Commodore Amiga A500 Repairs Part 1 (Guru Meditation / Atari ST Helps Amiga / PSU Update / Overview)

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The first look at one of a number of Amiga 500 / 500+ boards that I am looking at. Not much repairing in part 1 - mostly testing and waffle.
Part 2 - • Commodore Amiga A500 R...
Amiga Diag ROM - www.diagrom.com/

[@chrismorley5393]

Wires from Gary are only needed for trapdoor expansions bigger than 512KB to get the extra address lines. JP4 is the PAL/NTSC jumper IIRC (but you should change the crystal too if modding)

[@GadgetUK164]

Yep, that's the wire I was thinking about! I used to have a 1.5M expansion with MFM interface!

[@RetroMarkyRM]

excellent. i love these long multi part fix videos. (the beeb one especially and this amiga one are great examples) :)

[@georgelea4297]

Thanks Chris for the awesome father's day gift glad that there's another Amiga repair

[@Crashedfiesta]

Nice one. More Amiga please! 😁

[@glenndoiron9317]

On powerup, Kickstart shows up in the processor address space @ $000000, as well as at $F80000. This is because this is where the 68000 retrieves its cold boot initialization vector (zero page memory). One of the first things Kickstart does is configure an I/O line on one of the CIA ports (the line is labeled OVL in the schematic), which causes Kickstart to disappear from $000000 and the RAM to show up. This control line is still software controllable by writing to the appropriate CIA port. The lines in your diagnostic software at 24:39 in the video suggests that the test software has switched the ROM back on at $000000 with this CIA bit, but did not read the ROM value it was expecting. This is suggestive of a Gary or 8520 failure.

[@rasz]

I interpreted that screen as "everything is ok", unmapped from 0, readable at f80000 where it should be

[@GadgetUK164]

Thanks! That again makes perfect sense now you explain it =D However, I think there's a red herring somewhere because having tested the machine with a keyboard and FDD, it does work perfectly (despite random issue in diag ROM). I am not 100% certain yet but I think it may have something to do with the use of an EPROM (perhaps needing a resistor array on the data or address bus maybe), but it could also be the caps. I have another 500+ that behaves in a simularly crazy way where depending on whether the machine has just been powered dictates whether a random guru will appear just after boot.

[@coyote_den]

This matches the guru you're getting, 00000003.* is an address error. It's hitting ROM when it should be getting RAM, or vice-versa. Pin 2 of the ODD CIA is OVL, drives pin 30 on Gary. Check that, I think it should go high at reset, then low early in the boot process. What is that bodge resistor on the ODD CIA? Is that supposed to be there?

[@glenndoiron9317]

@@rasz I agree that it could be interpreted that way as well, which would mean that the ROM overlaying is working correctly. Using "Pass/Fail" instead of "Yes/No" would have removed any doubt.

[@spidermcgavenport8767]

Thank you, GadgetUK164, for the preservation of this Commodore Amiga 500.

[@spidermcgavenport8767]

One day I'll own a C64, Amiga 500, Atari ST, Spectrum Z80, Sharp X68000 and my long lost Packard Bell Legend 386sx again.

[@spidermcgavenport8767]

Say, GadgetUK164 could you devise a new solder iron one that has a fine point and can be held like a pen, many are just wood burners, I'd like for one to be closer held for precision would you be willing to even make a heat shield for existing soldering irons, I know hot air can be used for some applications it's just I would like something unique.

[@spidermcgavenport8767]

Would Pauly and Gary have anything to do with copy protection or would the Amiga 500 predate those implementations. Just thinking back to Dungeon Master II how it had a region on diskette for copy protection and the Fuzzy Bit.

[@GadgetUK164]

Hehe =D Funny you should say that, I've had a few people in the past saying my iron looks like a wood burner lol. Doesn't surprise me - I make the tips last about 10 years each lol.

[@GadgetUK164]

Well Gary is primarily the floppy controller, but Paula has connections to Gary too. So in theory there might be Amiga only copy protection techniques used back in the day that perhaps depended on the way the FDD interface works in the Amiga. Honestly no idea - I imagine it's not dissimilar to other systems of that era like the Atari ST (which just used a standard FDD controller from Western Digital I think). The fuzzy bits I think were created using different hardware.

[@xyzconceptsYT]

I have got my hands on an Amiga 500! Had one as a kid back in 89-93 ish loved the thing. Can't wait to get the nostalgia juices flowing again. This is quite valuable to me. Hopefully mine doesn't need to much work to get her ticking again. Looking forward to the restore. My biggest challenge would be finding a display for it. I used to have a Philips 8833 for it but can't remember what I did with it. :(

[@AdamSommer70]

Great video, really like the description of the Amiga chips and what they do. Don't think I've seen a video with as much detail, great stuff!

[@runcmd8851]

Great video fella keep these amiga 500 ones coming.. Love them and love your knowledge..

[@sethrd999]

From what I remember only the 68000 can read both chip fast/slow ( extended ) memory. Most in the demoscene used the 68000 to move stuff in and out of chip / fast ram and memory clean up. The most parts used Copper | Blitter | Sprite hardware and obviously the Audio. Track / disk routines ( known as MFM ) was also an art ( known as a non dos disk ) ...

[@TexRider]

some of them jumper pads where ram to chip expansion back in the old days

[@ShafHussain]

These vids are soothing

[@BocaRetroGames]

Anxious for the next ones !

[@DerMartexus]

Cool. :) Repair-videos always give me some kind of input. My A1200 doesn't want to boot. I should check ENROM next time.

[@GadgetUK164]

_ROMEN is the pin name =D Bear in mind that the 1200 has a different chipset, but one of the chips there will be responsible for that signal to the OE pin on the BIOS chips. Regards a 1200 not booting - most likely bad capacitors. It has SMD caps which leak on the PCB and if not dealt with it will get worse and eventually kill the system.

[@DerMartexus]

@@GadgetUK164 Of course, _ROMEN. ;) I know, that it is a different system but I'm still thankful for the hint. :) The caps have already been replaced, vinegar has done it's job and I did an inspection of the tracks. Probably I have to do more measuring and find a broken track. Lots of fun for a hot summer! :)

[@clintonelliott340]

Subbed going to watch all your Amiga content!

[@GadgetUK164]

Awesome! Thank you!

[@Four_X]

Some quality Amiga 500 information there Chris, my Amiga 500 will throw out a Guru Meditation (random garbage) if I power cycle it too fast, I have to wait at least 15 sec before I power it back on after a power off. My Amiga 500 has been like this since day one. I've known others who own an Amiga 500 to run into the same issue. It seems to affect some Amiga 500's more than others. Looking forward to the other Amiga 500 videos by the way Chris, keep em coming buddy.

[@GadgetUK164]

I think you are right! I've seen that before on my 500+. It seems some versions of the 500 don't behave the same as other versions. There's also a problem with EPROMs that I need to talk about too.

[@xnonsuchx]

Jay Miner (RIP 1994) is the main one who did the Atari 8-bit support chips (ANTIC & CTIA...and the TIA on the 2600) and the Amiga support chips

[@Plan-C]

Another great video! Cool tricks and detailed knowledge as per usual. Keep it up.

[@EgonOlsen71]

64 colors are displayed in the extra half bright mode (EHB), which uses a 6th bitplane to indicate that a color is displayed with half the brightness. Hold and modify (HAM) also uses 6 bitplanes and allows for 4096 colors on screen with some restrictions concerning color changes.

[@GadgetUK164]

Doh! Thanks for clarifying! My memory of HAM was mixed with EHB! I thought HAM was much higher than 64 colours - I remember seeing photo realistic stuff using HAM.

[@glenndoiron9317]

Video Hybrid - The reason its called a hybrid circuit is because it has analog components which can't be produced with the standard IC fabrication processes. If you look at it closely, it isn't actually flat like an IC, there are additional components placed on the carrier and then the entire package is epoxied. The video hybrid is basically a triple-DAC (for RGB out) chained to a composite video encoder. The primary reasons to use it are (1) Commodore produced it, so its cheaper than the 3rd party boxes, and (2) it takes up less board space on your circuit board, as it is a vertical component.

[@GadgetUK164]

Thanks for clarifying that - it makes perfect sense when you look at the schematics! I was aware of the connections going to the hybrid there but didn't think twice about what was going into it. As you say, it is just a DAC for the RGB signals, so it couldnt have been an after thought in any case. Will give you a mention in part 2 or 3 (whenever I get to talk about this point)! =D

[@paulmichaelfreedman8334]

A pad of scotch brite will clean those contacts in no time. For those who have no glass fibre brush.

[@Neffers_UK]

I'm gonna be properly invested in this series, as I'd like to see what you do with your 500+ as mine is also in the loft, and that damn battery, sigh. I daren't look. Please, if you appreciate the effort and dedication Gadge puts into making this kind of content, drop him a quid on Patreon. Ta. It's not much and he is a properly nice person, I'm not saying this on most vids for any reason other than the dude is super supportive, that's all, thanks :)

[@GadgetUK164]

Cheers mate =D The good news is another has arrived (with keyboard and FDD), so part 3 and part 4 are started too lol.

[@xephorce]

That wool sweater may cause you some ESD issues, That and the carpet lmao. I am just joking around love the vids man keep it up

[@75slaine]

There’s definitely something related to the trapdoor and GARY. My A500 has a 1.5MB upgrade in the trap door expansion and if I recall I had to pull the GARY, put in an adapter board and put the GARY into a socket on the adapter.

[@paulmichaelfreedman8334]

Gary has logic for bus handling so my guess is the adapter is to be able to bank swap chip and fast mem.

[@AnOfficialAndrewFloyd]

Copperlists work exactly like Display list interrupts on the Atari 8-bit. And no wonder - the same guy designed both chips.

[@AcornElectron]

That’s kickstart 1.3 not Workbench but I get what you mean. Never opened mine back in the day, I think mine fell in between the early ones with red and green lights and the 500+ as I had the 1.3 kickstart and had to install a rom switch for 2.0 compatibility and fast switching. Had the almost obligatory 1/2 meg in the base slot and a 2 meg ram expansion on the left hand side. Never even noticed any improvements between the 1 and 3 meg. I guess you don’t when you’re already happy with performance and load times (previous micro being an Acorn Electron). Interesting video, I await part 2.

[@GadgetUK164]

Opps - yep, brain slipped there for a minute!

[@Ichinin]

Earlier Amiga 500s (around Kickstart 1.3) had 8 slot with 4 memory chips in them. I just looked in my 1.3 machine that i got from my friend. I had a KS 1.2 machine earlier, but i cannot remember how many memory banks it had.

[@GadgetUK164]

16! I have two more boards arrived here and both have 16 chips! Luckily the first one seems to have good DRAM =D

[@Liberty309]

OMG The screwdriver in the back of the chip, BIG GASP !!! 😆😆😆 btw, great video 👍

[@glenndoiron9317]

Fat Agnus got stabbed in the back.

[@Liberty309]

@@glenndoiron9317 I heard she had it coming. They suspect Paula did it because Gary was cheating on Paula with Fat Agnus !!! 😆😆😆

[@GadgetUK164]

LOOOL

[@AntonyTCurtis]

Hybrids are usually made on a high dielectric board, usually ceramic. Quite expensive and they'll usually limit how much circuitry theu'll put on one but it is most definitely not an afterthought.

[@GadgetUK164]

Thanks! Yes, I thought afterwards about the RGB signals going to the hybrid - that's more than a clue that it wasn't an after thought. They needed a DAC and that's the route they went - perhaps to get cleaner display and to take less space up too maybe?

[@9ElevenGamer]

I am only 30 min's in but I have a weird feeling it might be the Kickstart Rom, I'll keep watching.

[@loganjorgensen]

Yeah pretty small traces, a lot like dental pick cleaning heh. Wonder if they make a fiberglass pen or something else with a harder smaller tip, usually flat top but a rounded grit pen tip shape could be handy for that kind of cleaning. I find rubber erasers pretty good for card edges most of the time with IPA followup on carts, other than rust you don't need to be that harsh with them, doesn't need a belt grinder heh.

[@amigadude6409]

Super awesome video.... I'll share this to my page...😀

[@GadgetUK164]

Thanks! A few mistakes in this video, which I will correct and expand upon in the next parts.

[@PATTHECATMCD]

My guess it's one or more of the decoupling capacitors on the RAM chips. Sometimes it self tests fine and powers up, some times it Gurus on a memory issue. JP2 and JP7A are usually altered for 1MB chip RAM mods on a rev 6A.

[@danielmantione]

You think ceramic capacitors are failing? I have yet to see one, but we'll see.

[@PATTHECATMCD]

@@danielmantione , could be just a dry joint at the factory. Intermittent faults are rarely down to chips. Multimeters just give an average sample, so it's very difficult to tell if a decoupling capacitor is really smoothing local spikes from the local power rail or indeed adding to them. This is when an oscilloscope is handy to check whether a decoupling capacitor is giving a clean or dirtier supply voltage to a chip. The fixer seems convinced that it's a fault with a 74244 or 74373 chip, which while very likely, may not be correct. Worth checking the simple things first.

[@GadgetUK164]

I think it's very unlikely to be ceramic decoupling caps causing the behaviour! It's very rare for that type of cap to fail on one of these boards. It can happen when they get chipped or cracked like they do on arcade boards for example though!

[@PATTHECATMCD]

@@GadgetUK164 have seen it and also failing 74244. On different A500s. The RAM chip second from the left looked like very blobbed cap soldering. To me, anyway. Best wishes with getting it reliable. :)

[@glenndoiron9317]

With a ceramic decoupling capacitor, it would be one of the very last things I would replace, even though its ridiculously easy to replace. I have worked on 35+ year old machines and I have never seen a ceramic cap out of their rated tolerance. I've seen them physically damaged, with bad solder joints, with cut traces/legs, but I have never seen them "go bad" due to age.

[@mark12358]

Better get rid of those nasty SHOEI caps. Good job and nice video, thanks!

[@GadgetUK164]

Thanks, yes - on this first board I recap the whole thing later!

[@GeorgeGeorge-xj2bc]

Try to replace all the IC sockets the corrosion is not always visible but affects contact.Its a bit difficult to desolder trough hole components to a double layer pcb,so at least try to clean the pins and remove and place ic chips again to see for any changing.

[@GadgetUK164]

Yes, it's sometimes a good idea to replace the sockets entirely! On this occasion though I can get away with just replacing one of them and "fix" the others I think. Some of the other boards I have here will definitely have new sockets though!

[@KarlToona]

brother, you need to look into xylol for cleaning stuff. seriously. please look into it it's amazing. i use it in the printing industry and its an amazing solvent also used in the pcb/electronics mfg line. removes all kinds of gunk and residue, it's a godsend. Thanks for the vids brother :D

[@nigelrhodes4330]

It is also used as a solvent in some marker pens, one tip use it in a well ventilated place or you could find yourself in a spot of bother.

[@paulmichaelfreedman8334]

You do realise Xylol is rated with moderate toxicity and that the main form of intoxication is inhalation. LD50 = 200 mg/kg In short if you inhale this daily your lungs will be shot sooner or later. COPD dude, or your nervous system degrades giving you a form of parkinson.I'd put more faith in a brake cleaner, that also has excellent solvent properties and doesn't evaporate too fast.

[@BB-ce3bj]

You should have replaced all those crappy DIP sockets with decent ones, with round contacts with spring in it. That cheap crap will oxiidise and cause problems in time. Also, it is sensitive to termal cycling. After so many cycles chips tend to climb out of the sockets just so much that contact loosens...

[@GadgetUK164]

I haven't finished yet - it's part 1!!!!!!! ;)

[@glenndoiron9317]

General troubleshooting steps: Does tapping on the PCB or individual IC's cause it to flake out [when you have the kickstart screen up]? (If so, check sockets and solder joints). Does it ever happen immediately after you turn it on (after its been off for a while) , or does it take a while to manifest? (If so, it could be heat related, and some time with compressed air/heat gun and thermocouple (to make sure you aren't going above 85°C surface temperature) could find the culprit.)

[@_.OX._]

Wish I could get you to fix my A500 plus Gadget, my half-arsed and ill educated effort (which was basically cleaning up some battery corrosion and replacing a chip) was unsuccessful, definitely requires the thoroughness of a GadgetUK fix.

[@GadgetUK164]

You might get some ideas when you see part 2 or part 3! The next video is looking at a 500+, then I go back to that first board.

[@rasz]

30:00 trapdoor is for slow/chip ram only. Fast ram goes on CPU bus on the left side( edge connector is almost Zorro II). Fastram expansions require additional memory refresh controller = pretty much nobody had fast ram back in the day on their A500s due to cost. Even A1200 didnt ship with any fastram. Isnt Agnus a boy's name? :-)

[@GadgetUK164]

Thanks for clarifying! I've always though the RAM in the expansion bay was classed as fast RAM - it shows up in the fast RAM section, but I guess its slow RAM or chip depending on the Agnus and how the board jumpers are set. Angus is a boys name, Agnus is a scotish female name.

[@jockinafrock]

@@GadgetUK164 Trapdoor was 512k Slow RAM by default, but the solder hack on that test point (TP2 if I recall?) mapped the trapdoor Ram into CHIP RAM instead, allowing for more graphics memory for Fat Agnus. Some games needed 1Mb Chip RAM

[@GadgetUK164]

Yes, I think the jumper near the ROM adjusts where the ROM sits with respect to the RAM, and when the other jumper (near the RAM) is also switched it puts that 512K as the 2nd block of chip RAM.

[@brentbiel5425]

How the heck do you pull out the Fat Agnus chip with the PLCC puller tool without damaging the end pins? Every time I do it I damage at least the 2 pins closest to the tool. They are in far too tightly!

[@GadgetUK164]

The technique with those PLCC (cheap) extractors is to squeeze it quite hard, and often it will then pop out. If its very firm in the socket, spray it with IPA first. Also inspect under the motherboard where the socket sits, often there's a hole or two that you could use to push a flat tool to push the Agnus out from underneath the motherboard.

[@atec9228]

Hello. I have an A500 Revision 3 that sometimes when reading a disc I get a Guru meditation message. With the same game, sometimes he reads it well, other times he doesn't and that message skips me. I was thinking of changing the electrolytic capacitors on the board and doing the same with those of the power supply because in the power supply I found some in bad condition. I don't know if it may be due to power instability or it may also be a fault in some Ram modules. What do you think?? Thanks

[@GadgetUK164]

I would start by getting a Diag ROM chip and test with that. The complication on a rev 3 Amiga is the pinout is different on the ROM socket and a few connections need flipping. You would need an adapter to use a standard EPROM with Diag ROM on it. Maybe someone on Amibay sells a ROM adapter for rev 3 A500 boards, which would allow you to plug in Diag ROM. Alternatively you might be able to get a boobip EPROM board or one of the ones that Solidcore sells on Amibay. I doubt the capacitors are the cause, unless the ones in the PSU are bad.

[@atec9228]

@@GadgetUK164 Thanks for all. I replace all the capacitors in the Amiga and in the PSU and persist the problem.

[@EdwinNoorlander]

That was not a desolder station but a steam train..

[@michellegall2358]

Bonjour. quelqu'un connait'ils la valeurs des résistances entre BU508 et le condensateur 385v 47uf . La grosse résistance de puissance entre 68nj63 et les deux résistances brûlées montée en séries, sur l'alimentation P-No 312503. Merci pour l'information. Michel. Hello. does anyone know the values of the resistors between BU508 and the 385v 47uf capacitor. The large power resistor between 68nj63 and the two burnt resistors mounted in series, on the power supply P-No 312503. Thanks for the information. Michel.

[@GadgetUK164]

The best thing to do is look at the component designation on the silk screen (white print). Then compare to the service manual or schematics for the revision of A500 you are working on. You can work out from there what size resistor is required.

[@TexRider]

I still have my 500 from the late 1980's . if you still have a super denis I would like to buy one from you

[@GadgetUK164]

I don't have a spare sorry! My last one went into my A2000!

[@noname-fj4sl]

The problems you have, because of the corroded sockets! Change them and problem will be gone. I'd similar problems.

[@GadgetUK164]

Surprisingly that isn't the problem! But it's a good suggestion - it was my first thought too!

[@noname-fj4sl]

Oh, sure? Ok, i'd a corroded gary socket, some games worked, some not. Memory test failed after a while. Spend hours on this proplem and after replacing corroded gary socket problem was gone. Maybe you're right with data path ics ir...try keirf systest and check ram about an hour. Maybe simple ram problem.

[@claycoates5056]

you are being blocked by endless adds what did you do ???

[@GadgetUK164]

Strange? Did you try refreshing the page? I viewed it at the time you posted this and I only saw one advert at the bottom that could be closed down.

[@obsoletepowercorrupts]

12:09 That old desoldering gun looks like some sort of fallout3 weapon. See a500 copper2chunky done in the scoopex video "grade my waterbear". kzbin.info/www/bejne/o4apmH6rpM-VZpI Copperbound and blitter bound games (mostly before AGA) suffer from waitstates with some accelerators. So having an FPU on an accelerator helps modern homebrew-games and demoscene coding perform pre-calc, be it on older (e.g. A500) or AGA machines, and so the remaining scraps of CPU time can be thrown to the copper and blitter (or akiko for c2p) to make games like Elite2Frontier run much faster (hence that game needs recoding) and to make gloom style games use c2p more efficiently. The whole _"you don't need akiko if you have an 030 or higher"_ is an untruth sadly repeated by many (as it is only true with existing games coded poorly for accelerators). See AtariQuake as a good example of pre-calc (and it is influenced from the amiga code). Having a local oscillator on accelerators commonly exaccerbates waitstate problems on an asynchronous accelerator. 0:25 & 29:00 & 37:00 Will you show a video adding a 1meg for that later revision? Then maybe making it work with a 1meg trapdoor expansion so as to have 2meg ChipRAM total like an a500plus? Maybe in Part3or4? p.s. Ignore the question-marks. This comment is actually just using the imperative tense, masquerading as a "suggestion". >:P 38:38 The CIA A&B could be modded IMO so that the parallel port could use the more 'modern' IEEE from a 68030 or 68040 (in an accelerator) to boot a parallel CDROM drive (whereas the 68000 was too weak to). That is handy because some accelerators these days have disabled the zorro sidecar slot thereby rendering CDROM unused, and yet many people desire AmigaCD (because collectors like shelves stuffed with bigbox games). Even the latest Amigarama (by Lorfarius, episode 86) had 4 ISO download links for very recent audio amiga CDs. Cartridge games (like ac64) could thereby boot off the parallel port (and save games to them) and the cartridge could have a passthrough for the parallel port CDROM drive.

[@GadgetUK164]

Thanks! Yes, I will cover the 1M chip mod, as well as the NTSC / PAL thing, and talk / show stuff related to the 2M agnus too. I will take a look at the parallel CIA stuff too.

[@obsoletepowercorrupts]

@@GadgetUK164 Oh cool! I just replied to an old video (Y9KDk1OfkYc) with your recent comment and I spoke in my reply of using a PiZero to trick the parallel port of almost any amiga like an a500 (as long as the amiga has parallel IEEE on the CPU instruction set in the form of a 68030 or maybe just about a 68020) into thinking a usb CDROM-drive in the Pi is a universal CDROM drive as CD0. Of course, said PiZero shoud also have a passthrough to allow a printer or whatever to still go in the parallel port too. Or even better, a parallel to usb-penddrive as HD1 or a lallafa-plipbox rj45 port. As an aside (not needed for all that) I reckon a PiZero or similar 3rd-patry "sort of Pi" SBC could mimic a CIA chip via GPIO and add features to it like faster ports. EDIT: One cool way to add a usb port to a TF530 (or similar) to make it boot from a usbCDROM as if it were CD0 woul dbe to make an adaptor to go in the FPU slot (and still allow an FPU of course). I reckon also it could have a SCSI so one of those "SCSI2SD" adaptors could go into a SCSI on it too since it would make up for the lack of a590 compatability. One of these things could plug in (see YT watch link): gupXx9lpawE

[@montesmadness9303]

Will the expansion port still work if you remove the gold plating with a fiber glass pen?

[@GadgetUK164]

Yes, absolutely! The gold plating is just to make a better connection. Gold is a super conductor and has a very low resistance. That's why most top of the range connectors are gold plated!

[@danielmantione]

There is copper underneath, which conducts electricty, so yes it will still work. However, unlike gold, copper corrodes easily and has lower mechanical strength. Therefore, removing the gold is not a good idea.

[@GadgetUK164]

@@danielmantione Yes, I forgot to mention that gold is pretty inert - that is, it won't oxidise the same as copper will.

[@TheHighlander71]

I like learning about the Amiga. This has been helpful. Although I do get a little confused when engineers come up wit cutesy names for things. I mean "Guru Meditation" sounds nice, but what is it?

[@GadgetUK164]

A "Guru Meditation" is basically a joke from the original developers of the BIOS - it's how BIOS error messages are presented. So when some critical error occurs (be it an address error, data, invalid opcode, file read or file write error etc) - the BIOS displays the "Guru Meditation" along with the error code to help you work out what has gone wrong.

[@TheHighlander71]

@@GadgetUK164 Thanks Chris. As a programmer these days I get bombarded with "funny" naming conventions. I find it really annoying when it gets in the way of doing actual work.

[@gamemaster2618]

Spray isopropyl in the plc socket 100x easier than without isopropyl. Slides out

[@GadgetUK164]

Nice tip =D

[@gamemaster2618]

GadgetUK164 - Retro Gaming Repairs & Mods no worries . Can you drop me your address in messages so I can send you out a quad 1200 rom board . Thanks bud .

[@GadgetUK164]

@@gamemaster2618 Cheers mate =D Are you on Twitter? If you follow me on there I can follow back and we can message from there!

[@josephnealescratchcards]

❤️

[@GadgetUK164]

Corrections: (Thanks to the people that posted - credit will be given!) - The expansion RAM typically is classed as "Slow RAM" - despite the fact it shows up as fast RAM within workbench! There are 3 or so other types of "Fast RAM", which are faster... Confused? You will be lol! At some point in the video I might have said "Workbench 1.3" - I meant Kickstart 1.3! Kickstart is what the ROM was called, Workbench is the "OS" which you boot from FDD. The hybrid doesn't just "tidy up" the video - if you look at the schematics the connections to it from Denise are the RGB (split into bits), so the hybrid is a DAC - defintely not an after thought in the design. Amiga Diag ROM - www.diagrom.com/

[@spidermcgavenport8767]

Would each RAM simm dimm lol edo, be interchangeable be it fast RAM where slow RAM is located or would it function and operate the same due to limitation(s)?

[@GadgetUK164]

The different types of RAM you've mentioned there are different types commonly used with PCs. I do know that with a lot of patience you could in theory use an old SIMM or DIMM wired up correctly, but its a lot of work. The speed of the RAM is not what is meant by fast / slow RAM on the Amiga. The term "fast" comes from RAM connected directly to the CPU, RAM that is only accessible by the CPU - no wait states involved whilst other stuff fights for access etc. The expansion RAM slot that I said provides "fast RAM" actually is slow RAM - ie. RAM addressed via Agnus, so the CPU has to wait for access to it. True fast RAM on the A500 would be connected to the left hand "sidecar" expansion slot.

[@spidermcgavenport8767]

@@GadgetUK164 .thank you for this knowledge it's quite impressive, have you gone through university for electronical engineering. Because this was my fields of study however mine focused on cad namely Pro/E wildfire 2.0 as the coursework goes. I wasn't able to finish before my disability ruined that chance. I was only speculating if other types of volatile memory could be used that's some phenomenal knowledge there. This is why I watch constantly you do what I wish I could be doing as a profession.

[@GadgetUK164]

I haven't! I studied electronics (City & Guilds) up to level 3 or 4, but followed up with other courses later (eg. Microprocessor Architecture with the OU). Most of my academic qualifications are related to software engineering.

[@amonmetalhead7034]

The reason Workbench calls it 'Fast Ram' is because it's only accessible by the CPU and not shared with the rest of the custom chips. As the RAM is only accessed by the CPU it can't be blocked by other chips also accessing the RAM (as is the case with chip ram)

[@jockinafrock]

Nobody wants corrosion around the Gary.....

[@HuntersMoon78]

Atari ST Helps Amiga - That'll piss off the Amiga fanboys

[@GadgetUK164]

LOL! I think the ST diag cart has an RS232 interface too, so in theory the Amiga can help the Atari ST get back on its feet =D I could also have used the USB port on my PC (with an adapter) - might talk about that in a later part.

[@AmigaWolf]

I say do NOT use PLC extractor, and just use a crew driver treu the holes or just very softly true the Corners, I have used a PLC extractor and it almost destroyed my socket and chip, using a screwdriver is much better and easier.

[@GadgetUK164]

I wouldn't say a screwdriver is safer - it sounds like the PLCC extractors you've been using aren't up to the job. I had that problem with the first ones I bought. But my current one works better!

[@AmigaWolf]

@@GadgetUK164 OK, can you give a link for the same you are using? And thanks, for your good repair video's BTW.

[@GadgetUK164]

I think the one I am using is one of these:- www.ebay.co.uk/itm/CK-Germany-PLCC-Chip-Extractor-Tool-For-All-PLCC-Chips-OM1088/390651475624?hash=item5af4a476a8:g:2g4AAOSwENxXmenE