UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Computers

Notices

Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

Closed Thread
 
Thread Tools
Old 28th Mar 2022, 6:25 pm   #1
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default "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.
SiriusHardware is offline  
Old 28th Mar 2022, 8:10 pm   #2
Timbucus
Octode
 
Join Date: Mar 2019
Location: Barry, Vale of Glamorgan, Wales, UK.
Posts: 1,362
Default 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?
Timbucus is offline  
Old 28th Mar 2022, 8:23 pm   #3
Mark1960
Octode
 
Join Date: Mar 2020
Location: Kitchener, Ontario, Canada
Posts: 1,265
Default 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
Mark1960 is offline  
Old 28th Mar 2022, 9:02 pm   #4
locknut
Pentode
 
Join Date: Mar 2022
Location: Retford, Nottinghamshire, UK.
Posts: 193
Default 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!
locknut is online now  
Old 28th Mar 2022, 9:40 pm   #5
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default 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.
SiriusHardware is offline  
Old 28th Mar 2022, 10:25 pm   #6
locknut
Pentode
 
Join Date: Mar 2022
Location: Retford, Nottinghamshire, UK.
Posts: 193
Default Re: "RAM Turbo" Spectrum Joystick + Cart interface - failed.

Quote:
Originally Posted by SiriusHardware View Post
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).
Whip out the small pcb with the 74LS first, see if it allows the Spec to boot? Fingers crossed.

Quote:
Originally Posted by SiriusHardware View Post
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.
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.
locknut is online now  
Old 28th Mar 2022, 11:21 pm   #7
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default 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.
SiriusHardware is offline  
Old 29th Mar 2022, 12:23 am   #8
locknut
Pentode
 
Join Date: Mar 2022
Location: Retford, Nottinghamshire, UK.
Posts: 193
Default Re: "RAM Turbo" Spectrum Joystick + Cart interface - failed.

Quote:
Originally Posted by SiriusHardware View Post
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.
You sometimes have to suffer in pursuit of perfection

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.
locknut is online now  
Old 29th Mar 2022, 1:24 am   #9
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default 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).
SiriusHardware is offline  
Old 29th Mar 2022, 11:15 am   #10
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default 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.
SiriusHardware is offline  
Old 29th Mar 2022, 4:18 pm   #11
locknut
Pentode
 
Join Date: Mar 2022
Location: Retford, Nottinghamshire, UK.
Posts: 193
Default Re: "RAM Turbo" Spectrum Joystick + Cart interface - failed.

Quote:
Originally Posted by SiriusHardware View Post
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).
I'm pretty sure the magic chip won't be involved. I wouldn't have thought the RAM Turbo interface will be much different to the ZX Interface 2, and the cartridge slot on that connects directly to the Spec edge connector.

Inserting the cartridge pulls the ROMCS line high, which disables the internal ROM.

Quote:
Originally Posted by SiriusHardware View Post
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.
Sounds like a job for the hot air station.
locknut is online now  
Old 29th Mar 2022, 5:04 pm   #12
Mark1960
Octode
 
Join Date: Mar 2020
Location: Kitchener, Ontario, Canada
Posts: 1,265
Default 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.
Mark1960 is offline  
Old 29th Mar 2022, 5:10 pm   #13
Mark1960
Octode
 
Join Date: Mar 2020
Location: Kitchener, Ontario, Canada
Posts: 1,265
Default 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.
Mark1960 is offline  
Old 29th Mar 2022, 5:24 pm   #14
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default Re: "RAM Turbo" Spectrum Joystick + Cart interface - failed.

Quote:
Sounds like a job for the hot air station
No, PCBs / PCB tracks / pads of this vintage do not respond well to being heated. The little PCB for the TTL IC is the same semi-transparent fibreglass as was used for the original MK14 and I know from experience that you only need a whiff of excess heat for the glue holding the pads down to give up the ghost. I would never use hot air on this type of PCB.

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.
SiriusHardware is offline  
Old 29th Mar 2022, 5:30 pm   #15
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default Re: "RAM Turbo" Spectrum Joystick + Cart interface - failed.

Quote:
Is it worth trying to add the resistors seen in this link
Interesting find, but I would say not. Look again at the image I linked to in #1 - that PCB is exactly the same revision as mine. Look at the small PCB and then look just past the right hand edge of that PCB, you will see 5 vacant pads which were clearly meant for a 4 x SIL resistor package. On mine it looks as though there was one fitted but it has been wobbled until it snapped off, leaving only the stumps of its leads in the holes. If so, it has been in that state all through my ownership and it worked when I last used it.
SiriusHardware is offline  
Old 29th Mar 2022, 5:33 pm   #16
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default Re: "RAM Turbo" Spectrum Joystick + Cart interface - failed.

Quote:
How did you test the 74ls366?
My device programmer has a chip test mode for 74xx / 4xxx logic and a few other devices. I also looked at the pins, out of circuit, relative to the power pins using a V/I analyser. All the inputs show the same trace, all the outputs show the same trace. Normally, damaged digital IC inputs or outputs have a characteristic 'bent line' trace.
SiriusHardware is offline  
Old 29th Mar 2022, 5:53 pm   #17
Mark1960
Octode
 
Join Date: Mar 2020
Location: Kitchener, Ontario, Canada
Posts: 1,265
Default Re: "RAM Turbo" Spectrum Joystick + Cart interface - failed.

Quote:
Originally Posted by SiriusHardware View Post
Quote:
How did you test the 74ls366?
My device programmer has a chip test mode for 74xx / 4xxx logic and a few other devices. I also looked at the pins, out of circuit, relative to the power pins using a V/I analyser. All the inputs show the same trace, all the outputs show the same trace. Normally, damaged digital IC inputs or outputs have a characteristic 'bent line' trace.
I was wondering if there might be a logic level issue, possibly due to old age of the components involved, so the 74ls366 would still work in a tester that gave better input signal levels.

It looks like your tests with the pcb after removing the ICs is pointing to something else though.
Mark1960 is offline  
Old 29th Mar 2022, 8:07 pm   #18
locknut
Pentode
 
Join Date: Mar 2022
Location: Retford, Nottinghamshire, UK.
Posts: 193
Default Re: "RAM Turbo" Spectrum Joystick + Cart interface - failed.

Quote:
Originally Posted by SiriusHardware View Post
- 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.
I can't see why the ICs would have anything to do with the cartridges, unless the patch board passes some lines over, so the latter does seem a distinct possibility. You would only need a break or short somewhere.

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?
__________________
Paul

Last edited by locknut; 29th Mar 2022 at 8:33 pm.
locknut is online now  
Old 29th Mar 2022, 8:43 pm   #19
Mark1960
Octode
 
Join Date: Mar 2020
Location: Kitchener, Ontario, Canada
Posts: 1,265
Default 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?
Mark1960 is offline  
Old 29th Mar 2022, 10:39 pm   #20
SiriusHardware
Dekatron
 
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default 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.
Attached Thumbnails
Click image for larger version

Name:	loaded.jpg
Views:	74
Size:	43.3 KB
ID:	254349  

Last edited by SiriusHardware; 29th Mar 2022 at 10:45 pm.
SiriusHardware is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 10:50 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.