7:15 The silkscreen on these boards isn't always totally reliable, so always pay attention to the direction the installed capactitor you're removing. I'm not good at this, the few times I've had to do this, I do them one at a time for exactly this reason.
Of course, I cannot make an accurate diagnosis from watching your video; however, the display this ZX Spectrum produces is highly indicative of a RAM fault. Whether it is in the upper or lower RAM (or both, it can happen) will have to be determined. Sometimes it is possible to detect a faulty upper RAM IC by using an oscilloscope to examine the signal on the data line (Din and Dout are connected) of each upper RAM IC. It's difficult for me to describe exactly what to look for in a brief way; it's something one gets used to noticing after having repaired hundreds of these computers. Nevertheless, a common problem is a faulty upper RAM IC attempting to pull its data line high or low at a time when it shouldn't. This can interfere with the CPU's ability to access the lower RAM. If you are familiar with the ZX Spectrum's initialisation process, the exact position of the thin vertical red lines on the display can sometimes give a clue about which data bus line is afflicted. The persistence of these lines suggests the computer is unable to complete its initialisation RAM test routine. The exact nature of the fault could very likely be determined by using a logic analyser. I have published a video that contains information on doing this: ruclips.net/video/WOzpM0YgcH0/видео.html Faulty lower RAM ICs can most easily be replaced by new old stock or used, but tested 4116 ICs. Upper RAM ICs can be replaced by 4164s. All replacements should be designed for access times of 150 ns or less. Alternatively, I sell modules that can be used to replace a whole set of upper or lower RAM ICs (see zx.zigg.net). If you are not highly familiar with the hardware of the ZX Spectrum, you might find another video I have published helpful, it's called ZX Spectrum Hardware Description. Good luck with the repair!
I can recommend these modules. in addition to replacing the whole bank of original chips, the fact they use the 5v line exclusively will make the 48k a lot more fault tolerant.
You can also touch the ram chips to see if any are warmer than others, any that are hot are definitely shot, i fixed a few speccies with this method, regards. Hope you have another go at this, definitely go for the ram chips for your next move.
If you ever have to replace an IC, and worry that you may strip the pads or something, it is worth considering using small cutters and snipping the leads of the package to get it out of the way, and then removing each lead individually. This technique can, of course, also be used for any other sort of trough hole component where the leads are available, for example when recaping a board like in this video. I would probably have removed that heat sink for this work, I was worried it would get hung up on something or just put too much strain on the regulator leads.
Speccy could be tough to fix sometimes. There are different upper 32kb chips which consist of 8kb chips with only 4kb working on them. Depends which section if good (top 4 or lower 4) then there is a switch that lets the board know what kind of chips are installed. Now i think it could be lower 16kb and you should let the computer run for a bit and check which of the 8 chips gets hot or hotter than the other once and replace it. Also there could be a bad rom or even ULA. If you have all voltages then I would look at lower ram first. If you decide to remove all lower ram chips then you could always put sockets and try to replace them with the good ones or I would go for a lower 16kb board that just clips in the sockets (if I remember correctly). It covers the whole area of 8 chips and uses some of the pins from the sockets. Either way this will give you an idea if the ram is good or bad and it's a good starting point. But you will have to be very careful with removing the original 8 chips as the lines could lift and break. Just be careful and use low temp setting and you should be ok. I think you would really enjoy speccy with AY and trackers as the demo scene pushed that chip to limits in speccy. You can even get a sample tracker (crazy ey!) but more memory would be very beneficial but you could still experiment with it with 48k. Good luck to you and if ill see some other videos with your speccy I'll try to help some more. Cheers!
Easier to cut the legs to faulty components before trying to remove the pins when desoldering. You're also better off using a solder sucker to remove the bulk of the solder then use the braid to wick off the rest and the leg will simply fall out. The object here is to ensure no damage to the PCB. Should also try and get hold of axial lead capacitors rather than the newer radial lead.Has been very interesting watching and is inspiring me to fix my two spectrums I've had in my cupboard for years. Thankfully these are in better shape but may also be suffering RAM faults due to power supply failure.
Good job. I use an acrylic resin, make a mixture of powder and liquid, making a paste that dries fast. I apply around the power connector and it would also be securely attached. OK!
Louis Rossman usually start testing components path by path with the voltimeter (I think) to find the broken one. Why didn't you take the same approach?
I ended up getting busy with another project.. I came back to this later and went further but there's more wrong with this and I need time and full concentration to fault find.. So its still waiting.
Actually in the previous video I had done the RF hack and converted it into a composite, so it works well and is bipassing the RF modulator.. however this seems to be a ULA or memory issue. :o)
Thank you! unfortunately no, this project has been put aside for now, I have some ideas but getting the things to test will be a bit expensive, I may return to it though. Thanks for asking.
My pleasure !! Me too, I've recapped my Issue 3 and it works like a charm, better output video, modified in composite video, very nice picture, good old memories :-)))
One more thing, you could look up Spectrum Next. You could just purchase a mother board which has a loooot of improvements over a stock speccy with more ram, additional video options, accelerator option, SD card I/O and has a AY chip and SID from c64 implemented and you could put it in your speccy case (some modding required but it is very very nice) ;)
Haha i've had my eye on the concept designs of the Spectrum Next for about a year now and have been drooling over it since the kickstarted happened, it seems great and the fact that you can use it as a real spectrum (I wanted a toastrack spectrum before knowing the next was actually available... now to save those pennies :o)
MsMadLemon very true! It is a bit expensive and as for me personally I promised myself to invest in one project at time (my a600 first) but knowing that the NEXT boards will be available next month makes it very very tempting! (Not sure if I can resist lol) :)
Would love to see this computer working again. It’s fun to watch the repair process, especially as casually as you do it! Great videos!
7:15 The silkscreen on these boards isn't always totally reliable, so always pay attention to the direction the installed capactitor you're removing.
I'm not good at this, the few times I've had to do this, I do them one at a time for exactly this reason.
Of course, I cannot make an accurate diagnosis from watching your video; however, the display this ZX Spectrum produces is highly indicative of a RAM fault. Whether it is in the upper or lower RAM (or both, it can happen) will have to be determined.
Sometimes it is possible to detect a faulty upper RAM IC by using an oscilloscope to examine the signal on the data line (Din and Dout are connected) of each upper RAM IC. It's difficult for me to describe exactly what to look for in a brief way; it's something one gets used to noticing after having repaired hundreds of these computers. Nevertheless, a common problem is a faulty upper RAM IC attempting to pull its data line high or low at a time when it shouldn't. This can interfere with the CPU's ability to access the lower RAM.
If you are familiar with the ZX Spectrum's initialisation process, the exact position of the thin vertical red lines on the display can sometimes give a clue about which data bus line is afflicted. The persistence of these lines suggests the computer is unable to complete its initialisation RAM test routine.
The exact nature of the fault could very likely be determined by using a logic analyser. I have published a video that contains information on doing this:
ruclips.net/video/WOzpM0YgcH0/видео.html
Faulty lower RAM ICs can most easily be replaced by new old stock or used, but tested 4116 ICs. Upper RAM ICs can be replaced by 4164s. All replacements should be designed for access times of 150 ns or less. Alternatively, I sell modules that can be used to replace a whole set of upper or lower RAM ICs (see zx.zigg.net).
If you are not highly familiar with the hardware of the ZX Spectrum, you might find another video I have published helpful, it's called ZX Spectrum Hardware Description.
Good luck with the repair!
Thank you so much for this valueable info! I will check out that video and what ram modules you sell.
I can recommend these modules. in addition to replacing the whole bank of original chips, the fact they use the 5v line exclusively will make the 48k a lot more fault tolerant.
I definitely cannot fault @JoulesperCoulomb's diagnosis. He managed to debug my speccy by a badly described issue from me via email .
You can also touch the ram chips to see if any are warmer than others, any that are hot are definitely shot, i fixed a few speccies with this method, regards.
Hope you have another go at this, definitely go for the ram chips for your next move.
If you ever have to replace an IC, and worry that you may strip the pads or something, it is worth considering using small cutters and snipping the leads of the package to get it out of the way, and then removing each lead individually. This technique can, of course, also be used for any other sort of trough hole component where the leads are available, for example when recaping a board like in this video.
I would probably have removed that heat sink for this work, I was worried it would get hung up on something or just put too much strain on the regulator leads.
Speccy could be tough to fix sometimes. There are different upper 32kb chips which consist of 8kb chips with only 4kb working on them. Depends which section if good (top 4 or lower 4) then there is a switch that lets the board know what kind of chips are installed. Now i think it could be lower 16kb and you should let the computer run for a bit and check which of the 8 chips gets hot or hotter than the other once and replace it. Also there could be a bad rom or even ULA. If you have all voltages then I would look at lower ram first. If you decide to remove all lower ram chips then you could always put sockets and try to replace them with the good ones or I would go for a lower 16kb board that just clips in the sockets (if I remember correctly). It covers the whole area of 8 chips and uses some of the pins from the sockets. Either way this will give you an idea if the ram is good or bad and it's a good starting point. But you will have to be very careful with removing the original 8 chips as the lines could lift and break. Just be careful and use low temp setting and you should be ok. I think you would really enjoy speccy with AY and trackers as the demo scene pushed that chip to limits in speccy. You can even get a sample tracker (crazy ey!) but more memory would be very beneficial but you could still experiment with it with 48k. Good luck to you and if ill see some other videos with your speccy I'll try to help some more. Cheers!
Easier to cut the legs to faulty components before trying to remove the pins when desoldering. You're also better off using a solder sucker to remove the bulk of the solder then use the braid to wick off the rest and the leg will simply fall out. The object here is to ensure no damage to the PCB. Should also try and get hold of axial lead capacitors rather than the newer radial lead.Has been very interesting watching and is inspiring me to fix my two spectrums I've had in my cupboard for years. Thankfully these are in better shape but may also be suffering RAM faults due to power supply failure.
Hi Maddi. The guy to ask (or to send to repair) is JoulesperCoulomb. You can watch his videos.
Thanks Fernando! I appreciate the help, I need to get the spectrum out again and investigate, I left it aside for too long.
I’ve recapped my 48k Spectrum + too. Turned out to be quite easy, actually.
Good job. I use an acrylic resin, make a mixture of powder and liquid, making a paste that dries fast. I apply around the power connector and it would also be securely attached. OK!
Louis Rossman usually start testing components path by path with the voltimeter (I think) to find the broken one. Why didn't you take the same approach?
have you replaced the ULA ? how do you troubleshoot it ?
Did you check the voltages to the lower RAM bank yet ?.
Oh dear, is that where it ended...?
I ended up getting busy with another project.. I came back to this later and went further but there's more wrong with this and I need time and full concentration to fault find.. So its still waiting.
Ahh shame it wasn't so simple. Excellent work though. Love your repair videos and the humour. (you have to laugh or you'd go mad!!) :)
Hi again. Have you checked for a dry joint on the rf modulater before you start and swap and change chips. 😀
Actually in the previous video I had done the RF hack and converted it into a composite, so it works well and is bipassing the RF modulator.. however this seems to be a ULA or memory issue. :o)
Spot on, I love your skill, thumbs up! Any news?
Thank you!
unfortunately no, this project has been put aside for now, I have some ideas but getting the things to test will be a bit expensive, I may return to it though. Thanks for asking.
My pleasure !! Me too, I've recapped my Issue 3 and it works like a charm, better output video, modified in composite video, very nice picture, good old memories :-)))
sometimes the faulty ram chip will be hot, very common problem with a zx spectrum
I will look out for that, thank you!
One more thing, you could look up Spectrum Next. You could just purchase a mother board which has a loooot of improvements over a stock speccy with more ram, additional video options, accelerator option, SD card I/O and has a AY chip and SID from c64 implemented and you could put it in your speccy case (some modding required but it is very very nice) ;)
Haha i've had my eye on the concept designs of the Spectrum Next for about a year now and have been drooling over it since the kickstarted happened, it seems great and the fact that you can use it as a real spectrum (I wanted a toastrack spectrum before knowing the next was actually available... now to save those pennies :o)
MsMadLemon very true! It is a bit expensive and as for me personally I promised myself to invest in one project at time (my a600 first) but knowing that the NEXT boards will be available next month makes it very very tempting! (Not sure if I can resist lol) :)
Check TR4 and TR5 before switch it on again, then maybe IC11 has to be replaced, ULA chip should be fine.
soLder ! .. thanks. #oneofus
Sorry for the bad spelling haha
IC11 is your best bet ;-)
positive its negative ;-)
Don't you start! ;o)
There's no fixed convention, it is confusing, especially when trying to get your head round recording a video.
bad ram chip.