Author Topic: Accidentally used a 9v PSU on the 6128 plus, what's the damage?  (Read 5090 times)

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Offline TFM

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Glad to see it works again! As we say "Mehr Gl├╝ck als Verstand". Hope it will never break again.  :)
TFM of FutureSoft
Also visit the CPC and Plus users favorite OS: FutureOS - The Revolution on CPC6128 and 6128Plus

Offline keropi

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@TFM
thanks, I'll make sure the PSU won't be mistaken again  8)


@||C|-|E||


You Sir are correct  ;D


I replaced the caps when I got the machine, it just seemed a good idea to replace the ones after the power input and then I just decide to replace them all with chemicon/panasonic ones as there are not that many to begin with...


There is indeed an ABBA switch under the 3.5" floppy:





And this is the red wire deal:








I have installed a small switch above the power input , after discussing the video quality issues with a good friend (roy.bates for those that are on AmiBay as well).
Basically he pointed that the "+5v RGB ON signal" that is used in scart RGB cable schematics is the TTL-SYNC output from the motherboard which is not meant to be used like that and causes image quality degradation especially on LCD panels (at least my LG sets did not like that much, had issues from ghosting to pixel crawling).


So this switch just selects what PIN1 on the RGB port is: either stock TTL-Sync for use with Amstrad monitors or +5v via a resistor so you get correct RGB Switching voltage at a scart plug. After I did this all my image quality issues went away.


Now I must also mod the TTL-LUMA signal at the scart plug, I believe it will be better if I use a 680ohm resistor in series which along the internal 75ohm termination of monitors it will result in a better/more-standard signal.


Ofcourse if anyone has a better idea please share - the machine came with the b/w monitor and TBH this went to storage as I will be using the 6128+ most of the time with a 1084 or a rgb-capable tv set in case I remove it from my desk.



Offline Bryce

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Very neat work there. I like the plastic strip you added under the drive. The RGB switch is a cool idea too. Haven't seen that done before.

Bryce.

Offline keropi

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Thanks Bryce!
Credits for the 5v/ttl_sync idea should go to roy.bates though, it was his idea  8)


The plastic profile under the drive was indeed a success, if you look at the other pics there are actually 2 profiles that are screwed under the drive and the whole assembly is hotglued on the bottom shell part.
The plastic profiles are measured in height so that the drive also tops under the upper shell, meaning there is no space for it to move upwards after the case is closed. It's really solid once closed.


The only thing I don't like at the whole deal is a part at the floppy head switch filling, you can see it's not even on top... luckily you can't really see it in real life , the photos do enhance it though  ::)
« Last Edit: 11:28, 22 June 16 by keropi »

Offline Bryce

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I'll congratulate Roy then, next time I'm talking to him :D

Bryce.

Offline ||C|-|E||

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All very neat, as Bryce said, and useful!! I really like how it is done. On the other hand, this is the first time I see the video mod as well, very nice indeed  :)

Offline keropi

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Yes it was a nice idea, it does solve issues with lcd panels as they are mostly more sensitive than crt ones. But even on a crt panel having a ttl signal acting up as voltage is not that great either - sure it works but it's kinda wrong (unless ofcourse you have something like the 1084 were rgb switching voltage is not needed at all)

Offline ||C|-|E||

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It would be very nice to properly document the mod in the wiki  :)

Offline keropi

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Maybe these pics help so others can understand it?

The main point here is to control what goes to SCART pin16 (it is the RGB enable pin and if it is in the 1~3v range then the monitor gets the signal that a RGB source is connected) . So we need SCART pin16 to have a correct voltage for this plus we want to it to be "real" voltage and not a TLL signal that can carry with it other information that mess up with the monitor.


For this purpose we need to install a Single Pole Double Throw (SPDT) switch, so we control what goes to pin1 of the 6128 PLUS.
- we need to lift R87 from one side just like in the pics below (resistor end is the stock TTL Sync signal and the motherboard via that is now not-connected goes straight to pin1 of the RGB port)
- find a good 5v point nearby to get our RGB enable voltage via a 150ohm resistor to bring it around ~1.7v so that it is within specs.


Here are a couple of pics with the points that I used, I hope they are self-explanatory: