SNAP-ON Automotive Oscilloscope MT 665 - Page 1
Forum section: electronics / testgear

author: jcrubin
author_rank: Frequent Contributor
timestamp: February 02, 2017, 03:33:55 am
content: Greetings,I will be investigating one of these in non-op condition for a friend. I was wondering if anybody has a schematic for this unit, I have had no such luck online, I believe it is from about 1977-1979.

author: jcrubin
author_rank: Frequent Contributor
timestamp: February 04, 2017, 09:50:05 pm
content: It begins.... here is the official trailer.....https://www.youtube.com/watch?v=o19R3yYx96E&feature=youtu.be

author: jcrubin
author_rank: Frequent Contributor
timestamp: February 20, 2017, 03:38:52 am
content: So I noticed that there was nothing coming from the CRT, no illumination even though the heater was glowing, no accumulation of static and no raster even though the contrast was turned way up. We made a discharge tool using a razor blade and a welding ground cable, there was no arc on the blade, so nothing discharged from the tube, ergo, no voltage. I dont have a kilovoltmeter so Ive removed this flyback module and tested the individual components, but i'm not up to speed on the actual flyback itself, which appears to output into a second box as shown.In this test a razor blade is connected to a welder ground connection. With the unit disconnected it is expected that when the razor blade touches the metal under the cap it will discharge and leave a mark. There was no discharge and no mark observed.Can I push low voltage through this for testing? 3V instead of expected 35V?Every component on this board has been individually tested for function except for the flyback, the big box uptop, and the one transistor (You can See the IT-1121 just on the left, ive just finished repairs on for transistor testing this week)Unknown box reads VARO MH919 N 01

author: james_s
author_rank: Super Contributor
timestamp: February 20, 2017, 05:58:13 am
content: That looks a lot like the classic single transistor self oscillating converter. I suspect that potted block is a cockroft-walton doubler. Is the HV circuit drawing any current? If it is, you might try disconnecting the transformer output from the brick and see if you get anything out of it, should be a few kv AC, probably a few tens of kHz. The older Electrohome G05 vector monitors used a similar HV multiplier and failure of the multiplier is somewhat common, resulting in low or no HV.

author: jcrubin
author_rank: Frequent Contributor
timestamp: February 20, 2017, 01:00:50 pm
content: I found an image for a two stage doubler, it doesnt seem like there is much testing possible besides diode for good function.If I remove the doubler, and check the outputs of the flyback, im wondering if having the entire unit on a variac would further reduce the output voltages for testing or not. Unless there was of couse a way to seperately test the doubler outside the unit and prove it broken, i could just be replacing that part, if broken.

author: james_s
author_rank: Super Contributor
timestamp: February 20, 2017, 05:48:25 pm
content: I would apply the rated voltage to the unit for testing, it may not start properly if you go much lower, and often circuits like this rely on power being applied with a fast rise time otherwise they can fail to start oscillating. A small neon indicator lamp held near the HV transformer should glow if it is functioning, or with one wire connected to the output and the other wire floating. The HV is very low current, it's not going to make a big spectacular arc or kill you or anything, we're talking microamps at just a few kV. The final anode voltage at the tube is likely only 12kV or less.A doubler contains only two diodes and a capacitor, the second capacitor is formed by the inner and outer aquadag coatings of the CRT. When they fail it's usually the capacitor in the doubler that shorts.

author: jcrubin
author_rank: Frequent Contributor
timestamp: February 20, 2017, 06:45:08 pm
content: Im just wondering, given no HV, if the best or safest way is to disconnect the doubler portion and measure the output that would go to it from the flyback, then i would know that the doubler was bad if there was voltage at that junction.

author: andy2000
author_rank: Frequent Contributor
timestamp: February 20, 2017, 07:04:53 pm
content: Quote from: jcrubin on February 20, 2017, 06:45:08 pmYou can't easily measure it because it's high voltage RF.The trick TV techs used was to disconnect the HV winding from the HV multiplier. Then see if you can draw an arc from the transformer's output wire to an un-grounded screwdriver tip (with an insulated handle!). If you get a nice bright arc, then the transformer and circuit are working.Even if an exact replacement isn't available, you should be able to find a suitable sub. You will need to determine if it's a doubler, tripler, or quadrupler.

author: jcrubin
author_rank: Frequent Contributor
timestamp: February 21, 2017, 12:47:20 am
content: Hmmm that would necessitate disconnecting the white wire from the flyback. Should I not connect another wire to it in its stead lest i draw an arc near one of the components on the board during testing?I notice you say the screw drive should be ungrounded, What would entice the arc across from the HV to the driver if its floating?also i found thishttps://www.repairfaq.org/sam/flytest.htm#flyfft

author: james_s
author_rank: Super Contributor
timestamp: February 21, 2017, 02:06:19 am
content: Capacitive coupling to the air and your body, high frequency behaves in strange ways compared to what you're used to. I would first check and see if the circuit is drawing current, that will suggest whether it's doing anything at all. Then if you can find one of those little NE-2 neon glow lamps and hold it near the transformer bobbin it will usually glow if that part is working. No connection necessary, just hold the lamp in your fingers by one of the wire leads and touch the glass part to the outside of the transformer. The output is high enough frequency that it's essentially radio waves and will ionize the gas in the bulb without a direct connection.

author: jcrubin
author_rank: Frequent Contributor
timestamp: February 22, 2017, 11:10:10 pm
content: Yeah ok i see, so its RF, we used to use florescent bulbs in the NAVY to ensure that the HF transmitters werent operating when ascending towers by checking for glow. I wasnt aware the output was AC waveform.

author: james_s
author_rank: Super Contributor
timestamp: February 22, 2017, 11:30:21 pm
content: Yep, a fluorescent tube will work too. The output is going to be somewhere in the area of 10-50 kHz, from the transformer it will be AC, and then the multiplier (probably doubler) in that brick will turn it into DC.

author: jcrubin
author_rank: Frequent Contributor
timestamp: February 23, 2017, 04:01:29 am
content: As I attempt to google these penn-tran part numbers and find no usable number on the CRT, i cant help but get a sinking feeling.........penn-tran was bought by a company that was bought by a company that was bought by a company. If this troubleshooting technique works. Id have to procure parts for a device where the tube may not have a viable part number for which the whole unit has no known schematic on all of planet earth.I should probably add this note too..... during testing, the two incredibly large resistors on the H/V driver board, only one got blazing hot, the other only mildly warm. Ive done individual component tests on the board for all that i can identify but decided unless this portion can be, well rectified, theres no need to go further.Insane, that there is literally NOTHING on the internet about this device....

author: james_s
author_rank: Super Contributor
timestamp: February 23, 2017, 06:51:38 am
content: Penn-Tran later became WinTron, they're notable for making the replacement HV transformers for the Amplifone color vector monitor used in a few Atari arcade games.The transformer will be a custom part, you won't find info on it but it's probably fine. If it isn't, it's really not very hard to disassemble and rewind but that likely won't be necessary. Don't worry about finding information about the CRT, it's going to be a standard monochrome CRT, they're all electrically very similar.Did you try disconnecting the transformer from the multiplier? Did you measure the input current draw of the HV board? Have you tested the power transistor?This is really not a difficult repair. You could pick up a cheap modern flyback transformer from ebay and wind a new primary and feedback winding on the exposed core, rig it up and it would probably work just fine. It's really not very critical, all you need is around 10kV at a few micro-amps.

author: jcrubin
author_rank: Frequent Contributor
timestamp: February 23, 2017, 12:50:46 pm
content: I wont have access to the unit until saturday, thats why im trying to collect all of the information i can now. It is at an auto shop in the adjacent city.

author: Gregg
author_rank: Super Contributor
timestamp: February 23, 2017, 06:52:29 pm
content: Most of the older Snap-On scopes were made by Sun to Snap-On's specs which mostly involved relocating components, putting Snap-On's logo on many parts and building in extra planned obsolescence. The only value Snap-On may have added was convenience, financing and bragging rights at an increased price. You may be able to find schematics and parts by searching for Sun instead of Snap-On.

author: james_s
author_rank: Super Contributor
timestamp: February 23, 2017, 07:10:51 pm
content: Another option, there are some inexpensive Chinese HV modules out there, I have one I use for experimenting that was under $20 and goes up to about 15kV. I think the original HV PSU here should be fairly straightforward to repair though, it looks very much like the "Tesla coil" I made with an old TV flyback transformer and a 2N3055 when I was a kid. The circuit is very simple and uses no particularly exotic components.

author: jcrubin
author_rank: Frequent Contributor
timestamp: February 24, 2017, 03:16:52 am
content: Ive got some components on the vertical horizontal driver with 4in x4in heat sinks going direct to a fan duct. Efficient this thing was not. While I dont want to pull this off the current issue. Just for kicks here is the V/H driver

author: james_s
author_rank: Super Contributor
timestamp: February 24, 2017, 09:05:44 am
content: It's a vector monitor, similar to the ones used in classic arcade games like Asteroids. They are not particularly efficient because unlike a raster monitor where the horizontal axis is part of a resonant tank circuit, a vector monitor has to use brute force to push enough current through the yoke to rapidly deflect the beam around. The deflection circuit is a linear amplifier, similar to an audio amp except it uses current through the yoke to produce the negative feedback. It is in effect a voltage to current converter.

author: jcrubin
author_rank: Frequent Contributor
timestamp: February 24, 2017, 01:42:10 pm
content: Given both resistors are of equal rating and one is over 300 degrees and the other is mildly 100 in operation , could this be a product of the failure of the High voltage circuit or something internal to the Hor/vert board

author: james_s
author_rank: Super Contributor
timestamp: February 24, 2017, 04:30:03 pm
content: Hard to say without knowing what the resistors do in the circuit. It's possible there's a fault in the deflection amplifier, or it's possible that the input signal is not right. I doubt it's due to a problem with the HV board unless you're talking about a resistor on the HV board.

author: jcrubin
author_rank: Frequent Contributor
timestamp: February 25, 2017, 02:23:39 am
content: So in a rare moment of rational thought i said. Should there be, with all of the diodes pointed in the same direction forward voltage in one direction between the output of the doubler and the input? Or at least from this photo from the ground to output as displayedI got nothing on either, in either direction, surely i should be getting some kind of reading in one directionI set up the mighty [and newly repaired] IT1121 for diode testing you can see a control here at .1v divisionsTake a look at this section i stumbled across, i backlit these three diodes so you can see the traces, see the symbols on the board, they essentially all point in the same direction in series....Look at CR903, it has different markings than the other two in series and its dash line is contrary to the etched symbolThe diode itself tests fine, but obviously only when the leads are reversedSo I can test from the power transistor all the way TO CR903But not THROUGH CR903 to P907 wire connector as shownCan it be possible that the diode is backwards??? Its definitely different looking than all of the others. Your thoughts?

author: james_s
author_rank: Super Contributor
timestamp: February 25, 2017, 07:19:06 am
content: HV diodes are made internally of a stack of diode junctions so the forward drop is typically 5-10V per diode. Most semiconductor testers will not produce enough voltage to overcome the drop.

author: jcrubin
author_rank: Frequent Contributor
timestamp: February 25, 2017, 02:54:02 pm
content: talking about two different issues here, these are not HV diodes, ive already seen that their forward voltage drop is in and around .7V so they look like Si.Since today is the day i go down to the shop ill do all of the tests we discussed this week. on this portion however, I will see which way current flows across these diodes, to or from the wire connection, i imagine from... If it stops at that diode and goes no further ill know there is something wrong and adjust accordingly.

author: james_s
author_rank: Super Contributor
timestamp: February 25, 2017, 06:28:38 pm
content: Oh, I was confused about what was being discussed since there were some pictures of the deflection board mixed in with closeups of the HV board. I think it would be very helpful to draw a schematic of the HV board, there are only about 20 parts on it so that would not be a major undertaking. Those look like ordinary rectifier diodes, what connects to those terminals? I would expect that board takes DC power in, then it will put out the HV for the second anode, then several lower voltages. Focus will usually be adjustable up to about 500V, usually there is also a G2 or screen voltage that may be anything up to a few hundred volts, and then 50-80V for the Z amplifier that controls the beam intensity. The neck pinout of most CRTs is pretty standard so you may be able to work backwards from there to figure out what some of the signals are. Assuming it has one of the small diameter 7 pin necks this is the typical pinout counting clockwise from the gap:1. G12. K3. Heater14. Heater25. G16. G27. Focus

author: jcrubin
author_rank: Frequent Contributor
timestamp: February 26, 2017, 02:24:02 am
content: I had prepared a long list of tests conducted as we had discussed starting with the initial screw driver test , then the neon lamp test then onto various components, luckily, I may be able to spare you all of the data ive gathered.In the end ive discovered that the neon lamp test DOES INDEED WORK. Holding the neon near the flyback will cause it to glow. But only when the doubler/tripler is disconnected from the flyback. It would seem as though from what ive observed, connecting this component inhibits the operation of the flyback.Having now understood this. Can I now confirm that this device is shorted? as opposed to shorted at a given voltage (arc)What is this device (doubler, tripler)Where can i get a replacement

author: james_s
author_rank: Super Contributor
timestamp: February 26, 2017, 04:38:28 am
content: I think it's extremely likely that is the case. I suspect it's a doubler, it's hard to say for sure without xraying it. I'm not sure if there are any off the shelf parts that will work, but it's pretty easy to build one. Some diodes like this ought to workhttp://www.ebay.com/itm/4-pcs-2CLG-30KV-10mA-High-Voltage-Diode-HV-Rectifier-Tesla-Ham-/281294010312?These capacitors ought to dohttp://www.ebay.com/itm/5pcs-10KV-1000PF-102-High-Voltage-Ceramic-Capacitor-/161045380741?You can put a few in parallel if needed. The second capacitor in the doubler is formed by the CRT itself. Once you have something that works, you probably want to pot it in epoxy to prevent corona and arcing. Put it in a small plastic project box with holes drilled just big enough for the wires to go through and fill it with resin.

author: jcrubin
author_rank: Frequent Contributor
timestamp: February 26, 2017, 07:06:39 pm
content: hmmmm, Id hate to think my foray into this would be hand-jamming a doubler-trippler together without solid specification. Given that the numbers are clearly identifiable on this particular part, is there a forum, perhaps, of the video game variety that you might know of where someone might know that particular part and a suitable replacement. Also, as a short is suspected, can it be confirmed, or is it possible that it is only occurring at a high enough voltage to arc across. should i be testing from + to grn or HV to + or HV to grn?

author: james_s
author_rank: Super Contributor
timestamp: February 26, 2017, 07:40:00 pm
content: It is a custom part made for the manufacture of the scope, the part number on it is not going to be of any help anymore since it is long out of production. The Atari vector monitors were built by Electrohome and Wells-Gardner and have not been produced in 35 years. All three companies are long gone and the original doubler was never available during the time I was heavily involved in that hobby starting in the late 90s. I built several replacements just as I described above including the one in my own Asteroids which is still working fine more than 15 years later. Nobody is producing CRTs anymore at all, so nobody is building the ancillary parts either and the AC output transformer with external doubler was a 1970s thing prior to the development of "modern" vacuum potted internally rectified flyback transformers.A voltage doubler is really not a critical part, a very wide range of component values will work fine. You're not going to be able to buy an off the shelf part that will work here unless you manage to find a 30 year old spare that is close enough. You're going to have to build something yourself.

author: jcrubin
author_rank: Frequent Contributor
timestamp: February 26, 2017, 08:15:04 pm
content: I guess were building a doubler, and if need be, enough parts in stock for a tripler......Again. If there a way to prove a short in the existing unit?

author: Johnny10
author_rank: Frequent Contributor
timestamp: February 26, 2017, 11:58:37 pm
content: All those pretty pictures.Looks to me like a good source of parts for a tube amplifier.Orange drops, Sprague Atoms, 1/2 watt and higher resistors!I was going to buy one of these off Craigslist but hey, I bought a used Snap-On Verus.More money, less fun!

author: james_s
author_rank: Super Contributor
timestamp: February 27, 2017, 01:10:11 am
content: I don't see much there that is any use for a tube amplifier. There are some decent quality capacitors but probably not in the values you'd need. Equally good quality capacitors are still readily available brand new, as well as good medium power resistors that have not drifted around in value. It would be pointless to harvest a few dollars worth of old parts when you'd already be spending hundreds for a set of decent transformers and tubes.

author: Johnny10
author_rank: Frequent Contributor
timestamp: February 27, 2017, 02:21:47 am
content: That was sort of tongue in cheek.The look of the units circuit boards reminds me of the 70's era stuff I collect.In the vintage tube amp restores orange drops are still used in re-capping old boards.You are right, all those caps are long in the tooth and as you said resistors have drifted.It looks to me as though they used quality parts.I am sure this is a serious undertaking.

author: jcrubin
author_rank: Frequent Contributor
timestamp: February 27, 2017, 02:38:18 am
content: Yeah so anyway......Ive ordered the requisite components as you specified and i will put together the unit for testing, at that point ill get it back in the unit and if we can get a good result, pot it with some sort of epoxy that I image we will discuss when that appropriate. I imagine in the mean time, there would need to be physical separation of components during the testing phase to ensure that the was no arching in the doubler during testing.

author: jcrubin
author_rank: Frequent Contributor
timestamp: February 27, 2017, 03:45:02 am
content: Now ebay is just out to screw with me........eBay auction: #http://www.ebay.com/itm/HP-AGILENT-1740A-VARO-MH924A03-CRT-HIGH-VOLTAGE-MULTIPLIER-/232009615217?hash=item3604d9c771:g:znYAAOSwyDxXg8HgBut look what Ive dug up...... The one from the device is stamped MH919fromhttps://archive.org/stream/VaroSemiconductorSiliconRectifiersAndBridges1981-82#page/n161/mode/2upand this one from another datasheet lists it as a tripler with specs, but mine doesnt have a ficus connection, the only ones missing a focus connection are doublers, model MH911, clearly mine is labels as 919 though. perhaps this was built to the specs of snapon.its schematic shows no resistor but a non existing focus

author: james_s
author_rank: Super Contributor
timestamp: February 27, 2017, 05:20:40 am
content: Hey check that out, I've never seen a datasheet for one of those. That's a little different than the doublers I'm familiar with but you'll have the parts either way. You might tack solder a doubler together and try that, measure the HV at the tube if you have a HV probe, otherwise look at the picture size and focus. If the image is too large and blurry then you probably need to add another stage to make it a tripler.

author: jcrubin
author_rank: Frequent Contributor
timestamp: March 12, 2017, 06:14:59 pm
content: I just wanted to provide a quick update.The parts started to come in, it was in 3 deliveries, unfortunately by Saturday at noon only two of the required 3 had arrived. Not having enough components to do the onsite construction of the tripler we decided to push it out to next weekend. On that note, Once we have a working circuit, hopefully, will fiberglass resin be sufficient to encapsulate it in a project box? Should it be slowset to allow as many air bubbles out as possible?

author: james_s
author_rank: Super Contributor
timestamp: March 12, 2017, 11:20:24 pm
content: That ought to work, or just some ordinary hardware store epoxy. The slower the set, the less air bubbles. If you have a vacuum pump, even one of those hand operated things for automotive work you can make a crude vacuum jar for potting things but it's not really necessary. Especially if you warm the resin a bit to make it thin.

author: jcrubin
author_rank: Frequent Contributor
timestamp: March 14, 2017, 01:40:17 am
content: Guess what showed up?

author: jcrubin
author_rank: Frequent Contributor
timestamp: March 19, 2017, 02:37:04 am
content: Today was a busy day,We used the plastic case of a VW control module and door clamps to create a non metallic shell to house the new unit on the flyback housing. I built up a doubler, then a trippler, which gave out the HV needed to drive the CRT!!We were about to get a picture up and running, however the horizontal sweep board was bad... the horiz/vertical driver was working though so I was happy about this. When the horizontal sweep is fixed and im happy with the full deflection we will pot the trippler.I drove the horizontal sweep with some low voltage DC, not optimal but worked for a testBuild startFull TripplerPicture

author: Paul Moir
author_rank: Frequent Contributor
timestamp: March 19, 2017, 03:27:02 am
content: Awesome!Personally I wouldn't bother potting it at all. If worried, I might coat it in silicone but that would be about it. There's special electronics silicone that doesn't produce acedic acid when it cures, but if you cheat make sure it's completely cured before applying the HV again.I'd be worried using polyester resin; the heat, stresses and eventual cracking I think make it a pretty lousy potting compound.

author: james_s
author_rank: Super Contributor
timestamp: March 19, 2017, 04:22:09 am
content: Looks great!I love it when a plan comes together.

author: jcrubin
author_rank: Frequent Contributor
timestamp: March 26, 2017, 02:35:20 am
content: Greetings, as id mentioned , Id forgone any potting until id gotten the horiz trigger sorted out. This didnt take a whole lot of work to fix the failed circuitry and eventually I was able to make proper repairs as shown below. With that behind me the final potting was completed. The project has come far enough that Ive set the release cycle of the videos for all of this to start appearing on youtube just after my IT-1121 project, so that would be one month from now.Showing a trace! Horizontal fixedMastic to plug holes

author: maginnovision
author_rank: Super Contributor
timestamp: March 26, 2017, 07:30:38 am
content: I know this isn't usually a popular question, but can I ask why you'd go through the trouble? Or why the owner of the equipment would? It's fairly ancient and much better tools have come about to replace it. Just a show piece? They aren't even all that rare, despite the age, because they're tough to get rid of. I've seen many shops for sale with one or more jammed in storage or some other place. Anyway looks like a fun project just curious how it happened.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: March 26, 2017, 11:33:44 am
content: Nice work! But... why in the world would you need an oscilloscope to fix an old-style VW ?(1967 factory 12V Type II (Bus) owner for 17 years, drove it over 350,000 miles, drove it in Death Valley and over Independence Pass in the Rockies, always did my own work, something like 7 complete engine overhauls, 1640cc, single-port heads, Solex 28 carb, and mech. advance Porsche distributor and Bosch blue coil, same distributor and coil the entire time)

author: JPortici
author_rank: Super Contributor
timestamp: March 26, 2017, 09:20:08 pm
content: Quote from: maginnovision on March 26, 2017, 07:30:38 amdidn't you see? it has BLUE PHOSPHOR

author: jcrubin
author_rank: Frequent Contributor
timestamp: March 27, 2017, 12:46:58 am
content: Quote from: maginnovision on March 26, 2017, 07:30:38 amI usually tear folks up for post project success trolling, but since this is only yoursecond thread contributionon thewhole eevblog forum, ill dial it back a notch.... this once.1. When you start a post with "I know this isn't usually a popular question" it really means, "I'm gonna stir the shitpot." We all know this. But for you i'm going to entertain this2. There are tens of thousands of projects on this forum which may or may not defy conventional wisdom, you ask a lot of questions here for not being a contributor to anything of value, i checked.3. My justifications are my own and don't require your validation.4. You make bold statements and arrive at your own conclusions based on them6. The fact that the date codes were supplied in the thread and you pointing out that its ancient, only lends in your ability to point out not only the obvious, but the readily supplied.7. Your statement on this devices disposition, model, make, and most importantly value , shows you are presumptuous, and shallow8. Id encourage you to do a lot more reading, before writing in this forum on any thread for the foreseeable future.But yeah, fun project, thanks for asking.

author: maginnovision
author_rank: Super Contributor
timestamp: March 27, 2017, 02:00:31 am
content: Quote from: jcrubin on March 27, 2017, 12:46:58 amI really was legitimately curious, but I guess we can forget about it.EDIT: I do want to add, I helped a friend a couple years ago fix his own, few years older model, when he bought a shop. I worked in the automotive field until I retired, and I routinely put more money and time into projects than I could ever rationally justify.

author: Johnny10
author_rank: Frequent Contributor
timestamp: March 27, 2017, 02:39:27 am
content: Quote from: maginnovision on March 26, 2017, 07:30:38 amI think maginnovision had a valid question. How did it happen that you picked this project?Something I ask myself and others quite often.Why spend hours on equipment that has seen its day?My answer is always, because, I need to know how it works!

author: jh15
author_rank: Frequent Contributor
timestamp: March 27, 2017, 05:20:07 am
content: * jh15 throws cold water on the fighting dogs.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: March 27, 2017, 05:45:26 am
content: These are integral to Ted's Dynamometer's operation, aren't they? I always wanted to be one of those guys in the lab coats.What was going on with the horizontal? Anything exciting?

author: james_s
author_rank: Super Contributor
timestamp: March 27, 2017, 07:45:56 am
content: Well, I fix stuff like this now and then because it's fun to fix stuff, and it's a neat gadget regardless of how useful it actually is. I'm sure it is of some use at least on cars of a particular era. I suspect the reason so few of them actually get used is largely that the average automotive technician has no clue how to use one or what to do with the information it gives them.

author: jcrubin
author_rank: Frequent Contributor
timestamp: March 28, 2017, 02:21:53 am
content: Quote from: Paul Moir on March 27, 2017, 05:45:26 amI had that hotwheels suitcase set with the handle when i was a kid.....In the previous week id found that an accidental application of the probe to the IC caused a deflection and confirmed that the horizontal was handled on that separate board. I was looking at the circuitry and couldn't figure out why all of this effort went into the weird timing they used for it but since i knew that board was the culprit, I brought it home. I started checking all of the components but the 741 caught my eye, having messed with several on the IT-1121 project, I decided to swap them out with that one and check the known V/H values from my heathkit. Sure enough The output pin was reading positive input voltage.When I got the board back into the unit i checked the supplied voltages of +24 and -8, which sounds kinda strange but they come right off the low voltage DC power supply and i confirmed it, so I popped in a new 741 and it lit right up.The project isnt over and several things still require repair. However on primary parade we were able to hook it to a car where a known worn cam lobe was known to exist and expressed itself as predicted on the crt. Both primary and secondary parade have a test signal for exact RPM's from a signal off the coil. RPM's that send a signal to .... yup... the horizontal driver board to align all of the cylinders for testing, we can fake it for now but the other components will need to be repaired. The videos for all this will start releasing in one month.

author: james_s
author_rank: Super Contributor
timestamp: March 28, 2017, 05:11:20 pm
content: What does the scope actually connect to? How does it tell you a cam lobe is worn? Now I'm curious to know more about this thing, I had assumed it just measured ignition timing or something.

author: jcrubin
author_rank: Frequent Contributor
timestamp: March 28, 2017, 05:49:08 pm
content: Ill admit that the application of the device is a bit foreign on some of these tests. Its not like there are any in operation. Jason has been trained on them and works on older cars and specializes in air-cooled engines such as VW. Luckily we have the original Manual so ill be able to retrieve it and provide information on the tests. I may steal it this weekend. Towards the end of all this obviously the movies will migrate from repair to calibration to operation.Id be interested to see how my old shovelhead looks on the device, which can be dialed down to 2 cylinder operation so it will also work with motorcycles

author: jcrubin
author_rank: Frequent Contributor
timestamp: April 01, 2017, 10:43:27 pm
content: Yeah, so more issues, Secondary raster and parade produces no signal, it never ends.......... not the worst place ive been with this thing. Could just be a bad clamp on the cable or another 741... ANYWAY as promised!!!!!!!Though, im not at the point where I can casually go through the whole book yet, i made it my business to find this section and snap a photo

author: jcrubin
author_rank: Frequent Contributor
timestamp: April 24, 2017, 01:03:32 pm
content: The first of the movie postings start to go online this week, and while the project is not completed, still having logical issues, its still far enough along to have content.

author: jcrubin
author_rank: Frequent Contributor
timestamp: May 01, 2017, 12:27:28 pm
content: The second movie in the series is now available.

author: jcrubin
author_rank: Frequent Contributor
timestamp: May 29, 2017, 06:07:30 pm
content: Video 4 posted

author: Muxr
author_rank: Super Contributor
timestamp: June 19, 2017, 11:32:47 pm
content: +1 for vintage gear. Thanks for sharing, and nice repair

author: texaspyro
author_rank: Super Contributor
timestamp: June 20, 2017, 03:37:31 am
content: If you look at the data sheets for high voltage rectifiers, many of them have different max voltage ratings for unpotted and potted usage. I have some rated at 3KV unpotted and 20 KV potted.Also, when building high voltage circuits don't leave any sharp edges sticking out of the wiring (like cut component leads). They are sources of corona discharge and arcing. Make sure the joints are fully embedded in a smooth solder blob.And ideally you should vacuum process the potting. Air bubbles are a no-no. It's really hard to get a proper bubble-free mix with standard epoxies... even with a vacuum. One thing that helps is to add a few drops of thin silicone oil to the mix... I use silicone oil used in model race car shock absorbers.

author: jcrubin
author_rank: Frequent Contributor
timestamp: June 20, 2017, 05:34:36 pm
content: Video 6 posted

author: jcrubin
author_rank: Frequent Contributor
timestamp: June 26, 2017, 01:10:26 pm
content: Video 7 posted

author: jcrubin
author_rank: Frequent Contributor
timestamp: July 03, 2017, 01:00:42 pm
content: Video 8 postedhttps://youtu.be/ahTyNg3xj1U

author: jcrubin
author_rank: Frequent Contributor
timestamp: July 10, 2017, 01:03:01 pm
content: Video 9 posted - the end

author: texaspyro
author_rank: Super Contributor
timestamp: July 10, 2017, 03:14:06 pm
content: You can parallel two 1 ohm resistors to get 0.5 ohms. So to fix your low ohm cal, just parallel one of those one ohm resistors with another one ohm resistor.

author: jcrubin
author_rank: Frequent Contributor
timestamp: September 09, 2017, 01:17:18 pm
content: Recent movie on the buggy work shows the MT665 in full operation

author: KArnold
author_rank: Newbie
timestamp: November 15, 2017, 02:57:13 am
content: I need advice regarding my MT665. We work specifically on antique cars, mostly air cooled Franklins. The scope would be a big help. With the scope on, and the engine not running, I only see a dot on the screen. I can adjust the the dot vertically with the the vertical position adjustment. I cannot expand the dot horizontally to form a line. I can move the dot off the screen to the right with either the horizontal position or horizontal expand controls. I can move it back on the screen about 1/3 of the way from the RH side of the CRT - no further.I removed the Horizontal card and cleaned the plug and contacts with electrical cleaner. This made no difference in the above results. With the scope hooked up and the engine running I have a vertical line which appears to be be made up of more than one spike (like a very tight secondary pattern). What is the possibility that this could just be the Horizontal card, and if so, would one of you be willing to look at it?Thank you ,Kirk Arnoldkirka9152@aol.com

author: james_s
author_rank: Super Contributor
timestamp: November 15, 2017, 08:35:50 pm
content: It's obvious that either the horizontal deflection amp is not working or the horizontal oscillator is not oscillating. Why this is I can't say but it's probably something fairly simple.

author: jcrubin
author_rank: Frequent Contributor
timestamp: November 16, 2017, 04:06:42 am
content: Not to say it would be the same issue, but in my case it was the failed OPamp as shown in that movie for horizontal troubleshooting,