Newbie with Tek 465 - Page 1
Forum section: electronics / repair

author: Restorationnut
author_rank: Contributor
timestamp: August 28, 2020, 07:48:37 pm
content: Hi All,First post on this forum. I spend all my time restoring pre WWII radios, and being active on the two main antique radio forums.But I thought I'd take a break, and get my 465 working. Haven't done much "modern" stuff (after 1960).So I need a little assistance. Power on, get a few lights, but display is dark. Grid illumination works. When I turn the intensity knob, I get an intermittent fuzzy dot. I should preface this by saying the last time I turned it on (a year or so ago), it worked, but any waveform wasn't really stable.Time to play. I started by checking the fuse. It's good Then on to the voltages. All are low. +55 was around 39. Manual says it could be a leaky filter cap. I hate those can electrolytics anyway. So I thought I'd start by changing them. I removed the trigger board to get to them, and removed all 5. They are not 'lytics I use, so I had to order them. But while I wait...As I removed the trigger board, I noticed two wires (about 22 ga.) branching off. They are attached to the timing board on one end, but were broken off where they attach to the trigger board. I can't seem to find where they go, and can't easily find them in the service manual.They are, of course, the two wires circled in red in the pic. Can someone tell me where they go? Thanks for reading.

author: Labrat101
author_rank: Unknown
timestamp: August 28, 2020, 08:49:52 pm
content: this is an an oldie I would check the power section if all the voltage are low .and check the caps in this section first start with the big 400vdc cap and work though the power supply . Make sure you discharge the caps first .The other wire you marked don't know without diagram .its a thin wire so its probable low voltagethe power supply section sounds like your problem and a faint screen also confirmsget the 55v sorted .I would leave the trigger board alone until you solve the power problemI looked also on the manual there a few variation on this model is it the 465A ??as the voltages differ on versions 60v . Make sure you use the correct service manualits downloadable from Tektronix archive . follow there trouble section sec 40/6it gives all the voltages on the pins etc . be careful not to loose the NVRAM or you will loose all the calibration and its a pain in the ass to recal . .. I have done a few TEks not this model .

author: Restorationnut
author_rank: Contributor
timestamp: August 28, 2020, 09:07:22 pm
content: Quote from: Labrat101 on August 28, 2020, 08:49:52 pmThanks, but I think you may have misread my post.

author: Labrat101
author_rank: Unknown
timestamp: August 28, 2020, 09:42:32 pm
content: Quote from: Restorationnut on August 28, 2020, 09:07:22 pmFrom that picture No .. maybe the black plug make a better photo of the area .When a wire pulls off there are usually tell tell signs you will have to look close plus need the model and year is it the A does it have the option brds .. ??to find it on the circuit one need to know where the other end goes ..

author: jdragoset
author_rank: Frequent Contributor
timestamp: August 28, 2020, 09:52:58 pm
content: If it is not a 465 A, tell the the SN above/below.If it's the same range as mine (recall above 22000) I will pull the cover and look

author: Restorationnut
author_rank: Contributor
timestamp: August 29, 2020, 01:48:10 am
content: Quote from: jdragoset on August 28, 2020, 09:52:58 pmThanks. No, not an A. Serial # is B260117.

author: med6753
author_rank: Super Contributor
timestamp: August 29, 2020, 04:26:05 am
content: There was no "465A". There was a "465" and "465B". And the Vertical and Timing boards are vastly different.I have a 465 carcass sitting in my spare parts stash. I'll pull it out tomorrow and see if I can identify the wiring in question.

author: Restorationnut
author_rank: Contributor
timestamp: August 29, 2020, 09:54:08 am
content: Quote from: med6753 on August 29, 2020, 04:26:05 amThank you.

author: Labrat101
author_rank: Unknown
timestamp: August 29, 2020, 11:19:33 am
content: Quote from: Restorationnut on August 29, 2020, 09:54:08 amYou should read the original TEK service manual the first series was not always marked with 465 (A)on the front panel as it was the first series .but its on the brd . ref. The B serials comes after the 'A' durr..and there is a big difference between the 2 models .. Time base board & the PSU voltagesThere were also option brds as well .They may look similar by eye .Case closed

author: med6753
author_rank: Super Contributor
timestamp: August 29, 2020, 12:06:16 pm
content: Quote from: Labrat101 on August 29, 2020, 11:19:33 amOK, who pissed in your wheaties this morning?Tek was always revising their equipment resulting in boards and other assemblies possibly being labelled with an "A" revision or "B" revision but usually it just resulted in a part number change which later prints of the manuals would list and the serial numbers affected.The point here is that there was never a 465 officially labelled and sold as a "465A". There was a "465" and "465B".Maybe you need to fill out one of these.

author: med6753
author_rank: Super Contributor
timestamp: August 29, 2020, 12:39:32 pm
content: Quote from: Restorationnut on August 29, 2020, 09:54:08 amI think this is what you are looking for. Both those wires come out of that harness and attach to that sub board under the main timing board. This 465 originally had a DM44 so there's some additional wiring that yours may not have. (Which I removed to make the picture clearer). If you need anything else let me know.

author: Restorationnut
author_rank: Contributor
timestamp: August 29, 2020, 02:04:03 pm
content: Thanks. Well.....we're getting close. It's the OTHER end of those two wires that connect to the trigger board that I need. Even after inspecting the trigger board closely, I can't see where they attached.

author: hnjmkl
author_rank: Regular Contributor
timestamp: August 29, 2020, 02:10:29 pm
content: I am not aware they had NVRAM

author: med6753
author_rank: Super Contributor
timestamp: August 29, 2020, 02:31:58 pm
content: Quote from: Restorationnut on August 29, 2020, 02:04:03 pmOK, I undid the harness and here's the results. The wire from the FAR right on that sub board goes to the LEFT point as shown on the Timing board. And obviously the wire from the LEFT side of the sub board goes to that RIGHT point.Edit....it's those two 100 ohm resistors on the top side of the timing board.

author: med6753
author_rank: Super Contributor
timestamp: August 29, 2020, 02:33:40 pm
content: Quote from: hnjmkl on August 29, 2020, 02:10:29 pmThe 465/465B doesn't. Just another piece of misinformation. The calibration on these scopes is old school analog twist pot.

author: Restorationnut
author_rank: Contributor
timestamp: August 29, 2020, 02:41:57 pm
content: Quote from: med6753 on August 29, 2020, 02:31:58 pm

author: med6753
author_rank: Super Contributor
timestamp: August 29, 2020, 02:45:13 pm
content: Quote from: Restorationnut on August 29, 2020, 02:41:57 pmYou're welcome.If you need anything else post up. I have lots of experience with these scopes.

author: Restorationnut
author_rank: Contributor
timestamp: September 02, 2020, 04:19:17 pm
content: Now that I have the caps replaced, I started checking voltages. All look O.K., EXCEPT no -8V. Looks like I need to pull the board to be able to check CR1561. Any suggestions? By the way, would the lack of -8 V be the cause of no trace?

author: med6753
author_rank: Super Contributor
timestamp: September 02, 2020, 04:24:42 pm
content: Quote from: Restorationnut on September 02, 2020, 04:19:17 pmYes, without -8V chances are there would be no trace. Check to make sure the -8V bus isn't shorted to ground. If it is that would indicate a possible shorted tantalum capacitor on one of the boards. The manual does give a isolation procedure for tracking down which board has the short.

author: Restorationnut
author_rank: Contributor
timestamp: September 02, 2020, 04:40:32 pm
content: Thanks, Already eliminated the trigger board, so I will continue!

author: Restorationnut
author_rank: Contributor
timestamp: September 02, 2020, 06:37:13 pm
content: Not shorted, but I found C1220 had been leaking (visual). It should be 1000 mfd @ 10V, but it measures around 455. I assume this is a Tantalum (never worked with them before)? I don't see where either Mouser or Digikey has them. Can I use a regular electrolytic?C1220 is tied to a 22Ω resistor in the horizontal amp circuit, and has -8V applied to it.

author: med6753
author_rank: Super Contributor
timestamp: September 02, 2020, 07:36:32 pm
content: C1220 would be an aluminum electrolytic, not tantalum.

author: Restorationnut
author_rank: Contributor
timestamp: September 02, 2020, 08:31:23 pm
content: Thanks.

author: tggzzz
author_rank: Super Contributor
timestamp: September 02, 2020, 09:02:57 pm
content: Quote from: Restorationnut on September 02, 2020, 06:37:13 pmThat will be specified in the manual.If it is leaking then it is unlikely to be a tantalum. When very expensive milspec wet slug tants leak, PCB tracks completely disappear

author: Restorationnut
author_rank: Contributor
timestamp: September 03, 2020, 12:25:53 am
content: Quote from: tggzzz on September 02, 2020, 09:02:57 pmI finally found it in the manual specifying which are tantalums and which are not. So old tantalums have a habit of shorting?

author: med6753
author_rank: Super Contributor
timestamp: September 03, 2020, 01:38:22 am
content: Quote from: Restorationnut on September 03, 2020, 12:25:53 amYes, the beaded tantalums are notorious for shorting and the 400 series Tek scopes are loaded with them.

author: tggzzz
author_rank: Super Contributor
timestamp: September 03, 2020, 06:26:46 am
content: Quote from: Restorationnut on September 03, 2020, 12:25:53 amYes, tantbeadsdo short circuit. There are many many references giving many examples of that.We now know that it is sensible to derate the tant beads voltage so that the DC voltage aross them is less than, say, 2/3 of the rated voltage.

author: Restorationnut
author_rank: Contributor
timestamp: September 03, 2020, 09:04:07 am
content: Quote from: tggzzz on September 03, 2020, 06:26:46 amObviously, I'll need to check each tantalum. But should I just replace them all with aluminum electrolytics or film, or reduce the DC across them? And in the second case, how would I do that without calculating and adding a series resistor to each one?

author: tggzzz
author_rank: Super Contributor
timestamp: September 03, 2020, 09:39:31 am
content: Quote from: Restorationnut on September 03, 2020, 09:04:07 amThere is no uniquely right/wrong solution, except that reducing the applied voltage is not an option, of course.There are many discussion of the topic on this forum and elsewhere, e.g. TekScopes. There's no point in my repeating some of them poorly!Start by replacing tant beads with tant beads with an appropriate voltage rating. Simply replacing a 15V tant on a 13V line, as in the 485, would not be wise

author: med6753
author_rank: Super Contributor
timestamp: September 03, 2020, 10:12:34 am
content: Quote from: tggzzz on September 03, 2020, 09:39:31 amReplacing them all in a 465 will be a quite expensive proposition. And if the design originally called for a tantalum in general you should replace with same. My experience with these little buggers is that the higher values, approx 15uf to 47uf, tend to be the most trouble prone. And 47uf the worst of them all. Start with those values if you decide you want to replace them. That will cover the vast majority of the magic smoke releases.Edit, and if the original cap was rated at 25V and the applied voltage is 15V or greater replace with a 35V rated part.

author: Restorationnut
author_rank: Contributor
timestamp: September 03, 2020, 10:30:04 am
content: Understand. Do you have a specific source for the tantalums? My normal suppliers don't carry them.

author: tggzzz
author_rank: Super Contributor
timestamp: September 03, 2020, 10:35:34 am
content: Quote from: Restorationnut on September 03, 2020, 10:30:04 amhttps://octopart.com/https://www.findchips.com/Note that in many cases a precise equivalent is not necessary. Classic example is PSU line decoupling caps.

author: Restorationnut
author_rank: Contributor
timestamp: September 03, 2020, 10:42:55 am
content: Quote from: tggzzz on September 03, 2020, 10:35:34 amThank you.

author: med6753
author_rank: Super Contributor
timestamp: September 03, 2020, 11:36:55 am
content: Quote from: Restorationnut on September 03, 2020, 10:30:04 amMouser has exact replacements.

author: Restorationnut
author_rank: Contributor
timestamp: September 11, 2020, 04:03:22 pm
content: Well....not having much luck. It's not easy trying to get to the back side of the interface board.Still no -8V. I followed procedures to isolate the CRT circuit. No luck. Then isolate the horiz. amp. No luck. Replaced all the electrolytics, and a lot of the tantalums. No luck. Checked all the rest of the tantalums: all check good.Removed the bridge rectifier (CR1561). It tests good. However, with the rectifier in the circuit, I only get +3V AC from the transformer. Can't see any way to disconnect the bridge in order to retest the secondary winding.All other voltages check O.K. When I move the intensity knob back and forth, I get a blip on the screen.I'm now officially lost.

author: med6753
author_rank: Super Contributor
timestamp: September 12, 2020, 12:02:05 am
content: Quote from: Restorationnut on September 11, 2020, 04:03:22 pmWhen CR1561 is removed what is the AC voltage from the transformer across pins 21 and 22?

author: Restorationnut
author_rank: Contributor
timestamp: September 12, 2020, 01:53:28 am
content: Quote from: med6753 on September 12, 2020, 12:02:05 amThat's the next problem. I can't seem to figure out how to remove CR1561 from the board without lifting the board up. And I can't lift the board up without removing the two adjacent boards. And that means removing all of the connecting wires. And at that point, I wouldn't dare apply power. Catch 22. It's only pins 21 and 22 on the schematic. The transformer is wired directly to the interface board at two points: 6 and 6. and have to remove the interface board in order to gain access to the bottom, where the wires are attached.They certainly didn't make this simple. Am I missing something? Why would they hard-wire the xformer directly to the interface board?

author: med6753
author_rank: Super Contributor
timestamp: September 12, 2020, 03:41:25 am
content: OK, I just did a comparison between the -8V supply in a 465 vs a 465B and they are almost identical. The only difference is the 465B has a 5 Amp fuse between the transformer and the bridge rectifier which the 465 lacks and the value of the main filter cap is different. So tomorrow morning I'll pull the case on one of my functional 465B's and take some resistance readings at various points and pass them on to you. I still suspect the supply is shorted on the output and this will settle that.

author: med6753
author_rank: Super Contributor
timestamp: September 12, 2020, 10:01:54 am
content: OK, as promised I pulled a 465B out of the case and took some measurements.-8 TP. Measures 47.1 ohms referenced to ground (chassis). Now your 465 might measure a little lower since it has a higher discrete vs integrated component count. But I would think it should measure no lower than 30 - 35 ohms. The voltage is right at -7.99VTransformer secondary. Measures 11.4VAC at the rectifiers.C1562. Measures +12.9VDC across it.Pay special attention to R1569 (1.1 ohm) on the emitter of Q1566. I've seen it burn up before. Make sure CR1564 is OK. Verify all the resistors around U1554B.Hope this helps. I will leave this 465B out of the case for the rest of the day if you need additional measurements.

author: Restorationnut
author_rank: Contributor
timestamp: September 12, 2020, 11:09:43 am
content: Quote from: med6753 on September 12, 2020, 10:01:54 amYou are going above and beyond, and I really appreciate it. I'll reply once I make the measurements.

author: Restorationnut
author_rank: Contributor
timestamp: September 12, 2020, 01:14:33 pm
content: O.K. Got my 12VAC back at the transformer. Broken wire. -8 to ground is 50Ω. Still nothing across C1562. R1569 is 1.2Ω. CR1564 is good. All resistors around U1554B are within tolerance. Even though I get 50Ω between -8 and ground, CR1569 shows short both directions on my diode tester.

author: med6753
author_rank: Super Contributor
timestamp: September 12, 2020, 01:47:06 pm
content: Lift one side of CR1569 and check it again. If it is indeed shorted that would explain no output. But it doesn't explain how you measure 50 ohms at the TP to gnd. It should read short also. Perhaps that diode only shows short in the presence of a higher voltage than your ohm meter can provide. If true that would be an unusual event.Note: you can pull and install components from the front side of that double sided board. It has fully plated feed thru's.

author: Restorationnut
author_rank: Contributor
timestamp: September 12, 2020, 01:55:08 pm
content: Quote from: med6753 on September 12, 2020, 01:47:06 pmDiode's good.

author: med6753
author_rank: Super Contributor
timestamp: September 12, 2020, 02:07:08 pm
content: Yea, I thought so. So, if you have good transformer secondary (12VAC) but nothing across C1562 that basically leaves 2 things. Either there is an open somewhere or bridge assembly CR1561 is bad.

author: Restorationnut
author_rank: Contributor
timestamp: September 12, 2020, 02:24:01 pm
content: Quote from: med6753 on September 12, 2020, 02:07:08 pmI've already run continuity at every point on that part of the circuit, and everything checks out. I'll retest CR1561, but it did test O.K. once. Then I'll retest all components.If I still can't find anything, I guess it'll go on the shelf for a while.

author: Restorationnut
author_rank: Contributor
timestamp: September 12, 2020, 02:35:06 pm
content: Now CR1561 shows open on one side! All I have are 1N4007's. I know it's an overkill at 1000V, but can I build a bridge with those, or should I try an find something else?

author: med6753
author_rank: Super Contributor
timestamp: September 12, 2020, 02:47:04 pm
content: Quote from: Restorationnut on September 12, 2020, 02:35:06 pmThey will work just fine. Or any bridge 50PIV/3A and above will be fine.Report back if you finally have -8V.

author: Restorationnut
author_rank: Contributor
timestamp: September 12, 2020, 03:12:24 pm
content: Quote from: med6753 on September 12, 2020, 02:47:04 pmTried it twice. Double checked polarity. With it out of the circuit, I get 12VAC going into the bridge, and 11VDC coming out. But as soon as I insert it into the circuit, the lower diode smokes. Both times.

author: med6753
author_rank: Super Contributor
timestamp: September 12, 2020, 05:02:17 pm
content: From the symptoms you describe it sounds like Q1566 is shorted itself OR the collector is shorted to ground via the mounting. The mica insulator might have given way.The transistor itself is a MJE2801 which crosses to a readily available NTE182 on Amazon.Edit, when I measure resistance from the plus side of C1562 to Gnd I get almost 12MEG.

author: Restorationnut
author_rank: Contributor
timestamp: September 12, 2020, 06:10:42 pm
content: Quote from: med6753 on September 12, 2020, 05:02:17 pmFirst, I want to say thanks for all the assistance. But I've spent entirely too much time on something that I don't use, anyway. So it's going on a shelf. Perhaps in the future I'll re-visit it, and all the help you have given. But for now, it's back to radios.Thanks again.

author: med6753
author_rank: Super Contributor
timestamp: September 12, 2020, 07:36:36 pm
content: You're welcome. If you decide to continue working on it feel free to post up and we'll help you thru it. I get the feeling you are REAL close to fixing it.

author: 0culus
author_rank: Super Contributor
timestamp: September 12, 2020, 08:00:53 pm
content: Quote from: Restorationnut on September 12, 2020, 06:10:42 pmBased on reading this thread, I think you're very close to fixing it, and med here is bending over backwards to help you...why give up now? If you get it fixed, youcanuse it, rather than continuing to collect dust. I'll encourage you to take a little time off and then come back to it fresh.