Amstrad CPC 6128 RAM Repair & Swapping Banks (From Yellow Belly)
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- čas přidán 13. 09. 2024
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A quick look at a RAM fault on an Amstrad CPC 6128. In this video I also work out how to swap banks 0 and 1 around, so you can use memory testers that focus on the expansion RAM, to test the base 64KB.
Yellow Belly - / @yellowbelly9005
Other channels mentioned:-
Novabug - / novabug
Noel's Retro Lab - / @noelsretrolab
Dermot Sweeney - / @gametechrefuge
#amstrad #cpc #ram #repair
![Forcing 2nd RAM Bank on an Amstrad CPC 6128 [Nibble Edition]](/img/n.gif)
Note: I did test with a number of other RAM test programs too, but didn't film those. I also tested the ESR of the caps on the motherboard too - all OK.
Yellow Belly - czcams.com/channels/aV8T1QxAyq4GPEIgpBZcpg.html
Other channels mentioned:- Novabug - czcams.com/users/Novabug Noel's Retro Lab - czcams.com/channels/2-SP1bYi3ueKlVU7I75wFw.html Dermot Sweeney - czcams.com/channels/MeqbD202qj2mytjr7Uu1Rg.html
I love the way you are so conscientious in your cleaning of these retro computers - not just cleaning up after your soldering, but all the rest of it. Shows real pride in your work.
Thank you very much! =D
Great job on that repair! I so wish we had better memory testing programs on the Amstrad... That's been an outstanding project of mine, but at this point I've come to terms with the fact that I don't have time for that 😃
Also, I'm not a fan of piggybacking at all! I suppose sometimes it works, but often times it doesn't do anything at all.
Thanks =D I might have a go at knocking up some test code! Yeah, the piggy back technique can be hit and miss, but I have to admit to around 70% success rate using it to diagnose faults with these types of RAM. It depends on the type of failure at the end of the day.
@GadgetUK164 I just received this 6128 from Yellow Belly today, thank you for all the hard work you put into fixing this. 💕
You are so welcome! =D A lovely gift from Yellow Belly =D
Your comment about electric shock and ESD straps - this is exactly why ESD straps have a 1 Megaohm resistor in them (somewhere, usually the cable). At kilovolts which is typically what ESD is, that resistance is nothing, but at mains voltage it is significant - not even a milliamp will flow. You'll still feel it, but it wont cause you any harm. That said, it is still a sensible precaution to wear the strap on your dominant hand.
Haha, yes - you're right! I had forgotten about that! My fault for responding to a comment without thinking about it first!
The ESD strap *should* have a large value resistor in series in it (on the order of 1M).
Great video, the piggy back test is super interesting. Thanks for posting!
I love this, such brilliant work sir.
Surprised that faulty ram wasn't warming. I guess being on bank 1 it wasn't getting enough input. Lots of extra tips o never knew before to add to my own cpc memory bank. ;)
Thanks Chris =D Much appreciated!
Nice fix and informative vid as always.
Thanks 👍
All wrist straps (well maybe not some 10 cent chinese ones) have an integrated 1 meg or 10 meg ohm resistor in the connector to the strap. This is so that you don't have any lethal levels of current pass through you to ground, i.e. from a mains electric shock. The resistor doesn't affect any ESD through the strap as the currents associated with any form of ESD are tiny.
I bet mine is a 10 cent one ;)
14:45 Hopefully, all proper ESD wrist straps have a series resistor inside. Usually 1M Ohms.
So any risk from electric shock that way is incredibly low. It would have to be a shock from a pylon or something. lol
yep at 240V youre not even going to get a milliamp, it'll tingle but wont be fatal. it's still a good idea to have it on the dominant hand though
Have to ask mate, your wrist strap, have you tested it, it's supposed to have a 1Mohm resistor to limit the current in case you do touch something live, so it's supposed to make it safe to wear on either hand
Thanks, yes a few people have mentioned this - I will check! I was aware of the resistor but had forgotten about it over the years.
Cool
6:36 ops, lol
LOL
Never piggyback an expensive IC (and definitely not an unobtanium one!) - desolder it first, and verify the fault is not on the circuit board, or the fault could blow your new IC, too. With cheap-as TTL/CMOS, this isn’t too much of a problem, but you probably don’t want to pop the microprocessor, or a PAL/GAL that you can’t reprogram! 😏 ouch time!
Yeah,, the only time I would piggy back is with 74 series and easy to obtain DRAM. It doesn't always help with certain types of fault. It does work well where an IO pin is not pulling strong enough one way or another.
I was wondering if the change of a PSU could alter picture colour? It seems to have, I switched a 3rd party SNES PSU for a proper one and the reds in-particularly look a fair bit darker.
On the SNES I would be surprised since there's a voltage regulator to step down from what you feed in anyway. But on the CPC, that's totally possible since the 5v rail is unregulated, so the PSU will have an effect.
Cheers, I really don't know then maybe a snugger fit, or the fact I gave it a good clean prior to the swap over, I've since switched it to HDMI, but ideally I'd want it through a SCART on a portable C.R.T. what it your preferred method?
Im looking for some advice for my 6128, it wouldnt boot, only showing a black border and solid colour screen. so i piggybacked the ram to find it was the one on the bottom right that was playing up. Booted perfectly. So I desoldered the faulty ram chip but to my surprise.. there was a tiny wire soldered to the 3rd leg from the left of the bottom row of pins on the ram chip (it was wrapped around the leg and soldered underneath the chip before it was soldered to the board, so i didnt see it when i desoldered the chip, but lifting the chip then revealed the wire and it just broke away.. i dont know where it was connected to or why it was there. theres no other wire on any other chips.
Now when I boot it with the new ram installed in its place, it goes back to not booting again. (black border, solid colour screen) . This wire did something but im not sure what it was or how to get it working again.
thank you
What you need to do is look at the schematics - and work out what that wire was doing - it was very likely fixing a damaged trace from manufacture, or fixing a missing connection. There are some common connections that make testing connectivity on RAM easy - eg. address lines, VCC, ground, some of the RAS / CAS signals on specific banks.
So what you can do is check one of the chips to the one next to it and you may find all pins of a certain position are joined up - EXCEPT for the the chip you are looking at. Doing those 2 things you might be able to work out which pin is not connected!
ie. measure on connectivity (beep) test on your multimeter from the 1st pin on the RAM chips, to the same pin on the next chip - you may find they are all joined together on that pin, except for the IC you removed! Not all of the pins are joined together though. The data pins are usually seperate, and the RAS / CAS may change between banks of RAM.
thanks for this@@GadgetUK164 I had found out what was wrong. its as u said. The pin of the bottom row on the chip, the 3rd one across, if you do a continuity test on the same pin but on any of the chips - they are all connected in parallel together, the last chip it failed to beep - there was a broken trace on the board and that wire simply was connecting to the same pin but on the chip above it, so i just connected a new wire to complete the connection and bam all working! I will take out all of the chips and install sockets and repairs the trace and all will be well :) thanks for your reply!
Ive actually gone and totally ruined this amstrad :( so frustrated with myself. I desoldered all of the ram chips, but the traces on it were very sensitive and some had come away. So i believe i corrected all of the traces, continuity tested everything and powered on and its got a pink screen (i think its pink! being colourblind here is no good) with a black border. So i thought I know, il do this bank swapping trick. took out the pal chip and a leg snapped off! Soldered a new leg on, still same issue, when powering on I stupidly put the 12v wire into a 2 pin socket on the top left by the relay..... nothing went pop, but i still get this solid colour screen with black border! Im not sure what else to check with my multimeter. im trying to rule out ram and also if that 12v in the wrong connection has done something. was supposed to be a nice ram swap for a few hours - ended up being 10am til now trying to sort it all day with still no progress. i should have left it as is :(
I`m getting an OUT OF MEMORY on a CPC 464 when I load small games. I`ve just wrote a little program to poke and peek. I started at the top of the memory and it got down to 49151 address and the computer locked up. Pity I can not read the address to find out the chip. Not that I know which chip is which. :)
Try the piggy back method - it may shed some light!
@@GadgetUK164 I`ve changed all the ram chips now and it`s still the same. Strange.
bloody amstrads...still waiting for my AY chip to hopefully fix my keyboard...
1 comming from spain.. and they saying brexit issues is delaying it.... :(
and found one from china.. something like 2 months wait.... its on a slow boat or somethin....
These 6128s are now going on ebay for some crazy prices...
just cant afford another one.... :(
just hope me ram does not die aswell....
will send coffee...
N x
90 lbs?? And manufacturers wonder why people pirate these things... sheesh. 🥸