• Category Archives Electric Troubleshooting
  • [Article 6358]Sprint One :: PCB recap

    My Sprint One PCB started to have some stability problems.

    Touching the big capacitors on the PCB I saw the liquid came out.

    Actually they were not in so good condition.


    I tried to find coax capacitors to replace them but it had been quite hard so I decided to apply one method learned years ago from radio-tubes collectors.

    First of all you have to cut the capacitor


    Then you have to empty it saving all external parts


    Prepare the new content using a new capacitor or a combination of capacitors.


    Fill the old shell and use hot glue to seal it


    Make it for all caps you want to refurbish



    Re-solder the new/old caps


    Done :)

  • [Article 6341]Tempest PCB: a new board

    I’m working on a Tempest PCB bought some months ago on ebay. It missed some PROMs and custom chips on the aux board.

    I needed a little bit to find all missing parts and I tested the aux board using my working main so I’m sure it works.

    So, plugging the boardset I can see this strange TEST screen:


    all “0” are on the same line… They should be on 5 different lines…

    Exiting fro the test the game resets.


  • [Article 6328]Major Havoc board (1)

    I’ve a not working Major Havoc board.

    Let’s go to have a look to this rare board.


    It has the “Quad Pokey” installed. In the same picture you can see the SN UR148



    First of all as you can see it is quite different from all other (vector) atari boards. Vector D/A circuit is more complex than usual.




    It has some “wires” and actually I dunno if these additional wires are factory modifications or not.

    As you can see in the 3rd picture and in the next one this board was dedicated to the prototype TOLLIAN’S WEB so I don’t know if the modifications are due to adapt the board to the final software release.majorhavoc08

    RAMs and ROMs have been verified and seem to be ok.



  • [Article 6316]Troubleshooting Asteroids PCB (4)

    Problem solved.

    After checking  (as suggested in the VECTORLIST) the Vector Timer Circuit, with a particular attention to 74LS83 ( four-bit adder) at location M, I expanded my research to all the data flow from the ROMs to the XY Position counters. Everything seemed to be ok but paying attention to the scope I could see signal LOAD6  was different from other LOAD* signals. Replacing 74367 at locatio H6 the problem was solved.


  • [Article 6307]Troubleshooting Asteroids PCB (3)

    Ok, I spent a bit of time to understand what happened.

    I could solve the problem number 1, now all the screen is used. I just replaced a 74191 in F9 position. UNMDACY11 was always low.




    Now I’ve one problem only. The game starts, the TEST doesn’t show anything wrong but what I see is very strange. All DIP SWITCHES were in the same position so the language is SPANISH with 2 COINS PER 1 GAMES. As you can see the problem affects some asteroids (just one on the left ) and the alphanumeric messages.



    zoomed “2 FICHAS 1 JUEGO”


    as you can see the message moves downwards and “ASTEROIDS BY ATARI” is not shown.

    I’m quite blocked now because I checked all Y circuits from the output to the VECTOR ADDRESS COUNTERS…

    ROMs have been checked and vector RAMs replaced.

  • [Article 6300]Troubleshooting Asteroids pcb (2)

    Checking the counters I found a faulty 74191 in D9. Replacing it I can see something better:


    but the vectors seem to be “sampled” vertically. After a fast look I found pin 19 and 20 shorted of 74374 in B10 position.

    This is the situation now:asteroids pcb oo3

    There are 2 problems:

    1. 25% of the screen is not used
    2. all labels are corrupted

    the next picture shows better the problems



  • [Article 6277]Omega Race (2) :: Sound and Monitor

    Sound now works properly. I had to clean the speaker contacts.

    About the monitor:

    It is in very good shape.

    Plugging it to the cab I had the spot killer on and no lights on the neck.

    I cleaned all connectors but it was not sufficient. Then I realized that moving the cables I had some reactions and I checked the connectors solders and the red one on the main board connecting it to the HV unit has at least 5 pins interrupted. So 10 minutes with a solder and I remade the board like new.



    Assembling the monitor inside the cabinet and cleaning the yellow layer and the black cardboard I can say most of the job has been done…

    omegarace_1604 omegarace_1605

    Most of the job has been done. Now the back panel is missing. Actually I don’t remember if I have it somewhere in my garage or I have to remake it. We will talk about this next week.


  • [Article 6270]Omega Race (2) :: PCB – part 3

    Here the problems I had yesterday.

    1. BBU RAM S4: BAD
    2. V RAM2 J1 and or (L/M)1: BAD
    3. V RAM4 (J/K)1 and/or (N/P)1: BAD
    4. V ROM2 F1: BAD


    1 – It was related to a power problem. I can’t understand connecting the oscilloscope ground to the game ground the probe wire becomes hot. Anyway problem solved.



    2 – V RAM2: This was the most complex error. The analysis made yesterday had no success but considering now the problem was related to J1 and or (L/M)1 only I pointed my attention to the “Chip enable” circuit. After some tests I could see I forgot to rebuild the track between 7404 in position PR1 PIN 8 to 7432 in position R1 pin 10.


    3 – V RAM4: (J/K)1 2114 was faulty. I just replaced it.


    4 – V ROM2 F1: ROM was actually bad and I replaced it with a new one.


    This is the self-test result. I’m sorry I didn’t manage Z signal 😀 😀 😀


    so, PCB now is ok…


    What have I to do now?

    • No sound to the right speaker
    • Monitor (not working)
    • Back panel


  • [Article 6250]Omega Race (2) :: PCB – part 2

    Once cleaned all damaged parts I made photos of each chip position in order to always have a visual representation of the trucks behind the new sockets. I signed the IC position and it’s location on the PCB. Here some examples:


    Then I socketed and replaced resistors and filters.


    And then Kynar Wire!



    Plugging the board I had a good surprise because the game started BUT after few seconds the vectors hide for a while.

    Running the self test I have the following errors:

    • BBU RAM S4: BAD
    • V RAM2 J1 and or (L/M)1: BAD
    • V RAM4 (J/K)1 and/or (N/P)1: BAD
    • V ROM2 F1: BAD

    Actually not so bad.


    All the  RAMs/ROM (but BBU RAM) share the VECTOR ADDRESS BUS, from SMEM0 to SMEM9 controlled by 74157 in positions K3, L3, M3.


    MAIN ADDRESS BUS (MA0..9) and PROGRAM ADDRESS BUS (SEQA0..9) are connected to these 74157


    I can see BBU RAM (5101) uses the MAIN ADDRESS BUS too, so I’ll check if S4 pins 1, 2, 3, 4, 5, 6, 7 and 21 are correctly on the bus and if all lines arrive to 74244 in (P/N)6 (pins 3, 5, 7, 9, 12, 14,16,18). This will be the first test I’ll perform.


  • [Article 6237]Omega Race (2) :: PCB – part 1

    This was the PCB

    omegarace_1301So the acid made its job.

    The board had been socketed already


    But I realized the entity of the damages once I removed such those sockets!

    And I decided to dedicated a lot of time to remove all damaged parts


    This is the board now

    …even if some tracks have gone


    Now I’m keeping pictures place by place so resocketing the board I can check which track works and which not.





  • [Article 5970]Super Bug :: Board troubleshooting (Car)

    During the last party (VMASP_2016) this game became to have a problem to the car sprite.


    A “black” bar was in the center of the car. Actually that part of car was missing so we had a sort of “transparency”…

    First of all I removed the mask prom for that sprite having a confirmation that something was going wrong with the vertical signal that identifies the sprite zone to draw


    This part is shown on the schematics and you can see H and V are controlled by the same flip-flop.


    In fact checking the signal to the  7474 pin 6 in M7 I had the following waveform (very similar to the problem I had on the screen)


    I was quite sure H and V signals were ok (in any case I made a check)  and so I replaced the 7474 having, now, this waveform.


    Definitely better…

    Plugging the board I had this pattern


    and resocketing the PROM I could verify the problem had been solved.


    .. mission complete!


  • [Article 5947]Defender :: Hacking 19-in-1

    I was quite scared about the possibility my Williams boardset could fall while people was playing.

    So I decided to plug in the (famous) 19-in-1 board, because I could see the game is very well emulated. But just see and not play, because once I received the board I discovered in half a minute that BUTTON 5 (S5) is supported by software but not by hardware (actually button 5 and 6 for both players). This button is needed because corresponds to the HYPERSPACE button.

    Setup shows both buttons 5 and 6, it means who wrote the sw wanted to use them and probably he allocated in the right way the specific resources.

    Backtracking all inputs I could see all of them arrive to the 74244 close to the JAMMA connector, with the exception of P1S5, P1S6, P2S5, P2S6.

    There are 5 74244 and I discovered that S6 for both players are anyway connected to these buffers but part of the the pull-up circuit misses (and the connection to the JAMMA of course). On the contrary no way to intercept S5.

    So I moved to the bus tranceivers (74245) between RAM and FLASH. If buttons are managed, they are managed there (!!)

    Playing a little bit with +5 power and using my finger I could change the status of P1S5 and P2S5. This means that S5 signals are undetermined.


    defender_19in1_02 defender_19in1_01



    Using a pin (pulled up with a wire connected to the pull-up pin of JP1) I touched the pins waiting for a reaction related to the involved buttons and the PIN 3 of U22 (one of the two 74245) was what I was looking for. So I had to start from there.


    First of all I connected a wire to the data-bus on the PIN3 of U22


    Then I used a 74244 to complete the circuit.

    PIN 10 to JAMMA ground

    PIN 20 to JAMMA +5V

    PIN 16 to the databus

    PIN 4 to JAMMA Component side PIN 26 and to a 10K resistor; this resistor then is connected to +5V

    PIN 1 to PIN1 of U30; in fact this board uses 4 different signals to enable the input drivers and I tried with the one dedicated to PLAYER1 and his buttons. Just a try.



    I’m sorry I haven’t any tool to manage SMD components and boards so my soldering is very bad.

    Anyway this is the result:



    fixed with some hot glue




    It works great and now I have a good board backup 😀

    PS reading this post I can see my English is very bad; I’m sorry for that. If you have any question please don’t hesitate to contact me.

  • [Article 5928]Circus :: PCB SK2 Troubleshooting (2)

    What I know about this problem is that connecting to ground the PIN 1 of the 74H21 in position 15D (signal MVID) I have the game running with a correct attract mode, the spinner works, accepts coins and the game starts. The problem is (obviously) that the “MAN” is missing; in fact that signal manages the jumping man.


    So I had a look to the “MAN” circuit but after some evenings replacing components I replaced ALL components but nothing changed….


    All IN signals seem to be OK.

    Now I’m blocked, I can’t solve this problem.

  • [Article 5922]Circus :: PCB SK2 Troubleshooting (1)

    I want 2 boards for each cabinet I have; that’s because in case of problems I can continue to play my games until the main board has been repaired. So I found an original EXIDY CIRCUS board, sound board included. Actually when I tested it I could see garbage on screen but I could insert coins and “play”.

    I tested this board on my cabinet:


    I pointed out directly to the RAMs and related components. After replacing a couple of RAMS I had this result:


    I needed a bit of time (wasting time to replace components into the video section) to understand the problem:



    Cutting all pins I could reach this status:


    A good result, but not enough. In fact the game freezes after few frames.


  • [Article 5358]Twin: Crash – Intruder :: Troubleshooting the sound boards

    CRASH sound boards had both “strikes” always on.

    I studied the schematics

    Image2 (1)


    but I didn’t find anything wrong.

    Then I understood that I had less than 12V and the difference was enough to cause this malfunctioning.

    I changed 2 resistors:

    R64 from 10K to 18K

    R67 from 10K to 18K

    in this way the circuit can tolerate less than 12V.


    About INTRUDER sound board: some sounds were missing and backtracking them I understood that a couple of LM3900 were faulty…

    This is one of the pages of my troubleshooting diary ahahahah




  • [Article 5289]Vanguard :: Troubleshooting Speech board (SK-6)

    This is the speech board. vanguard074 It has 2 very rare components but I’ve been lucky because the problem was very easy to fix. This is its schematics. 20150605_021335   I had good signals on pins 19 and 20 of IC9 but not signal at all at AUDIO OUTPUT terminal I checked all intermediate points and I could see the the signal interrupted immediately after the 1st amplification step, at    pin 1 of IC5 (LM324). Here the details:



    So I checked all resistors, all points, everything. Then I understood that the signal on pins 2 and 3 had the same waveform so I changed the C8 and C9 and now Vanguard says: BON VOYAGE…. again. These are the new capacitors (and the new LM324 too)…







  • [Article 5178]Quasar :: Old KT-3 Vs. New KT-3

    Actually I made an easy job swapping the old KT-3 chassis with the new one.

    I only changed the color input board and removed the tuning card.


    This is the input color board I’m using (taken from the old TV)



    I can see that the new power card is more populated than the old one. I used the new one including the Degauss circuit. The old chassis had a small dedicated circuit screwed on the left of the metal frame for that.

    quasar140On the left you can see the old power card and on the right the new one.


  • [Article 5113]Quasar :: KT-3 Troubleshooting 3

    I changed some transistors and TDA, replaced some capacitors and checked some resistors values.

    Now I want to troubleshoot the switching regulator board




    In order to avoid any burn I removed the T465 connecting pins 6 and 8 only in order to close the circuit.


    The troubleshooting manual describes the waveforms on this circuit in several parts. This is the most important part of the circuit:



    with related waveforms:


    I checked points “B”, “D”, “E” and “F”

    this is the waveform in B. I think it is ok



    Checking the point “D” I had the same result as in the previous troubleshooting post, with regular spots blinking. Regulating R7317 (the pot. on the daughterboard) I could stop the blinking effect having a static image as the following




    It is an extreme case of the waveform where the lower part of the square is reduced to a point. Transistor T7353 works properly because point “E” has the same shape but inverted





    In the end the waveform in “F” is the following. It is static and doesn’t pulse anymore



    Looking at the pictures t2 seems to be close to zero….