to list the ROMs that are installed in the board.

It's a very useful bit of hardware and the only downside is that you can't install an Econet module with the AA board fitted (partly because of physical space and also because they share the same CMOS RAM locations).

I think the AA board is fairly rare so, if you are looking to sell, it might be worth selling it separately to the Master.

[SteveLovell]

Thanks RobC et al,

Given that the machine doesn't currently remember config, I was surprised that with the AA Board disconnected, it didn't automatically revert to ram in slot 6. And when it's disconnected the *HI command won't be available. Any thoughts?

In terms of selling, is it worth taking the ROMS off the board too (except for the CTRL ROM which is needed for it to work)? I've no idea.

Pleasingly, several of the other games which previously hung also work fine after the *HI R command. Quite a few disks with bad sectors though. They look in decent physical condition and have all been kept in sleeves (and boxes), so no signs of mould.

I need to do some other odds and ends today, but for the Master it looks like it's mostly just needing the CMOS battery, which Mark at retroclinic now has available on eBay. Not too sure about the "bad" keys though. Three of them are pretty unresponsive. They aren't stuck, but need pressing hard/wiggling to make them respond. What would you guys do?

I'd still be interested in anything else others might do to health check the system. Mark (@1024MAK), any suggestions as to worthwhile things to test with my multi-meter? Or perhaps I shouldn't worry unless I'm getting "symptoms".

Cheers, Steve

P.S. In case anyone is interested, the command to list ROMS on the AA Board is *LBOARD. My ROMS were all labelled, so it didn't tell me much.

[RobC]

I think the reason it's not reverting to RAM with the AA board removed is that the connectors from the AA board replaced the original jumpers on LK18 and LK19.

The jumpers select between RAM and ROMs in the two spare 32KB sockets on the motherboard - there's a detailed explanation in this post.

On the keys, it's not uncommon to see this on a Master. I often find that repeatedly pressing bad keys with more than usual force is enough to wake them up. If that doesn't do the trick, it's time to inspect and clean the keyswitches...

[SteveLovell]

Thanks again RobC,

Jumpers had been my only thought but I didn't trust my guesses enough to even mention it. But you appear to be right. I found this guide which says where I need to position the jumpers. Now I just need some jumpers as those have understandably gone missing.

[1024MAK]

Unless you find a problem, the main things to test with a multimeter are:

• +5V DC supply within specification (red wires from the PSU to the main board)
• -5V DC supply within specification (purple wire from the PSU to the main board)
• +12V DC supply within specification (external power socket)
• IC11 pin 24 getting the battery voltage when the mains is switched off/disconnected

The +5V should preferably be within +/-3% (4.85V to 5.15V) and certainly no worse than +/-5%.
The -5V and +12V should be with +/-10%.

For more details on the hardware, I refer you the the service manual (available here)

Where possible, you should try to test as many of the external interfaces as possible.

You have not said much about the internal second processor, but if you can, it worthwhile testing this as well.

Mark

[SteveLovell]

First three voltages checked and all seem fine. Hard to get at IC11, which I believe is beneath the 512 board which is itself very securely attached.

I've no idea about testing the 512 board or co-processor. I do have the 512 discs 1 to 4, which I guess may be of use? I may have a play with those later.

[1024MAK]

IC11 is the CMOS RTC chip (416818).

If you can’t get to it, and if you can get to the metal pin, test on the pin header where the battery lead connects to the main board (PL8). The positive connection is the middle pin.

With the machine switched on, about 4.3V to 4.7V should be present. With a working battery pack fitted, the voltage should be appropriately the same as the battery voltage.

Mark

[geraldholdsworth]

Reading this thread made me think - why do we put in non-rechargeables. Would not chargeable AA's work just as good, and remove the diode and resistor?
OK, might need to put four in to make up the 4.5v (well, 4.8v).

[danielj]

The advantage of the Li-SOCl2 ones is they last 7 years and are AA in size
I know sydney tried a supercap at one point, which I think held charge for a pretty long time?

d.

[1024MAK]

Acorn did design the Master with a rechargeable battery charging circuit. But it all went rather wrong Hence Acorn abandoning using rechargeable batteries. And then supplying the Master machines without the recharging circuitry fitted, and with alkaline battery packs.

The second problem used to be that ordinary AAA and AA NiCad cells are not designed to be trickle charged for long periods. Note that the smaller PCB mounting memory / RTC back-up NiCad cells and batteries were/are designed to be continuously trickle charged.

Mark

[SteveLovell]

New CMOS battery (c/o of Mark at RetroClinic) and jumpers (c/o RS Components) in place, and the Master seems to be behaving itself pretty well without the AA Board (well, Elite plays at least).

Will be cleaning the keyboard and then trying out some of those GEM 512 disks. Not sure I've got it in me to replace the key-switches should the cleaning not suffice (which I suspect it won't on at least one of the three bad keys). My brief reading suggests de-soldering (and presumably re-soldering) would be necessary for that.

Thanks for everyone's input so far!

[SteveLovell]

Keyboard cleaned and one of the three dodgy keys is fixed. One I'm not too fussed about (the * key on the number pad, which can be typed differently and will work if you try hard enough). The other I'm more bothered about. It's the "Z" key. Obviously anyone who wanted it for retro gaming would find that pretty irritating since it generally maps to "left".

Man, re-fitting the space bar was fiddly! I wouldn't have removed it if I'd seen what was coming.

Anyway, the next question is how to test the 512 / co-processor stuff. I tried the 4 GEM disks, but they all seem to have bad sectors or generally don't "boot" in any obvious fashion. No idea what I should be doing/expecting here. This was an area of the Master I never touched as a kid. I was all about the games (and dabbled in a bit of BASIC programming).

Any thoughts? My disc drive unit includes a drive for 3 1/2 inch discs. Can I use "normal" imaging tools to put images of the GEM discs onto 3 1/2 inch on my PC?

And is it best to start another thread at this point?

[danielj]

Carry on here if you like - the GEM discs aren't a normal format. The first one is a strange hybrid ADFS format, the later ones are an 800kb acorn format (actually the same as the archimedes format) - however, the images are online:
http://www.cowsarenotpurple.co.uk/bbcco ... ystem.html

Do you have omniflop working? You should be able to write them with that.
Edit: Or the resources on that webpage!

[SteveLovell]

Thanks danielj

No joy with OmniFlop as I only have a USB Floppy Drive for my PC (haven't had an internal one for years). However, when time allows I may try that site's third option.

[danielj]

If I were you I'd invest in a couple of £12 gotek floppy emulators, then you can just dump the images on a USB stick and the beeb will treat it like a normal disk drive

[SteveLovell]

Thanks danielj, they look like handy devices.

Turns out that even method 3 is problematic as my remaining 3.5 inch discs are HD rather than DD.

However, I'm wondering how necessary it is, especially as I don't intend to keep the Master (if for no other reason than that I don't have the space). So, really I'm not interested in the GEM software except as a means to test the 512/co-processor hardware and be able to say it's "working" when I sell it.

I'd guess there are other ways to go about this. I don't mind hammering in a bit of code.

[RobC]

One way to test the co-pro without booting into DOS/GEM would be to load the co-processor filing system ROM (CPFS). It's on the cowsarenotpurple website. You're still left with the problem of how to get it onto the machine though (assuming you haven't got an EPROM programmer).

To be honest though, if the machine boots to the Master 512 banner ("Acorn TUBE 80186" etc.) then the co-pro is probably fine. You may need to do *CONF. TUBE and *CONF. INTUBE to get it to recognise the co-pro.

[SteveLovell]

Thanks RobC,

No, no EPROM programmer. The only other bit of kit I have, which I can't see being of use here, is a CARE SMART Cartridge (with the red button) ... though I'm happy to be corrected on that. I remember using that to avoid loading things from tape and to create my own "save points".

After a bit of play, I've discovered that I simply wasn't doing the right things in my attempt to boot the first GEM disc. I'd been assuming the discs would themselves enable "the tube". After issuing the config commands you mention and then hitting shift-break, it booted fine into DOS-Plus. From there it went less well ... It complains that the second disc is bad (GEM itself with the "desktop" etc), and some of the first disc also seems bad, e.g. when issuing a "HELP" command I get a "bad program" error.

Anyway, as you say, I think this is all a pretty good indication that physically the co-processor is in good shape. I just don't have any software to make use of it.

[RobC]

Glad that it's working.

If you desperately need/want the disks, I can knock a set up for a few quid to cover the cost of the floppies.

[SteveLovell]

It's been a few days, so here's the latest ...

I'm mostly happy that the Master is working. On and off I've been testing the various discs I've got to see which are in working order. And that's where my current puzzles arise.

The same disc can go from working to not working and back to working again within the space of a few hours. Sometimes it seems like none of the discs are working. Then give it a few hours and try again, and most are fine.

Is this the discs being degraded, the disc drive playing up or the Master itself being flaky? What would others check in this situation?

My guess would be that lots of the discs are close to sufficiently degraded to not work at all, and that small changes in the environment (temperature, humidity etc) are then enough to give the disc drive problems. It just bothers me if I want to sell things as "working" to not be sure what the issues are here.