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Old 24th Jan 2020, 6:19 pm   #21
Diabolical Artificer
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Default Re: Tektronix 585A issues.

Thanks Graham. Dropped back onto this one and still stumped. I eliminated everything that the 140v AC and 114 0 114v AC windings are connected to by lifting components, disconnecting wires, checking caps, removing and testing valves and just about every other thing I can thing of, it all comes down to this as far as I can make out. When the link K601-4 is connected by the relay latching, the main fuse blows. I subbed the wire link for a 3w 1k resistor, it lasted about 5 seconds then died.

Therefore all I can surmise is that the wire or wires from K1 connecting these windings is shorted to ground somewhere, so further investigation is needed. In the meantime what is the purpose of this link?

Lastly to try and make sense of what wire is what, I think I read that Tek used a colour code on these 500 series scopes, do anyone know where I could find this? The HT test point that Mike mentions is puzzling as the voltage legends on the chassis could correspond to several points on the ceramic wafer.

Andy.
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Old 24th Jan 2020, 8:10 pm   #22
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Default Re: Tektronix 585A issues.

Quote:
Originally Posted by Diabolical Artificer View Post
Lastly to try and make sense of what wire is what, I think I read that Tek used a colour code on these 500 series scopes, do anyone know where I could find
Didn't post #13 by coil1234 give this colour-code?
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Old 25th Jan 2020, 8:47 am   #23
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Default Re: Tektronix 585A issues.

"Didn't post #13 by coil1234 give this colour-code?" For some yes, I was thinking in more broader terms. Tek used dozens of different wire colour combinations the ID of which in a mucky 60 year old scope, wrapped in looms and somewhat similar is tricky. Easy to confuse a white with yellow stripe for white with brown stripe. The stripes are very thin too.

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Old 28th Jan 2020, 5:48 am   #24
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Default Re: Tektronix 585A issues.

Hi!

If you have, or can get hold of one from another Member, why not try one of the red button mains thermal cutout from an old Thorn 3500/8500 telly in place of the fuse?

These were rated about 4A and are ideal for tracing this sort of fault – one of these'll help conserve your stock of fuses!

To check the mains transformer, try disconnecting the original wiring from the 105V and 140V secondaries, (noting where they came from of course!), then try a 15W 240V pygmy household lamp across them – the transformer should have enough current to light it without risk of damage to the secondary windings!

Chris Williams

PS!

A "pat" insulation resistance tester will assist you in tracing this – I bet you've already probably discovered it's not a direct meterable short!

Another tip I can offer, if you have one, is to disconnect the h.t. supply leads from the h.t. rectifiers to the i/p side of the contacts of K601, (insulate them carefully!) and connect a 12V power supply in series with a car–sidelight bulb to each contact in turn and chassis (negative of PSU to chassis), powering up the 'scope after each trial – the defective line will light the bulb when K601 energises, and you can start lifting things in turn until the bulb goes out!

PPS!

I wonder if you've got a short near to where the h.t. supplies are connected to the "plug–in" connection sockets on the mainframe – there might just be a short where wiring looms, etc., are bent round the chassis, support rails or some other place like this, and the insulation has got nicked?
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Old 28th Jan 2020, 7:13 am   #25
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Default Re: Tektronix 585A issues.

Thanks Chris, some good tips there, will check and report back.

Andy.
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Old 30th Jan 2020, 4:56 pm   #26
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Default Re: Tektronix 585A issues.

One technique to use looking for a short is to apply some current limited supply and measure the voltage drop around the circuits, pcbs etc etc.


The current needs to be lowish and non-damaging as you will need to leave it connected for a while, you can either use a current source ( be sure to set the voltage limit to something sensible ) or probably better, a normal PSU / battery with a suitable series resistor. You need to be able to measure the voltage drop along wires and traces and the limitations are down to how much current, resistance of wires / traces (m Ohms) and your voltmeter sensitivity. A 6+ digit meter makes this easy even with a small currents but I imagine your 585 could pass a bit more current!

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Old 31st Jan 2020, 7:20 am   #27
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Default Re: Tektronix 585A issues.

"One technique to use looking for a short is to apply some current limited supply" That's what I would normally do Dave, power up on a CLPSU, check to see what getting hot either by touch, freezer spray or a fancy thermal camera, but this beasty is complicated having four or five different inter-dependant PSU's, though only one or two seem to be at fault, that and it's supposed to get hot it being valved.

This is also tricky in that as soon as the time delay triggers the relay, the main fuse blows, game over, so my approach has been to check every cap etc around where I think the fault could be and disconnect various parts of the circuit, power up and see if I guessed right. I've gone through a box of fuses but luckily I have a box NOS 3A Russian jobbies- tried a circuit breaker, but it wasn't quick enough.

This short as far as I can see if basically a couple of lengths of wire joining two bits of BR's, but I'm damned if I can find the short by traditional means, however Chris's idea of using a lamp to limit current is a good idea and thinking about it I could use my 500v 3A supply that has a CCS mode. I keep having a go, get nowhere, have a think, then have another go. I'll get there and hopefully be able to tell the saga of the 585A in the long hall over a few cups of mead one day after the kiddies have gone to bed.....

Andy.
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Old 2nd Feb 2020, 5:24 pm   #28
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Default Re: Tektronix 585A issues.

Andy: I can't quite get my head around the consequences of that relay kicking in, viewed from the perspective of the transformer secondaries, some of which are floating wrt ground. There's a possiblity that you have an insulation breakdown between a couple of those secondaries, and only when the supplies are "coupled" does the fault manifest itself. Bit of a PITA to actually eliminate this fault, but perhaps start by disconnecting wires from 20, 21 and use a megger from 20 to 5 etc?



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Old 3rd Feb 2020, 7:17 am   #29
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Default Re: Tektronix 585A issues.

"Andy: I can't quite get my head around the consequences of that relay kicking in" your not the only one.
In a nutshell Scope working then one day it turned off, mains fuse gone and found R670 fried, also found several diodes in D672 SC. To eliminate a short downstream I disconnected R670, R700 R's 730/31 as well as checking smoothing caps (a bit tired but not grossly leaky) and taking out all valves associated with those rails.

Every power up blows a 3A mains fuse (should be 4A but 3A works ok) good and proper, were talking black gunk and silver on the glass so fuse element vapourised. By process of elimination everything ok therefore fault seems to be K601-4 which is a short length of two wires and obviously part of K601.

A visual check reveals no dodgy insulation, a ohms check on both sides reveals no SC, therefore your idea of secondary breakdown worth checking. Interestingly a while back mains fuse started blowing at power on and not after delay so looked at mains tfmr secs, several show SC to chassis, however some of that is normal but found one diode in D702 SC.

Also a check of the mains tfmr primary showed that the pri has a very low resistance, a few ohms, I thought haha! but a similar 500 series scope tfmr I have is the same.

I'm busy on another job at present but will check the secs with that Airmec ionisation device/insulation checker (essentially a Megger) you gave me as you suggest. One question though why winding 20/21? By that do you mean check all secs or that one specifically? AFAIK that part of the circuit is fine.

Andy.

PS schematic attached again for easy reference.
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Old 3rd Feb 2020, 11:14 am   #30
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Default Re: Tektronix 585A issues.

Andy: I've read right back to try to make sense of this: can you just clarify. 1. If all the contacts of K601 close apart from 601-4, you don't blow the fuse?
2. R700 gets hot when 601-4 closes?

That's pointing to C700 issue?

3. Had diodes D702 & D672 fail?

If C700 is beyond reproach, we may be back to the transformer secondaries . Those diodes and the original fault which cooked R670 suggest that the windings 8-15 and 5-14 may have been stressed. Now, these are coupled by 601-4 closing, and the windings are adjacent on the transformer, so check with an ohmmeter with the windings isolated from the rest of the scope.

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Old 4th Feb 2020, 7:49 am   #31
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Default Re: Tektronix 585A issues.

1. If all the contacts of K601 close apart from 601-4, you don't blow the fuse? Yes.
2. R700 gets hot when 601-4 closes? Yes, at one point replaced with a 5w 1k which died. That's pointing to C700 issue? C700 and all caps in vicinity checked or replaced, fault remains.
3. Had diodes D702 & D672 fail? Some diodes in D672 replaced, can't remember if they were faulty but I just replaced with known good un's. One diode in D702 was SC after powering up and several times, and was replaced with a new one, replaced it's sister too.

"Those diodes and the original fault which cooked R670 suggest that the windings 8-15 and 5-14 may have been stressed. Now, these are coupled by 601-4 closing, and the windings are adjacent on the transformer, so check with an ohmmeter with the windings isolated from the rest of the scope. " Will do as suggested.

Thanks, Andy.
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Old 12th Feb 2020, 10:20 am   #32
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Default Re: Tektronix 585A issues.

Back on this, made a few tests with an Airmec Type 251 Ionisation Tester, which essentially is a Megger to all intents and porpoises. First I tested winding 8/15 in relation to the primary and got 11,000 meg. Next I tested wndg 8/15 to 5/7/10/14, the meter pegged on all ranges, meaning I think that resistance between these wndg's is too low for the tester to measure.

As I'm not 100% familiar with this test & tester so I got a 120M resistor and measured it, it measured pretty spot on. Next tried two 120M in series, again a reasonably accurate measurement. Lastly I measure another Tek series 500 tfmr, EG one from a 545A and got a reading of 1000M between similar wndg's.

These were resistor measurements, this tester can also apply 1kv or 10kv and listen for dialetric breakdown. I've used this test to test home-wound toroids, however I couldn't get a reading, the tester having insufficiant current or oomph. I've had similar readings on caps that have high leakage. Therefore I presume the 585A tfmr is f***ed.

I'll make a few other tests as per Chris's & Dave's suggestions, IE with a CCS PSU/bulb. more later....

Andy.

Edit, after typing this I connected the tester between gnd and wdg 8/15 + a voltmeter, I then put another meter between gnd and wng 5/7/10/14 and cranked the voltage up, the meters tracked each other bang on, IE same readings up to 500v, but even at low V, EG 11v. To confirm I attaced the meter to another wndg = no reading, so that's that, the tfmr is toast. Will have to see if the 545A tfmr will do as a replacement.
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Old 12th Feb 2020, 4:35 pm   #33
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Default Re: Tektronix 585A issues.

Worked a bit more on this, this afternoon, and got the scope working-ish. I connected a HV PSU in place of the 140v wndg by connected my PSU gnd to D672, junction of D&B, IE gnd, and the positive to the junction of A&C, D672, this with the wires off wndg 8/15. I set the PSU to 180v @ 700mA.

I got a trace, but no flyback, the trace was about 2" long, this on the .5m/Sec setting. It could be I'm not connected in the right place, I'm confused by the tap off the middle of 114/114v wndg, 7/10 which joins R700 & 702, the 325v unregulated rail. I can't see how you get any DC as this isn't rectified, or could it be that the rectified DC 180v from the D672 BR goes through D702 A&B diodes, through the 114/114v wndg?

As regards eventual restoration of this scope and replacing the tfmr with one from a 545 I have, it's a no go. The Tek 585A has a #120 - 141 mains tfmr, the 545 a 120 - 140 which is a tad smaller laminations wise. The 120 - 141 has AFAIK the same HV wndg's, EG 2 x 113v, 137v, 180v & 195v (Tek 120 - 141 has 2 x 114v, 140v, 180v & 198) but the 120 - 140 has 7 x 6.3v HTR wndg's, whereas the 120 - 141 has 8 + a 15.4v wndg for 12v regulated HTR's. Also shown on the 585A schematic is a 37v DC fan wndg, but on my scope, ser # 012823, I can't see a DC fan anywhere.

I've had a good look in my shed for a 140v tfmr, the idea being to replace the 140v wndg on the main tfmr, but can't find anything suitable. If the Tek 585A uses a similar 140v 0.8A wndg, that means quite a big 120VA at least tfmr. Finding room for this isn't going to be easy, but doing it this way is preferable to A) replacing the 120-141 with the 120-140 + a separate 15v & 6.3v tfmr B) stripping the tfmr and rewinding (easy if the compromised wndgs are easy to get at, but the chances are I'd have to rip out numerous wndg's to get to them)

Andy.
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Old 12th Feb 2020, 5:37 pm   #34
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Default Re: Tektronix 585A issues.

Transformer winding spec attached. The bad news is that the 140V winding is right in the middle of the winding pack.

Craig
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Old 13th Feb 2020, 7:02 am   #35
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Default Re: Tektronix 585A issues.

Thanks Craig, thought so, bummer, where did you find that? I looked but found only old threads in forums. That also confirms my suspicions that the wndgs in question are next to each other, bit of a FU for Tek there if they knew the wndg's would be connected in circuit makes sense to separate more thoroughly.

Andy.
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Old 13th Feb 2020, 9:48 am   #36
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Default Re: Tektronix 585A issues.

Tested the PSU voltages this morning, all spot on but I had to stop using my HV PSU as it went into current limit. I changed to using my variac and iso tfmr in place of the 140v wndg.

The traces are there stop short of the RHS of the screen, despite adjustment of X knob, see pics. Would I be right in thinking this is a hor amp issue? Top trace also off center. I'm still trying to figure out what caused the original fault.

Andy.
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Old 13th Feb 2020, 9:50 am   #37
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Default Re: Tektronix 585A issues.

The vast depository for all things Tek is here http://w140.com/tekwiki/wiki/ . Well worth a browse. Among many other things here are two large pdf's of winding data for Tek transformers (including HT and micro toroids). The winding data I sent above came from there. From the Replaceable Parts Registory for transformers, the same mains transformer was fitted to the 581, 581A, 585 and 585A.

They are scans from the 20,000+ Tek fiches set by https://vintagetek.org/.

There is also a document on Tekwiki that describes the winding processes that Tek used. That involves vacuum impregnation. So even if you got the transformer out, you would not be able to easily off-wind back to the 140V one. Although there might be room on top of the winding pack to put a new 140V winding, now you know how many turns and what guage.

The place you could have been able to buy one from Deane Kidd in the US alas got old, went into a nursing home and is now at the great Tek factory in the sky. You could try Walter Shawlee at https://www.sphere.bc.ca/test/tek1.html and see if he has one.


Craig

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Old 13th Feb 2020, 10:55 am   #38
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Default Re: Tektronix 585A issues.

Thanks Craig. I looked there first but i guess you have to go searching and also know what to look for, what it's called etc. At the moment I'm trying to get this working to see if sourcing a new tfmr or whatever is justified, so far the answer is yes.

Back to trying to find out why the trace is off it seems there's a fault somewhere with the miller runup circuit, B171 is unlit. Checked B171 = ok. Also checked R173 as suggested in the manual and swopped a known good ECC88 for V173. Looking at the schematic there aren't many DC voltages given so I need to look at waveforms I think. I'm winging it as usual, not having much of a clue how this circuit works.

Andy.
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Old 13th Feb 2020, 4:33 pm   #39
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Default Re: Tektronix 585A issues.

Pity you are so far away, Andy! I'm sure that between us we could crack this. But Seaford is 3 hours drive each way from my neck of the woods.

But you are pretty close to Ben Duncan in Tattershall, who might be able to help out. http://www.benduncanresearch.com/ . He's a mate - mention my name.

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Old 13th Feb 2020, 4:43 pm   #40
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Default Re: Tektronix 585A issues.

Spent the afternoon fault finding, fault still present. Checked all DC rails, all correct and free of ripple. Checked DC voltages around B171, EG -150v, 350v & 500v, all correct. Tested V152 = ok & replaced V161. Also checked R's and C's around B171, all within spec/no faults found.

Took readings as per schematic in post #38, the ones in light grey, these are with the stability control, CCW & CW. - first figures in brackets as per schematic.
Cathodes V173 (+5.4v/-10.5v) +68v/-8.7v.
Pin 7/R172 (+44v/-23v) +60v/+21v.
V161 pin 6, anode (+29.5v/+98v) +33v/+115v.
Lastly V183 cathode (-62.5/_62.5v) -95v/70v.
Voltages on legs of neons B167 (lit) 55v, B171 (not lit) 12v approx, 60v at the top, 68v at the bottom. Presume latter is low and wrong, also something wrong with/around V173 & V183.

Scoped and got waveforms as per schematic on V173 & V183. i then put a 400hz sine into the plugin and got distortion, what the manual calls non-linear traces I think, see pics. Adjusting the X position knob also effects the trace length as well as position, see pics. The last pic is interesting, Y amplitude is maxed out, but the part of the LHS CRT display is smaller than the RHS, IE trapezoid rather rather rectangular.

All this is very confusing as it looks like a combination of TB A fault as well as Y amp fault with possible CRT faultAny help guidance where to look much appreciated. Andy.

Edit Craig posted at same time. Yes, am a bit out of my depth here, will try Ben, thanks Craig, much appreciated.
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