RF Video Distortion

[RetroMike]

I've taken some white paint to the logo on my Speccy this avo and it's looking quite nice at the moment. Needs a little touching up, but I was using a Windsor & Newton 000 Series 7 paintbrush, which has a very fine point, and resting my hand on the case to keep it wobble-free.

[RetroMike]

My Traco Power rectifiers have arrived... now I need to scout about and find which way round to orient them! Unless anyone's got the answer right here, I'll have a shufti at some schematics

[Moggy]

The white dot on the left as you look face on at it is the power in, middle leg ground, right leg power out.
Same config as the regulator it replaces.

[RetroMike]

Thanks for that - just to clarify further, we're looking at the pins of the old regulator from the printed side, I presume, as my old reg doesn't have a dot on it. Is it standard practice to have Input/Gnd/Output from left to right?

[1024MAK]

For a 7805 voltage regulator, if you view it with the heatsink tab (metal tab) at the top and the type number markings on the plastic case towards you so that you can read it, then the left leg is the input (often marked pin 1 on data sheets), the middle leg is 0V/ground/common and the right leg is the +5V output. A quick test with a meter on voltage will confirm this

And no, not all regulators use the same pin-out. 79XX types and adjustable types are different for example.

If you search for 7805 pin-out pictures using a search engine, it should find you a nice picture...

Mark

[RetroMike]

Thanks again Mark - as you might have guessed, I'm a bit of an electronics neophyte, so I'm cautious when I'm doing something new. I've fitted both the parts to the Zed and the Speccy, and have tested the Zed, which I've also shortened the wires on the Pokemon Composite board, as suggested earlier in the thread. They both work well, and I've also had the ZXpand working on, plus the three redundant memory packs attached to it while I was faffing (one at a time of course) .

The PSU on the Speccy has turned out to be proper unreliable, and I think there might be a break in the cable somewhere else other than the already identified location, so might have some work ahead of me there. I'll have to find a Speccy board other than World of Spectrum to check into, as I've been waiting over a week to be verified

Must get round to selling the two Sinclair units and the board out of the Memopack sometime soon, as I'll be mounting my ZXpand in the pack for tidiness

I'll bide my time putting the Z80A in, as I think I need a rest from soldering, and should spend a bit of time having a play with the Zed. As well as the Speccy, I've also got an Amiga A1200 in bits in the computer room, which I'm trying to get somewhere near good working order. Leaky caps causing damage to the IDE riser being one of my woes

[balford]

Well while you're waiting on WoS, please feel free to PM me with any Speccy related questions - and I'm sure Mark would be receptive also

I've repaired a few Spectrums and have a small collection so am fairly well versed in what's what.

(I've also PMed a mod there to give them a heads up.)

B

[RetroMike]

Thanks chap

Well, I got itchy fingers and put the new Z80A into the Zed, and it worked straight off the bat. I think I'm starting to get a bit better at soldering as well as de-soldering now too, which is nice

The weird thing is, I'm sure it is faster now... it just feels snappier somehow, unless it's just psychological... a placebo effect? I lifted the lid after 10 minutes of it being on, and the little regulator box was just a little warm to the touch, not the scalding hot of the previous inhabinant of that area and its heat-sink

[1024MAK]

The weird thing is, I'm sure it is faster now... it just feels snappier somehow, unless it's just psychological... a placebo effect? I lifted the lid after 10 minutes of it being on, and the little regulator box was just a little warm to the touch, not the scalding hot of the previous inhabinant of that area and its heat-sink

Maybe it feels snappier now because the Zeddy is cold, as you have removed the winter finger warmer system

BTW, the fact that the heatsink for the 7805 got hot showed that it was doing its job
Some figures for you: the Sinclair PSU typically has an output of around 10.5V to 11V.
The current used by an unexpanded ZX81 is around 300mA.
The output voltage of the 7805 is 5V.
So the power that the 7805 (and therefore it's heatsink) has to dissipate into the air is:-
(11V - 5V) x 0.3 = 1.8 Watts

The power used by the rest of the ZX81 circuitry is 5 x .3A = 1.5 Watts

Mark

[RetroMike]

Quite a significant difference, isn't it? I'm sure my Speccy was knocking out about 14v, but as the wire is froobed, it was transient to say the very least Incidentally, where does the power that used to be turned to heat go on the new one

I need to dig out my ZXpand instructions next, and get into some of the books I got for a song off eBay. Time is the killer. If I could get some books on Kindle on my phone and tablet, I'd have more chance when I'm sitting at the doctors or waiting at the hozzy, or even to distract myself from the Tombliboos when I'm on stag watching the Boy