Tektronix 465

[Grapsus]

Hello,

I'm starting to really like talking about my life on this forum. Therefore I will share with you my next repair project.

It's a Tek 465 oscilloscope that I got from local ads for 60 euros, sold for parts or repair.

Some knobs are damaged, the case is upside down, but most importantly there nothing on screen even after playing with focus, intensity and beam finder.

I will now try to troubleshoot it. I hope it's something with the HV PSU and the tube is not damaged somehow.

Any advice on testing the HV circuit ? I have decent DMMs but no HV probes.

See you !

[SoundTech-LG]

After you tested all of the Low Voltage supplies, what were the readings?

[Grapsus]

After you tested all of the Low Voltage supplies, what were the readings?

I haven't measured anything yet, I just received the scope and I will familiarize myself with the service manual before touching anything. But you're right, low voltage PSU will probably be the first step, I see humongous electrolytic caps.

I just opened the case and already found some scary things even if they probably aren't related to the fault. There is a cap with a dangling leg and a tiny transformer that has been ripped off the board.

Some info that I forgot to mention earlier: the scope has been made in 1973, there is a cal sticker from 1993 and when I turn it on, channel 1 and timebase have "uncal" lights on.

[tautech]

You MIGHT need to check the HV CRT supply, commonly minus ~2 kV and a Meter that can do this is useful. I keep an AVO just for this purpose.
As far as checks for the PDA voltage of 10 kV or more ....don't.
Quadruplers rarely fail.

If the 465 has an inverter style PSU for CRT HV you can quickly check for oscillation using a scope probe like a near field probe to search for EMI.
The inverter will have test points listed in the SM for accurate measurements.

Before you waste lots of time on "her", check for CRT heater operation. Beware some scopes have an elevated heater filament voltage. Visual check might be all thats needed.

[PaulAm]

The uncal light just means the center knob on that control has been turned off the detent.

The heater is tied to the cathode which is at -2450V, so you want to be careful with that..  I'd leave that until later.

If somebody's been mucking about, the crt bias control could have been altered, which will result in no visible trace.  You need a HV probe and be able to safely measure the -2450V on the cathode to set that correctly.

By far the most common fault is open power supply filter caps, bad bridge rectifiers and the odd tantalum failure. ALWAYS check the low voltage power supplies to see if they are in spec for V AND ripple.  Faults here can cause all sorts of weird problems.  Only then should you start poking around somewhere else.

It's possible the crt could be bad, but that's about the last thing I would expect.

Get the service/repair manual.  There are free ones on the net with very decent quality scans.  Just search for 465.pdf and you'll find something.

Nice scopes and they are very repairable.

[Grapsus]

I tested the low voltage PSU for DC voltage and ripple by following the service manual. Everything is well within spec. The ripple amplitudes are close to table 6-4 "typical low voltage power supply ripple" values.

According to the SM the next step is to check the CRT high voltage. I tried to pick up the 50 kHz inverter frequency with the probe loop trick but it's suspiciously quiet. I have an analog multimeter but its highest scale is 1000V with 20M impedance. Do you think I could measure the CRT voltage by connecting my AVO trough a 40M resistor ? I would connect everything with the scope powered off, then power it back on without touching anything.

[tautech]

I tested the low voltage PSU for DC voltage and ripple by following the service manual. Everything is well within spec. The ripple amplitudes are close to table 6-4 "typical low voltage power supply ripple" values.

According to the SM the next step is to check the CRT high voltage. I tried to pick up the 50 kHz inverter frequency with the probe loop trick but it's suspiciously quiet. I have an analog multimeter but its highest scale is 1000V with 20M impedance. Do you think I could measure the CRT voltage by connecting my AVO trough a 40M resistor ? I would connect everything with the scope powered off, then power it back on without touching anything.

The AVO's I keep for this have 2.5 or 3 kV terminals, yours not?
There should be test points for waveforms on the primary side of the HV inverter, and also make sure there is supply to the primary side.
It may be the inverter has shut down for an over current event, not familiar with the 465, post an image of that part of the schematic or provide a link.

In you second image a few posts back there are a few orange Tant caps...... renown for failures, others might advise replacement but lets get "her" going first.
All I wish is to give you a "heads up".

[ModemHead]

Pull the "Chopped Blanking" cable out for testing.  The little toroid transformer is part of a blanking circuit that feeds the z-axis (intensity) section.  A fault there can result in the trace being permanently blanked.

[rqsall]

When the screen of my 465 died, it turned out to be the HV multiplier. Black box near the rear, you need to remove the vertical amplifier board to get to it. And also the tube to remove it. However, you may be able to desolder the ground lead of it, without removing the V-board and then turn the scope on. If the HV multiplier is shorted out, you will then see a trace on the screen, but not over the full width. If the HV multiplier is shorted, it will also load down transistor Q1404. Check the voltages on it, they should be

• Collector: +4.4V
• Base: +0.7V
• Emitter: +0.1V

A shorted out HV multiplier will load down the base of Q1404. With the HV multiplier taken out of the circuit, the screen will look like this:

In this picture, the V-board is also not present as you can see. If this is what you then see, replace the HV multiplier if you can find one, or make your own.

Good luck!

[Grapsus]

Thank you all for your replies !

The AVO's I keep for this have 2.5 or 3 kV terminals, yours not?
There should be test points for waveforms on the primary side of the HV inverter, and also make sure there is supply to the primary side.

Nope, I have a Metrix 462C and there is a separate socket for each range, the highest one is labeled 1000V. I should have thought about measuring 1-5 kV
 voltages before picking up an AVO.
 

In you second image a few posts back there are a few orange Tant caps...... renown for failures, others might advise replacement but lets get "her" going first.

Those are absolutely all over the place, if I start replacing them, there will be like 150 caps to change. I'm not sure I'm ready to do all this unless I see at least something on the screen.

In this picture, the V-board is also not present as you can see. If this is what you then see, replace the HV multiplier if you can find one, or make your own.

I'm not sure yet, so I don't think I will be touching the HV circuit unless there is strong evidence that it's at fault.

Pull the "Chopped Blanking" cable out for testing.  The little toroid transformer is part of a blanking circuit that feeds the z-axis (intensity) section.  A fault there can result in the trace being permanently blanked.

You were absolutely right ! With the damaged toroid, chopped blanking was doing something bad to the trigger circuit. When I pulled the chopped blanking cable like you said, the trigger panel suddenly became a lot less dumb. Now the TRIG light blinks periodically and "single sweep" does what it's supposed to. However this wasn't enough to get any visible trace. There must be another problem.

I noticed yesterday, with lights off, that the screen was slightly green, a sort of halo, so I assumed that the bias HV was somehow working (I don't have the equipment to properly measure it) and continued the troubleshooting with that hypothesis.

According to the troubleshooting guide, I have a problem inside the "Sweep Start logic circuit". I will continue working on it tonight. I only hope that the culprit is not U870, that would be a bummer for a scope with so few ICs !

Edit: I have a question: when they say "check QXXX" are you supposed to characterize it with a curve tracer ? I don't have one, so I just checked both junctions with a DMM in diode mode. If both junctions in a BJT are OK, can we say that the transistor is OK in general ? I suppose there may be some weird defects where the junctions are ok and the transistor still not doing its job, but I have no idea how frequent those are and what are the testing practices in the field.

[rqsall]

Thank you all for your replies !

The AVO's I keep for this have 2.5 or 3 kV terminals, yours not?
There should be test points for waveforms on the primary side of the HV inverter, and also make sure there is supply to the primary side.

Nope, I have a Metrix 462C and there is a separate socket for each range, the highest one is labeled 1000V. I should have thought about measuring 1-5 kV
 voltages before picking up an AVO.

You cannot check the HV circuit with an AVO. The input impedance of the AVO is way too low and it will load the circuit down giving you a completely faulty measurement. You need a high impedance (several gigaohms) voltmeter to measure the voltage in this circuit.

Check the base of Q1404. It will tell you if the multiplier is shorted. It's only 0.7 volt if the HV is not shorted and probably only 0.3 volt if the HV is shorted.

[PaulAm]

Sometimes the beam gets deflected way off to the side.  If you see any kind of green glow from the screen the HV is probably OK, or at least working well enough to track down other problems.

[Grapsus]

After I disconnected "CHOPT BLANK" cable like ModemHead said, everything changed. Now I have a proper z blanking signal on TP1486 exactly as described in SM. Still nothing on screen. I guess I will have to check the HV stuff. I will try to start with the lower voltages in the inverter and CRT circuits, maybe I'll find the problem in that way.

[Grapsus]

Still no success with this scope 

I focused on the CRT inverter. There is no debugging chart for this one, so I tried to understand it by myself which was not easy since it's a feedback loop with a lot of transistors and some inductive voodoo.
Now I'm sure that this circuit isn't working at all. On the primary side everything looks good. The primary driving circuit is formed by Q1404, Q1408, Q1413, Q1414, Q1416 and Q1418 which is the power stage. This circuit does try to start because at Q1418 collector there is a clean sine with the right frequency and half the amplitude in comparison with the screenshot 92 which shows the same signal at equilibrium. However, at the same time, there is garbage on the secondary of the transformer, the output signal looks like noise picked up by a dangling wire.

My guess is that the transformer T1420 has a broken connection or is burnt. The problem is that it is in a metal can under the main board and is not easy to access. Tomorrow I'll have to disconnect a lot of stuff in order to access this transformer.

[tautech]

Did you check C1419 & C1412 for correct values and ESR?

I seen the high value resistors fail or drift substantially in value on the secondary (HV) side of the inverter.
But I would eliminate anything dragging down the secondary voltage first, diodes, caps , stuff with a path to GND.

I'm lookin a a SM from here: http://elektrotanya.com/tektronix_465_oscilloscope_full_sm.pdf/download.html

It has some penciled in DC values that may help. (P228)

[rqsall]

Can you just measure the voltage on the base of Q1404? If it's substantially lower than what it specifies on the schematic (link amd page nr in previous post), that's a clear indication of a shorted HV multiplier as I've said earlier. A shorted HV multiplier is a very common failure point of these scopes.

[Grapsus]

Can you just measure the voltage on the base of Q1404? If it's substantially lower than what it specifies on the schematic (link amd page nr in previous post), that's a clear indication of a shorted HV multiplier as I've said earlier. A shorted HV multiplier is a very common failure point of these scopes.

Yep I've already checked Q1404 base. Looks like it's a very important point where the feedback from the secondary comes through R1431D and pulls down in order to provide regulation for the HV. In my case this point is at 3.7 Volts. The SM reference value is 0.7V, but I think you only get this value when the circuit is at equilibrium and some negative HV is present on the secondary. In my case, the circuit tries to start and there is nothing coming from the transformer, so Q1404 stays at its max value.

Did you check C1419 & C1412 for correct values and ESR?

I seen the high value resistors fail or drift substantially in value on the secondary (HV) side of the inverter.
But I would eliminate anything dragging down the secondary voltage first, diodes, caps , stuff with a path to GND.

I remember checking a few electrolytic caps yesterday, but I guess now I'll have to check every component attached to the secondary in order to understand why nothing comes out of it.

I'm lookin a a SM from here: http://elektrotanya.com/tektronix_465_oscilloscope_full_sm.pdf/download.html

It has some penciled in DC values that may help. (P228)

Yes I use the exact same PDF. The only drawback are the PCB component maps, almost impossible to read.

Those typical DC values are very nice but I think they are only true when the circuit has already started, before that, those voltages could be different without necessarily have bad components nearby.

[rqsall]

Can you just measure the voltage on the base of Q1404? If it's substantially lower than what it specifies on the schematic (link amd page nr in previous post), that's a clear indication of a shorted HV multiplier as I've said earlier. A shorted HV multiplier is a very common failure point of these scopes.

Yep I've already checked Q1404 base. Looks like it's a very important point where the feedback from the secondary comes through R1431D and pulls down in order to provide regulation for the HV. In my case this point is at 3.7 Volts. The SM reference value is 0.7V, but I think you only get this value when the circuit is at equilibrium and some negative HV is present on the secondary. In my case, the circuit tries to start and there is nothing coming from the transformer, so Q1404 stays at its max value.

  seems like something failed open... hopefully it's just a HV cap somewhere on the main board, but could be the transformer or the HV multiplier 

[Grapsus]

This is by far my most scary repair ever 

I measured everything I could around the inverter transformer T1420, and the windings seem ok, around 0.5 Ohms on the primary and 5 Ohms on the secondary. However, the main rectifying diode CR1421 seems to conduct in both directions. It can't be measured directly because it's under the board with the transformer, but I measured it through a winding, between R1428 and C1421, there's no threshold voltage and only the winding resistance. Why the hell did the only part that can't be accessed decide to fail ?!

The only way to access that can with the transformer and the diode is to remove the main board which can't be removed without first taking out everything else. It's a nightmare, it took me an hour the disconnect the trigger pcb alone. There's still the input board. Then I'll have unsolder every wire that goes to the main board including the high voltage lines soldered with some special silver alloy. It will be a miracle if it can be put back and work again.

Did people take a month vacation back in the day to service those things ?

[tautech]

 
Be aware these HV DC restorer diodes have a high V_F.
Sometimes in excess of 10V, check a matching datasheet especially if your are to substitute it. 

[rqsall]

This is by far my most scary repair ever 

I measured everything I could around the inverter transformer T1420, and the windings seem ok, around 0.5 Ohms on the primary and 5 Ohms on the secondary. However, the main rectifying diode CR1421 seems to conduct in both directions. It can't be measured directly because it's under the board with the transformer, but I measured it through a winding, between R1428 and C1421, there's no threshold voltage and only the winding resistance. Why the hell did the only part that can't be accessed decide to fail ?!

You need to remove the vertical board, not the main board.

Good luck

[stephunk]

Do you really have ALL voltages from power supply OK? Check if the -8V rail is OK. The display function(high voltage) depends also on this. When i repaired a 465, the bridge rectifier CR1561 was bad.

[Grapsus]

Be aware these HV DC restorer diodes have a high V_F.
Sometimes in excess of 10V, check a matching datasheet especially if your are to substitute it. 

Yep I understand that I won't be able to replace CR1421 with a jellybean part. The service manual says "VG-12X; SILICON 1200V 5 mA". No public datasheet for "VG-12X". 1200 V must be the breakdown voltage right ? I hope there is at least something equivalent for this part that can still be purchased.

Do you really have ALL voltages from power supply OK? Check if the -8V rail is OK. The display function(high voltage) depends also on this. When i repaired a 465, the bridge rectifier CR1561 was bad.

I've already thoroughly checked the low voltage PSU and it complies with the service manual in terms of DC value and ripple for all rails.

You need to remove the vertical board, not the main board.

Are you sure you can access the transformer and the diode by removing only the vertical board ? Have you already done it ?

[tautech]

Be aware these HV DC restorer diodes have a high V_F.
Sometimes in excess of 10V, check a matching datasheet especially if your are to substitute it. 

Yep I understand that I won't be able to replace CR1421 with a jellybean part. The service manual says "VG-12X; SILICON 1200V 5 mA". No public datasheet for "VG-12X". 1200 V must be the breakdown voltage right ? I hope there is at least something equivalent for this part that can still be purchased.

Certainly not jellybean, however carefull substitution is very possible now you have a datasheet. 

http://www.datasheetarchive.com/dlmain/Datasheets-21/DSA-414399.pdf

[Grapsus]

Certainly not jellybean, however carefull substitution is very possible now you have a datasheet. 

http://www.datasheetarchive.com/dlmain/Datasheets-21/DSA-414399.pdf

Wow, well done ! We can see that there is a typo in the service manual: according to the datasheet VG-12X has 12kV maximum reverse voltage and not 1200V !!!

[rqsall]

You need to remove the vertical board, not the main board.

Are you sure you can access the transformer and the diode by removing only the vertical board ? Have you already done it ?

Yes, I've done it. I had to replace the HV multiplier on mine. The diode is soldered directly on the input of it. The manual describes the procedure for replacing the HV multiplier, follow that, and you should be fine. If it's just the diode, you will not have to remove the tube.

Good luck.

[Grapsus]

You're right, page 54 "High voltage multiplier" looks like I need to remove the vertical board and the CRT, it's way better than removing the main board

[Grapsus]

Even worse news today 

I finally disconnected the vertical board and got into the HV can. In fact the high voltage diode seems OK. The low impedance I observed from the outside of the can seems to come from the HV multiplier block. The resistance I measure between GND and IN terminals is around 90 Ohms, no wonder the secondary stays at ground. Tomorrow, I'll try to run the scope without the multiplier in order to make sure it gets the transformer going and confirm the fault.

rqsall looks like your initial guess was right, my HV multiplier is toasted. How would you approach repairing it now ? Buying a replacement multiplier will probably cost 3 times the price I paid for the scope. You mentioned making one yourself ? Is it a classic Villard cascade ? Is so, I never designed one myself, what is the exact topology used by tektronix ? the component ratings ? Is it possible to remove the potting from the existing multiplier and replace just the faulty component ?

[tautech]

SM identifies it as 152-0442-00, Sphere have a lising that they describe as for late production models: 152-0635-00 but sold out. Described as Murata MSL8521

http://www.sphere.bc.ca/test/tek-parts/tekparts5.html

Might be another option. 

[rqsall]

Even worse news today 

I finally disconnected the vertical board and got into the HV can. In fact the high voltage diode seems OK. The low impedance I observed from the outside of the can seems to come from the HV multiplier block. The resistance I measure between GND and IN terminals is around 90 Ohms, no wonder the secondary stays at ground. Tomorrow, I'll try to run the scope without the multiplier in order to make sure it gets the transformer going and confirm the fault.

I should have checked my notes when I replied earlier instead of going from memory. The base of Q1404 sits at a higher voltage when the HV multiplier is shorted. It was 3.2 on mine apparently, which makes sense because it being a negative circuit, "collector pulled to ground" means "pulled up". Sorry for that.

rqsall looks like your initial guess was right, my HV multiplier is toasted. How would you approach repairing it now ? Buying a replacement multiplier will probably cost 3 times the price I paid for the scope. You mentioned making one yourself ? Is it a classic Villard cascade ? Is so, I never designed one myself, what is the exact topology used by tektronix ? the component ratings ? Is it possible to remove the potting from the existing multiplier and replace just the faulty component ?

You can forget about removing the potting. And yes, it is a Villard, or Cockroft-Walton, I guess that depends on whether you're French or not ;-)

First thing I would do now is to verify the CRT is still working. Desolder that diode from the input of the HV multiplier, optionally also desolder the multiplier's ground lead (you're going to have to anyway if you're going to replace it). And turn the scope on. No need putting the vertical board back in. You should see something like I posted in post #8 of this thread. I don't think fiddling with the horizontal control or beam finder should be necessary, but if you don't see anything showing up, it can't hurt to try.

If you see a trace I suggest you sign up to the yahoo tekscopes discussion group. There's a photo section on it where the module is X-rayed and also some photos of DIY multipliers. I almost went that way, bought the caps and diodes to make the cascade, but then I came across a used unit for a decent price. If I had payed no more than a few dozen euro for the scope (I got it free out of an inheritance), it would be worth it to me to shell out roughly the same (max 40 euro including shipping) for a multiplier that is known to work.... if the CRT can be confirmed to be OK.

Good luck.

[Grapsus]

No more doubt about fried multiplier. Here is what is looks like with multiplier's GND disconnected. I'm still waiting for access to this TekScopes list.

[Guni]

They have it at stock for... 48Eur
http://www.qservice.eu/shopdisplayproducts.asp?page=4&id=61
and here
http://www.ebay.com/itm/TEKTRONIX-152-0703-00-CMX426-High-Voltage-Multiplier-/380543774994?pt=LH_DefaultDomain_0&hash=item589a2d3112

[Grapsus]

CMX-426 doesn't look like the multiplier in the tek 465. Maybe it can be adapted in some way ? The exact part I need is 152-0552-00 and the link you provided says it's out of stock.

[PaulAm]

While you're waiting for the Tek  group OK, take a look at this thread:

http://www.vintage-radio.net/forum/showthread.php?t=85145

It starts out about the 7603, but includes some info on the 465.  Apparently that's a X6 multiplier.  The going price for one seems to be around $50, but you could roll your own if you're careful and follow good HV practice.  12KV is not something to be careless with.

[tautech]

You might like to try a few chemicals on the PDA module potting, MEK, IPA, Toluene and the like. 
Have a measure up first, you'll probably need to rebuild with a new enclosure.

[Grapsus]

While you're waiting for the Tek  group OK, take a look at this thread:

http://www.vintage-radio.net/forum/showthread.php?t=85145

It starts out about the 7603, but includes some info on the 465.  Apparently that's a X6 multiplier.  The going price for one seems to be around $50, but you could roll your own if you're careful and follow good HV practice.  12KV is not something to be careless with.

Hey, thanks for the link. I previously found another relevant topic on the same forum:

http://www.vintage-radio.net/forum/showthread.php?t=96958

The guy replaced the multiplier with an x5 part and manually added one stage. They misleadingly talk about a "tripler", but you're right it must be a x6 multiplier. It's the only way to go from -2.45 to 14.5.

I don't know much about HV, but I thought that in a Cockroft-Walton circuit each part had only to withstand the input voltage. Why did they choose 12kV diodes ? Is it extra security ? 4 kV diodes seem to be easy to find, but 12 kV ?! those aren't even listed on Farnell, Mouser and others. I'd be ok with a DIY replacement, but I don't have an HV probe so there will be no possibility for experimentation, I'd have to built a circuit that's been proven to work. And frankly it kind of scares me. When I was getting the multiplier out of the scope, I must have touched a cap that still had some charge from the -2.45 kV rail, it made one of my fingers numb for a minute, 14 kV must be even worse and it can make sparks at > 1cm 

[Grapsus]

You might like to try a few chemicals on the PDA module potting, MEK, IPA, Toluene and the like. 
Have a measure up first, you'll probably need to rebuild with a new enclosure.

Yep, I still have hope for dissolving the potting too. But it feels like very thick and dense epoxy. rqsall says it's impossible. Maybe with an x-ray image at hand I could strategically drill around the first stage and only replace one faulty diode ?

[tautech]

You might like to try a few chemicals on the PDA module potting, MEK, IPA, Toluene and the like. 
Have a measure up first, you'll probably need to rebuild with a new enclosure.

Yep, I still have hope for dissolving the potting too. But it feels like very thick and dense epoxy. rqsall says it's impossible. Maybe with an x-ray image at hand I could strategically drill around the first stage and only replace one faulty diode ?

Possibly.
Potted stuff I have re-worked was of a barely transparent nature that allowed one to inspect as you go in good light. X-ray image should be a great help, you'd imagine the units to be all very similar, but they might differ in immersion depth. 

Gentle work with a Dremel and by hand would be my choice if chemicals won't work.
Take photos and measurements first, it might end up unrecognizeable. 

[Grapsus]

Apparently that's a X6 multiplier.

The guy replaced the multiplier with an x5 part and manually added one stage. They misleadingly talk about a "tripler", but you're right it must be a x6 multiplier. It's the only way to go from -2.45 to 14.5.

My bad, it's called a tripler because it multiplies 4900 Volts peak-to-peak by three. The additional section must have been added because the replacement multiplier was too weak. It also explains the 12 kV rating of the diodes, it's two times the peak-to-peak voltage.

I have the x-ray images now, I will try to somehow disassemble the broken multiplier before looking for a replacement or a DIY build.

[SoundTech-LG]

I have a spare blown tripler off a 465 as well. Are you going into business? 

[Grapsus]

I finally got access to the TekScopes group. The x-ray images are publicly accessible here: http://pp5ms.com/tek_hv/1.jpg (it goes up to 9.jpg)

I also found a long discussion about building a replacement multiplier from discrete components. And there is like a 30 post discussion about whether it's a "tripler" or a x6 multiplier. It was really confusing. So I watched carefully EEvblog #469 "Voltage Multipliers" and I finally understood the circuit. On the x-ray photos we clearly see 6 capacitors and 6 diodes. Therefore the circuit is a three-stage Cockroft-Walton multiplier. It multiplies the input peak voltage by 6. The input voltage is 2.45 kV peak. Hence the HV output is 14.7 kV which agrees with the service manual. Also we see in Dave's video that each stage gets the previous stage DC voltage and the input AC voltage riding on that DC. So each stage has to withstand the input peak-to-peak voltage around 4.5 kV which is 10 kV with a 2x security margin. That explains why 12 kV diodes and 10 kV caps were used.

I tried to disassemble my dead multiplier to make sure it was the same. I confirm that it's hopeless trying to remove the potting. Acetone and IPA didn't work, I don't have toluene. But it really looks like a polymerized kind of stuff that is almost inert once it settled. I tried drilling it and even at low speed it got so hot that it started burning. Desperate, I smashed the thing with a hammer and it took a lot of hammering to see something.

My HV multiplier was a little different from the one on the x-ray photos. The arrangement is the same, but the capacitors are bigger so that the circuit occupies the whole box. I managed to measure one of the capacitors, it just had a small corned chipped so I could access both plates. They are 1800 pF. Also I found a 470k carbon powder series resistor before the HV output. We can see the same resistor on the x-ray photos, it appears as a gap in the output line.

There doesn't seem to be any replacement part available right now, so I guess I will have to build my own multiplier. rqsall pointed me to the ebay store "high-voltage-hv" which has 100 nS 12 kV diodes and 10 kV caps. Do you think 100 nS recovery will be enough for this 50 kHz multiplier ?

Regarding the output resistor, why do you think they used a regular resistor instead of a HV one ? Does it have to be carbon powder or can I use a metal film as well ? I found those on Farnell :

"OHMITE  SM108035003FE  RESISTANCE 20KV 500K 1%" 6 euros piece
"OHMITE RESISTANCE COMP CARBON 470K 0.25W 5%" pretty cheap

Any suggestions about the potting compound ? I don't think paraffin is a good idea, the scope gets pretty hot. Maybe silicone or polyurethane ? something that can be removed later without destroying everything.

[oldway]

You can try to use an ERO multiplier.
Look for "ero kaskade" on ebay.de

I think an ERO HV multiplier from an Hameg HM604 or HM605 (BG1899-882-201) could do the job.
Hameg is still selling spare parts for those oscilloscopes.

http://laehnversand.de/repair/ersatzteile-audio-video-tv/ero-kaskaden.html

[tautech]

Any suggestions about the potting compound ? I don't think paraffin is a good idea, the scope gets pretty hot. Maybe silicone or polyurethane ? something that can be removed later without destroying everything.

https://www.eevblog.com/forum/testgear/high-voltage-oscilloscope-probes-make-or-buy/msg652364/#msg652364

There is a good choice of potting compounds available from all the major suppliers.
Dielectric strength rating will be most important IMO.

It would seem it won't cost much for componentry, probably the potting will be the most expensive.
Might be a good idea to buy enough components to make a couple more in case you need to.
If you get the "recipe" right firt time you can make some more from the left-overs and flog them off.
Best you get a few months use in first. 

[rqsall]

There doesn't seem to be any replacement part available right now, so I guess I will have to build my own multiplier. rqsall pointed me to the ebay store "high-voltage-hv" which has 100 nS 12 kV diodes and 10 kV caps. Do you think 100 nS recovery will be enough for this 50 kHz multiplier ?

Regarding the output resistor, why do you think they used a regular resistor instead of a HV one ? Does it have to be carbon powder or can I use a metal film as well ? I found those on Farnell :

"OHMITE  SM108035003FE  RESISTANCE 20KV 500K 1%" 6 euros piece
"OHMITE RESISTANCE COMP CARBON 470K 0.25W 5%" pretty cheap

Any suggestions about the potting compound ? I don't think paraffin is a good idea, the scope gets pretty hot. Maybe silicone or polyurethane ? something that can be removed later without destroying everything.

I've heard from people on tekscopes that used beeswax, or would use it. But the thought scares me. Not being able to find affordable potting compound that I trusted is why it took me so long to get started that I eventually found a replacement.

As far as the resistor, I don't think it needs to be high voltage rated. There's barely any current going through this circuit, and even if it was 1 mA: V = I*R => 470000*0.001 = 470Volts and I doubt the current is more than a few dozen uA. Since it's so low a current, I doubt it matters if it's carbon or metal film. But someone should correct me if I'm wrong.

100ns for the diode is what I bought and I remember reading somewhere that was enough.

[Grapsus]

I ordered 12 kV diodes and 2200 pF capacitors from this ebay store high-voltage-hv. It ships from China, so I guess I'll have to wait for a week or two 

Regarding the potting compound, how about this one ? http://fr.farnell.com/pro-power/ppc124/potting-resin-pu-250g/dp/1776512

It's super cheap. It's polyurethane, so it may be removed if maintenance is required. And it has a dielectric strength of 11.5 kV/mm. If I'm careful about leaving at least a centimeter between every terminal it will give me a 100 kV security margin. Is it enough ? I really don't have any experience with HV.

If I get the right recipe and the resulting module proves itself working in the long run, I'll be glad to make extra units to save some fellow scopes.

[rqsall]

I think that potting compound should do it. Not sure if 250 grams is enough though. I guess I could weigh my old (broken) one.

[Grapsus]

I read on TekScopes that the compound used in the original multiplier was filled with glass or ceramic dust (that's why it's so hard to cut) so it is extremely dense. I think it would be more appropriate to estimate the required mass of compound with the volume of the box. But even if I need two bags of compound it's still pretty cheap.

Also I'll start looking for a kind of vacuum tupperware that will be necessary to get the bubbles out of the compound before it settles.

[tautech]

I'd consider heating the potting and pot to reduce viscosity to let bubbles rise to the surface more easily.
Datasheets of the compound you use should give guidance to application temps and conditions.
How you construct the trebler might also help how the compound to "floods" the enclosure.

[Grapsus]

Victory !

[tautech]

That potted real nice.
What diode did you use?

To avert any risk of the GND and HV lead breaking off, you could have used an eye terminal and solder leads to it, if you have the room around the potted trebler. Thinking of the old stand-off PCB test point type terminal. Then a snug fitting sliding sleeve over the joint.

Anyway looks fine for purpose. 

[rqsall]

Well done! And thanks for showing off your work... might come in handy for me one day as well 

[netdudeuk]

It's always good to see someone come here with a faulty machine and get it working with the help of the forum members 

[tautech]

We all want to know when Grapsus is going into production with these? 

[Grapsus]

Hi again,

Thank you for your comments, for sure I would never have done this repair without the help of people from this forum.

I hesitate to start a small blog to document things like this so that the info can be found more easily. The forum discussion is good when the device is being repaired but for someone who will have a similar problem years after, reading through tens of pages can be unpractical.

What diode did you use?

The diodes are kind of no-name. I bought them from the ebay seller "high-voltage-hv" who was recommended by forum members here. It just says in the description "10mA 20kV 100ns High Voltage Diode". I wanted to buy the diodes from a good brand but didn't find any on Farnell or Mouser. They only sell diodes up to 4 kV and the requirement was 12 kV.

To avert any risk of the GND and HV lead breaking off, you could have used an eye terminal and solder leads to it, if you have the room around the potted trebler. Thinking of the old stand-off PCB test point type terminal. Then a snug fitting sliding sleeve over the joint.

I agree that there are better options for ground and input connection, but I wanted to finally make this multiplier with what I had at hand. Also the original multiplier does exactly this: the input lead is directly a leg from a capacitor and the ground is just a wire with low-voltage insulation going inside the box. I secured the output wire sleeve to the box with cyano-acrylate, it doesn't move at all.

We all want to know when Grapsus is going into production with these? 

I think it would be safe to wait for a couple of months to see if the new inverter works reliably in the long run. Then I'm totally ok to make other units for just the cost of the parts if it can save other Teks from the landfill.

[tautech]

I agree that there are better options for ground and input connection, but I wanted to finally make this multiplier with what I had at hand. Also the original multiplier does exactly this: the input lead is directly a leg from a capacitor and the ground is just a wire with low-voltage insulation going inside the box. I secured the output wire sleeve to the box with cyano-acrylate, it doesn't move at all.

I probably would have done as you have in your position.

The OEM usually does much the same, however if you have them in and out a few times the leads fatigue, even insulated cable types unless made of quality fine stranded cable.
Something to consider if you make them for others. 

[oldway]

One of these beauties...

It is worth it.

I wish you much pleasure with your 465.

[Kibi]

I realise that I am a bit late to the party. I have this specimen that perhaps could have helped you out with it's multiplier.





Having said that, you have done a lot of hard work which you have been kind enough to share and will no doubt help a lot of people in the future.

In your first post you highlighted that some knobs are broken. I can see that CH1's red "VAR" knob in particular needs replacement. Are there any more broken of missing knobs? I may have some if you are interested.

[Grapsus]

In your first post you highlighted that some knobs are broken. I can see that CH1's red "VAR" knob in particular needs replacement. Are there any more broken of missing knobs? I may have some if you are interested.

You're not late at all ! Yesterday I began cleaning the front panel and the knobs before putting everything together. I am going to post a few photos to show the damaged knobs.

You're right the worst damage is on one of the vertical VAR knobs, it's totally shattered and bits of plastic are missing so it can't be glued together. A few hours ago I sent a message to the guy from sphere.bc.ca to ask if he could send me one without $30 international parcel fees.

Another very important piece that's broken is a flexible shaft coupler that connects the timebase VAR shaft to a variable resistor deep inside the horizontal board, the plastic piece in the middle snapped and the shaft rotates without turning the resistor. I was going to salvage the coupler from the astigmatism control which is less important. But if you have one of those, that would be great !!!

There are also cracks on the vertical attenuation selectors, one trigger level selector and the small plastic pieces on the coupling selectors but I think I'll be able to repair all of these with cyanoacrylate.

All these repairs are less important than having a trace on screen, but for sure it would be better to give the scope a perfect undamaged look, it will be more pleasant to use in this way. What drives me crazy is that all this damage comes from rough handling and probably forced disassembling, like someone tried to remove the knobs without loosening the setscrews. Why can't people show some respect to old and cool gear like this 

Edit: I added a picture of the damaged knobs. Except for the shattered VAR knob, I think I will just carefully pour some superglue into the crack and press on the sides until it dries.  Also the pictures of a shaft coupler like the one that snapped and a rubber foot that's missing.

[Kibi]

I would appear that I can fulfil most of your requirements. I cannot do the Vertical attenuation knobs because they were the first to get smashed. As you can see from  my previous photo that those are all bent and smashed. That 'scope was mounted in a bay using the special 19" rack mounting frame designed for these particular 'scopes. Unfortunately whoever installed it did not screw the 'scope into the frame, so when it was being removed from the bay at a height of about 35U - 40U, the 'scope slid out and fell face first onto the floor.

I have everything else though. The coupling selector plastic parts that I have are brand new out of a packet so they will not match the colour of the other lever switches on the front panel.
The "VAR" knob is slightly scratched, but should clean up OK.
All of the knobs pictured below have their grub screws.

[Grapsus]

Hi again,

Here is an update about the restoration of my Tek 465. Now that the screen is working, I started to progressively reassemble and test everything. Unfortunately it has many other problems. "It's one sick puppy" as Dave would say  But those problems are a lot easier to troubleshoot.

First I had to re-attach the small chop mode transformer and several other components that have been ripped by someone who carelessly opened the case. I used rigid copper wires to reach as close as possible to the windings. Then I made a small plastic cover so that is wouldn't break again.

After that, I removed the two horizontal boards in order to access the VAR shaft coupler which snapped and replace it with the same coupler that I borrowed from the astigmatism pot. I also cleaned all leaf switches with IPA and paper. I got so fed up with having to desolder 20 wires each time I want to remove those boards that I decided to install connectors. A lot of other connections use the same standard connectors, I don't know why Tek didn't do it the first place, those wires don't carry any high-frequency signals. Now I can get the vertical board whenever I want by just soldering the trigger BNCs

Then I reinstalled the timing boards and the timebase selector which was a huge pain to properly align. I never used an old Tek before and this selector wasn't properly attached when I got this scope but now that it works I must say that this is the coolest mechanical switch ever. The thing is a masterpiece of mechanics with all the mechanisms to handle the two timebases and the feel and the sound of it operating is totally pornographic.

With the scope in one piece I started to see traces, but they were all jumpy and noisy. Things where getting especially bad whenever I moved or touched the device. The problem concerned both channels even in GND position. The issue was somewhere close to the CRT, so I started lightly bumping various parts of the scope until I found where it was especially sensitive. It was on the scary circuitboard that connects to the delay line and the vertical deflection plates. Fortunately my unit has the integrated circuit version unlike ModemHead's where 100 components are just soldered together in free air. I took it out and it really looked like someone with poor soldering skills took a go at it, the output wires were almost broken, so I replaced them. Then I looked for cold joints and there were maybe one on one of the silicone resistors. Also the delay line connector was in an ugly condition and its shield legs were broken not making contact with the PCB. I did my best to straighten it and solder rigid wires in place of the broken ground legs. I don't know which of these repairs did the trick, but after them the traces became very stable.

After the multiplier replacement I hadn't adjusted the HV power supply and the CRT bias so the traces were kind of thick. Not having any DMM that goes beyond 1 kV, I had to improvise an HV probe. Luckily I found a high voltage 100 Meg resistor on an old printer PCB. I used it to make a 1000x probe. It did the job and I could adjust the -2450V rail which was way off. I followed the manual to set up the CRT bias and the traces became nicer.

Remaining problems:

The 1X/10X probe lights don't work, probably the bulbs are burnt. I hesitate to replace them with LEDs.

There's something wrong with the intensity control. The knob is very hard to turn and it's very jumpy when I operate it. Also the calibration procedure often says to set the intensity on +15V with respect to a dedicated test point. On my unit this voltage only goes down to 23 Volts.

The B timebase is not sweeping. The A intensified mode works, I can highlight a portion of an input signal, but when I switch to either "MIX" or "B (DELAYED)" there's nothing on screen.

Calibration seems off here and there, I'll have to follow the complete adjustment procedure.

Various knobs cracked as described in my previous post, but thanks to Kibi and his scraped 475 I may be able to give the scope back its perfect visual aspect.

[tautech]

When you get to Cal, check Dave's vid from ~20 min in:
http://www.eevblog.com/2013/08/03/eevblog-502-19-hameg-analog-oscilloscope/

[Grapsus]

Hi again !

I think I finally finished restoring this scope. All in all, it was a nightmare to get it to a state where everything works as expected. By far the hardest repair I ever did.

I found why the B timebase wasn't working, Q1098 was dead, internally short, I replaced it with a 2N2222.

I replaced the 1X/10X bulbs with white LED and they look pretty good.

Huge thanks to Kibi for sending me replacement knobs and other mechanical parts. I reinforced the cracked range knobs with superglue. And the front panel is now good as new.

Once everything re-assembled, I found that channel 1 range switch wasn't working properly. I had to remove the vertical board again and clean all the contacts. After re-assembling, the range switch worked fine but the AC/DC selector started misbehaving. So I had to remove the vertical board for the third time to finally get everything right. 

Regarding the intensity control, I still don't know if I really have a problem. I can get both sharp/dim and thick/bright traces. But turning the intensity knob around half-way already maxes out the intensity.  The service manual says that the peak-to-peak amplitude of the blanking signal at TP1486 should be between 0 and 75 Volts. What I get is between 0 and 105 Volts. If there are any other 465 owners here, can you please tell me if your intensity control behaves in the same way or does my scope have a problem here?

On the positive side, it looks like the 100 MHz bandwidth is really there ! A fast rising edge looks even faster on the 465 than on my 100 MHz Rigol. Also my homebrew voltage multiplier still works like a charm.

Thanks again to people from this forum, it wouldn't have been possible without your help.

[GreyWoolfe]

Beautiful repair and restoration job.  Enjoy the fruits of your labor!

[tautech]

All the scopes that I have fixed, the Intensity can be adjusted until trace is not visible, can you do this?
Normally there is another Intensity bias adjustment to make this possible and the procedure should be described.
That presumes all other CRT voltages are correct.

[Grapsus]

All the scopes that I have fixed, the Intensity can be adjusted until trace is not visible, can you do this?
Normally there is another Intensity bias adjustment to make this possible and the procedure should be described.
That presumes all other CRT voltages are correct.

Yes, I can make the trace disappear if I turn the intensity fully counter-clockwise. This threshold can be adjusted with an internal pot named "CRT BIAS", but I didn't even need to. My problem is the other way around, I find that even with intensity at the middle position the trace is way too bright, but I can't tell if it's normal since I've never used another 465. I'd say the useful range for intensity is around 40% of the full rotation, even with x10 mag and the fastest timebase. Maybe it is supposed to work this way, but I found it strange.

The voltages in the service manual are really useless for checking this issue because the whole Z circuit works with currents. Each module that affects the intensity (external input, blanking, A with B intensified etc.) contributes a small current and all the control currents are summed to get the final intensity value.

[tautech]

All the scopes that I have fixed, the Intensity can be adjusted until trace is not visible, can you do this?
Normally there is another Intensity bias adjustment to make this possible and the procedure should be described.
That presumes all other CRT voltages are correct.

Yes, I can make the trace disappear if I turn the intensity fully counter-clockwise. This threshold can be adjusted with an internal pot named "CRT BIAS", but I didn't even need to. My problem is the other way around, I find that even with intensity at the middle position the trace is way too bright, but I can't tell if it's normal since I've never used another 465. I'd say the useful range for intensity is around 40% of the full rotation, even with x10 mag and the fastest timebase. Maybe it is supposed to work this way, but I found it strange.

The voltages in the service manual are really useless for checking this issue because the whole Z circuit works with currents. Each module that affects the intensity (external input, blanking, A with B intensified etc.) contributes a small current and all the control currents are summed to get the final intensity value.

Sounds OK then.
You will need the additional intensity when using the delayed timebase, particullary "A intensified by B" if the 465 has that or similar. This is where the seemingly unneeded intensity is used.
Some scope manuals describe Intensity adjustments in this mode.

[Addicted2AnalogTek]

that sounds about right for the Intensity adjustment knob. my 465 is the same way, and from what I understand it's supposed to be that way on these analog Teks with the delaying timebase - for exactly the reason Tautech stated. when you use the B timebase, the intensity will automatically dim in some settings and you will then need the additional 60% or so of the turn to be able to make it visible again.

[Grapsus]

Ok, thank you for this insight. At least it's not another thing broken in this scope

I finally put the case back and now I'll start using this puppy for my circuits. I really like the feel of various controls on the front panel and the very sharp traces. Also it's my first dual timebase scope, I really enjoy using this "analog zoom" where I can highlight a portion of the signal with the intensified mode and then view the detail with the B mode.

My next repair will be a Schlumberger 5224 analog scope (100 MHz, 4 channels, dual timebase), I'll open a thread if there's something interesting or not obvious about it.

[Addicted2AnalogTek]

sounds like you're getting the hang of it's features a lot quicker than I did.   

That should be interesting to see inside of.   You hoping to score the one from Italy or do you already have one?    Looks like it would be a nice 4 channel analog to have for someone on a budget, or just to have.

[ModemHead]

Really nice job on the repair and restoration.  It looks great too.  Hope you get quite a few more years of service from it.   

[Muxr]

I just read the whole thread. Awesome stuff. This is why I love this forum. Nice job!

[electr_peter]

Very interesting thread. Great job with restoring oscilloscope

I also have Tek 465 in working condition, but it needs some care. Buttons/switches sometimes fail to operate (cleaning should help), channel 2 BNC is slightly wobbly, few dials are cracked. I am a bit worried about B sweep trigger because it does not seem to work. Otherwise all seems to be OK.

Channel two BNC is slightly loose. How is it connected internally - with a screw or solder? Do I need to desolder shield to get access to it? I am a bit worried such small repair job could take considerable amount of time

Regarding B sweep - delayed time sweep operation (with B sweep trigger set to "Delayed sweep") works fine on A, Mix, A intens, B modes without any issues.  However, when I set B sweep trigger source to something other than delayed sweep (like Ch1, Ch2, ext), nothing appears on the screen for B - B trigger seems to not trigger at all. I tried same buffered signal to B ext trigger input as Ch1 one, but had no response.
I may not be providing correct type of signal to B trigger input.
Does B trigger circuitry need specific conditions to trigger (timing - right after initial A trigger or similar) or could it be broken?

[jstwinkles]

Hello all,
Just wanted to say thank you for this great thread.  Bought a broken 455 a while back and finally got it working thanks to the information posted here!  It's still got some wonky business with the trace, which seem intermittent, but I'm confident that I can figure it out now that there's at least a trace to debug.

Cheers!

[Addicted2AnalogTek]

Hello all,
Just wanted to say thank you for this great thread.  Bought a broken 455 a while back and finally got it working thanks to the information posted here!  It's still got some wonky business with the trace, which seem intermittent, but I'm confident that I can figure it out now that there's at least a trace to debug.

Cheers!

Intermittent traces tend to be dirty switch contacts and dirty/bad pots. shoot some deoxit gold on the contacts

[NilByMouth]

I found why the B timebase wasn't working, Q1098 was dead, internally short, I replaced it with a 2N2222.

I don't understand. In the SM I have for low S/N 465, Q1098 is a 2N3906 PNP transistor. The 2N2222 is NPN?

Malcolm