Tek 453 Safe Repair? - Page 1
Forum section: electronics / testgear

author: Desertrat
author_rank: Newbie
timestamp: April 27, 2015, 05:18:50 am
content: Hello AllI'm new to the forum and in need of some advice. I have bought 2 Tek 453 from Ebay which seem to have potential. My question or maybe questions are these. First a disclaimer, I am a complete novice but have always been interested in electronics and kind of took a leap into the deep end. I am needing advice on how to make the Teks safe to work on. By sage I mean that I need to remove boards and other components to get into the solder point for the fan motor and to remove much accumulated dust. I have heard by many on YouTube and on sites how dangerous these devices can be and accept that fact and intend to do my best to be safe around them. I just need a starting point on what to do to get the charge out the unit so I can take it apart and clean it. As for the rest, the voltage measuring and so on I think I can get by with the manual but would likely be back here to pick your brains more. So, with that any and all information would greatly be appreciated.

author: tautech
author_rank: Super Contributor
timestamp: April 27, 2015, 05:42:23 am
content: Welcome to the forum.You'll need the link in this post:https://www.eevblog.com/forum/repair/repair-documents-and-links-sticky-me-please-mods/msg477909/#msg477909Plenty of links available for 453 Service manuals like this one:http://www.ko4bb.com/manuals/index.php?dir=Tektronix/Tektronix_-_453_OscilloscopeAny CRO has dangerous voltages within. Study of the CRO itself, schematics and the PCB's will reveal areas to avoid. Old documentation often has a theory or principle of operation chapter, use it as your bible.

author: smjcuk
author_rank: Frequent Contributor
timestamp: April 27, 2015, 09:14:04 am
content: I have one of them. They are quite dangerous inside. Be VERY careful. Treat it with utmost respect. Most of the caps seem to have bleeder resistors and after 10 mins I've seen no voltage but don't assume that is the case on yours or they work.The standard transformer has no isolation covers on the secondary side so there are hazardous AC voltages to get poked with at the PSU end. The main CRT potential is really high - think it's 8kvish but that is quite well protected. The standard reference potentials on the front ends are +/-12v so it's not terrible but there is 75v DC in there in a number of places which is border-line. One to watch out for is that the construction is based on boards with plugin single wires. these tend to corrode and break off and short out against the chassis and other parts so assume there's a dangerous voltage everywhere.Also they're 45-49 years old so don't assume they haven't been damaged, bodged or even that they're OK if they look like they are.Also the triggering on them is a complete bastard as it's got tunnel diodes and difficult to find FETs on it. It has been nothing but a nightmare to fix. The fan is easy to get to - it's all under the back cover which has no major safety issues once the mains is isolated. You don't have to open the main unit to deal with that.Service manual is second to none however as the poster above says.Big safety notice: wear safety glasses - old caps explode as the first warning, always probe with one hand only (other behind your back so you don't make a circuit across your chest) and make sure there's someone else on hand with instructions on what to do if you get zapped i.e. isolate and call for medical help. Never work alone on high voltage kit.There's probably more scientific approaches to the above but if this is your first repair, I'd probably start with something a little less scary.When they do work though they are REALLY nice scopes. They originally cost more than your average car of the age as well. They don't make anything like that now.Edit: also please note that there are two variations of the 453. The 1st version is serial numbers <20,000 and the latter >20,000. The early ones had nuvistors in the triggering circuits which are pretty much impossible to find. The latter ones used a FET instead. Otherwise they are the same. If you have a pre-20,000 unit, use that for parts harvest if you want one working one and fix the SN>20,000 unit. If you trace a fault to a tunnel diode, forget repairing it - they literally don't exist now.General check out is:1. Visual inspection for burn marks.2. Check supply voltages against the service manual (with a decent multimeter - see other discussions here) and that there is no earth issues.3. If that's bad, check caps, wiring and PSU transistors and replace accordingly.4. Check trace finder.5. Connect calibration source to input A via a straight BNC, set all controls to "cal" position and defaults as per service manual.6. Check timebase moves trace.6. Check vertical amp A (BNC to cal source)7. Check vertical amp B (BNC to cal source)8. Check triggering.9. Probably ok then.Edit 2 - sorry for the rambling: you usually need a scope to fix a scope past the basic issues so if one mostly works or even partially works then you can probably use it to fix the other one.

author: PaulAm
author_rank: Frequent Contributor
timestamp: April 27, 2015, 01:57:48 pm
content: Some of the free scans do not have the light blue waveforms or notes that are in the original paper docs. You can sometimes find the original paper manuals for $5-10. If you can, it's worth the money.If you have a later one with FETs instead of nuvistors, I'd try to concentrate on that, but it's not a big deal. You can buy the nuvistors off of ebay for around $5 apiece, NOS maybe a bit higher. I have spares for my 453 and 454, but I've never had to replace one.I wouldn't freak about the tunnel diodes either. They're reliable, but if you ever needed to replace one, you can find spares if you scrounge hard. Worst case, you can probably use one of the Russian TDs; there's been some success with that. At the very worst case, you already have a parts mule, although the tendency is to fix up both if possible. I bought a 454 for parts off of ebay and now I'm looking at it and thinking "it's not so bad ..."Most voltages bleed off pretty quickly, except for the HV on the tube, but there should be no reason to get near that. If you're poking around with it live, stay away from the CRT circuit and use insulated probes. You don't want to accidentally short something while poking around. Follow good practice.If this is your first repair, a scope is fairly intimidating. However, if you're just looking at the fan and a general cleanup, you should be fine. You can use compressed air or a can of duster spray to clean the dust off the boards. Watch the transistors; they're all socketed.Anything wrong besides the fan and general cleanup?

author: DanielS
author_rank: Frequent Contributor
timestamp: April 27, 2015, 03:47:35 pm
content: One thing to keep in mind with (very) high voltage circuits like the a CRO's cathode: while the sting from the a cathode tube discharge really hurts, it is otherwise usually harmless on its own. The biggest dangers about it are usually collateral damage such as accidentally yanking the TV, scope or other nearby equipment off the workbench or shelves in reaction to the sting. I have heard stories about people stabbing co-workers with screwdrivers or ripping the anode end of a tube off from that sort of accident.The rest of the circuitry should either have bleeder resistors or a load that will drain caps within seconds from removing power. As others have said though, these may have failed and you should assume they have failed until you know for sure.

author: Rupunzell
author_rank: Frequent Contributor
timestamp: April 27, 2015, 04:35:03 pm
content: Tek tunnel diodes can be had from these folks:http://www.reprise.com/ash/clients2/Tunnel diodes are still being made. They are used by the microwave and RF folks. They are just not "common" parts.http://ams.aeroflex.com/metelics/micro-metelics-prods-TD-MBD.cfmCRT scopes are no longer made this way for a host of reasons, yet the fact many of these old Tektronix instruments are still around, in service and remains quite useful to this day says much about them. Consider for a moment how many modern plastic wonder test gear items will be around 30-50 years from now?BerniceQuote from: smjcuk on April 27, 2015, 09:14:04 am

author: tautech
author_rank: Super Contributor
timestamp: April 27, 2015, 06:57:41 pm
content: Quote from: PaulAm on April 27, 2015, 01:57:48 pmThat in itself IME is a problem.Corrosion of the leads and sockets.I'm of 2 minds to suggest removing and reseating all socketed devices.Specs of dust attract moisture that corrode the leads in old equipment. I've seen them nearly corroded through.Disturb them and they break.Leave them be and who knows when they might give problems and you will have go looking anyway.So best they each be very gently moved in their socket to ensure good contact and very thin or broken leads will then be discovered.

author: PaulAm
author_rank: Frequent Contributor
timestamp: April 27, 2015, 09:42:47 pm
content: I've fixed several scopes of that era just by reseating the transistors.It's a real mixed bag. It makes it really easy to pop a transistor into a curve tracer to identify marginal parts, but it is a serious reliability issue as well.

author: tautech
author_rank: Super Contributor
timestamp: April 27, 2015, 09:51:01 pm
content: Quote from: PaulAm on April 27, 2015, 09:42:47 pmYes socketed units can be a joy to find faulty components, even a cheap DMM with a Hfe tester and a check of datasheets to confirm gain is within specified range.Pulling active components also allows for more accurate testing of passive components in circuit.

author: Desertrat
author_rank: Newbie
timestamp: April 28, 2015, 05:16:12 am
content: I want to thank all those that have replied. I have continued my research into this cry shock hazard and came across a site which is listed below.lowendmac.com/2007/the-truth-about-crts-and-shock-danger/Upon some recollection I remember also that I have been tagged by 2kV or higher before. And I think so of you might have too. Not from CRT but if you happen to like working on cars and do your own tune ups, you may have been tagged by the ignition system. I know I have, it's not very pleasant but I have been tagged a couple of times. I'm still here to tell the story. Not trying to say that people should go looking to get nailed by 2kV or anything like that. But I think like the article above states I think there is a lot of fear mongering or ignorance when it comes to speaking of electricity. Now, like I said I am not saying anyone should trying their luck, quite the opposite. I'm just saying is that people should do as much research into the subject at hand and getting a good hold of the risks. And as the saying goes, "IF IT AIN'T BROKE, DON'T FIX IT !!!!". Now, I received some 2K 5W resistors and I going to make my own discharge tool for the CAPS and start to map the readings on an inert scope. If any residual charge is found, well I'll un zap it with my dis-tool. Just hope I don't brake any of the many little wire posts these things have. Also, the reason I need to remove the boards, the dust that has accumulated inside the scope is pretty caked on. I blast it with canned air and no joy. I'll have to get in there and use a brush to work it loose. As for the fan motor, the red wire goes off to who knows where, to another board I guess. I think the start CAP has a bleed resistor grounded to the chassis and the remaining wires shouldn't be a problem to unsolder them, but that red wire will be fun.

author: tautech
author_rank: Super Contributor
timestamp: April 28, 2015, 05:45:52 am
content: For general instrument clean up study some of the threads linked within this thread:https://www.eevblog.com/forum/repair/vintageclassic-renovation-techniques/

author: JohnPen
author_rank: Regular Contributor
timestamp: April 28, 2015, 09:00:53 am
content: I have owned a 453 for many years, not used very much until recently, which developed a few problems on bringing it back into use. Because mine is a 453, not the later 453A, it has nuvistors rather than FETs. My main problem was the failure of the A timebase Nuvistor it just got a lot hotter than the others and also the triggering didn't work. On investigating I also found that the associated A trigger Tunnel diode had failed. I obtained some replacement Tunnel diodes from Russia and replaced the TD. Using Nuvistor substitution from the B timebase proved the A timebase nuvistor was indeed faulty. Rather than trying to find a source of Nuvistors, not easy, I modified the timebase circuitry to match the 453A FET circuitry. It can be done relatively tidily using the existing nuvistor socket and adding and subtracting a few resistors and capacitors. When completed the A Triggering and A timebase operation worked OK. However I then found the B timebase triggering was not working this though turned out to be only a failure of the TD. Currently I have left the B timebase as a Nuvistor although I may convert that to the FET version at a later date. Converting the Y amps to FETs looks rather more complicated so that is for another day!Other thoughts check the supply rails for ripple, as well as voltage, since I had a single rectifier failure (o/c) which caused some confusion. I did replace the main smoothing capacitors first thinking that was the problem.Final thoughts it is a very good scope and should, when fixed, be very useful and reliable. Only downside is it is a bit large for current day and awfully heavy!John

author: smjcuk
author_rank: Frequent Contributor
timestamp: April 28, 2015, 09:04:49 am
content: Thanks for the above - interesting read and good solutions.Does anyone know a reliable source of tunnel diodes? The tek spares shop mentioned above has none in stock apparently. I've got one channel triggering on my 453 but I suspect the tunnel diode on the other channel isn't working.You're right about it being too heavy. I bought a Goldstar 20MHz scope for £10 yesterday and I'd forgotten how heavy other ones aren't

author: PaulAm
author_rank: Frequent Contributor
timestamp: April 28, 2015, 02:36:33 pm
content: Just a nit, but 453s with sn > 20000 used FETs instead of nuvistors. The 453a (introduced in 1971) gave you a larger screen, a mixed sweep mode and a 60 MHz bandwidth as well.One thing I just found out about it was this was the first scope, and possibly test instrument, that used a lockable dual duty tilt bail carrying handle. Tektronix held a patent on that.This scope was designed to fit under an airline seat and at 29 pounds was a featherweight compared to most of the equipment of that era. No comparison to today's gear, but it was cutting edge at the time.As for TDs, look up the part number and then watch ebay; they show up once in a while but you need patience. Also try a google search on the part number. Once in a while recyclers will show some stock. They're not really a stock item anymore, you need to find somebody selling off NOS parts.Edit: Qservice has 5 in stock. I have always found them to be a reliable vendor.

author: Rupunzell
author_rank: Frequent Contributor
timestamp: April 29, 2015, 02:43:01 am
content: Specifically for Tektronix O'scopes.Early solid state instruments from Tek were made with the best sockets available at that time. Eventually Tek figure out those where just not good enough even when they had few connection problems with them. Tek worked with Berg electronics to develop a much better socket and they did. Later Tek instruments use a special socket with two floating heat treated beryllium copper springs, nickel-gold plated in a specially drawn socket. The top entry port of these sockets are sealed with a dab of silicon rubber to seal the socket once the pin has been inserted. These are extremely reliable and nice to work with. Given all the Tek stuff owned for decades, there was never once a problem caused by these sockets.As for corroded device leads and sockets. It was common practice for companies to send instruments out for cal every six months or so. Part of the basic cal procedure was a good air blow out, de-ionized water wash with speciality soap. After the wash instruments were put in a 100 degree F over to slow dry. There were more than a few hewlett packard bench briefs that out lined proper cleaning of instruments to keep them happy. There was a time when purchasing used test gear that was still in cal resulted in finding the insides of these instruments being spanking clean, in cal, switches-controls clean and properly lubricated.BerniceQuote from: tautech on April 27, 2015, 06:57:41 pm

author: JohnPen
author_rank: Regular Contributor
timestamp: April 29, 2015, 08:56:36 am
content: The order below shows where I purchased my TDs, Russia, and their identity. These parts matched fairly closely to the limited spec shown in the 453 manual and certainly worked OK. Be careful when soldering as Ge parts are a bit more sensitive to heat than Silicon parts.JohnSeller: elena8913 ( 620 )Item title PriceP&P priceQuantity Item totalGI304A Ge Amplifier Tunnel Diode military USSR Lot of 6 pcs ( item: 131190945655 transaction: 948858361003 )Paid on 25-May-14 US $10.00 US $8.00 1 US $10.00Standard Int'l ShippingEstimated delivery: You can contact seller for more information.Subtotal US $10.00Postage and packaging US $8.00Total US $18.00