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jbtech

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jbtech last won the day on March 13 2021

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    Blue Mountains, NSW
  • Machines in your collection
    Arcade: Autorec upright / Exerion, Taito Missile Command TT, Taito red upright / Space Invaders Colour, Gottlieb Challenger / MAME conversion, Golden Tee Fore 2005, Hankin upright / Green Beret, Mirco Challenge (Pong clone), Lowboy / SFII, Logitec Space Invaders Colour TT., Silverline JAMMA upright cab.

    Consoles: Tempest PC50x, Atari 2600 'Vader', Atari 2600 'Junior', NES 'Toaster', Sega Mega Drive II, Super Famicom, Playstation 1, 2 and 3.

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  1. No, if that degauss circuit takes its power from the same AC supply which powers the monitor chassis neither of the supply wires should be connected to mains earth. Only if it had a completely separate, isolated winding of its own would it be safe to earth either of the wires. Regards, John.
  2. Hi, the thermistor is a PTC, has a positive temperature coefficient. When AC is applied it initially has a low series resistance and passes the AC current to the degauss coil. As the junction heats up the series resistance increases so what the degaussing coil receives is a strong AC current initially which diminishes fairly rapidly and once the thermistor has warmed up becomes very high resistance reducing the current to virtually zero. The effect is similar to using a degaussing wand and drawing it away slowly from the screen, reducing the residual magnetic field to nothing. An easy way to check the operation of the circuit is to observe the effect it has on the image which should vibrate strongly with colour changes at the corners and then settle down within about 5 seconds or so. You can usually hear the coil humming as this occurs. If the picture continues to wave about the thermistor or the resistor could be faulty, temporarily disconnecting the power to the circuit will prove if the degaussing unit is the cause of any picture instability. The reason for a diminishing, alternating field is to overcome the magnetic strength any magnetised components and reduce that field to zero, but here's the catch - if the applied field is simply reduced to zero some 'residual' magnetism will remain due to a factor known as hysteresis. The applied field has to go beyond the zero point and slightly into the reverse direction, so an alternating field must be used which gradually reduces to zero otherwise some residual magnetism will always remain. Likewise if a degauss wand is used and the button released while still close to the screen the CRT will almost certainly remain magnetised unless by some miracle the button was released at the exact right moment when the residual field was reduced to zero by instantaneous level of the 50Hz alternating degaussing field. The trick is to move in close and circle the CRT, drawing away gradually and only releasing the button once far enough away that the screen is no longer affected by the wand at all. Hope that helps, regards John.
  3. Hi, I'd imagine that type of switch would normally be mounted to a metal panel so think it's unlikely you'll find one with a much longer thread. It could be mounted to your 16mm deep panel by counterboring the hole. To do that you need a larger speed bore type drill, something like this: https://www.bunnings.com.au/irwin-30mm-speedbor-spade-drill-bit_p6354247 First drill a small (say 3mm) pilot hole through the panel at your centre point. Then drill the large counter bore from the back but only half way, to a depth of about 8mm. Then use the same pilot hole to drill your 19mm hole through, from the front. If unsure, test the method out on some scrap timber first, clamped to your work area to hold it steady. You might need a socket set or tube wrench to tighten the nut so make sure your counter bore diameter is large enough for the tool to reach in as well. One more point, if the switch is for mains the metal body should be earthed for electrical safety so if not mounting to a metal panel put a washer, lug or wire ring under the nut which is connected to mains earth. Edit: it looks like that switch may have a solder terminal for earth so a washer wouldn't be required if that's correct... That's one suggestion anyway, if you're keen to use that type of switch and can't find any with a longer mounting thread. Hope it helps, regards John.
  4. HI, I don't think you'll need either of those methods to tie the degauss coils in place, once the whole assembly is in the machine right way up they should stay put well enough. The exact position isn't super critical and they look like they're fine now that you've made a space for them in the mounting panel. I imagine that steel L bracket would rattle badly when the coil is energised and the wire isn't ideal either as winding a wire around a coil could result in a current in the wire or an unexpected load on the coil. A plastic fixing such as a cable tie would be safe to use but not necessary in my opinion, I really think it will be fine without any extra support, regards John.
  5. Hi, a couple of common tube types use this variation of the degauss coil(s) Rather than a single coil which completely encircles the metal band around the CRT there is a pair of oval shaped coils which are wired together, one placed along the 'top' edge and one along the 'bottom' edge of the CRT and held in place by the plastic tags at either end of the oval which loop over the mounting ears of the tube before fitting to the cabinet. The correct placement is as per your middle photo and would require a gap along those two edges of the plywood, to be fitted without pinching. Each coil does need to be an oval in shape, if squeezed togeter too closely their effectiveness would be reduced as the field would tend to cancel out. The extra grooves in the plywood only need to be long enough to clear the coils and won't affect the CRT mounting points, each corner needs just enough clearance for the plastic tag. In your first photo the corners look right but the coils don't have enough clearance to fit correctly. Hope that helps, regards John.
  6. Hi again, the CRT type number would be something like 370ESB22 but that is obviously an original type CRT as it has the correct chassis number printed on the label which, according to https://translate.yandex.com/ocr roughly says: Regards, John.
  7. Hi, if the B+ Voltage on the monitor is out of spec the picture size will be incorrect so it may be worth checking the Voltage at TP91 on the PCB ( if you can find it) which should be +112V or very close. If it's hard to reach in situ temporarily attach a pair of wires to B+ and chassis ground to connect to your meter leads, taking care not to short anything or come into contact with the wires yourself once running. It may sound backwards but if the B+ is too low resulting in a lower EHT Voltage the picture will increase in size. Does the CRT have a TOEI label attached to the surround? what is the CRT type number? Regards, John.
  8. Hi all, this is just a little update to the Autorec arcade machine project, some minor repairs and finishing off some internal wiring, adding a few new features. A little while back the machine started humming through the speaker and the image became a bit wavy. I suspected the power supply unit, the monitor chassis having already been re-capped recently. Temporarily substituting a known good power supply to correct the problem, the original Kaga power supply unit seemed worth fixing as it had not failed altogether but soon would if left unrepaired. As the problem was a hum on the power supply rails rather than a high frequency noise the most likely cause would be the large capacitor which smooths the rectified AC near the (110V) input to the supply. Having removed the unit to repair on the bench it seemed worthwhile to order in a full set of electrolytic capacitors, using a higher temperature rating than the originals where possible. After installing the new components the supply ran well on the bench using a couple of halogen lights for a load. The 12V 50W lamps are seen here running from the +5V rail so each was only drawing about 2.5A at this Voltage. Returning the power supply to the machine I opted to mount it horizontally with the component side of the PCB facing upwards to allow heat to escape more readily as well as improving access to the internal Voltage adjustment pot. which can be operated by a trimmming tool through one of the holes in the perforated side panel. The power supply had previously been mounted at an angle with this side facing downwards for some unknown reason. And so with the machine working well again with its 'original' power supply back in place it was time to complete some unfinished work on the machine wiring. The multigame PCB previously fitted had no problem with two separate coin inputs but the Exerion PCB having only 1 coin input requires an external credit PCB to correctly handle two denominations, in this case 10c and 20c from the two Coin Controls roll-down type coin mechs. The original coin mechs were both set for 20c but were missing parts and not connected so I had replaced them, with one 10c mech and the other 20c. Although the machine is not used commercially it's nice to have all the components functioning correctly so I'd previously fitted a Gottlieb Electronics (Australia) triple coin credit PCB but not yet wired it in. It also has outputs to drive coin counters so I'll install a pair of those as well. New wiring added to take the signals from two coin switches, driving the single coin input on the Exerion PCB as well as two coin counters. There is a Service switch input on the credit PCB which is directly connected to the coin output but instead I'll add a service switch to the third coin input allowing a number of credits to be set for each button press. A little panel added inside the cash box door for the coin counters and another inside the coin door for the 'service' and 'test' switches. The test switch has no effect with the Exerion PCB, having no built in diagnostics but does work when the multigame PCB is plugged in via its Jamma adaptor. No test panel would be complete without Volume and manual monitor Degauss controls so these have also been added. The degauss switch and volume potentiometer are wired in series with the degauss coil and the speaker, respectively. The Volume control is a 250 Ohm, 5W wire wound potentiometer which allows a good range of control without the sound ever being cut off completely. Having placed a switch in line with the degauss coil, the monitor no longer automatically degausses each time the machine is powered on. This is fine as degaussing is only required periodically or if the machine has been moved, to correct any colour impurity on the CRT. A couple of price labels to identify the 10c and 20c slots, the left hand coin mech being factory set for 10c coins has a smaller slot which helps to prevent that side being fed larger coins. The credit PCB has been set to output 1 credit for 2x coin 1, 1x Coin 2 or 5 credits for 1x coin3 (service switch). As I mentioned in the previous post above this isn't a machine restoration, just returning an original '80s machine to fully working condition and adding a few period correct details. More projects and repairs to follow, Regards, John
  9. Bump - I still have this but could use the space... 28" standard resolution CRT TV, works well, nice picture. Ideal for later style consoles with widescreen capability or should suit gun game setup. RGB analog Scart inputs standard, not modified. Stereo speakers, with remote. Will consider offers, can keep TV cabinet if not required. Pick up only, Blue Mountains West of Sydney. Thanks for looking, John
  10. Hi, the body of that machine should definitely be connected to mains earth for safety so yes, a lead with 3 prong plug is the answer. Regards, John Edit: any external metal parts of the body such as control panels and coin doors, in the case of plastic or wood bodied machines...
  11. Hi Frank, Yes, the Atari circuit is correct with R, G and B outputs coming from the Q outputs of IC L8 via 22 Ohm resistors. Is there any signal on any output of your ICs at present? The Atari PCB does work correctly with an analog RGB monitor and outputs composite sync so perhaps your boards are designed for some other standard monitor without composite sync? A bootleg rom set which is not yet in MAME sounds interesting - have you seen any of these boards working, is the game more or less identical? It might be interesting to compare ROM files to known sets and see if the differences are major or minor. If the sound setup is very different that would account for many changes though. The Atari diagnostics relied heavily on the Pokey working for outputting tones and was probably just left out... I did write a simple loop to make the CPU read every address, then trace the signals with an oscilloscope to find problems with the address decoding or stuck bus lines if that is of any help. It goes in place of the boot rom and there is a link to the file in one of my repair logs. It also keeps the watchdog busy if your board is setup the same way. Good luck, regards John.
  12. Hi @robm sorry that didn't seem to help, if there's no ac noise or ripple on the +5V rail you appear to have ruled that out as an issue, I'd stick with the slightly higher Voltage at the board though, 5.08V sounds ideal in case there are any parts of the boards with lower levels. Whenever there is a strange interaction between boards or modules it is worth double checking power supplies, just in case as issues there can cause all sorts of unusual symptoms. So, if not the +5V being noisy or otherwise affected by loading there must be some other interaction between your PCBs which is affecting the sound board - which did not show up on a different machine using your sound board either. Not necessarily on the sound board itself but if you have tried a different fliptronics board and a different cable with no change these would seem to be cleared of suspicion. I couldn't say for sure that it isn't an MPU fault but as it is the sound board which is resetting I would still think the fault is more likely within that board, even though it worked OK in a different machine. The previous suggestion to check U18 and U19 might still be worthwhile as signals between boards could be marginal and work in one machine but not the other. There doesn't seem to be anything more obvious which you haven't tried already but I'm not familiar enough with this system to offer any other suggestions - anyone? Regards, John.
  13. Hi, this still seems like a power supply issue. If removing one other board from the ribbon cable makes a difference and the sound board then works I'd be very suspicious of the supply Voltages. Even if you're measuring 4.93V DC at the ROM chips the supply could be struggling and outputting a lot of ripple, crashing the sound cpu. If DC levels seem OK I'd take some AC measurements at the same points to see if there is a noise or ripple problem with the supply. Also, where are you placing the 'black' meter lead, on the ROM chips negative pin or some other ground point? Another simple check you can do is look for excessive Voltage drop along the cables by measuring between +5V at the power supply and +5V at the point where it enters the sound PCB. Likewise for the ground from the power supply to ground on the sound PCB, if there is a large Voltage drop on either there could be a cable problem. These are just general power supply checks, not specific to your machine but hopefully may help. Regards, John. PS You could also try taking the same Voltage measurements with either of the other PCBs removed from the ribbon cable as you mentioned before to see if you can notice any change to the power supply Voltages wth a reduced load...
  14. Hi again Franky, Yes, pin 3 of the flyback transformer is the return path for all of the current in the h.v. windings including current which flows through the resistors and potentiometers for the grid Voltages, and the Anode current. The current which flows via the Anode goes to.... the Cathodes. The cathode rays are a stream of electrons which flow in a vacuum from the cathodes towards the anode, causing the phosphors to illuminate. The flow of electrons constitutes a current, in terms of 'conventional current' which is the oppposite of actual electron flow that is from Anode to Cathodes. Yes, the emitter of Q501 is powered from L501 which actually carries the +12V rail, which is derived from pin 7 of the Flyback transformer and also powers other parts of the circuit. That detail is not specifically stated on the circuit diagram but is briefly mentioned in the circuit description in the manual: On that note, you may have not heard a term which is often used in the electronics industry and expressed as an acronym - R.T.F.M! which of course stands for Read the Manual, fully... I wasn't suggesting R528 somehow acts independantly to control Q501 or produces a delayed reaction of some sort, simply that adding resistance to the current flowing from the base of Q501 reduces the base current (once the transistor begins to conduct) protecting it from damage as well as allowing it to conduct in a linear range for slight h.v. current overloads rather than saturating and cutting off the cathodes completely. And yes, this beam current limiting effect would be a response to an overload situation which is beyond the expected operational range. A correctly adjusted monitor should be able to display a white screen without exceeding safe current but if the R, G and B gains are set too high, the CRT is very worn or some other fault exists this circuit should reduce the brightness or cut off the drive completely, depending on severity. How negative would the Voltage at pin 3 of the flyback transformer go? We can estimate the average Voltage at pin 3 at the point where Q501 begins to conduct and limit current by using Ohms Law again, the Voltage drop (v = IR) would be about 0.0015A x 32390 Ohms (R529+R528+R512) or just under 49V. Starting from +12V, minus 49V would be about negative 37Volts. In reality the waveform at pin 3 is pulsing, not a steady DC Voltage though so the peak level of the pulses would be more negative than that. It wouldn't be easy to work out exactly without measuring but as a guide, if the circuit was designed correctly the Voltages should all be within the safe Voltage rating of the components used. That means, looking at C525 which has a 200V rating, the peak Voltage at pin 3 should never exceed -200V, hopefully by a good margin. so somewhere in that range from -37 to -200Volts. Yes, Pin 11 of the flyback transformer is ground, those resistors and potentiometers form a Voltage divider with current flowing through the resistors to ground. But the return path for that current (to make a complete circuit) is still via pin 3. Hope that helps to clarify some of those concepts and not add confusion! regards, John.
  15. Hi Franky, I agree the purpose of this part of the circuit seeems obscure at first. It may help to note that the connection at pin 3 of the flyback transformer is not an additional winding added to power another part of the circuit, it is the negative end of the series of windings and diodes which provide the high Voltage to the anode and the grid Voltages. That means it is the 'return path' for any current which flows in the h.v. windings. In a simplified circuit this would be connected to ground, i.e. 0Volts. It isn't connected directly to ground, though. There is a small capacitor to ground C525 which would help to absorb high frequency transients and 'spikes' but the main current flow is via some resistors, with a capacitor C529 to smooth out the pulses. Why connect this end of the h.v. coils via resistors instead of just grounding the pin? To create a Voltage drop which can be used to control a transistor which will regulate the drive to the CRT cathodes. It is a current sensing circuit. As it's the negative end of the h.v. windings and diodes, current will flow into this point via the resistors. The greater the current 'load' on the high Voltage the more negative the Voltage at pin 3 will tend to become as the Voltage drop across the resistors increases. R512 which is connected to pin3 and C529 form a low pass filter, smoothing out the pulses from the h.v. coils. From this point the current flowing through R528 and R529 is a d.c. 'average' of the current flowing in the h.v. coils. As far as D.C is concerned, C529 is an 'open circuit' which is why R528 and R529 are in series, not parallel. The value of R529 determines the current which would begin to turn on Q501 and regulate the drive to the CRT cathodes. Assuming this occurs at about 0.6V between Emitter and Base of Q501, using Ohms Law I = V/R that current would be approx. 0.6 / 390 or about 1.5 mA. It doesn't seem like much but bear in mind 1.5mA at 24000 Volts or so represents about 36 Watts of power. The purpose of R528 in the 'middle' of the series of resistors would be to limit the current flowing from the base of Q501, preventing damage as well as allowing it to turn on more gradually in the case of a moderate h.v. current overload, regulating the drive to the CRT cathodes rather than suddenly cutting them off altogether. Hope that helps, regards John.
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