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Hello group.

I have on my desk a Tek 465 scope (not M) with low serial number, given to me as dead from navy surplus. Well it its not dead anymore, but I have a fault I can't trace and figure out.
Also have a "donor" scope that actually works fine, sadly cant say it looks fine. So parts awailable at least to try if its IC''s or something.
On the -8V rail there is a short to gnd somewhere. The other voltages are fine. However, when I lift the "jumper" that isolates the timing board the -8 is stable even with small load and no ripple, so I dont think the psu is faulty.
Screen shows both channels in voltage, but the sweep is missing. Can move around the dots and focus is fine. Tube seems to be fine.
Have measured just about every transistor and cap on there, but the short to ground still exist.

Does anyone in here have experience in this and could point a finger in the right direction? I'm stuck.......

Rgds
Hugo / LA4WKA

The usual trick is to start unplugging board (PS wise) , measuring the errant supply each time.? Unless there's ECL logic on the scope (don't think so), the -8 volts likely feeds just analog circuitry.? DC resistance measurements might be in order.

Harvey

Hugo,

Do you mean the "A7 Timing board" with the A/B sweep cam switch on it, or the "A8 Trigger Generator & Sweep Logic Board"?

The A8 board has a 15uF, 20v electrolytic cap, C897 which could be a source of a pwr/gnd short. I'm not seeing a power decoupling cap on the A7 board that would so neatly explain the short. I have found a number of shorted electrolytic and Tantalum decoupling caps now on several pieces. So that's my first suspicion. Could still be something else, U640 for example.

What serial number? Though, I'm seeing the same C897 on 070-1330-00 (pre SN B250000) and 070-1861-00 (SN B250000 & UP). But what else might be different? Knowing which is important.

Also, what jumper are you referring to?

Dave

Hi Dave and Thanks for reply.
Look here
In the square red box he shows the jumper I lifted.
Found the short…CR1306 and CR1309 on A8 board were dead short. Replaced and -8V is OK.
Still no sweep. So swapped U870 still nothing. U870 works fine in another scope.
Horizontal pot does not move the spots on either channel. Vertical works.

I notice a fair amount of ripple on all the DC. Can this cause the sweep to not work?

I’m aware it can give erratic signals, but not sure I want to swap all the caps in something that’s not repairable.
So with the voltage there I guess it’s on to horizontal troubles. Glasses on for manual reading.

Serial is 109982, no lettering just numbers. Early model but looks like new inside.

Rgds
Hugo

You have a Guernsey (Channel Islands) produced 465. I would fix that DC Ripple first of all if I was working on it, but that is just how I roll..

You can also see if have a sawtooth waveform at collector of Q1038. I would start looking at the A&B Sweep generator circuitry for all the correct trigger, reset and unblanking signals and then for any Horizontal Amp issues.

--
Michael Lynch
Dardanelle, AR

Michael.

Im afraid the ripple is all over the place, and not able to see any sawtoot pattern at Q1038.
Will order up new caps for psu and dismantle the board for access. Will order up for both scopes, as the other ona that actually works but looks terrible also suffer from ripple.
Hugo

you will be dealing with mechanical issues when recapping.
here are some ideas:

this is the best solution i have seen when it comes to replacing old caps with new:
/g/TekScopes/files/Replacing%20Electrolytic%20Filter%20Capacitors%20in%20a%20Tektronix%20465.pdf

here is another (i used this a few times before i knew about better...imo...solution above):


phil

On Wed, Nov 24, 2021 at 10:12 AM, pdxareaid wrote:

you will be dealing with mechanical issues when recapping.
here are some ideas:

this is the best solution i have seen when it comes to replacing old caps with
new:
/g/TekScopes/files/Replacing%20Electrolytic%20Filter%20Capacitors%20in%20a%20Tektronix%20465.pdf

here is another (i used this a few times before i knew about
better...imo...solution above):

Phil,

I have been repairing 475's lately, so I have been using the discs from E-bay. I really like the "standoff board" concept and I will contact Barry off list to see if he has some of these boards so that I will have one on hand for my next 465.

The discs are a good option as well, just not as simple the next time the caps require replacement.

Getting the old caps out without damaging the PC board is still the bigger issue. Lots of patience required.

Regardless, the power supply ripple must be brought under control or further troubleshooting will be futile. .

--
Michael Lynch
Dardanelle, AR

On Wed, Nov 24, 2021 at 04:11 AM, <la4wka@...> wrote:

and not able to see any sawtooth pattern at Q1038.

Hugo,
Once you get that LVPS ripple under control, I would take a close look for the presence of the various signals coming into and going out of the "A & B Sweep Generator Circuit". This is schematic #6 in the "Late S/N" manual. I do not have a copy of the "Early S/N" manual, but they should be similar.

I have seen several failures of Diodes, Transistors and FETs in this part of the circuit. Of course, do not discount the possibility of "Bad" connections and "Dirty" mechanical switches. I have also seen some of the socketed components that have simply been dislodged from the boards and just plain missing. I had a very nice 465 that evidently had been dropped and some of the transistors became dislodged from their sockets and were rattling around inside the chassis. Really "simply" things can and do happen.

Good luck!


--
Michael Lynch
Dardanelle, AR

Hugo,

To follow up on Michael's excellent advice, I have also seen socketed DIP ICs in a 475 (very similar to the 465) where the pins have become tarnished in the socket and are no longer making electrical connection. I diagnosed this problem by tracing the signal to the IC in questions, then checking connectivity between the trace on the board and the leg on the IC (and seeing that there was no connectivity). So even if the IC is not dislodged/missing, it may still not be connected to the circuit.

Removing the IC from its socket and cleaning the pins with a cotton swab soaked in isopropyl alcohol solved the problem.

-- Jeff Dutky

Hugo,

Anything that is in a socket is subject to corrosion, it is a good idea to check anything that in mounted in a socket. There is also the matter of the crappy "TI" IC Sockets, a problem which has been widely recognized and discussed on this forum.

--
Michael Lynch
Dardanelle, AR

Don't forget the wealth of useful information from the TekWiki site. Even more to the point, the 465 has it's own repair section:



When sorting out how to fix the sweep on a 465 I found the "TROUBLESHOOTING YOUR OSCILLOSCOPE: Getting Down to Basics" document _very_ helpful.



The sweep logic is a loop, and knowing how to debug this loop can be tricky. Following the instructions in the above doc should help sort it out.

Dave

Dave,

EXCELLENT Advice. That "Troubleshooting Your Oscilloscope" document is excellent. The sweep logic loop is the most challenging part of these scopes, for my poor brain at ;least. I had to read through that document many times while in front of the scope before the lights came on.

--
Michael Lynch
Dardanelle, AR

Hello Phil, thanks for reply.

Removing the caps was not so hard at all. All came out quite easily after removing a board for acces to caps. No pads broken or lifted from board..
When I test then out one by one they all show good readings, both in capacity and esr.
Tested all the tantylum ones, but havent found any shorted yet.
Will fiddle around with the socketed IC's and transistoor checking on the horizontal board.

So while waiting for new caps to arrive, I did get 2 ea 2335 scopes to work. They are quite good looking for their age (arent we all :-). Shorted caps and burned resistors on both of them....the rest is like new.
Received also a Tek 491 Spectrum analyser, but the CRT is blown....shame. And a 184 Time Mark Generator with dead tubes......not easily sourced in Norway.

Hugo / LA4WKA

When the sweep quit working in my 465 it was Capacitor C1220 in the Horizontal Amp section that shorted to ground. I replaced this capacitor with an Aluminum Electrolytic, (it was a wet Tantalum), and scope has been working fine since then. I read a Service Notice somewhere that recommended replacing this Cap in units below a certain serial number series but can't remember the numbers. Apparently this cap is known for failures in certain old scopes. I would check it for short.
David

Hugo,

Check all the 151-0367-00 transistors in your scope. These usually are leaky from C to E. It will test as a diode. Any of these 0367 types that have the round leads with black leads (tarnish) will be leaky and should be automatically replaced. The 465, 475 and 485 series have these in them along with some of the 7000 series plug-ins. The leakage can cause problems. Use KSP10BU. These have a BEC pinout. If you see ones that are leaky after checking a few, then the rest will be leaky and will need replacing.

Davis is right about the 1000mfd electrolytic. I used a Nichicon UHE in mine, 1000mfd 16V. These should be changed no matter the age.

In my 465, and others of the series, I raised the wattage of some resistors.

Check the 9.1V zener, VR1522. It is most likely open. Use BZX85B9V1 to replace it. The 6190 ohm resistor to this zener should be increased to 2W. A 6200 ohm will work. I put in a 1% type in mine. I have not seen any 9V zeners that are original still be good. This is the only voltage zener I have found that is always bad.

If you trace is bright when turned on and dims over 10-20 minutes without adjusting the intensity, the 22meg 1/4W carbon in the high voltage section has become too high in resistance. I replace these in the circuit to prevent this problem. This resistor is R1486. Use Vishay VR37 series to replace this resistor. These are 1/2W 1% types. This resistor and the zener are ones I keep in stock. If any of the d-c restorer diodes go bad, the trace will be too bright with no control. The replacement for those is a 1N4937.

If you find bad tantalums, raise the voltage of the new ones, e.g. 20V to 25V, 15V to 20/25V, etc.. You can use low ESR electrolytics like Nichicon ULD 47mfd 25V. The additional capacitance is fine. The raising of the value is for decoupling circuits, not any timing circuits.

If you want/need to replace any of the bridge rectifiers that are 1.5A, use 4A types. The original bridges can fail. The original voltage is 200V. If you have or want a higher voltage, fine. The current capacity is the main thing.

If you want the fan speed to increase to move more air, put a 10,000-13,000 ohm resistor in parallel with the thermistor on the fan board. The lower resistance is the higher speed.

The 1200mfd in the power supply, I put in 2200mfd because I wanted the long life, low ESR and high temperature types. That higher value was the closest available and the additional capacitance did not hurt anything. Recapping yours might make things start working. At the age it is, new caps are a good idea to necessary.

The cleaning contacts is something advised by several on this thread that is always advised. I know I have a list of things to check/replace/can happen. If you have any of these during or after operation, it will help you find the problem(s).

Mark

On Sun, Dec 5, 2021 at 03:17 AM, Mark Vincent wrote:

151-0367-00

Hi Marks.
Thanks for the nice inputs.
9V zener is OK so is its resistor. The 1K uF cap replaced even if old measured good.
After recapping the entire psu, all voltages test good, and no/little ripple shows on any line.

On my screen I have a single dot. Focus and intensity works fine. Stays same for long time.
When I turn the timing switch, the blinking of this dot varies, but it does not move along the screen.
I can connect a signal but there is still just a dot, so think the vertical part also has a beating as it should show up 2 dots (high and low).
Dot can not be moved with vert position pots neither for chan one or two.
Horisontal movement with pot is only about one division on screen.
Pressing beam find moves the dot slightly and ofcourse the timing / blinking stops.
Transistor testing is tidious, and I have not found any leaky / shorted yet. Will continue. Swapped the IC's but they test good, and work fine in other scope.
I also have a working 465 wich can be handy to take live measurements on, however it looks terrible.(obviously been used mobile or been moved around some...could be run over by a truck as well :)
This one looks unused, but sadly not working.
Might swap parts or entire boards into the nicer looking one.

Hugo