7104 versions, and vertical amplifier issue


cmjones01
 

A couple of years ago I picked up a 7104 with the full set of plugins
(7B10, 7B15 and two 7A29s, one of which has the elusive option 04
variable delay) at a bargain price in an industrial disposal auction.
I didn't have time to do anything with it at the time and so put it in
the attic. I've just got it out again and experimented with it a bit.
The good news is that quite a lot of it seems to work. I've had a
trace and readout on the screen. All the controls and the plugin
connectors need a good dose of contact cleaner, as is to be expected,
but there's a more persistent fault.

The vertical deflection only seems to work about half the time. It
either works normally, or everything gets shunted up above the top of
the screen. The beam finder reveals that everything's still there,
just too high to see. With the beam finder enabled, I can see that
trying to move the trace downwards with the Y plugins' vertical
position control first moves it downwards, until about half way, then
it starts moving up again. At no point is it visible without the beam
finder.

I've checked the power test points on the vertical deflection board
under the fault condition, and all rails (+50/+15/+5/-15/-50) are
fine.

While I'm here, are there multiple versions of the 7104 hardware?
Because my scope seems to have a different vertical board to the one
in the paper manual I've got. The one in the manual has fewer Hypcon
devices than mine has, and at least one connector is numbered
differently.

Thank you
Chris


Roger Evans
 

Chris,

Have you tried exercising / cleaning the miniature coax connectors that carry the +/- Y signals between the backplane and the vertical amplifier. Since the whole of each half of the vertical amplifier is DC coupled any of these going open circuit will probably throw that half of the vertical amplifier hard off or hard on.

Regards,
Roger


Jean-Paul
 

bonjour the revisions of the manual apply to a range of serial numbers.

Besides coax connections, the CRT vert pins can get intermittent.

Finally beware of burn in during debugging or of readout area in use.

See if the CRT beam current timeout is operating correctly

Bon Chance


Jon


cmjones01
 

Roger,

Thank you for the tip. I looked a bit more closely and my machine
does, in fact, match the manual, but I'd got confused because the PCB
layouts in the manual often have blank spaces where great big obvious
Hypcon chips actually are.

I looked at the DC conditions in the vertical amplifier and found that
they went awry between the driver and vertical output chips. I removed
the vertical output chip and found some corrosion on the PCB pads,
which I gently cleaned off with a small stiff brush. I put it all back
together carefully and now the fault has changed: the DC conditions
are different, as if there's almost no current flowing in the Y output
chip's input transistors, but I now have a fully functional scope with
the entire image compressed in to about 1.5 divisions in the middle of
the screen. I tried removing and reseating that Hypcon again but
nothing more changed. I still suspect there's a poor contact there
somewhere though.

Chris

On Wed, Jun 16, 2021 at 12:24 PM Roger Evans via groups.io
<very_fuzzy_logic=yahoo.com@groups.io> wrote:

Chris,

Have you tried exercising / cleaning the miniature coax connectors that carry the +/- Y signals between the backplane and the vertical amplifier. Since the whole of each half of the vertical amplifier is DC coupled any of these going open circuit will probably throw that half of the vertical amplifier hard off or hard on.

Regards,
Roger





Mark Vincent
 

Chris,

The Hypcons are sensitive to being clean and the contacts being aligned right. You should remove each and clean the contacts on the chip and connector. Also do this to the other ICs and transistors. The square mounting frames for the Hypcons should be put on with an even pressure on all sides. The screws are tightened to snug in opposite corners at a time as the lug nuts on the wheel of a vehicle. I did add good heatsink compound to the Hypcons and the heatsinks. Roger is right about making sure the coax connectors are also cleaned. It is possible the neck pins have oxidation on them. Check the voltage at the input of the vertical if cleaning does not fix the problem. It is possible the problem is earlier. One dirty contact somewhere can cause headaches in finding it. Many here will agree to this having seen it enough times.

IF yours looses sync in the readout, the 741 IC under the handle on the horiz. board towards the rear will be bad. I had this happen in mine. It will occur when it warms a little. This happened in mine after a minute with the left side off. The trace will remain normal. This information is only in case this happens to yours or anyone else's.

Jon is right about keeping the intensity low. When I use mine, the intensity is enough to see the line and readout. When a trace is on the screen, I turn the intensities up a little. The intensities I keep it at are so that it is barely visible until I raise it enough to see a trace and readout which is still low. The yellow LED will not come on the way I keep the two set. It may be easier to use a lamp on the circuit while keeping the screen in a low light level to ensure the trace seen is safe for the MCP.

Mark


Jean-Paul
 

Rebonjour à tous

Bon courage, sure you will fix it,

The 7A29 have very special elastomeric switches AC/DC and attenuator that are prone to intermittents.

Use special precautions in cleaning as per manual.

Enjoy

Jon

PS This fine instrument is a real classic, the fastest analog CRT scope ever, originally for US AEC nuclear weapons testing. We are very lucky to have such a great design revitalized and in our labs. Vive la Tektronix !


Jean-Paul
 

Chuck Harris reccomended red plastic nut tools from old Heathkits, to gently place the hypcon nuts whilt holding the chip down to the socket

Jon


cmjones01
 

On Wed, Jun 16, 2021 at 4:57 PM Mark Vincent <orangeglowaudio@gmail.com> wrote:
The Hypcons are sensitive to being clean and the contacts being aligned right. You should remove each and clean the contacts on the chip and connector. Also do this to the other ICs and transistors. The square mounting frames for the Hypcons should be put on with an even pressure on all sides. The screws are tightened to snug in opposite corners at a time as the lug nuts on the wheel of a vehicle. I did add good heatsink compound to the Hypcons and the heatsinks. Roger is right about making sure the coax connectors are also cleaned. It is possible the neck pins have oxidation on them. Check the voltage at the input of the vertical if cleaning does not fix the problem. It is possible the problem is earlier. One dirty contact somewhere can cause headaches in finding it. Many here will agree to this having seen it enough times.
Thank you. I checked the DC conditions on the Y amplifier board and
the imbalance appeared between the Y driver hypcon and the Y output
hypcon. I'll go back and clean up the hypcon I removed more carefully.
There was loads of dust in the scope and it's definitely been a bit
damp at some point, so it's working surprisingly well, considering!

IF yours looses sync in the readout, the 741 IC under the handle on the horiz. board towards the rear will be bad. I had this happen in mine. It will occur when it warms a little. This happened in mine after a minute with the left side off. The trace will remain normal. This information is only in case this happens to yours or anyone else's.
Good to know. So far the readout has behaved itself, but I'll bear this in mind.

Jon is right about keeping the intensity low. When I use mine, the intensity is enough to see the line and readout. When a trace is on the screen, I turn the intensities up a little. The intensities I keep it at are so that it is barely visible until I raise it enough to see a trace and readout which is still low. The yellow LED will not come on the way I keep the two set. It may be easier to use a lamp on the circuit while keeping the screen in a low light level to ensure the trace seen is safe for the MCP.
Yes, I've been surprised by how dim the trace has to be to keep the
"limited viewing time" light off. But that's fine - I have no
intention of using the 7104 as an everyday scope and it'll get used
from time to time for high-speed stuff when I'm here in the UK. Even
in its current sick state, it's very impressive to trigger a single
sweep at 200ps/div and still see the trace in normal room lighting.

Chris


cmjones01
 

On Wed, Jun 16, 2021 at 5:35 PM Jean-Paul <jonpaul@ix.netcom.com> wrote:
Rebonjour à tous

Bon courage, sure you will fix it,
Thank you!

The 7A29 have very special elastomeric switches AC/DC and attenuator that are prone to intermittents.

Use special precautions in cleaning as per manual.
I have other 7A29s which I've used with my 7904A and 7912AD,and their
attenuator switches have been troublesome. The plastic cams crack so
the whole thing won't rotate properly any more. On at least one I
repaired them with epoxy a few years ago and they're still working
fine. The two 7A29s which came with this scope do have slightly stiff
attenuator switches so I'll treat them with care until I can fix them
properly. I'm especially pleased to have got the opt.4 version with
the variable delay.

PS This fine instrument is a real classic, the fastest analog CRT scope ever, originally for US AEC nuclear weapons testing. We are very lucky to have such a great design revitalized and in our labs. Vive la Tektronix !
Though I have digital scopes, I don't think I'll ever give up on the
analogue ones. For troubleshooting, even of modern high-speed digital
systems, the analogue scope's trace gives me so much information with
so little effort that it's hard to replace.


 

On Wed, Jun 16, 2021 at 07:49 PM, cmjones01 wrote:


Yes, I've been surprised by how dim the trace has to be to keep the
"limited viewing time" light off.
These 'scopes are very useful for watching voltage steps. Since the step almost always takes a small fraction of the signal period, average beam current is low. When watching at a relatively low s/div horizontal speed, as is done when checking as you are doing, the average beam current is much higher, so the yellow light, which sort of represents average beam current, comes on rather early. OTOH, MCP wear is not so much a function of average beam current as of integrated secondary emission from each microchannel channel.
In conclusion: The yellow light coming on isn't as indicative of (excess) wear while testing at higher duty-cycle beams. Still, reducing intensity as much as possible is just good practice with these CRT's.

Raymond


 

On Wed, Jun 16, 2021 at 07:53 PM, cmjones01 wrote:


I have other 7A29s which I've used with my 7904A and 7912AD,and their
attenuator switches have been troublesome. The plastic cams crack so
the whole thing won't rotate properly any more. On at least one I
repaired them with epoxy a few years ago and they're still working
fine.
I have the same experience and have used epoxy to repair them as well.
As a preventative measure against breakage and after repair, I applied a tiny amount of grease on the cams, to reduce the forces on the roller while being lifted by the cam. This has helped to prevent breakage in at least two of my 7A29's so far.

Raymond


 

On Wed, Jun 16, 2021 at 08:11 PM, Raymond Domp Frank wrote:


When watching at a relatively low s/div horizontal speed
That should have been "When watching at a relatively low horizontal speed..."

Raymond


cmjones01
 

Good news: the scope now works. I cleaned and reseated the Y output hypcon
U862 a couple of times but nothing changed. Then I cleaned and reseated the
driver U842 and, for good measure, swapped its elastomer and plastic frame
with U862. Now I have full vertical sweep, and a usable scope.

There are lots of niggles remaining: both 7A29s have attenuator contact
problems (the attenuation factors are randomly wrong) as well as an odd
effect rounding the end of the leading edge of the calibrator waveform,
which I suspect is due to the feed-beside adjustments. The 7B15 is
reluctant to trigger and the plug-in connectors have various
intermittent issues, as I'd expect on a scope which has been stored for a
while.

Chris

On Wed, 16 Jun 2021, 16:57 Mark Vincent, <orangeglowaudio@gmail.com> wrote:

Chris,

The Hypcons are sensitive to being clean and the contacts being aligned
right. You should remove each and clean the contacts on the chip and
connector. Also do this to the other ICs and transistors. The square
mounting frames for the Hypcons should be put on with an even pressure on
all sides. The screws are tightened to snug in opposite corners at a time
as the lug nuts on the wheel of a vehicle. I did add good heatsink compound
to the Hypcons and the heatsinks. Roger is right about making sure the coax
connectors are also cleaned. It is possible the neck pins have oxidation on
them. Check the voltage at the input of the vertical if cleaning does not
fix the problem. It is possible the problem is earlier. One dirty contact
somewhere can cause headaches in finding it. Many here will agree to this
having seen it enough times.

IF yours looses sync in the readout, the 741 IC under the handle on the
horiz. board towards the rear will be bad. I had this happen in mine. It
will occur when it warms a little. This happened in mine after a minute
with the left side off. The trace will remain normal. This information is
only in case this happens to yours or anyone else's.

Jon is right about keeping the intensity low. When I use mine, the
intensity is enough to see the line and readout. When a trace is on the
screen, I turn the intensities up a little. The intensities I keep it at
are so that it is barely visible until I raise it enough to see a trace and
readout which is still low. The yellow LED will not come on the way I keep
the two set. It may be easier to use a lamp on the circuit while keeping
the screen in a low light level to ensure the trace seen is safe for the
MCP.

Mark






 

On Wed, Jun 16, 2021 at 6:36 PM Jean-Paul <jonpaul@ix.netcom.com> wrote:

Rebonjour à tous

Bon courage, sure you will fix it,

The 7A29 have very special elastomeric switches AC/DC and attenuator that are prone to intermittents.

Use special precautions in cleaning as per manual.

Enjoy

Jon

PS This fine instrument is a real classic, the fastest analog CRT scope ever, originally for US AEC nuclear weapons testing. We are very lucky to have such a great design revitalized and in our labs. Vive la Tektronix !
The Soviets had 3GHz direct display scopes.


Tom Lee
 

And the 7104's ~1V/cm jug is good to 3GHz as well, a fact exploited in specially modded versions of the 7104 sold by at least one company (B&H Engineering) back in the day. The cost was given in dBdollars to help soften the sticker shock.

--Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 6/16/2021 15:05, cheater cheater wrote:
On Wed, Jun 16, 2021 at 6:36 PM Jean-Paul <jonpaul@ix.netcom.com> wrote:
Rebonjour à tous

Bon courage, sure you will fix it,

The 7A29 have very special elastomeric switches AC/DC and attenuator that are prone to intermittents.

Use special precautions in cleaning as per manual.

Enjoy

Jon

PS This fine instrument is a real classic, the fastest analog CRT scope ever, originally for US AEC nuclear weapons testing. We are very lucky to have such a great design revitalized and in our labs. Vive la Tektronix !
The Soviets had 3GHz direct display scopes.




Dave Seiter
 

Although they probably weren't "portable" like the 7104.  In the photos I've seen, they were more like installations.
-Dave

On Wednesday, June 16, 2021, 03:06:49 PM PDT, cheater cheater <cheater00social@gmail.com> wrote:

On Wed, Jun 16, 2021 at 6:36 PM Jean-Paul <jonpaul@ix.netcom.com> wrote:

Rebonjour à tous

Bon courage, sure you will fix it,

The 7A29 have very special elastomeric switches AC/DC and attenuator that are prone to intermittents.

Use special precautions in cleaning as per manual.

Enjoy

Jon

PS  This fine instrument is a real classic, the fastest analog CRT scope ever, originally for US AEC nuclear weapons testing.  We are very lucky to have such a great design revitalized and in our labs. Vive la Tektronix !
The Soviets had 3GHz direct display scopes.


 

On Thu, Jun 17, 2021 at 12:06 AM, cheater cheater wrote:


The Soviets had 3GHz direct display scopes.
AFAIK, the 7104 was (claimed to be) the only general-purpose, commercially available plugin 'scope with a bandwidth of 1 GHz.

Raymond


Tom Lee
 

I believe that is a fair statement.

-- Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 6/16/2021 15:33, Raymond Domp Frank wrote:
On Thu, Jun 17, 2021 at 12:06 AM, cheater cheater wrote:

The Soviets had 3GHz direct display scopes.
AFAIK, the 7104 was (claimed to be) the only general-purpose, commercially available plugin 'scope with a bandwidth of 1 GHz.

Raymond




 

Agreed

On Thu, Jun 17, 2021 at 12:35 AM Tom Lee <tomlee@ee.stanford.edu> wrote:

I believe that is a fair statement.

-- Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 6/16/2021 15:33, Raymond Domp Frank wrote:
On Thu, Jun 17, 2021 at 12:06 AM, cheater cheater wrote:

The Soviets had 3GHz direct display scopes.
AFAIK, the 7104 was (claimed to be) the only general-purpose, commercially available plugin 'scope with a bandwidth of 1 GHz.

Raymond









Dave Seiter
 

Didn't the French  have a 1GHz GP scope?   Or am I thinking of a French version of the 519(ish, and maybe not portable either)?
-Dave

On Wednesday, June 16, 2021, 03:35:29 PM PDT, Tom Lee <tomlee@ee.stanford.edu> wrote:

I believe that is a fair statement.

-- Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 6/16/2021 15:33, Raymond Domp Frank wrote:
On Thu, Jun 17, 2021 at 12:06 AM, cheater cheater wrote:

The Soviets had 3GHz direct display scopes.
AFAIK, the 7104 was (claimed to be) the only general-purpose, commercially available plugin 'scope with a bandwidth of 1 GHz.

Raymond