Oscilloscope horizontal issues - Page 1
Forum section: electronics / repair

author: MadeForThat
author_rank: Contributor
timestamp: October 06, 2024, 05:45:03 pm
content: Hi all, just came across a telequipment d66 scope, and powered it up with the finest spade connectors I could muster. It seems the vertical axis functions as it should, but the horizontal beam position jumps back and forth across the screen. Imagine a beam jumping from the 3 to the 9 positions on a clock, with no real rhythm or explanation. When attempting to use in xy mode the axis does react, so I don't think the amplifier circuit is fully dead, but I wonder if this jumping indicates a malfunctioning component within it. I also cannot seem to get it to sweep, so I assume the issues are related. Without a sweep I do not know if the trigger is functioning either. Any input would be greatly appreciated as my understanding of analog electronics are "not good" at best haha. Would like to start changing that

author: MadeForThat
author_rank: Contributor
timestamp: October 06, 2024, 05:56:39 pm
content: Can't post a video unfortunately, but it jumps between these 2 points randomly. A potentially helpful detail is that the axis adjustments still work to relocate the "points" and the horizontal offset between the 2 stay the same.

author: Xena E
author_rank: Frequent Contributor
timestamp: October 06, 2024, 06:35:08 pm
content: What effect does changing the horizontal timbase have?

author: rhb
author_rank: Super Contributor
timestamp: October 06, 2024, 09:56:11 pm
content: My money is on a cracked solder joint. Seriously, you can locate the area of failure by tracing the horizontal circuit and watching the vertical deflection. Rather a PITA without a schematic, but doable. Use the front panel connections to locate the sweep generator.Good luck,Reg

author: George Edmonds
author_rank: Frequent Contributor
timestamp: October 07, 2024, 02:34:09 am
content: HiMay I first say in the strongest possible terms that this is NOT a suitable repair project for someone who has little or no experience with CRT oscilloscopes. It dates from the early 1970’s where utility supply derived very lethal high and EHT voltage supplies were common,There are a number of very lethal, poorly shielded power supplies in use so unless you have been trained to work on such high voltage power supplies DO NOT WORK ON IT.There is a poor copy of the service manual on line that is easily found with Google.In the past I have had a great deal of experience with the repair of Telequipment oscilloscopes, one of the most common problems is with the fixed resistors going high in value or open circuit.Keep safeG Edmonds

author: tautech
author_rank: Super Contributor
timestamp: October 07, 2024, 08:36:00 am
content: D66 resources here:https://w140.com/tekwiki/wiki/Telequipment_D66Study hard.

author: MadeForThat
author_rank: Contributor
timestamp: October 07, 2024, 11:32:35 pm
content: Thank you all for the input! I will say the 1700v output on the transformer, immediately feeding a massive bank of caps, with absolutely nothing but air between the joints and the case, is nothing but intimidating. I will give the manual and any other documents a good study, my biggest desire is to figure out how to bleed the caps, as I read somewhere that they do not have a bleed resistor. I'm sure this is documented. I will probably end up making that wonderful "is this project worth the risk and effort" call soon.

author: rhb
author_rank: Super Contributor
timestamp: October 08, 2024, 05:12:41 pm
content: Keep one hand in your pocket if probing it live. AND use a proper probe over 1 kV. Just short the caps with a junk screwdriver. SOP first step when working on vacuum tube circuits. This is NOT dangerous unless you are very stupid. Even 300 V will hurt.A scope CRT generally has 15-25 kV on the deflection plates. I’m told that is quite painful. No personal experience, but I’ll take the word of those who have experience.The world is not safe. Never was nor ever will be. But we’re still alive.Have Fun!Reg

author: tautech
author_rank: Super Contributor
timestamp: October 08, 2024, 09:14:15 pm
content: Quote from: rhb on October 08, 2024, 05:12:41 pmThis I have never seen !CRT plate drive HV of ~150V is the more usual, sometimes much less.The HV is split to provide only 1/2 to each plate and any difference provides the beam offset to form the trace.PDA OTOH is much higherwhena CRO uses it.....4-15kV is normal and provided from a tripler or quintupler supplied from EHT which ranges from 1-3kV in most CRO's.PDA we never measure as equipment required is specialised and there are normally no test points to do so.

author: rhb
author_rank: Super Contributor
timestamp: October 09, 2024, 01:45:59 pm
content: Quote from: tautech on October 08, 2024, 09:14:15 pmWhat is PDA?My statement about the plates is incorrect. It’s the anode and cathode that run at 15-25 kV. 15 kV on a Tek 465 according to the manual, generated from the -2450V HV supply. I neglected to mention that the CRT will hold a charge. Another important hazard to be aware of. These hazards are integral to CRT TVs which were a common repair task until we got plasma and other flat panel technology. I’ve never heard of anyone being killed servicing a CRT TV though likely several people have succeeded in doing so.Sorry about the gaffe. Not been well the last few days. Very tired as in lie on bed all day for days in a row. Partly from radiation treatment for prostate cancer and something as yet unknown :-(Have Fun!Reg

author: tautech
author_rank: Super Contributor
timestamp: October 09, 2024, 07:00:29 pm
content: Quote from: rhb on October 09, 2024, 01:45:59 pmThis:QuotePost Deflection Acceleration.Only normally used in higher BW CRO's.Certainly no low BW early CRO's used PDA as they didn't need to so the EHT anode lined the CRT just behind the phosphors.QuoteGWS Reg

author: Greybeard
author_rank: Frequent Contributor
timestamp: October 09, 2024, 07:14:14 pm
content: Quote from: rhb on October 09, 2024, 01:45:59 pmPost Deflection Acceleration:https://aast.edu/pheed/staffadminview/pdf_retreive.php?url=352_32135_EC410_2012_1__2_1_A_Oscilloscope_Slides_1.pdf&stafftype=staffcourses

author: rhb
author_rank: Super Contributor
timestamp: October 10, 2024, 02:12:41 pm
content: Oddly, I had never seen a diagram of the construction of a CRO before in over 50 years of mucking about with electronics which included repairing 3 CROs, Tek 465, Dumont 1062 and a Heathkit IO-18. The IO-18 was my first scope, all tubes and incorrectly wired by the assembler.The point I’m trying to get across is that you should learn to recognize and appropriately deal with hazards.The D66 has a crap manual, but the horizontal circuit is not high voltage. The proper approach is to start at the horizontal sweep oscillator and work your way through the circuit looking for the fault. It is unlikely that you will get close to the HV section before you find it.The Tek 465 manual is a tour de force. Every segment of the circuit is explained in exquisite detail at the individual component level. Fixing a dead 465 with multiple faults is a master class in analog electronics. While it’s become common to diss analog scopes because of the incredible advantages of modern DSOs, even those are entirely analog in their physical implementation.The world is an unpredictable place. Any stray fragment of knowledge may prove vital at some future time. Working safely around lethal voltages and currents is an absolute necessity. The mains feed is more likely to kill you than the HV section of a CRO. Riding in or driving a car is *vastly* more dangerous than any electronics activity.You cannot learn certain things merely by reading. Mathematics and most fields of endeavor require *doing* things in addition to reading. I very much encourage the OP to join the Tekscopes list on groups.io and fix the D66 as an educational exercise. Then pick up a 465 for $50-100 and fix it. Once you get up to 100 MHz BW you’re in seriously gnarly territory. I spent months fixing my 465 and the 60 MHz Dumont 1062 using the wonky but adequately functional 465 to fix the horizontal of the 1062 and then using it to fix the many faults in the 465.I took the 465 to a retired Dallas area Tek serviceman for advice. He taught me a very useful technique for evaluating faults in the 465. Hit it! Seriously, clapping your hands on opposite sides or whacking the corners of the frame with a 12-14” piece of broom handle or similar piece of wood while watching the CRT is the first step with kit of that age. There is a very high probability that a cracked solder joint is the cause of the fault and this is how one can verify that with no other information. If the OP gets a single full sweep by hitting the D66, fluxing the horizontal section and reflowing with an SMD hot air gun will likely fix it.I’ve always been very proud of fixing my 465. I learned so much from that effort it’s hard to overstate. If you’ve repaired a >50 MHz CRO, you’ve “made your bones” with anyone who’s ever grappled with the task. My 465 and 1062 are both dead again after years in storage. I’m highly conflicted over repair or dispose of the 465 simply because of the manual. I prefer the 1062 because it is a true bench scope and doesn’t have a fan. Superfluous as I have a refurbished 485 that I bought as well as a 1 GHz 7104. There is no substitute for a good analog scope in certain circumstances. Fixing one is an excellent introduction to the mysteries of high BW AFEs in DSOs.Have Fun!Reg