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  • For new people : Repairing PCBs yourself

    Hello,

    Just wanted to add a sticky note to this section, I`m not having a go at anyone, But i think this needs to be said espicaly for new people thinking about buying cheap boards that don`t work and want to repair them.

    Generally arcade boards arn`t cheap to repair!!!

    If you buy a non-working board from e-bay for $30.. You may have to spend that again just getting it to work or even trying to diagnose it.. And i`m not including the hours of time this might take!

    Unless you have a stash of old boards you can grab parts off, Parts will have to be bought new, Sometimes they can only be sourced from the US. This can get expensive and time consuming as you can see.

    I`m not putting anyone off ... I have helped new people get into it and still help new people... But i think it`s a common misconception that they are easy and cheap to fix.

    Can an admin make this sticky as i don`t think i have permissions to do it.

    Thanks,

    Mrv.

  • #2
    Yeah I'll sticky the thread tonight. I been meaning to add a new section here called repair logs ill sticky it there.

    I agree with you 200%, I'm pretty reluctant to repair peoples boards because of the time involved, That's why like I've told a few fellahs on the board I just prefer doing my own boards because there's no pressure and if something pisses me off I can put that board to one side and come back to it another day/month/year. I have a lot of success putting a board to one side, fix another in turn gives you fresh ideas on a previous board.
    Sometimes Ive given up my weekends doing boards repairs for myself and others and I only have a few hours at night during the week to screw around with them .
    Sometimes you get lucky and the fault is obvious but a lot of the times it can take hours and hours to locate the fault specially when your pouring over schematics making sure everything to is connected as it should be and when theres no schematics available you can be in for a long ride.
    My advice is have a working board along side to help repair the faulty one, specially helps fault finding multi layered boards like moon patrol etc

    Welp time for work

    Comment


    • #3
      My 2 bobs worth

      Thought I would share my experiences in this hobby.
      I started out buying my first Cabinet etc from JP & my first Pinball from P/well.Mmmm not off too a good start,I hear you say.Both provided hours of fun,trying to get them to work!!!!.I have since collected many boards from ebay with mixed results.I did picked up a few dead boards.I have found it impossible to find anyone prepared to even look at the boards to repair them, even though I am willing to pay well for it, let alone anyone who would perhaps teach you a thing or two about doing repairs yourself.I have had such a frustrating intro into the hobby I have considered getting out of it on many occasions.I think peoples attitudes towards helping others is only driving people away from being involved.
      Finding this website has given me fresh hope though.

      Comment


      • #4
        That i can agreed with that.Finding this site is helping all of us.Even if it is a simple question or a complex question.I have had help from numerous people here.You all know you are.Thanks,i slaute you the backyarder way.I wont list there names or i be typing here for ever.And i have help others.I respect other people views and ideas.All i can say AA members are the best.
        Doggistyler

        Comment


        • #5
          I know what you mean.. When i first got into Jamma stuff (I have been doing electronic for many years before) i got 2 death threats.. Which wasn`t what i realy hoped for...

          It's been a steap learing curve.. But if i`m going to do stuff.. i always do it 100%. I don`t mind helping people... As long as the understand i don`t have much time.. and still have that thing called a life. I have a family as well.. and they must come first. Oh and a job too..

          Don`t worry Bertty, We will get your board going!!! Don`t give up hope just yet!

          I have fixed boards for a few people.. But they understand that if it takes 12 months to fix cos of my limited time.. then thats ok... Even if i can`t fix it.. then thats ok too...

          They know I do it for for the enjoyment and love of it.. NOT to make money... Big diffrance there!

          Unfortunatly due to my limited time.. i can`t help everyone.. I reckon with the amout of "regulars" we should be able to help everyone :-)

          Mrv.

          Comment


          • #6
            Yeah i don't mind looking at stuff so long as people understand I could take weeks or months to look and fix it. Like I said i have limited personal time these days and prefer doing family stuff.
            I try to avoid JAMMA stuff unless its bootleg or not riddled with custom chips that i have no replacements for, also if I find a board has no obvious fault within say 4 or 5 hours then your on your own, I hate working on dead boards its so time consuming....sometimes

            I'm no tech I taught myself how to fix boards and clocked well over 60 repaired boards in the short time ive been doing it. i didnt have anything except the will to learn. I used repair logs from the net to get a fell for it.
            Best thing anybody can do is just dive in and have a go, buy yourself some shitty boars to play with.

            Comment


            • #7
              And don't be afraid to ask stupid questions

              Comment


              • #8
                Originally posted by The Prof
                And don't be afraid to ask stupid questions
                Yep. For every dumb question there is 400 lurkers here too afraid to post
                ...maybe, but then again "maybe" covers a lot of things, like: maybe Michael Jackson really is LaToya in drag, or maybe if Dorothy clicks her heels 3 times and says "There's no place like home" while she is at home, she would telefrag herself..." - MadMikeAU

                | My | |

                Comment


                • #9
                  If it dosen't power up when plugged in, as far as I'm concerned its broke..! Thats the extent of my fixing ability. I do have a solder iron and a multi meter though..!



                  W.

                  Comment


                  • #10
                    Originally posted by woka
                    If it dosen't power up when plugged in, as far as I'm concerned its broke..! Thats the extent of my fixing ability. I do have a solder iron and a multi meter though..!



                    W.

                    Heheheh Maybe thats a good thing..... Better stick to PCs i reckon .

                    Mrv.

                    Comment


                    • #11
                      Originally posted by MadMikeAU
                      Yep. For every dumb question there is 400 lurkers here too afraid to post
                      Very well said. I have found where Im a mod at alot of ppl are too afraid to ask a question that several ppl want the answer to for fear of getting flamed/laughed at. Remember if u dont tell the girl u like her how the hell are u gonna get laid?

                      Comment


                      • #12
                        ...by giving her pimp some cash ?
                        ...maybe, but then again "maybe" covers a lot of things, like: maybe Michael Jackson really is LaToya in drag, or maybe if Dorothy clicks her heels 3 times and says "There's no place like home" while she is at home, she would telefrag herself..." - MadMikeAU

                        | My | |

                        Comment


                        • #13
                          Originally posted by MadMikeAU
                          ...by giving her pimp some cash ?

                          Oooohhh.. Thats nasty!!!

                          Back to the topic.. Can i order a sticky please? Need one in the ebay section as well

                          Thanks,

                          Mrv.

                          Comment


                          • #14
                            yah i'd stay away from a broken one.
                            cabinet's another story though.

                            i'm REALLY thinking about making a jamma tester - i'm sure people know what i'm talking about.
                            The HillDweller

                            Comment


                            • #15
                              There have been a few posts scattered around from people asking how to fix their boards, and or fishing for people to fix it for them. I wrote the following on another thread but the title of the thread is not that relevant to it, its probably more useful/findable here.

                              Mainly its to dispel the idea that fixing these things is cheap/quick/easy, its not even fun sometimes, but if people fancy getting their soldering irons dirty its not a bad introduction I think.

                              .....

                              I have had about 80% success with fixing boards, if you think of it like this there can only be 3 types of fault with a board.

                              When the correct power is applied...

                              1) if all the chips are working correctly
                              2) and are all connected up correctly (including passive components on the board)
                              3) and all the ROMS/PROMS contain the right code...

                              ...the game will work perfectly.

                              Power

                              Power is the very 1st thing to check,check the voltage level is correct, and that it is getting to the chips on the board. Check the voltage at the chips as far away from the power input as possible, volt drop across a board is normal, you many have 5V at the input of the board, but if that’s dropped to 4.5V at the farthest reaches of the board then things will get screwy. Either up the voltage a tad, or run a power wire to the far side of the board, operators often did this back in the arcade heyday. TTL chips do not like voltages much below 4.8V - they do odd things below that.

                              Chippery

                              Problems with faulty chips range from easy to find to virtually impossible. At the very least you will need a logic probe (without one its like trying to fix a car in the dark) and you will have to go round the board looking for pins that are floating, neither high nor low. This might be normal as some chips are dual, quad or octal chips - i.e. they have 2, 4 or 8 of the same logic gates on them, its not uncommon to find a quad chip where only 3 of the gates are used. The inputs to the 4th gate will be floating as they are not connected. To check this out you need to pull up the datasheets for that specific chip. If the inputs are active and the output is floating then you have found a dead chip. You can go one further here, if the inputs are active and the output should be doing something (based on the logic table in the datasheet) yet it never changes from low to high then you have a stuck pin, this gets harder to work out by eye the more inputs a logic function has. If you have say 6 inputs that determine what the output is doing, and all of them are active and flipping then its very had to tell if the output should be changing at any given point. The worst kind of fault is where the chip is still functioning but its thresholds are wrong, it changes as it should but is no longer latching cleanly or on time, finding these chips needs special hardware, logic comparators, oscilloscope...

                              RAM chips are a common failure, google the datasheet and check the address and data lines. If you find floating lines then you are on to something, follow those lines back and see where they should go. Something is dead somewhere, it might be RAM.

                              RAM needs controlling tho, you need to check the chip enable pin is actually enabling the RAM, and the WR and OE lines are doing something, if these are dead the chip will sit there doing nothing not the wrong thing.

                              ROMs, same deal as with RAM, the control lines need to be working, check the output pins for signs of life. The contents of the chip need to be checked too, you will need an eprom reader to do this. The game board could be in perfect working order but a single error in an elderly ROM will cause the board to crash straight away. You could spend hours chasing a hardware fault that doesn’t exist if the problem is due to duff software. PROMs are like EPROMS but they are write-once chips. Contents of these chips can be checked against the roms in the MAME set, there are apps to do this.

                              CPUs - virtually impossible to debug due to their complexity, if they are socketed its easy to rule them out, stick the CPU in another board that uses the same chip and use that board to test the CPU. Or stick a known good CPU in your board. If its soldered in and you cant remove it then you will have to assume it works until you have evidence to the contrary. Pull up the datasheet and see what the address and data lines are doing, bear in mind that a stuck pin doesn't necessarily mean the chip is bad, a track on a board has at least 2 ends, if the chip on the other end is shorted then the chip at your end wont be able to drive that line, so you may have found a fault from the other end.

                              Custom chips - these are project KILLERS. To save money on the chip count the makers made their own custom chips that combined dozens of other chips into one monster chip. They are usually surface mount, usually have upwards of 50 microscopic legs and often there is absolutely no way to test they are working correctly, even if you could test them there is no information around these days about what they do. Swapping them is not an option as the only place you wlil find another chip of the same sort is on another board of the same game and without specialist equipment there is no way to remove or replace them. If you have a dead custom chip then the board is scrap, its cheaper to buy a working board than take the dead one any further.

                              Audio Amp chips - these often are dead on old boards, they are usually the only chip bolted to the board, or to a heatsink. A quick and dirty test is to check the 12V feed is getting through then run your finger across the pins of the amp chip and or across the pins of the volume adjust pot. You should here a crackle, if not then push firmly on the body of the chip (if its firmly bolted or soldered down) you should here an angry buzzing noise. If you do get a noise then the amp chip is fine, especially if you can change the volume of the buzz with the volume pot. Bear in mind that the amp chip depends on the circuitry around it, often a cluser of capacitors, if any of these are damaged you may not get a possive result, even if the amp chip is fine.

                              Discrete Components - Resistors, diodes, capacitors - mostly you can spot damage by eye, but there are a couple of caveats, often you will find an orangey beige disk near many of the chips, these are ceramic capacitors used to smooth out any slight dips in the power supply in their area, they are often damaged, chipped of cut in half (to change their capacitance). Its possible that you have damaged on that is shorted out, but not likely, I would ignore these. Electrolytic capacitors are another issue, they are the ones that look like cans. Again these are often used as smoothing capacitors, often you will find 1 or 2 big ones by the JAMMA connector. If these are damaged the board will be more susceptible to voltage ripple, but the board will probably still run, it will just crash more. If they are the type where the two legs are at one end its easy for the cap to be damaged if it has been wrenched to one side, this will tear one leg out, but when the cap is straightened the torn leg goes back inside, the cap is wrecked but it might not be easy to spot with wiggling. One area where electrolytics are critical is in the amp section, if these are damaged or faulty then the amp may not work, or the sound maybe quiet, missing or raspy. Electrolytics can die of old age, some do, some don't. The problem with electros is they are wet capacitors, the electrolyte inside is a damp paste which can dry out if the cap has lost its seal. When they dry out ironically the capacitance doesn't change (so a capacitance meter is useless), its the resistantce of the cap that goes up - the resistance is known as the Equivalent Series Resistance (ESR). A healthy electrolytic will have a certain resistance, a tiny amount, often in sub ohm range. When it goes bad the cap can end up with an ESR that is 10 to 100 times higher, still too low to measure with a multimeter but its the equivalent of dropping lots of small resistors into the circuit so it can bugger a lot of things up. The only way to rule this out is using an ESR meter, or by replacing all the electros on the board, which is tedious and can get expensive if you have to buy new ones all the time. Personally I have an ESR meter which not only lets me spot the bad ones, but allows me to use caps from scrap or smashed TV PCBs which I can test as being fine. An old electrolytic cap is not necessarily a bad one, but a lot are, especially ones that lived in hot parts of the board, up close to an amp chip heatsink is not where electros have long long lives.

                              Connection problems - the PCB

                              Connection problems are common on old boards. While the board was safely bolted inside a cabinet the worst it had to face was dust and the odd spider. Once the game was superseded it was often slung in a box and not well cared for. The underside of a PCB is full of sharp pins which will scratch the arse out of any board pushed up against it. Scratches lead to cut tracks, cut tracks will often lead to floating pins, but if a pin has 2 input tracks you may not find a truly floating pin. Track damage can range from the bloody obvious, to the microscopic.

                              A circuit diagram is essential as you will often find things that just "look" odd, but are correct on that particular board. In the absence of a schematic you really are stuck unless you have a working board to compare connections to.

                              Age is another killer of tracks, tracks are usually shiny beneath the lacquer, but often you will see tracks that look dark, or just black. This is corrosion, often the track will still be conducting, and sometimes it won’t. Often these tracks duck under chips or other components on the board so you can’t actually see where they go or what condition they are in for most of their run. What makes things worse is that any liquids spilt on the board will get trapped under chips and remain there for ages due to capillary action. Sugary drinks are very corrosive, and arcade machines often had things spilt on them. If somehow this dripped onto the board it will get under the components and slowly eat away at the copper. Have seen a NeoGeo board with classis signs of a missing ROM dataline, but it all ducked under the huge cart connector which had been soaked in something dark and sticky, coca cola probably. I never did find the break as I had no cct diagram to show which should go where. Tracks often duck through the board itself via through holes called unsurprisingly "vias", tracing a board out by hand in the absence of a schematic is probably something that only the really bored, or borderline insane will attempt.

                              Other components on the board also need attention, basically its resistors, diodes and capacitors. Electrolytics age very poorly, they are also physically fragile, look for smashed bent or bulging electrolytics. Any capacitor with white gunk at its base needs checking, this could be leaked electrolyte, or it might just be gunk used at the factory to hold the cap down a bit better. Ceramic capacitors will be all over the board, they are pale orange disks, they are decoupling caps and often look very battered. Unless one has gone short circuit it’s not likely to cause any massive problems no matter how chipped they look. Only look at these closely if your board sometimes crashes or resets randomly.

                              The Bad News


                              To be honest repairing a dead board can take a very long time, even if you know what you are doing there are always boards that just sit on your "too hard" pile for months/years. That’s why most folk on here that can fix boards, do not offer to do so for other members. These boards are now so cheap on ebay that you only need to spend a couple of hours on a board before the cost of your time exceeds a new board. Combine that with the fact that many of the chips on these old boards have been out of production for 20 years and are therefore hard to find. These chips can often be found online but they are almost always overseas so you end up spending $20 postage to get 1 SRAM chip, of course in these cases you buy 15 or 20 of them, but the point is that postage costs add up. If you can’t get all your spares from the same place then the multiple postage costs soon start to approach a large % of a known working board.

                              All the above might sound very disheartening, but if you are willing to get in to electronics it is possible to chalk up some victories. If you are game to take the path I started out on some time ago I would offer the following checklist to start with.

                              Stuff you will need

                              Soldering Iron (as fine a tip as possible) $50
                              Solder (duh) $5
                              Solder sucker $12
                              ROM Puller $3
                              Multimeter $25 - if you are buying on make sure it has a beeper for continuity testing, the ultra ultra cheap ones don't. Checking tracks is hard enough without having to look up at the meter screen everytime to see if you have a connection, it if beeps its good and you can move on.
                              Logic Probe (sounds daunting and expensive but isn’t - the best $25 you will ever spend really). This connects to the powersupply you are feeding the board with and the LEDs on it will tell you if the probed pin is high/low/or flipping between the two. A floating pin will show up as nothing, neither high nor low, on some chips this is normal, in other places its a fault.

                              Stuff that will make your life easier

                              Desoldering station, makes getting chips off boards a breeze, its good to be able to check a chip is ok once its off the board so not having to cut its legs off is a bonus, also means you are less likely to roast the chip you want to use as you take it off a scrap board.

                              Oscilloscope - logic probes are cheap and useful, but if a pin is active you have no idea what the signal looks like without a scope, duff RAM chips often remain active but the signals are utterly mashed, easy to spot with a scope, impossible with a logic probe. All a logic probe can tell you is if the chip is totally dead, most RAM chips struggle on so you are left with the blanket replace and retry option.

                              Things to check on your dead board

                              1) Take the board outside in the daylight with a magnifying glass and go over the whole board both sides, sometimes the problem is obvious, natural light is essential for this tho, as is the magnifying glass
                              2) Check the power supply, voltage and voltage drop across the board
                              3) Check the power supply again, some older boards require their 5Vs to be more like 5.2V.
                              4) Get the logic probe on the CPU - check the clock pin - it should be very very active. Without a clock signal the board will do absolutely nothing.
                              5) Probe the RESET pin on the CPU - google the pinouts for that CPU to determine what it should be, on the Z80 a RESET pin thats low means the CPU is in RESET mode - ie its parked. A working Z80 should have this pin high! A pin with a line above its name in the datasheet means "active when not high".
                              6) With ROM puller, remove each rom chips and reseat it carefully, its easy to bend pins when putting it back in. Reseating can cure problems cause by oxidised legs. If you have an eeprom reader then dump the chips contents to your PC while you have them out of their sockets and ID them with the software that comes with mame. If you find a rom with legs bent under this will be a fault, its not likely to the only fault, its more a sign that someone has been there before you, also its worth not ruling out anything that looks like its been worked on before, I have found boards where someone was on the right track and gave up, or even soldered in a badly faulty chip to replace one they suspected originall.
                              7) Probe around the RAM chips, google the datasheet on those chips and check the Enable, OE and WR for activity. Check the address and datalines for signs of missing lines.
                              8) Same as 5 for the ROM chips.
                              9) Probe the address and datalines on the CPU, look for missing (floating lines)

                              It is best not to go round touching up solder joints on chips, it is not likely to be the cause of the problem and you can do a lot more damage that way, especially with surfare mount chips, once solder joins up the pins its impossible to to know if a couple of pins are joined because you joined them, or if they board is designed to join them up. Riser board pins and connectors are another matter, anything thats had physical flexing in its lifetime could well have developed bad joints, but again a blanket approach can leave you with more questions later about the boards original state.

                              That pretty much my standard tests, usually you get some leads from doing the above.
                              Last edited by Womble; 9 January 2010, 09:47 AM.
                              Sic transit gloria Atari!

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