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I knew I'd seen one before, but somewhere a bit off:

It's on the scope in the main picture for the 5440, , but without a 5L4N.

James,

It is great to hear you are making progress! It looks like you have a few 6,8mfd tantalums shorted. You can use tantalum at or higher capacitance than original or something like Nichcon ULD 47mfd 25V electrolytics as the decoupling for the 15V and less supplies. I do not know if you can get these in Brazil from Mouser. You may have other tantalums that are shorted. It would be a good idea to get more than you need as you may need them in this piece or extra stock. I know you would like to get the parts you need in Brazil.

I will assume you have checked the transistors on boards to see if any are shorted, open or leaky.

This about all I can tell you at this point. Follow what others have said as they are giving great advice. I hope you find and fix your scope.

Mark

Just to add, that the connector which isolated the short from the A2 vertical board, connected directly to one of the two caps which had been notedthis morning.

Evening all.

An update... and happy to say, with progress!

Before heading out this morning, I had a quick probe around on the A2 vertical board and found two tantalums which measured short to ground on both sides but didn't have the time to look further. I suppose because the original problem occurred after I shorted two pins on the A6 interface board, I had almost only looked on that board and the A10 which connects directly to it. That said, it had becaome clear that I needed to expand my search.

Following Rogers suggestion to disconnect the jumpers and take measurements, there was progress made and the 5v rail stopped being a dead short.
It is still only up at 15Ω, however that is great news to me! There is no longer a dead short on any of the low voltage rails :)

It does seem that the reference voltage is in need of resolving before reconnecting the rails, but I 'm not sure how much I'll get done today as it has been a long one, with only an hour or so free to work on the scope.

Tomorrow is another day, and as Harvey suggested, I should have a read through the reference voltage section before continuing.

@ David

I am sure it would be worth checking with a scope however this is the only one I have, hence the determination to get it fixed. But thank you.

@ Mark

Replacing the filter caps is not really an option, as I am in Brazil.
The unit had been working fine. It was only my 'fixing what wasn't broken' which spannered things.
As for the recommendations regarding upgrading certain components I shall look into that and follow up when the unit is out of intensive care.
The MC1458's are both fine.


I am truly grateful to everyone here who has given their time and thought into saving this wonderful old Tek scope.

Tomorrow the reference voltage needs attention but if anyone has any more suggestions as to the next steps then I am all ears.

Good night gents.

It is late here.


James

Hi All,

I've gotten my 5L4N tuned well enough to make use of it. Learned a heck of a lot in the process! It's still a bit sketchy. Getting frequency linearity was _just_ barely achievable, but I think it's within spec and will do fine for my skill level so far.

Now I _really_ want a logarithmic overlay/shield for the screen. I'm thinking it would help tuning the log sweep amplifier as well. The "Tektronix Cookbook of Standard Audio Tests" has some nice charts that "Tektronix, Inc. Encourages" us to copy or print for our own use. This includes 20k and 100k log scale charts. I was thinking of using them as a template or printing them on some projection foil sheets. But they would take some careful scaling to be the right size for a 5111A screen.

Does anyone have a line on these overlays? I'm not finding them as an accessory in the 5L4N manual, including the interim manual. So I don't know what part number to search for. Are there other overlays that might be useful as well?

Thanks,
Dave

(continued) BTW at Amplitude fully CW my "A" goes far more negative then -145 V. The "voltage and waveform conditions" just say CW. Albert

Dave, Albert,

I will do all what you’re both suggesting tomorrow. Yes Albert, I may indeed have misread. I’m running quite a bit of fever at the moment.
Tomorrow I will hopefully be better. I’ll report back as soon as I can.

Thank you both again.

On Wed, Mar 2, 2022 at 08:46 PM, Stephen wrote:

Today’s measurements:

1- Both 6EW6 measure good and strong.
2- Pin 6: +3V
3- Pin 7: +1.6V
4- Pin 8: -4.7V instead of -145V
5- Between Pin 2 and R55: +3V instead of -151V

Stephen, I suppose you misread pin 3 as pin 8 (cathode, "A") in the schematic. That -145 V is measured with Amplitude at maximum. Did you perhaps set Amplitude here to minimum? (But I still would expect pins 6 and 7 to be slightly negative then, not positive).

Albert

Check Q54, does it have base drive? And does it conduct when turned on? Sounds like NO to at least one of those questions. Which is consistent with the multivibrator not running. Scope it and see.

As clearly shown in the parts list, R56 was only used on serial number 200 through 634 and then deleted.
SW242B is on the power supply schematic, towards the upper right corner. It forces AMPLITUDE to maximum in the FAST RISE position.
If you see no change in the switch potentials when it’s flipped, maybe the switch is bad. That usually gives the handle a characteristic “feel” which unfortunately I can’t describe in words but it’s drastically different from a working one.

Dave Wise

From: [email protected] <[email protected]> On Behalf Of Stephen via groups.io
Sent: Wednesday, March 02, 2022 11:46 AM
To: [email protected]
Subject: Re: [TekScopes] Type 106 Saga (Again)

Today’s measurements:

1- Both 6EW6 measure good and strong.
2- Pin 6: +3V
3- Pin 7: +1.6V
4- Pin 8: -4.7V instead of -145V
5- Between Pin 2 and R55: +3V instead of -151V

I would say that it’s very, very wrong….

I didn’t locate V56 (10Ω) in the unit yet.

Also, since I can’t locate SW242B on the schematic, I’m not sure my readings are what they should be.
Meaning that I see that both sides (B side) are always connected no matter the position of the switch. As if the switch was just there for nothing…. I doubt this is normal, otherwise why even have them go through a switch in the first place…. Just connect them directly…

Today’s measurements:

1- Both 6EW6 measure good and strong.
2- Pin 6: +3V
3- Pin 7: +1.6V
4- Pin 8: -4.7V instead of -145V
5- Between Pin 2 and R55: +3V instead of -151V

I would say that it’s very, very wrong….

I didn’t locate V56 (10Ω) in the unit yet.

Also, since I can’t locate SW242B on the schematic, I’m not sure my readings are what they should be.
Meaning that I see that both sides (B side) are always connected no matter the position of the switch. As if the switch was just there for nothing…. I doubt this is normal, otherwise why even have them go through a switch in the first place…. Just connect them directly…

James,

Do what David T. said about ripple. That will tell a lot. David may have found your problem or part of the problem. If you have the original filters in, it would be best to put in new. Make SURE to jumper pads the originals had as a trace. The negative lugs were used instead of traces. Before you replace the caps, measure the voltages from ground to the output of the rectifiers on the + supplies. The negative supplies will need to be across each filter can for each supply.

Trace the voltages from the supplies in the power supply to see where they drop too low. I know you have low/no B+ on the outputs. A short in the rest of the circuit sounds the likely culprit. Any lifting of the supplies to eliminate a section will be best. You could have one or both bad MC1458 opamps. Some of the resistors in the power supply are too small in wattage (R1726 to 2W, R1722 to 1 or 2W, R1718 to 2W (a 68,000 ohm 1% will work), R1727 to 2W, R1733 to 1W). Sometimes a resistor is out of tolerance or open causing problems that can appear to be elsewhere.

C1737 could be leaky causing the 65V to be low. That one I said can be a higher capacitance, e.g. 10-33mfd.

If you have removed any of the screws that the series pass transistors are secured to a grounded heatsink, check to see of the insulating pad is still there and no short from C to ground. Shorting one of the collectors to ground will throw you supply voltages way off.

Read and do what the other posters said. They gave excellent advice.

Mark

I received a private response, which I will quote in part here for the sake of future generations:

"Looking at the schematic x10 gain is not user adjustable. Ratio is set by R1108/(R1108+R1107)=165/(165+1485)=0.1 (i.e x10 mode has 10 times the gain of x1).

Up to 2% error is within spec, do you see a lot more error? Only way to trim is to tweak R1107 and R1108, either replace them with more precise ones or you can add (large) parallel resistors to R1107 or R1108 depending on direction of gain error. To be exact, this would change x1 gain which needs to be corrected again with R1155, which in return corrects x10.

If the error is not much and you can live with it I would leave it as is."

I would credit the person, but not sure why they replied privately. My thanks to the person -- you know who you are! ;-)

interleaved:

On 3/2/2022 7:06 AM, James55 wrote:

Morning all and thank you for the help.

I was a bit tired last night and didn't provide the correct nor complete information, as in amongst all the 'de-' and 're-' soldering,
the minus 8v AC wires had become shorted. The correct DC readings at the test points are;
140v - 25v
65v - 21.54v
15v - 3.705
5v - 0.000
-8v - 0.625
-15v - 0.615

Disconnecting the Bridge rectifiers gives the following AC readings;

CR1721 (65v rail) - 47.53v
CR1751 (15v) - 12.96v
CR1761 (5v) - 6.58v
CR1771 (-8v) - 7.34v
CR1781 (-15v) - 12.34v

If you disconnect the bridge rectifiers (and I assume from the + end, so that they are still connected to the transformer), then what you measure at the + rectifier terminals will be pulsating DC.? What this does test is that the rectifiers themselves are not shorted, one still may be open, though.

The transformer still draws some current due to the core losses, and whatever is directly connected AC wise to the transformer.

The reference voltage tests at around 108v.. In the manual it says either 160 or 140 volts depending on where you read it.

One thing which may be worth noting, is that with all five bridge rectifiers disconnected, the dimbulb still glows.


@ Harvey...

It is a linear power supply.
I shall disassemble the unit more when I have time later today.
Shall be looking further into the reference voltage as right now all the LV rails are disconnected before the bridge rectifiers. Not quite sure I understand the manual though. On the power supply diagram page the reference voltage rail terminates with an arrow... It says, 'S1403B' (a switch) and also has a hexagon with the number '10' inside of it. I assume that the '10' links to a corresponding '10' on a different board?
Which -50v supply are you referring to?

Look at the power supply regulators, one will have extra circuitry taking a DC voltage and running it through a zener diode.? This is the only supply that is standalone.? The manual will tell you so.? The S1403b is a destination, the "10" is schematic sheet on which to find it.? In this supply, you'd want the on-board connections to the DC reference voltage.? Reading the theory of operation is important for these scopes because tektronix is very thorough about such things.? If there's a troubleshooting procedure, follow it.

If you wish more information of a general nature about linear power supply regulators (and tektronix is highly specific per scope), then there are a number of posts concerning 400 series scopes and power supplies.? 7000 series scopes use different supplies.? I'd also recommend searching out the theory of linear regulators.

Harvey

@Dave..

That is what I would have expected and to be honest there have been some shorted tantalums, but I have lost count of how many caps have now been tested. It is time to disconnect more boards until at least the 'area' is identified.

I'll report back either late tonight of tomorrow morning.

James

@ Roger.

Nice one for the heads up.
I had skipped over that page many times on my way to the power supplies diagram and never given it a proper look (it is quite small on the .pdf and needs to be zoomed in).

So, at least there is a solid plan of action for today.
I need to head off now for work but I am feeling determined and positive that this can be resolved.

Sincere thanks to you and everyone who has chipped in thus far.


James

Morning all and thank you for the help.

I was a bit tired last night and didn't provide the correct nor complete information, as in amongst all the 'de-' and 're-' soldering,
the minus 8v AC wires had become shorted. The correct DC readings at the test points are;
140v - 25v
65v - 21.54v
15v - 3.705
5v - 0.000
-8v - 0.625
-15v - 0.615

Disconnecting the Bridge rectifiers gives the following AC readings;

CR1721 (65v rail) - 47.53v
CR1751 (15v) - 12.96v
CR1761 (5v) - 6.58v
CR1771 (-8v) - 7.34v
CR1781 (-15v) - 12.34v

The reference voltage tests at around 108v.. In the manual it says either 160 or 140 volts depending on where you read it.

One thing which may be worth noting, is that with all five bridge rectifiers disconnected, the dimbulb still glows.


@ Harvey...

It is a linear power supply.
I shall disassemble the unit more when I have time later today.
Shall be looking further into the reference voltage as right now all the LV rails are disconnected before the bridge rectifiers. Not quite sure I understand the manual though. On the power supply diagram page the reference voltage rail terminates with an arrow... It says, 'S1403B' (a switch) and also has a hexagon with the number '10' inside of it. I assume that the '10' links to a corresponding '10' on a different board?
Which -50v supply are you referring to?

@Dave..

That is what I would have expected and to be honest there have been some shorted tantalums, but I have lost count of how many caps have now been tested. It is time to disconnect more boards until at least the 'area' is identified.

I'll report back either late tonight of tomorrow morning.

James

Forgive me for chipping in very late in this thread, there are many good suggestions and you have to be very systematic about the process and not take short cuts or do too much work when you are very tired.

I looked at the manual on TekWiki with the file name Tek-466-early.pdf. Immediately before the schematic of the Power Supply is the diagram of power distribution between boards. This shows which of the multi-way connectors need to be removed in order to remove the +5V power to A3, A10, A7, A5 and A2 boards. If you remove all of these connectors and the +5V short remains when measured at the +5V supply then the fault is on the A6 board, this is the worst case with many places to look. Otherwise one or more of the now disconnected boards will show the short circuit on +5V and you have a much smaller area to concentrate on. If you find a short circuit on the A10 storage board and all of the capacitors measure OK with one leg removed then it is possible that one of the 74xx logic chips is the cause. I have found at least one case of this mode of failure but it is very much less common than failed capacitors.

Best wishes for your repair,

Roger

David, Albert,

I will make some more measurements later on. My unit never had that issue you both experienced. It started up right away when it was working.
I remember measuring between R55 and R56, and from memory I didn’t have the proper -145V, but something like +15V (I think). I have to review my notes when I get back home.

BTW, R55 reads dead on. I’ll also check R56.

Thank you both again for your time and inputs.

I’ll report back as soon as I can.

It will almost certainly be a shorted blue-drop (or yellow-drop) tantalum capacitor.

That's what usually brings down a 465/466/475 and various 7K series and TM series plugins with the symptom of a shorted power supply rail.

On Wed, Mar 2, 2022 at 12:43 AM, Dave Wise wrote:

On my own instrument, after power-on, sometimes it doesn’t start until I
switch back and forth between HI AMPLITUDE and FAST RISE. Seems like the multi
needs a kick.

David, I noticed the same in my 106.
Stephen, just for comparison:
Setting 10 kHz, "A" = Vk = -40 V, output in 50R is 2 Vpp . Then Vgk is almost square wave between -1.5 V and -15 V.

Albert

ok, the standard way of testing scope power faults is as follows:

1) determine if you have a linear or a switching supply.? For the 466, I think it's going to be linear.

2) 0 volts or fuses blowing indicates a short

3) disconnect all boards from the power supply and see what it does.? If it's a switching supply you'll have to load it down since most switching supplies need loads to operate.

4) In most tektronix designs of that time, there is one supply that has an internal reference (typically a zener).? All other supplies use that one supply as a reference voltage.? If the reference supply is off, nothing else will be ok.

5) check that the reference voltage is ok.? Check that the supply is ok (it can be, for instance, the -50 volt supply).

6) check the other supplies for proper operation.

7) plug in the other boards to see which one pulls down the supply

8) record the voltages which may show you which supply is bad.

If you have the manual, read the power supply theory of operation (ought to be one), and then see if there's a power supply troubleshooting tree.


Harvey