Games don't load, RAM issue?

[Chr$]

This is a slightly odd issue that I've recently experienced.

I sold 4 of my NOS carts with some games on them (PD ones of course). I always test them before sending out and am very fussy about my whole re-felting/formatting etc process and any that are even slightly unreliable get rejected. They all worked fine before sending.

They were received and 2 out of the 4 carts didn't load on the new owner's QL. I sent replacements and they didn't work either! He send the replacements back to me and on my QL both loaded absolutely fine, fast and efficient. Having thought about it a little, I realised that the 2 carts that didn't work on the new owner's QL were actually the largest in terms of kb size. One was M-Metropolis with it's 75k code file size and the other was Pudge, and Pudge nudges just over 64k in total. All the other games (more than one per cart) were under 40k in size.

Is it therefore likely that the new owner's QL has a RAM issue that prevents the larger ones from loading, reporting a bad medium error because they simply don't fit into RAM/or the RAM has errors?

I don't think he has Minerva, so no RAM test at boot. I know that if Minerva finds bad RAM it will often start with a lower amount of good RAM and will also show it on screen.

[martyn_hill]

Hi Chr$!

Without meaning to displace the RAM fault idea altogether, I would be inclined to suspect instead the state of the recipient's MDV unit(s).

The fact that the larger files appear to fail compared to smaller ones is as likely due to the higher chance of a bit-error across a higher number of sectors on read-back rendering the whole file unreadable to QDOS.

The cartridges themselves are only half of the equation and variances between your 'mastering' MDV unit and the owner's - in the drive mechanics/tension, tape/head alignment, motor speeds and drive electronics (incl. any 'mandatory modifications' present) can all be expected to play their part. Thus 'inter-drive compatibility' is not something that can be safely assumed - even if both drive units in themselves seem to function well WITH the cartridges they have formatted.

Without getting in to the typically lengthy and often inconclusive activity of remotely troubleshooting the recipients' MDV unit, one action that would be fairly easy for you to take would be to re-format a fresh cartridge and re-save the image to it, but adjusting the motor-speed slightly (faster or slower) via the hidden adjustment screw on the underside of the motor.

In fact, of my various MDV units, once I have a few that mostly/almost work interchangeable, I also maintain a unit with a deliberately different motor speed.

If you want to pursue this approach...

Taking a spare cartridge that is known good and with the MDV unit extracted/accessible, I re-format a few times and on each iteration slightly adjust the motor tension/speed screw and note the 'Total' sector count - higher == slower and vice-versa. The screw can be turned about 270 deg. and the resultant sector-count range can be considerable and still (on that unit) read-back OK - especially with the Minerva MDV code which seems to have been written with speed variances in mind. Of course, its not just the code that is relevant here, its also the drive electronics and the ability of the ZX8302 to successfully decode the (nom. 100KHz) encoded signal. Faster the tape, the lower the bit-density (not desirable), but the higher the rate-of-change (desirable) and the lower the Total sector-count. At some point, Minerva will just reject the Format as 'bad' because there were considered to be too few Good sectors (cf. to Total) or too many Total sectors (interpreted as too-fast a motor speed.)

You'll find the motor-tension/speed screw recessed (quite deeply) in to the underside of the motor body behind a small hole (you'll need a "jeweller's" type screw-driver) that itself may be apparently filled-in with a tiny rubber grommet.

Good luck!

[Chr$]

That's very interesting Martyn, I didn't know about the motor tension/speed screw. I was aware that the alignment and other various factors do mean that no 2 drives are exactly the same and that in extreme cases some carts produced on one QL will not work properly on another (in fact when I sell them I do mention that fact).

All of these NOS carts that I have tend to format (running Minerva) with around the same total good sectors out of the grand total sectors, namely approx. 210-217 out of 215-224, something along those lines. I know that these carts have been together since 1983 so can assume that they were made at the same time and that the tape length they contain is perhaps around the same - I mean it's not like they were made years apart.

Any with more than 7 bad sectors I reject/put to one side. Sometimes I get a really good one with consistently 0 bad sectors on each format run (not sure how that's even possible with the tape join!). And over the last couple of years I've sold many carts with content written to them using my mdv1_, which seems to be slightly more reliable than my mdv2_. And in 99% of cases, when I do hear from the recipients they all seem delighted and often report back that they work for them (i.e. the contents all load). So I think I will leave my mdv1_ exactly as it is for now.

With mdv2_ it sometimes formats a cart with a low number of sectors and more bad sectors than I'd like, e.g. 203/216 (other times it fails, so I assume less than 200 good sectors). The carts often turn out much better in mdv1_. Other times mdv2_ seems to be in a better mood and consistently formats any carts I throw at it with identical sorts of figures as mdv1_, e.g. 215/220.

Another QL I have does seem to have problems reading carts that I've prepared with my main QL. It does just about load everything, but takes more passes and I often have to put some pressure on the cart in the drive and change its angle slightly (I suppose that points to the head alignment). Anyway, that less reliable QL will be an excellent candidate for motor tension tests!

If I were to format a few carts, make a note of the numbers and even write content to some of them, could I by any chance send them to you to see how the numbers compare on your drive(s) and to make sure everything loads etc? I'm keen to ensure anything that I write to a cart will work on as many QLs as possible.

[dilwyn]

I'm normally the last to contribute on hardware issues (most of you know what I'm like at destroying things).

Thinking back to experience from DJC days, when this sort of thing happened I used to find that cartridges formatted on my own QL sometimes didn't work on a customer QL. But after a while when a customer reported an error, I would ask them to return the cartridge, either reformatted on their own QL, or to send me a known working mdv cartridge formatted on their own QL. This cured a lot of the problems.

Obviously, this covers a multitude of sins without really knowing exactly where the fault lies.

[Chr$]

That's an excellent idea Dilwyn, I've written to him suggesting just that.

[martyn_hill]

Hi Chr$

I concur - though it does require four times the shipping cost and assumes that you can successfully write to (your) cartridge as formatted by the recipient, but it gives you a bit more control over the likelihood of it working when they get it back

More than happy to test out some of your sample carts and report back before returning them. PM me

[Chr$]

Hi Chr$

I concur - though it does require four times the shipping cost and assumes that you can successfully write to (your) cartridge as formatted by the recipient, but it gives you a bit more control over the likelihood of it working when they get it back

More than happy to test out some of your sample carts and report back before returning them. PM me

Thanks. Yes, it seems odd sending cartridges back and forth in 2021, but if I learn something from it then it'll be worth it (and it'll help the recipient narrow down a potential problem).

I'll PM you tomorrow and will prepare some carts over the weekend.

[Ruptor]

Don't forget the temperature issue. It would be interesting to know the temperature difference between locations and if they were made the same would the cartridges load?