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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment. |
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28th Mar 2022, 6:25 pm | #1 |
Dekatron
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"RAM Turbo" Spectrum Joystick + Cart interface - failed.
I've just dug my original Spectrum out for the first time in years and while the Spectrum and the 12" Portable CTV I keep only for this purpose both work just fine I have discovered that my RAM TURBO Joystick + Cartridge interface appears to have died - it stops the machine dead if connected. It was put away working. No, I didn't insert it with the power on.
Having taken it apart I find depressingly few components in there - there is a 28 pin wide bodied IC in there and mounted over the top of it, upside down on a daughter board, is a 16 pin IC which I suspect may be a patch. Because of the way they are sandwiched together I can't currently read the part numbers on either of them. I'll have to take it to work tomorrow to unsolder the sandwiched items. This is what the board looks like - I have had to post a link rather than an image because the image linked to is copyrighted / watermarked. I'm aware of the preference for the use of embedded images. https://www.the-liberator.net/site-f...-Turbo-PCB.JPG I strongly suspect the large IC is some kind of programmable logic - it's not a RAM of course, as the misleading model / brand might lead you to suspect. There is no RAM in this unit. Long shot, but does anyone have an original or reverse engineered diagram for one of these? Note there were two similar versions, one with the cartridge slot and one without - this is the one with, and I do need that bit to work. I see a few around for not much money but I may as well try to fix this one if possible. |
28th Mar 2022, 8:10 pm | #2 |
Octode
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Re: "RAM Turbo" Spectrum Joystick + Cart interface - failed.
Yes I think it is a custom mask device of some kind - I have a photo of one where the 28 pin chip is marked RAM TURBO 1054 8420. Mine does work. I don't have any technical details but, it must be active in some was it has a soft switch to change what standard the ports are I think.
Might be worth a good clean of the edge connectors first in case? |
28th Mar 2022, 8:23 pm | #3 |
Octode
Join Date: Mar 2020
Location: Kitchener, Ontario, Canada
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Re: "RAM Turbo" Spectrum Joystick + Cart interface - failed.
This looks like a later version of the same thing, might give a clue to the ics used. No schematic though.
https://sinclairzxworld.com/viewtopi...m+turbo#p38061 |
28th Mar 2022, 9:02 pm | #4 |
Pentode
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Re: "RAM Turbo" Spectrum Joystick + Cart interface - failed.
As Timbucus says, the two ICs will map the joysticks to the different standards. Presumably, the rom cartridge will be connected directly to the Spectrum edge connector as with the ZX Interface 2, so removing the IC bundle should allow that to work.
The IC looks like a custom logic, you might struggle to find a replacement. If all else fails, and using the ZX Interface 2 schematic as a reference, an option could be to bodge in the MT62001 IC used in the ZX IF2 and restore the Sinclair standard only - you can also find these on a scrap Amstrad-era Spectrum +2/+3, labelled as 40057. Good luck! |
28th Mar 2022, 9:40 pm | #5 |
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Re: "RAM Turbo" Spectrum Joystick + Cart interface - failed.
Yes, it is semi-smart in so far as it reads the state of the fire buttons at initialisation and then decides what sort of joystick interface to 'be'. Quite clever. Too clever, to be honest.
Thanks for the photos showing the two ICs, what a relief - it'll just be the 74LS chip and not the unobtainable, Alien ULA-like object. (...No it won't, obviously. But I will still check). I need the cartridge side of things because I have some 'cartridges', PCBs which will plug into the cartridge slot which can accept an EPROM or EEPROM. These were made by a guy called Paul Farrow, along with some neat software which loads them up with .TZX / TAP files and creates a startup menu for near instant loading of anything I can find in that format. I have some of the 'Rarer' games loaded up on EPROM but, as the interface has failed, I can't have the quick blast I was looking forward to. Ref: Dirty connectors, the Spectrum itself is working with its original Inferface 1 and original continuous - tape microdrive - which also unbelievably still works - so I think I can rule out the Spectrum's edge connector. On the RAM turbo side I have had a male-male 'joiner' plugged into that and have metered from there through the connector to the RAM Turbo PCB - no duds. It could be as long as ten years ago that I last had all of this powered up, but it's still disappointing that it came down broken when it went up working. I suppose I can laboriously meter out all of the tracks to make sure none of them have been corroded away - we have a fairly benign loft environment but like every other loft it is hot in the summer and freezing in the winter - everything is kept in a closed dust proof box. |
28th Mar 2022, 10:25 pm | #6 | |
Pentode
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Re: "RAM Turbo" Spectrum Joystick + Cart interface - failed.
Quote:
Last resort, if the fault is in the custom chip, removing the two ICs should allow the Spec to boot and rom slot to work. |
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28th Mar 2022, 11:21 pm | #7 |
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Re: "RAM Turbo" Spectrum Joystick + Cart interface - failed.
Ah, but are you really suggesting I try to play ATIC ATAC with the keyboard? It's a good diagnostic idea and I will try it, but nothing less than a fully working interface will do, unfortunately.
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29th Mar 2022, 12:23 am | #8 | |
Pentode
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Re: "RAM Turbo" Spectrum Joystick + Cart interface - failed.
Quote:
Would the Sinclair joystick port bodge option be an acceptable outcome? I know some of the early games only worked with Kempston, the ZX Interface 2 came along a bit later. It should also be easy enough to make the logic for Kempston on a small bit of vero, I think they used a 74LS138 and 74LS366 - but making something to work with both, like the original, seems a bit of a project too far. |
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29th Mar 2022, 1:24 am | #9 |
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Re: "RAM Turbo" Spectrum Joystick + Cart interface - failed.
I've made Kempston joystick interfaces before, back in the day. I may still have the mouldering remains of one somewhere.
Are we sure the magic chip isn't also involved in the ROM swapping process (internal ROM out, external ROM in?). I've honestly never looked into it but it seems crude, the idea of just jamming an EPROM onto the bus (I would assume there is an input line on the ZX edge connector which has to be put into a certain state to kick the internal ROM off the buses). |
29th Mar 2022, 11:15 am | #10 |
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Re: "RAM Turbo" Spectrum Joystick + Cart interface - failed.
I've taken the little daughter board with the 74LS IC off, the chip is a 74LS366. It's OK, of course. the larger IC is indeed labelled 'Ram Turbo 1054 8416'. The big IC will be a pig to get out - not only double sided PCB as expected, but the pins which support the daughterboard have been soldered down the sides of the legs of the large IC all the way down to flush with the PCB itself.
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29th Mar 2022, 4:18 pm | #11 | ||
Pentode
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Re: "RAM Turbo" Spectrum Joystick + Cart interface - failed.
Quote:
Inserting the cartridge pulls the ROMCS line high, which disables the internal ROM. Quote:
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29th Mar 2022, 5:04 pm | #12 |
Octode
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Re: "RAM Turbo" Spectrum Joystick + Cart interface - failed.
Is it worth trying to add the resistors seen in this link?
https://foro.speccy.org/viewtopic.php?t=4008 Wondering if that chip might have cmos input and needs pullup if driven from ttl. |
29th Mar 2022, 5:10 pm | #13 |
Octode
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Re: "RAM Turbo" Spectrum Joystick + Cart interface - failed.
Maybe the 74ls366 was to replace the resistors for a more reliable fix. How did you test the 74ls366? Maybe try a different one before giving up on the 1054.
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29th Mar 2022, 5:24 pm | #14 | |
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Re: "RAM Turbo" Spectrum Joystick + Cart interface - failed.
Quote:
I used an electric pump assisted desoldering iron to get that off and also to desolder the large IC from below but the heavy solder clags attaching the support pins for the daughterboard to the pins of the large IC meant that the support pins had to be snipped and individually desoldered from the large IC before I could mop up all the solder holding the large IC's pins to the top side pads. I got it out eventually, without any damage to the PCB. I may have forgotten to mention: With the ICs fitted as they were originally the system would not start even with no cartridge inserted - in other words the two ICs were the only thing sitting on the system bus. First test: Spectrum with bare RAM Turbo PCB (ICs removed) - this test was to make sure that it was not actually an inter-track short or other PCB fault stopping the system from working. Result: Spectrum starts up and runs OK. Second test: Spectrum + Bare RAM Turbo PCB with cartridge (1 of 2) plugged in - Result: system will not start Third test: Spectrum + Bare RAM Turbo PCB with cartridge (2 of 2) plugged in - Result: system will not start. So - - The ICs are involved in the operation of the cartridge interface after all, or - - Both cartridges have mysteriously failed in the same fashion as the main interface in spite of the fact that all three items were separated when stored (Unlikely). Or - - There is a track fault somewhere between the edge connector and the rest of the RAM Turbo circuit which prevents both the joystickery and the cartridge feature from working. Obviously, this is the hope I am clinging to now. It would be nice if the weird IC wasn't actually dud after all. Last edited by SiriusHardware; 29th Mar 2022 at 5:41 pm. |
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29th Mar 2022, 5:30 pm | #15 | |
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Re: "RAM Turbo" Spectrum Joystick + Cart interface - failed.
Quote:
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29th Mar 2022, 5:33 pm | #16 | |
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Re: "RAM Turbo" Spectrum Joystick + Cart interface - failed.
Quote:
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29th Mar 2022, 5:53 pm | #17 | ||
Octode
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Re: "RAM Turbo" Spectrum Joystick + Cart interface - failed.
Quote:
It looks like your tests with the pcb after removing the ICs is pointing to something else though. |
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29th Mar 2022, 8:07 pm | #18 | |
Pentode
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Re: "RAM Turbo" Spectrum Joystick + Cart interface - failed.
Quote:
There's not that many cartridge connections, it wouldn't take too long to bell them out to the edge connector, see if something is awry. Can you check the EPROMs? How long since they were burnt?
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Paul Last edited by locknut; 29th Mar 2022 at 8:33 pm. |
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29th Mar 2022, 8:43 pm | #19 |
Octode
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Re: "RAM Turbo" Spectrum Joystick + Cart interface - failed.
Is it possible that the ICs are disabling only part of spectrum rom or also part of spectrum ram when rom cartridges are connected? Might be worth tracing the ROM-CS from the spectrum connector. Is there also a RAM-CS?
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29th Mar 2022, 10:39 pm | #20 |
Dekatron
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Re: "RAM Turbo" Spectrum Joystick + Cart interface - failed.
There has been a development (see attached) This was loaded from 'Cartridge'.
I'm sure you are all going to ask me how I got it working. I wish I could tell you. As was noted earlier there aren't that many signals going to the cartridge port connector so I metered them all out from the corresponding signal lines on the Spectrum PCB to the spring connectors on the cartridge socket. They all checked out so I connected it all back up and... it just worked. Both cartridges work. Of course the ICs are still out and I left them at work so I will have to refit them tomorrow and see if the joystick side of things also works. This is the sort of fault I hate the most, the one which just goes away by itself. There is every chance that it could come back again just as easily. Last edited by SiriusHardware; 29th Mar 2022 at 10:45 pm. |