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 Post subject: Tektronix 453 Restoration
PostPosted: Sep Mon 08, 2014 10:35 am 
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Joined: Sep Sat 15, 2012 2:28 pm
Posts: 158
Location: Parksley, VA
I just picked up a low serial number 453. When I first powered it up, it seemed to work, got both traces clear and bright but they won't trigger. The only other issue was the fan was not working and there are two 311-0554-00 20K pots seized in it. One is the B Time/Div knob on the side and the other is the A Variable control.

I opened it up to take a good look at it and try to get the decades of dust out. I also cleaned out the pots with contact cleaner. I got the fan running, but I've noticed performance get progressively worse as I've played with it trying to get the triggering to work. At this point, I don't get either trace. If I hit the beam finder I just get a bright dot towards the left side of the screen for both traces. I've gone through reseating transistors and Nuvistors as a quick first thing to try as I've been inspecting the internals but nothing.

One other thing I noticed was that when playing with the triggering, I would get the trigger light to come on flickering and the trace would become garbage, and then I couldn't get it untriggered unless I powered down.

I did probe the low voltage supply last night, the + & - 12V and +75V voltages look fine. It's got to be something common to both traces as the problems have been the same on both since I first powered up with clean traces and no triggering to no sweeps at all at this point. For what it's worth I did verify the calibrator circuit with B+K 1465 scope that I also have.

Being new to troubleshooting a scope I just wanted to see if anybody had any advice on where to start.


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 Post subject: Re: Tektronix 453 Restoration
PostPosted: Sep Mon 08, 2014 2:37 pm 
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Location: Roanoke, VA
jsonova99 wrote:
Being new to troubleshooting a scope I just wanted to see if anybody had any advice on where to start.

a) Do you have the manual? You said "low serial number" but that is not sufficiently specific. Does it have Nuvistors or FETs in the front ends? The first version of the 453 (ca. 1965) used 8393 Nuvistors in the vertical amplifiers and trigger generators. The last version that I know of before the 453A was introduced began at serial number 20,000 (ca. 1967) and was completely solid state except for the 5642 pencil tube rectifiers in the high voltage supply. I do not know if there were versions in between.

BAMA has the manual for the Nuvistor version:

http://bama.edebris.com/manuals/tek/453/

BAMA's copy for the version with only pencil tubes is not yet complete. I first posted just the operating instructions but am only now getting the rest of the manual ready to go online, and it will likely not be online until late fall.

[Edit 18-Sep-2017] The complete 453 manual for serials above 20,000 is on my site - it is large (235 mb) because I always scan manuals at 300 dpi. [end edit]

b) Do you have a good working 'scope of specifications similar to or better than a 453? It takes a 'scope to fix a 'scope. I use my HP 1740A to fix my Tek453 and vice versa.

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Last edited by Dale H. Cook on Sep Tue 19, 2017 6:19 pm, edited 1 time in total.

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 Post subject: Re: Tektronix 453 Restoration
PostPosted: Sep Mon 08, 2014 4:12 pm 
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Joined: Sep Sat 15, 2012 2:28 pm
Posts: 158
Location: Parksley, VA
It's a pre-20000 with Nuvistors. I have a 465 that's working although due for some refurbishment. I do have a manual as well. I'm just curious if I should start by replacing the big caps or dig in as is.


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 Post subject: Re: Tektronix 453 Restoration
PostPosted: Sep Mon 08, 2014 7:51 pm 
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My 453 runs fine with the original caps. Replacing them is your choice - things are so packed inside that cabinet that it might be a chore. Modern 105 degree electrolytics are smaller than the originals, so that is a plus.

I would start by testing all of the Nuvistors with a good tube tester. Bear in mind that even if they test good they still may not work in the 453, which pushes them fairly hard. You might be better off, if you can get new ones, to shotgun all of the Nuvistors. Since they are used in the vertical preamps and in the triggering, and you are experiencing problems in both areas, replacing them might be wise.

Have you looked at the +150 unregulated, +75, +12, and -12 power supply busses where they enter both vertical preamp cards? There is also a -12 decoupling network and a -3 zener on each preamp card that should be checked. Also check all of the voltage busses where they enter the sweep and triggering sections, and the decoupling networks on those boards. I would also suggest checking the heater voltages on the Nuvistors, and the filament voltages on the pencil tubes in the HV supply with F937 pulled to disable the high voltage. These are all just general suggestions connected to what I would consider to be likely problem areas.

I don't really have any additional advice to offer, as my 453 has worked fine for the ~15 years that I have owned it aside from replacing the fan motor. It sees regular use in my shop - I used it yesterday to troubleshoot a soldering iron temperature control circuit that uses a thyristor, and it will likely see use later today when I will be working on a 1980s military transceiver.

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 Post subject: Re: Tektronix 453 Restoration
PostPosted: Sep Mon 08, 2014 7:59 pm 
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Posts: 158
Location: Parksley, VA
Thanks, good info and gives me some good places to start.


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 Post subject: Re: Tektronix 453 Restoration
PostPosted: Sep Tue 09, 2014 2:30 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Harviell MO USA 63945 (12 miles S of Poplar Bluff)
If you go to LINE triggering with a positive trigger slope and zero trigger level (keep the timebase at 1 or 10 ms/DIV), do you always have a solid sweep or does the trigger light start going nuts and the sweep go away? Have you definitely determined that the trace disappearing is lack of sweep vs. a lowering of intensity? What's your triggering source when things go off the rails and is it going off the rails with line triggering? Narrowing things down with triggering source selection will help eliminate a lot of things. I've never been a proponent of shotgunning parts, simply because I come from a philosophy of "it was working once so something must have happened to cause this one problem, so lets fix that". Unfortunately, shotgunning can often introduce new problems that will mask former symptoms of the original problem, and we don't want to do that.

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Contributing editor emeritus in Poptronics magazine, R.I.P.


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 Post subject: Re: Tektronix 453 Restoration
PostPosted: Sep Tue 09, 2014 5:13 pm 
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I don't recommend shotgunning the electrolytics, but the easiest way to determine whether there is a problem with the Nuvistors is to try known good ones or try the old ones in a known good 453, as the OP probably cannot characterize 8393s at up to 50 MHz.

All that said, however, I do not think it likely that his problems are mainly caused by the Nuvistors because the problems seem to be occurring in both channels. The power supplies are common to both channels so that seems a logical starting point.

If the OP has a digital camera and can post some photos showing the entire front panel in addition to the CRT that might help. I suggest the entire front panel in case some setting is inhibiting normal action.

He should definitely try the line triggering as you suggest as it may help to differentiate between his original non-triggering problem and the fact that, after opening it up, he now seems to have no sweep, and he definitely needs to see what happens with different triggering source selections. It may be best to attack the sweep problem first if he has no sweep in any triggering mode as correcting that will make it easier to troubleshoot triggering.

My 453 is always on the bench and can be a test bed for comparison with his. Even though mine has the FETs it is similar enough for comparison. If he needs to make some measurements on his with his 465 I can do some comparisons on my 453 using my HP 1740A which is just outside in the Explorer. Making some comparison tests would be aided by having some signal sources, say, an HP or other oscillator covering a broad range such as an HP 651B (10 Hz to 10 MHz, .3 mV to 3 V).

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http://plymouthcolony.net/starcity/radios/


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 Post subject: Re: Tektronix 453 Restoration
PostPosted: Sep Wed 10, 2014 4:47 am 
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Joined: Sep Sat 15, 2012 2:28 pm
Posts: 158
Location: Parksley, VA
Dean Huster wrote:
If you go to LINE triggering with a positive trigger slope and zero trigger level (keep the timebase at 1 or 10 ms/DIV), do you always have a solid sweep or does the trigger light start going nuts and the sweep go away? Have you definitely determined that the trace disappearing is lack of sweep vs. a lowering of intensity? What's your triggering source when things go off the rails and is it going off the rails with line triggering? Narrowing things down with triggering source selection will help eliminate a lot of things. I've never been a proponent of shotgunning parts, simply because I come from a philosophy of "it was working once so something must have happened to cause this one problem, so lets fix that". Unfortunately, shotgunning can often introduce new problems that will mask former symptoms of the original problem, and we don't want to do that.



Ok, didn't have much time to play tonight (about 10 minutes), but I did get the sweeps back. With either LINE or INT triggering and the other setting recommended above I get the trigger light going nuts and the sweep getting distorted and going away. It seems to happen no matter what the settings are at this point. It seems to be doing this every time now I power cycle. about 5-10 seconds after power up it goes nuts. It was working a for a few minutes, I had a solid sweep and the cal output was clear on both traces. It even appeared to trigger although the light did not illuminate.


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 Post subject: Re: Tektronix 453 Restoration
PostPosted: Sep Fri 12, 2014 12:52 pm 
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Location: Parksley, VA
Played some more last night just using the calibrator, for a while I could get clean traces, but then the traces would get completely distorted, and move off the screen with the trigger light flickering. It would get stuck like this, sometimes even after power cycling. Same condition I described previously and that somebody else had mentioned. What is the most likely culprit for this? All of the symptoms are common to both traces. I haven't dug into yet, and don't plan to just shotgun replace parts, but do hope to get in and start probing this weekend. I'm wondering if there's a thermal correlation, seems to work ok for 10 minutes or so than get flakey and stay that way until it's been put away for a day.


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 Post subject: Re: Tektronix 453 Restoration
PostPosted: Sep Fri 12, 2014 4:43 pm 
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Location: Manchester, MI
I hate intermittents. they'll drive you crazy for sure.

Try reseating the transistors in their sockets, you may have an oxidized connection somewhere.

Since it sometimes works, you may have a cracked solder joint or, worse yet, component lead. Get some freeze spray and, when the thing goes wonky, see if spraying different components will bring it back. It may help if you have a magnifying loupe or other device to inspect things. These kinds of problems can be extremely difficult to identify.

Sometimes, some careful tapping can help identify a problem. Use a plastic rod on the circuit boards for that.

The 46x series uses a ceramic resistor network in the HV supply. I had one scope that had a hairline crack at one of the terminals on that network. Drove me nuts before I tracked that one down.


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 Post subject: Re: Tektronix 453 Restoration
PostPosted: Sep Sat 13, 2014 12:02 am 
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The problem you describe:
Quote:
for a while I could get clean traces, but then the traces would get completely distorted, and move off the screen with the trigger light flickering.


Is that move off top or bottom? or move off to the left or right?
Or do you mean that they just disappear?

I would suggest connecting the calibrator output to both the Ext Trig Input and to a Vert Input with a BNC-T and a couple of short BNC cables. Then use External Triggering set to Normal and adjust for stable triggering.

Your described problem COULD be all in the vertical circuits, if the vert amp is going bad and "distorting" the signal amplitude and/or dc baseline which would then cause problems through the Internal Triggering.

So lets see if the Triggered light can be stable using the calibrator with no connection to the vertical circuits.

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 Post subject: Re: Tektronix 453 Restoration
PostPosted: Sep Sun 14, 2014 2:34 am 
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Joined: Sep Sat 15, 2012 2:28 pm
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Location: Parksley, VA
They drop off the bottom with a sinusoidal noise and they get very dim. I have to get a tee on Monday to try the last suggestion, but I played some more tonight. I'm definitely leaning towards temperature for one thing, the few times I tried to recreate it, it took a good 10 to 15 minutes if allowed to cool, 5 minutes if not fully cool. When operating correctly, it still won't trigger on any setting, just free runs. If I play with the trigger level knob I can get the light to flicker but it will never lock. I recreated all settings on the 453 that I had on the 465 that allowed it to lock on the 453 calibrator signal with no luck on the triggering.

So the next thing I tried was with the 465 hooked up to the calibrator output of the 453. Sure enough, the 465 locks right up on it no problem and it looks right. When the 453 eventually goes wonky, I notice that the calibrator signal now has a sinusoidal noise on the positive plateaus of the signal, not the negative. The p-p voltage is still good, but it's a very pronounced noise that appears. Verified this same behavior with my B+K 1465. Once the 453 goes wonky, there's no way to get it untriggered other than to power down and allow it to cool.


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 Post subject: Re: Tektronix 453 Restoration
PostPosted: Sep Sun 14, 2014 3:28 am 
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Location: Monte Vista, CO. USA
I am leaning towards power supply electrolytic capacitors. I know you said you don't want to shotgun any parts, but I have refurbished many Tek 24xx series scopes and have found that *all* the electrolytics in the power supply has to be replaced in order to get true reliability restored.

Have you monitored the power supply voltages with your 465 when the 453 starts going wonky?


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 Post subject: Re: Tektronix 453 Restoration
PostPosted: Sep Sun 14, 2014 4:32 am 
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Quote:
When the 453 eventually goes wonky, I notice that the calibrator signal now has a sinusoidal noise on the positive plateaus of the signal, not the negative.

That points the finger very strongly at the positive power supply level that feeds the calibrator (and whatever else).
In my 485 the cal signal generator runs on +50 and -5 power, and +15 feeds in to set the frequency of the square wave.

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 Post subject: Re: Tektronix 453 Restoration
PostPosted: Sep Sun 14, 2014 1:21 pm 
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Joined: Sep Sat 15, 2012 2:28 pm
Posts: 158
Location: Parksley, VA
Well I tried powering up this morning monitoring the +12, -12, & +75V supplies but of course couldn't get the scope to go nuts on me, stayed stable. Voltages were all stable for a good 30 minutes before the kids woke up and I had to break down. I'll try again later. I'm thinking with the cover off it was cooling better and maybe that's why I couldn't get the problem to happen.

The other issue though of not being able to trigger is still there, just free runs. I'm not sure if the problems are related or not.


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 Post subject: Re: Tektronix 453 Restoration
PostPosted: Sep Mon 15, 2014 1:33 pm 
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Location: Parksley, VA
I was curious how different the above 20000 serial number units are than the early ones? Are they suitable parts donors for one another?


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 Post subject: Re: Tektronix 453 Restoration
PostPosted: Sep Mon 15, 2014 2:21 pm 
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jsonova99 wrote:
I was curious how different the above 20000 serial number units are than the early ones?

The major difference is that the Nuvistors on the vertical preamp. trigger generator, and sweep generator boards were replaced by FETs. Aside from that they pretty compatable. If I had one of each I would use the older one as the parts donor to avoid having to replace Nuvistors.

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http://plymouthcolony.net/starcity/radios/


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 Post subject: Re: Tektronix 453 Restoration
PostPosted: Sep Fri 19, 2014 10:28 pm 
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Location: Parksley, VA
Made some progress today. Decided to go into the A Trigger Generator and swap the Nuvistor with one of a few I bought used off of eBay cheap. turned on and triggered immediately on the calibrator. Did the same on the B side as well. I may go with the earlier advice and just replace all of the Nuvistors, although they're not cheap! Checked the functions I could with the calibrator and everything seems to be working, will need a more thorough checking out though.

That's one issue potentially solved and luckily after getting that squared away, the other problem came back where the whole thing flakes out. It just so happens I had my multimeters clipped to the +75, +12, and -12 and caught the +12V dropping when this occurred. The +75 and -12 were perfectly stable. I played with the +12V pot to see if I could bring it up, but could not,. I could drop it lower, but it would not go any higher. So now I think I've isolated this problem, just need to figure out what's going on. I was even able to let it cool then power up and recreate it after about 2 minutes.


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 Post subject: Re: Tektronix 453 Restoration
PostPosted: Sep Sat 20, 2014 12:44 am 
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Location: Monte Vista, CO. USA
You have found your main problem, the power supply.

There is no troubleshooting required. Replace all the electrolytics in the power supply and you'll have it fixed.


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 Post subject: Re: Tektronix 453 Restoration
PostPosted: Sep Sat 20, 2014 1:57 am 
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Location: Manchester, MI
I wouldn't be too sure replacing the electrolytics is going to fix this.

There's only 4 transistors. Try reseating the ones in sockets or tapping/probing the parts. There's not a lot involved in that circuit. Check Q1154 and Q1159. If the voltage doesn't come up, either the pass transistors are flaky, or they're not getting enough base drive.

If you get a can of duster spray from an office supply store, you can turn it upside down and use it as a freeze spray. Hit each part one at a time with it when the supply is not working and see if you can find the part that's temperature sensitive.

That regulator depends on the +75 and -12V outputs, but you already checked those.


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