8-Bit Computer Teardown and Repair (mostly cleaning)

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Firstly, a little guessing game - from what popular computer is this printed circuit board. Then, the keyboard barely works, so I fix it using just water and some abrasive cleaning techniques. Then I write a two line program in BASIC. 30 minutes of 8-bit joy :)
Good afternoon all i've got a lovely big . circuit board here and i'm gonna put . power to it and see if i can get it. working but the question is what is this . circuit board well let's have a guess . what if we got here a big 40 pin chip 40 . pinch it 40 pinch it 40 pin chip some 28 . pin chip see another one there and then . we've got some what looked like 16 pin . chips but we're gonna have to get in a . bit closer to see some of these numbers . to try and work out what this is well . let's start here here we have mmm does . it say. mps i'm working upside down as well . it's . not the one that i cut my teeth on that . was the zed 80 but 6502 8-bit computer . eight bits of data 16 address line so it . can address up to 65 k of ram now these . two devices here the numbers don't mean . a lot but they're almost certainly roms . they're sitting right next to the . microprocessor what are these three . things here they might be pals or gals . or something of that nature not sure . what that is but these chips over here . these are very easily identifiable these . are two one one fours which are static . ram chips and so what we have here are . 10 actually 11 which is really weird why . are there 11 ram chips . here's a printout of a 2-1 month for ram . chip it is a 1 or 2 4 by 4 bit static . ram so they're having two side-by-side . is not surprising because that's 4 bits . this is the other 4 bit so that's 8 bits . one care ram 2 k 3 k 4 k 5 k 5 and a . half k what's that all about and that . thing there is a 406 6 . oh what's that is that some sort of . phase lock loop let's look it up no . that's a quad bilateral switch so sort . of four analog switches i'd still don't . understand why we've got 5 k of ram . and 1k by four bits of ram i just really . don't get that so if you haven't already . guessed well this is very obviously an . 8-bit computer but which computer is it. let's take a look at some more of these . chips these big 40-pin ones let's zoom . in on those we have six five two twos . it's some sort of eia or pio or . something like that a parallel interface . adapter and it goes to well they're . right next to this connector which says . if i bend c1 out of the way it says . keyboard connector so yeah this is an . 8-bit computer but which computer is it. well here's a clue what's this lot here . we've got a couple of pots here lots of . capacitors mmm transistors right next to . this big maus chip well i'll give you a . clue this is the video interface . controller and that's a big clue . actually as to what this computer is now . how do i know that this is the video . section of the computer in particularly . the color video section well let's have . a look at that crystal that crystal if . it's four point four three megahertz . that's the frequency of the color burst . for a pal tv signal so let's check it . out. what is it focus well it's not four . point four three mega hertz but it is . eight point eight six mega hertz so . that's twice the frequency of the color . burst . they're obviously dividing that down in . some way down to four point four three . meg's that's the color burst for a color . 8-bit computer now over here we've got a . big power supply section and this piece. of metal looks like it's actually all . one i think it comes down here goes down . there underneath folds over and back . over the top this looks like a big to3 . transistor but it's not it's almost . certainly a regulator horrible linear . thing lm3 - i can't . i read that oh that bends up lm three to . three so that's going to be a five volt . regulator would be my guess let's look. it up yes here we are. lm three to three it's a three amp five . volt positive regulator and it's. virtually blowout proof that's a bold . claim whomps inaccuracy three amp output . current. if suitably heatsink and this looks like . it is suitably heatsink i think it's . time we put the power to it now very . interestingly on this side i don't know . whether we can see this yes it says nine . volts ac ac right this is the wonderful . power pack that came with this thing . doesn't look anything like the beige . case that the computer is in it's this . rather stark black thing says. transformer 240 volts 50 hertz this is. just going to be a transformer cut show . you at the top of this because it gives . away what the computer is and what we . got night well we've got s dots nine . volts three amps but then we've got t . 200 milliamps for the fuse which is a . bit strange but yeah so it's just a . transformer in here. no rectification no smoothing certainly . no regulation that's being done here . nice old school uk plug on this so it's . a a uk computer i mean we notice a . european computer because it's pal . because we've seen the eight point eight . six megahertz thing. this is uk i thought you might just like . to see inside one of these that's a . captive bolts that won't fall out that's . the inside of a uk plug also used in . ireland i think malta cyprus hong kong . long time ago when i went to hong kong . we were using these to know whether they . still are but yeah that's how it's done . so this pin here these are a half . shrouded through the fuse and then that . goes to live neutral earth earth not . connected because we've been it got a to . call cable so let's plug that in put the . nine volts ac onto this computer see if . it does anything right here's the other . end that's the nine volts ac let's plug . it in really fat pins on there so it's a. a nice connector designed to take a . of current well it's hard to see whether . it's doing anything there are no leds on . here actually there was an led on the . front of the case connected to there but . i've taken that off so we have to take . it a stage further now and connect a. telly . now the only telly i've got television . is this nick a1 it's very low resolution . i think remember it's 240 lines that way . and probably not many more that way but . it is a telly it does have a tuner on it . it's also got composite in but i don't. think this computer has any composite i . think i'm going to have to use rf radio . frequency so let's see if we can get a . picture on the telly hmm tv no signal . now also supplied with this computer was . this but be careful not to short stuff . on this board cause it's powered up this . is well it's like a steel box which has. a din plug on one end of a long cable . 180 degrees pattern on that dim plug it . also has a phono rca phono as the output . and then also supplied is this rca phone . oh - well i think this is called a . belling lee rf type connector so that's . going to be the modulated rf modulated . with presumably oh well colour video . possibly also audio i don't know . actually. so let's plug that in and let's have a . quick look at the back of this computer . right now on the back we have - one of . these called din sockets nothing's . labeled but one is clearly the . 180-degrees pattern and the other one is . a pin this is a 5 pin so . it's obviously gonna be that one i'll . plug it into that socket and we'll see . what comes up on the telly all right . let's put this rather strange metal . steel weather look at it box there . there's this really long cable here and . i'll plug that into the rf socket. on the top of my telly and then the din . connector oh no it's going up with the . connectors on i think it's that way plug . that in and what do we get we get . nothing. hmm okay let's press menu this has got a . auto search thing how do you initiate it . press it to the right there we go is . doing an auto search i don't think it . will find it on vhf it's going to have . to go to uhf so that was vhf hello this. is vhf high right i'm gonna have to sit . and wait until it goes into the uhf band . you can see here that it's on powers the . car system the sound system is i and pal . i i think was used in the uk and hong . kong if i remember rightly but possibly . not in other parts of europe anyway i . like that just see if it can find some . tele signals yeah it's not finding . anything yet might as well just let it . carry on what's getting any telly . signals what's going on right i didn't. actually have the computer switched on . there's a little switch on the side i . thought i heard a high-pitched whine. when i plugged in the plug must have . just been my tinnitus . okay well then that will let this . scanning thing complete it stan oh it . seems to have found something it's . slowed down and oh now that looked . promising it's just going to finish its . scan and then we'll go back and have a . look at what it picked up and look at. that we've got cbm basic v font>. bytes free so it's only three and a half . k of ram i mean that's not much as it . this is a bit of a naughty computer and . it's ready ready for what i wonder so . you should better guess or possibly . guess from the cbm which manufacturer . this is and the clue i gave you earlier . that this chip is the video interface . controller vic. yeah this is a vic-20 yes so here's the. case front it's a bit big none of this . stuff's fitting on my desk bro well . commodore vic-20 that's what this thing . is yeah i don't know what vintage is is . is it 80s is it 90s now if we're gonna . get to this to do something we need the . keyboard this is the keyboard it has a . lot of wires so it certainly doesn't . look like it's a serial keyboard there . are too many wires really also for it to . even be a parallel keyboard in fact what . i suspect this is is just simply a . matrix of switches i think it's a . completely dumb keyboard and the cpu . must have to be scanning this keyboard . using these pil pios or whatever they . are vi is versatile interface adapters . they're just parallel ports really it's . gonna be are driving this big connector . here scanning this matrix of key so . let's put that on there i hope i don't . short anything out and plug this in here . which way
Tags:  6502  computer  electronics  vic-20  8-bit  computer  teardown  and  repair  (mostly  cleaning) 

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