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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

Looking back through the earlier replies, I shall probably disassemble the verticle board in the morning. It is midnight here now.

zzzzzzzzzzzzz

On Mon, Dec 13, 2021 at 02:39 AM, James55 wrote:

Hi all,
please excuse the lack of input, however I became deflated and just put a cover over the scope and walked away.

Thing is, I really do need a working scope, so today decided to give it another go.

The mains input is now running first through a dimbulb, which dutifully illuminates when the unit is switched on. All of the low voltages rails are close to zero. For example the 65v rail is up at a whopping 10.4v. The minus 15 rail is 0.5v. The minus 8 is 0.4v and the 140v rail is 5.3v with the 5v being shorted to ground at zero volts.

I removed the A5 Trigger, and A7 Timing, boards in the hope of narrowing down the search area.
Things got off to a good start with the discovery of the shorted R1377 resistor, although that made no difference to any of the readings. There is a pure short circuit on the 5v rail however for the life of me I cannot seem to find it.

I have tested and tested all over the A6 and A10 boards, testing voltages and also bell-testing for shorts with the power off. It really is at the point where I can only see trees, without a glimpse of any wood...
I have also covered the board in IPA which all just sat there wet for ages. There are no warm components, or even areas... I wish something would just explode or at least go up in smoke, as I have no real idea as to where else to look.
It did cross my mind that it might be the 5v rail 5500?f filter cap yet although I only have a DMM it still reads 7000?f, so I am assuming it is not shorted.

If anyone has any suggestions at all as to where I might check next please feel free to chip in.

Perhaps I'll just leave it plugged in, as surely a direct short has to start smoking at some point?

James

The EL84’s should be getting plenty of drive on their control grids. Go back along the signal chain from there to the multivibrator. 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.

Dave Wise

From: [email protected] <[email protected]> On Behalf Of Stephen via groups.io
Sent: Tuesday, March 01, 2022 3:20 PM
To: [email protected]
Subject: Re: [TekScopes] Type 106 Saga (Again)

On Tue, Mar 1, 2022 at 11:26 PM, Albert Otten wrote:

Stephen, the ripple sizes in your pictures are only a fraction of what I see
in my working 106. Perhaps they are so small because the 4 tubes never
conduct.
Even with almost exhausted tubes you should get some output square wave.
I would measure the waveform at the grid line w.r.t. the DC cathode
voltage(s). And then consult Ia-Vg characteristics of the EL84.
Albert

Albert,
You’re probably right. Hence the zero volt output measured on all 3. The question is why did they stop conducting all of a sudden, whereas the unit was working perfectly the day before, and had been for weeks.

I’m pretty sure it’s not the tubes themselves. Had it been the tubes, changing them would’ve solved the issue.
It’s kinda late in Europe, but tomorrow I’ll check R55 and the voltages at the plates and grids.

Will report back then.

Thank you.

On Tue, Mar 1, 2022 at 11:26 PM, Albert Otten wrote:

Stephen, the ripple sizes in your pictures are only a fraction of what I see
in my working 106. Perhaps they are so small because the 4 tubes never
conduct.
Even with almost exhausted tubes you should get some output square wave.
I would measure the waveform at the grid line w.r.t. the DC cathode
voltage(s). And then consult Ia-Vg characteristics of the EL84.
Albert

Albert,
You’re probably right. Hence the zero volt output measured on all 3. The question is why did they stop conducting all of a sudden, whereas the unit was working perfectly the day before, and had been for weeks.

I’m pretty sure it’s not the tubes themselves. Had it been the tubes, changing them would’ve solved the issue.
It’s kinda late in Europe, but tomorrow I’ll check R55 and the voltages at the plates and grids.

Will report back then.

Thank you.

Stephen, the ripple sizes in your pictures are only a fraction of what I see in my working 106. Perhaps they are so small because the 4 tubes never conduct.
Even with almost exhausted tubes you should get some output square wave.
I would measure the waveform at the grid line w.r.t. the DC cathode voltage(s). And then consult Ia-Vg characteristics of the EL84.
Albert

Greetings
I sent you an email offlist as I may have some resources willing to help ID this. Let me know if you want me to ask them for help.
-ls-

Hello--

I'm offering FS one only? Tektronix 02-1004-402 (s/n 27694) power supply for the 4957;

it's untested but in VG cosmetic condition.

graphics tablet. The power supply sources +12 VDC @ 0.3 A and -12 VDC? @0.1 A.

I'm asking $7.50 plus USPS postage.

Questions welcomed, PayPal honored.

Thanks, and 73--

Brad? AA1IP

On Tue, Mar 1, 2022 at 10:04 PM, Dave Wise wrote:

Stephen, I mentioned the socket mod as a PSA. I wasn’t exhorting you to do
it.

I get it. Sorry if I misunderstood you.

Stephen, I mentioned the socket mod as a PSA. I wasn’t exhorting you to do it.

From: [email protected] <[email protected]> On Behalf Of Stephen via groups.io
Sent: Tuesday, March 01, 2022 1:02 PM
To: [email protected]
Subject: Re: [TekScopes] Type 106 Saga (Again)

I’ve rechecked all the tubes, and they still read very strong on my HealthKit tester. Since a I had a quad of EL84’s laying around, I replaced all of them as precaution. They’re not brand new, but they read very strong as well. That didn’t make any change.
The DTPT switch seems to be ok. Although I can’t seem to locate the B side on the schematic.
I haven’t checked R55 yet.

David, are you suggesting that I rewire the tube sockets, even though everything was working properly before with EL84’s?

I’ve rechecked all the tubes, and they still read very strong on my HealthKit tester. Since a I had a quad of EL84’s laying around, I replaced all of them as precaution. They’re not brand new, but they read very strong as well. That didn’t make any change.
The DTPT switch seems to be ok. Although I can’t seem to locate the B side on the schematic.
I haven’t checked R55 yet.

David, are you suggesting that I rewire the tube sockets, even though everything was working properly before with EL84’s?

On Tue, Mar 1, 2022 at 10:29 AM, Colin Herbert wrote:

A2Q9 base-emitter junction shows infinite resistance one way and
452K the other.

Ideally if you have "diode check" mode on your DVM that is what you need to use with the transistor off but all indications point to a faulty A2Q9.

Both A2Q8 and A2Q9 were Motorola SM4713 originally and it looks as though a
2N3251 would be an equivalent now, though they are ?2.40 each.

For now you can use widely available 2N3906 to get your debug going. I don't have this equipment and didn't look at the design carefully so there may be better equivalents recommended by group members.

Ozan

To work with 6BQ5/7189, a minor wiring change is needed. Pins 1 and 6 are “unspecified internal connection” while the corresponding 7189A pins are explicitly G1 and G2 respectively.
On all four sockets, move the G2 wire from pin 6 to pin 9. That is all.
EL84 pins 1 and 6 are no-connect so this tube doesn’t need the mod.

The output tubes yank their plates toward their cathodes (which are being held at a negative voltage determined by the AMPLITUDE control), then release them and the load resistance pulls the line back up to ground.

As the tubes wear out, two things happen. (1) Cathode emission decreases. This ultimately limits the maximum negative excursion. (2) Sometimes the cathode develops an “interface layer” which acts like an RC time constant. Since only the positive corner’s quality is specified in HI AMPLITUDE mode, this doesn’t matter unless it becomes so bad that it compromises the negative output in FAST RISE mode.

Dave Wise

From: [email protected] <[email protected]> On Behalf Of Stephen via groups.io
Sent: Tuesday, March 01, 2022 10:20 AM
To: [email protected]
Subject: Re: [TekScopes] Type 106 Saga (Again)

On Tue, Mar 1, 2022 at 06:39 PM, Dave Wise wrote:

In Fast Rise mode, the output tubes provide base drive to the Fast Rise
circuit. See SW242A on the schematic.
SW242B bypasses the AMPLITUDE control in Fast Rise mode, jamming it to
maximum. So don’t leave it running for hours in Fast Rise mode unless you
have lots of spare 7189A’s.

Dave Wise

Hmmm. I have left it on a few times for quite a long time…
Mine doesn’t have 7189A’s. It has old Philips EL84’s which read very strong. But I’ll check them again when I get back.

I’ll report back when I can get check all that tou guys suggested.

And thanks for the tip regarding preserving the tube life. I’ll certainly be more careful now….

I was thinking about the 475A, but I really don't need it.
-Dave

Hi Ozan,
I checked both A2Q8 and A2Q9 with my checker and they both gave B of about 78 and uG at 752. I'm guessing that these show the transistors to be OK, but I am definitely rusty on this stuff - I might be getting everything wrong. I admit to giving A2Q9 a bit of a "cooking" when I put it back into circuit, but I don't think I ruined it.

Doing what you suggested to A2Q9, the base looks to be connected to ground OK with the device off and checking the resistance to ground; the voltage with the device turned on gives zero volts (I may have been making this measure incorrectly before, because the space available was small). With the power turned off, A2Q9 base-emitter junction shows infinite resistance one way and 452K the other.

Both A2Q8 and A2Q9 were Motorola SM4713 originally and it looks as though a 2N3251 would be an equivalent now, though they are ?2.40 each.
Colin.

On Tue, Mar 1, 2022 at 06:39 PM, Dave Wise wrote:

In Fast Rise mode, the output tubes provide base drive to the Fast Rise
circuit. See SW242A on the schematic.
SW242B bypasses the AMPLITUDE control in Fast Rise mode, jamming it to
maximum. So don’t leave it running for hours in Fast Rise mode unless you
have lots of spare 7189A’s.

Dave Wise

Hmmm. I have left it on a few times for quite a long time…
Mine doesn’t have 7189A’s. It has old Philips EL84’s which read very strong. But I’ll check them again when I get back.

I’ll report back when I can get check all that tou guys suggested.

And thanks for the tip regarding preserving the tube life. I’ll certainly be more careful now….

In Fast Rise mode, the output tubes provide base drive to the Fast Rise circuit. See SW242A on the schematic.
SW242B bypasses the AMPLITUDE control in Fast Rise mode, jamming it to maximum. So don’t leave it running for hours in Fast Rise mode unless you have lots of spare 7189A’s.

Dave Wise

From: [email protected] <[email protected]> On Behalf Of Stephen via groups.io
Sent: Tuesday, March 01, 2022 9:15 AM
To: [email protected]
Subject: Re: [TekScopes] Type 106 Saga (Again)

On Tue, Mar 1, 2022 at 05:55 PM, Albert Otten wrote:

Interleaved.

Broken switch SW242A? In High Ampl mode you should measure R99 600R at the GR
output plug.
What would happen when R55 is open?
Is the output 0V or some constant negative voltage?

Thanks Albert,

Interesting…. I didn’t think of a broken switch. I check that out when I’ll get beck home later.
I’ll check again, but from memory all of the outputs are pretty close to 0V. I’ll check that again.

I’ll also check R55.

I don't think this is weird. The -20 V on top of "A" supplies the grid and
trigger circuits. The 4x output tubes anode currents flow in a separate
circuit from GND to "A", regulated by anode-cathode voltage, not by grid
amplitude.

Ok, but the 4 output tubes only supply the High Amplitude section, if I understood correctly.

Why would all outputs be out? That must be caused by something they all share in common.
Maybe the switch…

Albert

On Tue, Mar 1, 2022 at 05:55 PM, Albert Otten wrote:

Interleaved.

Broken switch SW242A? In High Ampl mode you should measure R99 600R at the GR
output plug.
What would happen when R55 is open?
Is the output 0V or some constant negative voltage?

Thanks Albert,

Interesting…. I didn’t think of a broken switch. I check that out when I’ll get beck home later.
I’ll check again, but from memory all of the outputs are pretty close to 0V. I’ll check that again.

I’ll also check R55.

I don't think this is weird. The -20 V on top of "A" supplies the grid and
trigger circuits. The 4x output tubes anode currents flow in a separate
circuit from GND to "A", regulated by anode-cathode voltage, not by grid
amplitude.

Ok, but the 4 output tubes only supply the High Amplitude section, if I understood correctly.

Why would all outputs be out? That must be caused by something they all share in common.
Maybe the switch…

Albert

On Mon, Feb 28, 2022 at 07:38 PM, Stephen wrote:

My type 106 was working fine until a few days ago when I had no more output at
all on any output. Neither the High Amplitude nor the +/- Fast Rise.

Broken switch SW242A? In High Ampl mode you should measure R99 600R at the GR output plug.
What would happen when R55 is open?
Is the output 0V or some constant negative voltage?

Now the last one (-20) is extremely weird as the square waves follow the frequency I set on the unit, but not the amplitude at all.

I don't think this is weird. The -20 V on top of "A" supplies the grid and trigger circuits. The 4x output tubes anode currents flow in a separate circuit from GND to "A", regulated by anode-cathode voltage, not by grid amplitude.

Albert