| John-Del <ohger1s@gmail.com>: Jun 05 11:57AM -0700 On Tuesday, June 5, 2018 at 12:05:29 PM UTC-4, John Robertson wrote: > > I'm not crazy about adding resistance to drop voltage on any load that's dynamic. If you scope the collector of the horiz output with and without a dropping resistor, you'll see the waveform will be different. You may have short horiz output transistor life. If the monitor uses some sort of series/pass regulator (most 70s regulators are) you can drop the voltage by playing with the regulator and keeping the supply tightly regulated to the fly. > Dropping the system B+ reduces the vertical deflection too much to be > useful. Is the vert B+ sourced from the LV regulator? If you have to use series resistance to lower B+ to the primary of the flyback, I might try adding capacitance on the far side of the resistor to stiffen it. |
| John Robertson <spam@flippers.com>: Jun 05 12:30PM -0700 On 2018/06/05 11:57 AM, John-Del wrote: >> Dropping the system B+ reduces the vertical deflection too much to be >> useful. > Is the vert B+ sourced from the LV regulator? Schematics link is above. The vertical deflection is driven from the B+ (120VDC) directly. > If you have to use series resistance to lower B+ to the primary of the flyback, I might try adding capacitance on the far side of the resistor to stiffen it That is probably a good idea, I will check that with my 'scope. Need to adjust the Horizontal Blanking pulses to transistor X304 as the picture is being clipped way too much on the left side. I'll post some photos later. Currently working on another project which is related to WPC pinball games and their real-time clocks when using NVRAM. Then back to the GO7! Thanks, John :-#)# -- (Please post followups or tech inquiries to the USENET newsgroup) John's Jukes Ltd. MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3 (604)872-5757 (Pinballs, Jukes, Video Games) www.flippers.com "Old pinballers never die, they just flip out." |
| Dimitrij Klingbeil <nospam@no-address.com>: Jun 06 12:06AM +0200 On 05.06.2018 00:30, John Robertson wrote: > to 25KV which is 10% over their original maximum rating and my > concern is an increase of soft X-Rays. My HV probes show somewhere > around 25 to 30KV for the 19" flyback when used in a 13" chassis. Hi According to the numbers you provided, the EHT needs to be reduced by about 7 kV (while keeping other voltages derived from the transformer at their usual levels). The 7 kV difference is significant, but not insurmountable for a series dropper approach. The current draw of a CRT anode is small, the power dissipation should still be manageable: 7 W at 1 mA (if the CRT ever takes that much current). There are TVS diodes with voltages up to 600 V (nominal value at 1 mA test current) available (Littelfuse P6KE600A). A series string of 12 such TVS diodes will have around 7 kV of voltage drop across them. The continuous power handling capability should be enough (each TVS of this size can dissipate over 1 W, with heatsinking even multiple W). The TVS diodes are reasonably cheap (some 40 cents a piece at Mouser for QTY 10), so the main difficulty would probably be the insulation (potting) of the series string. Probably best to put the whole thing into a long insulating tube and fill the tube with epoxy. Regards Dimitrij |
| John Robertson <spam@flippers.com>: Jun 05 05:16PM -0700 On 2018/06/05 3:06 PM, Dimitrij Klingbeil wrote: > into a long insulating tube and fill the tube with epoxy. > Regards > Dimitrij Interesting idea Dimitri, however I don't see it working out - 12 diodes in series would make the anode wire ungainly at best. Then insulating, etc. where I think the average tech probably won't have HV rated epoxy or silicon glue. Appreciate the idea, and may use it elsewhere! Another poster had suggested changing the capacitance at the Horizontal Output transistor X01, and indeed that did work! I now have 19KV on the HV output, screen looks normal and all is well. Obviously I need to brush up on my Horizontal Output theory so I can understand why this worked, but for anyone reading this I added 2 X 2200pf @ 1500V and one 1500pf @ 1500V caps. Took them off a dead GO7-CBO - 19" chassis. Thanks! John :-#)# -- (Please post followups or tech inquiries to the USENET newsgroup) John's Jukes Ltd. MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3 (604)872-5757 (Pinballs, Jukes, Video Games) www.flippers.com "Old pinballers never die, they just flip out." |
| John Robertson <spam@flippers.com>: Jun 05 05:19PM -0700 On 2018/06/04 5:53 PM, John-Del wrote: >> John :-#)# > I wouldn't worry so much about the HV as I would about the filament. If the filament voltage stays at or below 6.3, I wouldn't give it another thought. Most of those tubes have no trouble with a few extra KV. If the filament is high, drop that or the tube will have a life span emissions-wise in months. > Another way of lowering the global output of the fly is add some capacitance to the retrace cap. This will of course affect all the secondaries. You (John-Del) suggested changing the capacitance at the Horizontal Output transistor X01, and indeed that did work! I now have 19KV on the HV output, screen looks normal and all is well. Voltages are all nominal, but I will compare with a proper 13" chassis that is still using the original flyback/LOPT. Obviously I need to brush up on my Horizontal Output theory so I can understand why this worked, but for anyone reading this I added 2 X 2200pf @ 1500V and one 1500pf @ 1500V caps. Took them off a dead GO7-CBO - 19" chassis. > I'm not crazy about adding resistance to drop voltage on any load that's dynamic. If you scope the collector of the horiz output with and without a dropping resistor, you'll see the waveform will be different. You may have short horiz output transistor life. If the monitor uses some sort of series/pass regulator (most 70s regulators are) you can drop the voltage by playing with the regulator and keeping the supply tightly regulated to the fly. Thanks! John :-#)# -- (Please post followups or tech inquiries to the USENET newsgroup) John's Jukes Ltd. MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3 (604)872-5757 (Pinballs, Jukes, Video Games) www.flippers.com "Old pinballers never die, they just flip out." |
| jurb6006@gmail.com: Jun 05 09:48PM -0700 Nice to find someone willing put put effort into shit like this. I commend it. And to use pretty high tech skills to do it, like about engineers level, modifications and KNOWING what works right and doesn't. Have any idea how hard it is to find people who CAN do that, let alone willing ? Keep it alive bro... (het, sounds like a good name for a company) I'll put my suggestions first and commentary later to be sufferable... The components around R 516, C 519 etc. have nothing to do with the HV level. They are for the ABL, they measure the actual HV current and cut the video gain down if it exceeds a certain level. There is not supposed to be voltage dropped there like in a CRO. Notice the difference in the print around C 512 - 514. The 19" version has 2 extra caps there. They downed C 514 down to 2,ooo pF from 2,500. Then they added C 531 & 532. which slows down the retrace, makes all retrace rectified sources lower and trace rectified sources a little bit higher. You can tell which it is by scoping the input the the rectifier, if you see a large negative trace on a positive source it is trace rectified, if the pulse is positive on a positive source it is retrace rectified. Question : this potted fly, CAN YOU GET TO THE CORE ? You do not have to get to the windings, if you can get to the core you can add bucking or boosting windings to any winding there. All that area that is encapsulated, can you see the ferrite thing around it ? If so, can you see a gap ? All we need is about 0.03 inches for good enough. That is big enough for # 24 AWG to get through and you can get it with like couple hundred volt insulation. Increasing the capacitance alone might not do it, but a combination of changing the B+ and that might. Comment : This thing was built before internal pincusion correction in the CRTs. There is a saturable reactor and another one that is permanent magnet biased. there are also VDRs. This means that This indicated that voltage and current levels muct be at least close for good geometry. We are not talking moon shot accuracy here but we must remain within the "linear non-linearitiy" operating range of those devices. It also seems that the B+ is lower in one than the other.; One says (somewhere) 120 regulated and the other says nothing, but both shutdown use the same resistors and Zeners, and that indicates that the B+ level is close if not the same. If, after adding the capacitance I suggested you find that it is not enough then the next thing is to reduce the B+. but don't do it with a passive device. The best method would be to add a Zener diode of the voltage desired with the anode to ground and the cathode to to the junction of C 905 & R 914. You'll probably want to choose a standard value anyway so choose a lower one and put a pot in series. It might decrease the tightness of the regulation but bucking that we had the gain of the IC itself. Look at most of them, they try to operate in their linear range. That works to our advantage. Keep this baby on the road ! |
| jurb6006@gmail.com: Jun 05 09:52PM -0700 >"Series resistors may not work well, a string of MOVs might be better. " True, but MOVs dissipate power. |
| jurb6006@gmail.com: Jun 05 09:56PM -0700 >" Have you checked the mfr specs of the tube? I doubt it's speced to 30kV but it's worth knowing exactly what you need to get it down to. " No 13" tube is speced that high, even in Zimbabwe. |
| Terry Schwartz <tschw10117@aol.com>: Jun 06 08:12AM -0700 Given the thickness of the leaded glass on those CRTs, I doubt X-rays are a concern. But you could always have the gamers wear tin-foil hats. |
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