Issue 3 ZX Spectrum 48K Refurb - DCDC Mod Walkthrough
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- Опубликовано: 8 сен 2024
- Today we are re-capping and DCDC Modding a donated Issue 3 Spectrum 48K. Enjoy!
Correction -- The DCDC Mod parts list has an error, it should read "22uF 25V" Capacitor, not "22 uF 5V"!
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Love this and can smell that coffee from here, lovely.
Wider tip on the iron would help get the heat into those joints especially on the big ground planes
Thanks for the heads up on the DCDC mod. I bought my first Speccy a few months back (Issue 2), but AFAIK it's not been DCDC modded. It's on my "to be recapped" list, so I should probably do the DCDC mod at the same time.
For an issue 2 I would take a look at retroleum's advice, the mod is different to what I presented here as far as I understand. blog.retroleum.co.uk/electronics-articles/spectrum-issue-2-pcb-mods/ Also look at the issue 2 repair video I posted in case there's anything useful there for you
@@HappyLittleDiodes cheers!
For a long time I've wanted to attempt one of those B-roll coffee making shoots; turns out it was much more difficult than I imagined.
The thin double sided tape is OEM. Sinclair made them cheap!
I used a 1/4 watt resistor on the 270 ohm R60 mod. I got 18 volts on the 12 volt rail. I hoping a 1/2 watt will get it back to 12 when it arrives.
The CPU has a date code from 1988 which means it can't be original.
I am glad the algorithm suggested you, subbed!!
Cheers Steve!
Hello HLD.
What acid did you use for the nut? And , did you use any product after the acid to prevent it from rusting again?
Also , where did you get the replacement feet?
And also, what's the point of the DC DC mod? When I read the title, I thought you were going to use a Traco Power.
Hello
It's called "Rust Buster" a product I bought a long time ago and I use it from time to time for things like this.
Replacement feet can be bought from ebay or Spectrum parts websites, I also have a sheet of rubber which is just about the right thickness and I just cut them from there if I don't have any genuine spares
The DC-DC mod is a factory mod that simply changes the power circuit to match that of later issue boards, the newer circuit is generally more reliable and an improved design.
@@HappyLittleDiodes Thank you very much for your reply and for your videos!
Did you insert the D19 backwards at R54 in the video? Shouldn't the cathode be on the LEFT side? You can see it at 13:40 in the video.
Yes it looks like in that one shot it's wrong but gets corrected. I'm not sure why that happened! I can't remember doing it
Thanks for the DCDC mod walkthrough. Since I can not find a 1uf/63uf cap do you think I can get away with lower voltage (50v) or I should absolutely go higher (100)?
50 V is fine
@@HappyLittleDiodes Great thanks!
Is it ok to use resistors with 5% tolerance or should I order 1%?
I use 5% for some but I can't argue with "smaller is better" !
Hi. thank you for a great video. When I look at the schematic for issue 4a, resistor 60 has a value of 68 ohm. You change it to a 220 ohm resistor. Can you tell why?
Hi Kim. Yes the issue 4A has a 68 Ohm, but the Issue 4B has a 220 Ohm. From what I understand, using 220 Ohm will help prevent TR4 from blowing
I also love the jokes :)
Is there a parts list for the DCDC mod?
Find the stores that sell kits, they attach a pdf to the store page with details
Can you post a link to these "checks" that you run as I have a fresh motherboard and would like to run through them?
Search for ZX Spectrum initial tests. A video by joulespercoulomb
@@HappyLittleDiodes Thanks! will do, I got the DCDC pack from Retro Revival and I plan to attempt this mod over the weekend, thanks SO much for putting up this quality video to help me out!
Nice job. By the way what is the purpose of this dcdc mod? (i do also zx spectrum restorations)
The power circuit on boards before issue 4a had a habit of blowing up transistors so this mod improves the reliability and robustness
@@HappyLittleDiodes i bought a zx spectrum+ with this modification and now i solved my inquiry
@@HappyLittleDiodes didnt the issue 3B board fix this? i recall it was a slight redesign from the issue 3 to fix the DC-DC circuit reliability
@@sharazjek338 I think if you compare a 3B power circuit to a 4A power circuit in the same way, you should find that C66 needs to be changed, so you're right I think most of these changes already took place with 3B boards over 3 boards.
Hell ! can you help ? i own a zx spectrum sinclair 48k that doesn´t load the games. They just get errors when first game screen opens or crash during the doalings and green little squares on some loading drawings. I inserted that to check the upper RAM chips :
PRINT PEEK 23732 + 256 * PEEK 23733 the value result was wrong
it was 32863 instead of 6553 »»»» I tested all the 8 upper RAM chips group on the board below (right side not the logical ones) using a fully working sinclair 48k and all 8 are good.
How did you test the upper RAM chips?
@@HappyLittleDiodes I removed one chip from other fully working board and tested the upper chips of the board that doesn´t load installing them one by one and the games loaded perfectly
So i reinstalled the upper chips back again on the problematic board but the non loading symptoms continued
I would recommend running a diagnostic ROM. RAM failures can be weird and this is the best way to root them out
@@HappyLittleDiodes that´s expensive. More than a speccy 48k unit it´s a monkey business.
Issue 3, isn't that quite rare?
Not that I'm aware of unless I've missed something, the mod also applies to 3B and 4A I believe
@@HappyLittleDiodes I likely could be wrong, but I thought the 3 was one of the rarer ones. There's a list somewhere.
Edit- yes sorry, I was thinking issue 2, which is 500,000 machines
I shall use this to guide my refurb - thank you.
This is the test video, right..?
ruclips.net/video/IzgCmldm2H4/видео.html
Yes that's the one, a great video to follow through