Does the usual composite mod damage Speccies?
Hi people,
Just browsing eBay -as you do - and I noticed this auction:
http://cgi.ebay.co.uk/ZX-SPECTRUM-48K-GOOD-COND-COMPOSITE-OUTPUT-SINCLAIR-/170625573186?pt=UK_VintageComputing_RL&hash=item27ba13a142
It's a completed listing, I'm not spamming. :)
Anyhoo, the seller claims that his mod is better than the usual "whack the line from ULA straight to the modulator output" mod which seems popular, because by wiring the ULA straight to the output (and thereby the TV) you can apparently damage the ULA.
Is this actually true? Am I risking damaging my oh so precious ULA by doing this?
Just browsing eBay -as you do - and I noticed this auction:
http://cgi.ebay.co.uk/ZX-SPECTRUM-48K-GOOD-COND-COMPOSITE-OUTPUT-SINCLAIR-/170625573186?pt=UK_VintageComputing_RL&hash=item27ba13a142
It's a completed listing, I'm not spamming. :)
Anyhoo, the seller claims that his mod is better than the usual "whack the line from ULA straight to the modulator output" mod which seems popular, because by wiring the ULA straight to the output (and thereby the TV) you can apparently damage the ULA.
Is this actually true? Am I risking damaging my oh so precious ULA by doing this?
Post edited by Spirantho on
Comments
No.
The composite mod has nothing to do with the ULA
Thats a lot of beans for Rubber 48k!
why is it so pricey?
Jealousy gets ya nowhere :lol:
Recently I had to do a comp-mod on a 48k+ as the RF unit had rotted internally.
As a thought - I really wish people stored their stuff in plastic sealed containers more, (instead of sheds and lofts!)... thats 4 RF units this year!... each one of them - rusty as hell!
Now, while I could of replaced the RF Modulation unit, it seems silly to do so as not only does it stress the board (with the hot air) but the end result outputs a worse signal that is prone to breaking down if not stored correctly.
The one I modified had serious issues a huge video slurr on the video output and aboslutely no colour.. I wasn't prepared to spend 30 minutes replacing the components for a crappy RF signal.
so about 4 minutes later, we have a wonderfull Composite out.
I will say though that I think in future I will be looking at amplifying and cleaning this out put a little as my Plasma doesn't like it that low.... I keep geting minor image artifacts with static screens - This also happens on my Amiga's via composhite as well... in fact the only one it doesn't is the boosted composite board I made from an old CMB A520!
Its a very simple circuit, and that small it could easily fit inside the RF modulator
The extra stuff in this composite mod I suspect is just the extra emitter follower amplifier, and anything that could damage the Spectrum via the composite out will still damage the Spectrum with this additional amplifier. So no, the mod he's done doesn't reduce the risk at all. It probably doesn't even improve the picture quality measurably (the composite video is actually a pretty low impedance output anyway if you calculate it; it already has an emitter-follower amplifier, and having perfect 75 ohm output impedance isn't really necessary for the Speccy unless you have absurdly long composite leads (you tend to start running into problems when the cable gets bigger than about 1/10th of the wavelength, given that the composite signal from memory is a baseband signal of about 6MHz or thereabouts, you'll need cables around 5 metres long before you begin to care. I don't know about you, but my composite cables for a Speccy are generally about 1m long.
The TL;DR version of this is: I call it snake oil.
yep, if you mean the little buffer circuit I built one into the modulator can on my first 48k. (the second one just got the normal one as I knew by that point that the buffer isn't needed in the 48k)
I suspect that most of the problem people have with modern TVs is the crappy approximation of a PAL signal that the speccy outputs. The timings are all wrong, it outputs the same field twice, etc etc. This confuses the brain inside an LCD, which is expecting a proper in-spec signal.
In an analogue telly it doesn't matter as to a certain extent it will display a signal with any crappy timing as long as it's not too far out of frequency.
the sound circuit is nothing to do with the video*, it's more likely a dodgy solder joint or something.
*on the 48k that is. On the 128k models sound is added to the video before the modulator but obviously that has to be disconnected to do a composite mod anyway.
Which AFAIK is pretty common for sellers of old homecomputer gear :D - after all, often it's been in the attic for decades & owner has forgotten the details, or seller is a new owner who never worked with it (or seen insides).
1. The modulator is trough-hole monted. Why not use a solder pump?
2. You may want to have a look at: http://zxhobby.leadhoster.com/CmpVideo/CmpVideo.htm
please don't use that stupid, made up, word 'compos*ite'.
CVBS is fine. not as good as RGB, and little worse than s-video, but compared to RF its excellent.
its like saying floppy is 's*ite' and we should only use HDD, but what about the cassettes then?
and keep in mind that CVBS uses only one signal line.
I agree that this particular made up word is a bit silly but I'm pretty sure Zetr0 was just slyly indicating how much he dislikes the composite mod. No harm done.
On the contrary I like the composite mod, nothing wrong with it, in fact I am all the more for it as it is simply far superior to RF.
However its way below SVideo (Y/C) and pretty poor compared to Component YPbPr / RGB Scart
I didn't use the term composhite to insult or hurt anyone's fuzzy feelings towards CVBS, I use it simply to describe the composite signal in the way I feel about it...
"I find CVBS a poor over-compressed signal which is substandard to my wants/wishes"
but, when compared to RF.... it will do... =)
@Dan Antohi
Well, the modulator in most cases on HUGE ground planes that SAP the heat right out of the iron, this is then compounded by the fact the modulator chassis acts as a heat sink taking even more heat out of the iron - even a 60watt unit will struggle - and if its an early release - you will likely find that the RF Modulator is soldered down to the actual tin box and the ground plane - not just the UHF Modulator box anchors - this requires a lot of head, and unfortunately an iron is only going to cause stress.
So, I have in my lair -
(click to zoom)
This is my soldering and rework setup (on a good, just clean the area up day), behind me is my array of programmers lol!
Anyway - in the shot above we have the mainstay of the jungle -
The Kada 852D+ hot air rework station, it has a 40 watt ceramic core Iron that will go up to 420c and hot-air gun capable of 480c.
The second unit is a AoYue 474 international Solder Sucker, capable of 380c its pretty good for most through hole stuff - it can struggle on large ground planes thought - but whip on some hot-air and its done in no time.
The trick with all re-work is to apply the right amount of heat for the least amount of time as possible - otherwise you can damage the components you are working on.
yes, I knew it wasn't about the mod. you don't have to explain me anything. that 'term' has been pooping up on amiga forums lately.
but, the whole thing starts to remind me about that old saying "audiophiles listen to their equipment while music lovers listen to music"
for years I played A500 games with poor RF. it had ton of interference because some TV station used same channel. picture was off-center, as you already know. but all that didn't matter that much once the game started. nowadays I use RGB whenever possible but games are not so fun anymore.
I honestly didnt want to hurt your feelings. My remark was meant purely as a friendly advice, based on practical experience. I desoldered the modulator on all my 4 machines (in order to replace the circuit board with a video line driver) using a 25W iron and a no-name de-solder pump.
Heating for 3-4s and one suck does the job.
The explanation:
1. The mounting vias have a very good thermal relief.
2. The modulator housing anchors are of steel and don't conduct heat very well
Crappy cheapo 20W irons might have difficulty.
I didn't take any offense, and I wasn't hurt or anything, just sharing my experience.
While I may have some skills in soldering/de-soldering, there is always some "new" method or technique to learn. I have to admit, I am in awe that you manage to remove a UHF Mod-Can with a 25 watt iron, my 40watt ceramic struggled to flow the solder, even with a good lump of flux paste!
Its entirely possible that the ones I have removed were infact repairs themselfs as the solder work was very shabby and on two boards the rear edge of the UHF Modulator was solder - welded to the PCB as well - this was on 1 48k rubber key, and 1 spectrum +.
I have been very lucky with the +2A/B and +3 in terms of UHF Modulators and with the exception of 2 48k's and 2 grey +2 I have not had any real trouble... but I fear thats what you get for buying "untested" job-lots on eBay.
But in fairness, my Spectrum 128 +2 (Grey) arrived today from eBay. It was marked as non-functional - spare / repairs but I won the auction for ?2.26 - in a worse case scenario I felt it was worth the plastics ;)
Well today, opened her up, gave it a good clean, and then got to test it the A 28" WIDESCREEN CRT and I was pleased to say she fired up and loaded a couple of games from tapes I thought where dead - Gryzor being one of them!
so the guys 'n I, over a yum-tastic curry spent some retrolicious awesome playing R-TYPE / Gryzor/Driller to name a few =)
I am also chuffed to say that the RF is pretty decent on the JVC CRT!
sounds like they've been replaced to me, the cans shouldn't solder to the PCB at all as there's solder mask everywhere except the two mounting holes.
I generally don't bother sucking out the solder, just get one hole molten and lever the can up, then lever the other side out. The solder is then easy to heat up and remove.
I have a 60W temperature controlled iron, so no bother at all :)
From the same seller as how I started the thread:
http://cgi.ebay.co.uk/NEW-ZX-SPECTRUM-POWER-SUPPLY-PSU-16K-48K-SINCLAIR-/170630125650?pt=UK_VintageComputing_RL&hash=item27ba591852
NOT suitable for composite modded Spectrums? What on earth is he blathering on about???
http://womblesretrorepairshack.blogspot.com/2008/11/zx-spectrum-composite-video-mod.html
I know that this mod makes 3v instead of standard 1v/ 75 ohm composite video signal.
Is it possible that the non-standard signal makes absolutely no picture on modern LCD TVs?
Im gona try the speccy on an older CRT TV, but I dont have any around atm, so Id like to comfort myself, that I did not destroyed my speccy.
Thanks
Very possible. If the computer chip inside the TV doesn't recognise the signal timings it may well just refuse to do anything. Every one is different.
The obvious test is to press some keys, if you get clicks from the beeper then it's okay.
I told you earlier, in another thread, exactly what to do to make your auction much better........but unfortunately.......you totally ignored the outstanding advice I wrote to you.
And for your information, none of which would have been untrue for your spectrum that you were selling :(
I bought one of these the other day. Mind you, care should be used with these compared to the solder-tape-remover (don't the know the English term) because if you don't apply enough heat for long enough, you suck the actual round-metal-that-is-attached-to-the-circuit-board (don't know the English word for that either)
Copper braid impregnated with flux
You mean the through plating I assume, a cylinder of metal that's riveted into the hole in the PCB.
Either method has its hazards, with desoldering braid it's very easy to tear up thin traces on the circuit board by getting the braid stuck and catching it.
Personally I prefer the spring pump method to braid, though a constant suction hose is the best (though most expensive) method.
Desoldering braid.
I use that mostly, but now I prefer the suction pump.
And yes too, the through-plating.
Thanks :)