Date   
Re: Tektronix 7904, no horizontal trace on input B

Hermansson Amplification
 

Thank you all for your responses!

I will look into the manual and read about the routing path!

To answer some of your questions:
Yes, the trigger light lights up on the timebase when I apply signal to the vertical input. And you can see the vertical signal on the upper trace when I press beam finder.

I’ve tried to put a vertical amplifier into the horizontal input B but I can only see the read out volt/div on the display.

The intensity B knob is very very stiff! I needed a pliers to move it, but it affects the brightness of the beam finder dots when I turn it. And I guess I wouldn’t see the dots when I press beam finder either if the potentiometer was the problem?

I believe this scope has been stored for a long time but it seems to be in very good shape for its age. It was inspected by Tektronix in Sweden in 1972 so it’s an early unit.

Best regards,
Henric

And you think our collecting hobby is crazy and takes up a lot of space

John Williams
 

Re: Tek 576 noise and looping

 

Hi Peter,
That is a clever idea to compare high frequency transistors (low Miller Effect capacitance results in small loops) to low frequency transistors (greater capacitance means larger loops).

Even bigger loops will be found in power transistors because their E, B, and C have to be larger to handle the currents. Their loops will be large provided their current gain (Beta) is good. But as a rule of thumb the gain of a power transistor is optimized to peak at high currents since it will be controlling high power. At very low currents a power transistor's current gain may not be very much resulting in a relatively small loop even though it has a large capacitance between base and collector.

The size of the loop is directly proportional to the capacitance between base and collector and to the Beta (current gain) of the transistor. So a transistor with low gain will have a smaller loop than a transistor with very high Beta all things being equal.

Dennis Tillman W7PF

-----Original Message-----
From: peter bunge
Sent: Friday, November 15, 2019 12:27 PM
Subject: Re: [TekScopes] Tek 576 noise and looping

<SNIP>
Thanks for your explanation which I tested by comparing curves with slow and fast transistors. I had some trouble trying to find a couple with matching gain but the high freq (900 MHz) transistor performed perfectly with nice curves at low current. On the other hand the slow transistor had huge loops.




--
Dennis Tillman W7PF
TekScopes Moderator

Re: 465B soft start?

Tom Gardner
 

On 18/11/19 22:58, Raymond Domp Frank wrote:
On Mon, Nov 18, 2019 at 10:01 PM, Tom Gardner wrote:

Switching power supplies operate to keep the output power constant.
Hence if the input voltage is lower, the input current must be higher.

Increased current stresses components such as the rectifiers and
switching transistors.
The 465B has a linear power supply.
Doh! Too much time spent inside a 2465 :(

Apologies.

Re: 465B soft start?

 

On Mon, Nov 18, 2019 at 10:01 PM, Tom Gardner wrote:


Switching power supplies operate to keep the output power constant.
Hence if the input voltage is lower, the input current must be higher.

Increased current stresses components such as the rectifiers and
switching transistors.
The 465B has a linear power supply.
Low-spec'ed (if so) working voltage hasn't affected those caps for the past 35-odd years. Also, those are (were?) high-quality caps so I wouldn't bother. Epoxy-encapsulated (i.e. dipped) tantalum caps are another matter, especially those with little voltage headroom. The 465B is stuffed with those but slow-on won't help those much I'm afraid. Lots about all that to be found in this group.

Raymond
Power-on current surge puts a strain on the bridge rectifiers. That has been an issue with some 465's.

Re: TDS3012B NVRAM

 

On Mon, Nov 18, 2019 at 11:45 PM, Raymond Domp Frank wrote:


You'll find what you're looking for in my message #157465 in thread " Clock
error on TDS3034", including link to pictures of the Dallas Module.
That's if you're prepared to open the module.

Raymond

Re: TDS3012B NVRAM

 

Hi Ferenc,
You'll find what you're looking for in my message #157465 in thread " Clock error on TDS3034", including link to pictures of the Dallas Module.

Raymond

Re: Tektronix 7904, no horizontal trace on input B

 

On Mon, Nov 18, 2019 at 11:34 PM, Raymond Domp Frank wrote:


Silly question: Are you sure the A-slot Intensity isn't completely off?
That should be "B"-slot of course

Raymond

Re: Tektronix 7904, no horizontal trace on input B

 

Silly question: Are you sure the A-slot Intensity isn't completely off? Could be the knob or a pot with problems.

Raymond

Re: Tektronix 7904, no horizontal trace on input B

Robert Dixon
 

Hi again Henric,

Another trick that may help narrow the problem, is understanding that 7000 series CROs can be put into X-Y mode by putting a vertical amplifier in a "timebase" slot, and then drive both amps with the same signal. I can't remember if you need a timebase for this, but the manuals will help.

Robert Dixon

On 19 Nov 2019, at 07:42, Robert Dixon via Groups.Io <lymphominator=yahoo.com@groups.io> wrote:

Hi Henric,
It looks like the trigger light on the timebase responds the same in both slots. Try varying your input amp settings to confirm this. If so, it suggests that the trigger signal is getting to the timebase, and the problem is B) as Dennis describes below.

Good luck. The 7904 is a nice piece of gear.
BTW, YouTube video for diagnosis is a great way to make the symptoms clear.

Robert Dixon

On 19 Nov 2019, at 06:24, Dennis Tillman W7PF <@Dennis_Tillman_W7PF> wrote:

Hi Henric,

The first thing I notice in your video is that when you put the time base in the B horizontal slot the 7904 recognizes it is present because it displays the on-screen readout time/div setting on the bottom right part of the CRT. That is a good sign.

The second thing I see is when you press the beam finder with the time base in the B horizontal slot the display you get shows there is no sweep present. You are just getting the vertical signals on the screen without any horizontal sweep.

There could be two reasons for this:
A) The time base is not getting a trigger signal when it is in the B horizontal slot. One test you can perform would be to feed a trigger signal into the external trigger input of the time base while in the B slot to see if this fixes the problem. If it does then that confirms the trigger signal is not getting to the B slot from the vertical amplifiers. That could be caused by a bad front panel B Trigger Source Switch or by the IC that controls the routing of this trigger signal which would be on the backplane PC board. Also on the rear of the 7904 (or maybe even on the front of it) there are several BNC connectors which bring out critical signals like trigger signals. If there is a B Trigger Signal output make sure it is present on the front or rear panel BNC connectors.

B) The time base is being triggered and generating a sweep but the sweep is not getting from the time base to the horizontal amplifier in the mainframe. Once again there are ICs on the back plane that route this sweep signal. The B Sweep signal comes out to one of the front or rear BNC connectors so you should check for it there. If it isn't there and if it isn't on the CRT the IC that switches it thru from the back plane to the horizontal amplifier may not be getting the right switching signal or it may be bad.

The most important thing you can do for your own benefit and to learn how your new scope works is to read the Theory of Operation section of the service manual. It explains everything! For the moment read the parts about how the trigger signal is routed and how the sweep signal is routed to learn the various places they go in the scope and which ICs they go through to get a better idea of exactly where to look for where it is being blocked.

Dennis Tillman W7PF

-----Original Message-----
From: @HermanssonAmplification
Sent: Monday, November 18, 2019 7:06 AM
Subject: [TekScopes] Tektronix 7904, no horizontal trace on input B

I just bought a Tektronix 7904 scope and realized that something is wrong with horizontal input B.
Horizontal input A works fine but I got no trace on input B. If I press “Beam finder” slightly I see dots for each inputs that are activated in the vertical slots and if I press the “Beam finder” harder I see bigger dots. I only see the dots when I press “Beam finder” otherwise the screen is blank when horizontal input B is activated.

Any suggestions where to start? I’ve measured the voltages on the Z axis-PCB but nothing alarming there. Since the horizontal Input A works something might be bad on the “Trigger B”-PCB? Or where should I start?

Here’s a video showing the problem:
https://youtu.be/KuPenOSkyJg

I’ve been exercising the switches and cleaned the input slots for the plugin.
Thank you in advance!

Best regards,
Henric




--
Dennis Tillman W7PF
TekScopes Moderator


Re: Tektronix 7904, no horizontal trace on input B

Robert Dixon
 

Hi Henric,
It looks like the trigger light on the timebase responds the same in both slots. Try varying your input amp settings to confirm this. If so, it suggests that the trigger signal is getting to the timebase, and the problem is B) as Dennis describes below.

Good luck. The 7904 is a nice piece of gear.
BTW, YouTube video for diagnosis is a great way to make the symptoms clear.

Robert Dixon

On 19 Nov 2019, at 06:24, Dennis Tillman W7PF <@Dennis_Tillman_W7PF> wrote:

Hi Henric,

The first thing I notice in your video is that when you put the time base in the B horizontal slot the 7904 recognizes it is present because it displays the on-screen readout time/div setting on the bottom right part of the CRT. That is a good sign.

The second thing I see is when you press the beam finder with the time base in the B horizontal slot the display you get shows there is no sweep present. You are just getting the vertical signals on the screen without any horizontal sweep.

There could be two reasons for this:
A) The time base is not getting a trigger signal when it is in the B horizontal slot. One test you can perform would be to feed a trigger signal into the external trigger input of the time base while in the B slot to see if this fixes the problem. If it does then that confirms the trigger signal is not getting to the B slot from the vertical amplifiers. That could be caused by a bad front panel B Trigger Source Switch or by the IC that controls the routing of this trigger signal which would be on the backplane PC board. Also on the rear of the 7904 (or maybe even on the front of it) there are several BNC connectors which bring out critical signals like trigger signals. If there is a B Trigger Signal output make sure it is present on the front or rear panel BNC connectors.

B) The time base is being triggered and generating a sweep but the sweep is not getting from the time base to the horizontal amplifier in the mainframe. Once again there are ICs on the back plane that route this sweep signal. The B Sweep signal comes out to one of the front or rear BNC connectors so you should check for it there. If it isn't there and if it isn't on the CRT the IC that switches it thru from the back plane to the horizontal amplifier may not be getting the right switching signal or it may be bad.

The most important thing you can do for your own benefit and to learn how your new scope works is to read the Theory of Operation section of the service manual. It explains everything! For the moment read the parts about how the trigger signal is routed and how the sweep signal is routed to learn the various places they go in the scope and which ICs they go through to get a better idea of exactly where to look for where it is being blocked.

Dennis Tillman W7PF

-----Original Message-----
From: @HermanssonAmplification
Sent: Monday, November 18, 2019 7:06 AM
Subject: [TekScopes] Tektronix 7904, no horizontal trace on input B

I just bought a Tektronix 7904 scope and realized that something is wrong with horizontal input B.
Horizontal input A works fine but I got no trace on input B. If I press “Beam finder” slightly I see dots for each inputs that are activated in the vertical slots and if I press the “Beam finder” harder I see bigger dots. I only see the dots when I press “Beam finder” otherwise the screen is blank when horizontal input B is activated.

Any suggestions where to start? I’ve measured the voltages on the Z axis-PCB but nothing alarming there. Since the horizontal Input A works something might be bad on the “Trigger B”-PCB? Or where should I start?

Here’s a video showing the problem:
https://youtu.be/KuPenOSkyJg

I’ve been exercising the switches and cleaned the input slots for the plugin.
Thank you in advance!

Best regards,
Henric




--
Dennis Tillman W7PF
TekScopes Moderator


Re: 465B soft start?

Tom Gardner
 

Switching power supplies operate to keep the output power constant.
Hence if the input voltage is lower, the input current must be higher.

Increased current stresses components such as the rectifiers and
switching transistors.

On 18/11/2019, treasurer@... <treasurer@...> wrote:
Is there much to be gained by powering up my 465B with a variac, lamp dimmer
or similar arrangement? It popped (shorted) its 1200 ufd C4429 at power on
recently. This cap does not have much head room with its 100 volt rating and
70 volts sitting on it. I'm thinking a soft power up may help prolong the
life of those caps. Any thoughts or past experience from the group using
this power-on approach?
Bruce



465B soft start?

treasurer@...
 

Is there much to be gained by powering up my 465B with a variac, lamp dimmer or similar arrangement? It popped (shorted) its 1200 ufd C4429 at power on recently. This cap does not have much head room with its 100 volt rating and 70 volts sitting on it. I'm thinking a soft power up may help prolong the life of those caps. Any thoughts or past experience from the group using this power-on approach?
Bruce

Re: Tektronix 7904, no horizontal trace on input B

 

Hi Henric,

The first thing I notice in your video is that when you put the time base in the B horizontal slot the 7904 recognizes it is present because it displays the on-screen readout time/div setting on the bottom right part of the CRT. That is a good sign.

The second thing I see is when you press the beam finder with the time base in the B horizontal slot the display you get shows there is no sweep present. You are just getting the vertical signals on the screen without any horizontal sweep.

There could be two reasons for this:
A) The time base is not getting a trigger signal when it is in the B horizontal slot. One test you can perform would be to feed a trigger signal into the external trigger input of the time base while in the B slot to see if this fixes the problem. If it does then that confirms the trigger signal is not getting to the B slot from the vertical amplifiers. That could be caused by a bad front panel B Trigger Source Switch or by the IC that controls the routing of this trigger signal which would be on the backplane PC board. Also on the rear of the 7904 (or maybe even on the front of it) there are several BNC connectors which bring out critical signals like trigger signals. If there is a B Trigger Signal output make sure it is present on the front or rear panel BNC connectors.

B) The time base is being triggered and generating a sweep but the sweep is not getting from the time base to the horizontal amplifier in the mainframe. Once again there are ICs on the back plane that route this sweep signal. The B Sweep signal comes out to one of the front or rear BNC connectors so you should check for it there. If it isn't there and if it isn't on the CRT the IC that switches it thru from the back plane to the horizontal amplifier may not be getting the right switching signal or it may be bad.

The most important thing you can do for your own benefit and to learn how your new scope works is to read the Theory of Operation section of the service manual. It explains everything! For the moment read the parts about how the trigger signal is routed and how the sweep signal is routed to learn the various places they go in the scope and which ICs they go through to get a better idea of exactly where to look for where it is being blocked.

Dennis Tillman W7PF

-----Original Message-----
From: @HermanssonAmplification
Sent: Monday, November 18, 2019 7:06 AM
Subject: [TekScopes] Tektronix 7904, no horizontal trace on input B

I just bought a Tektronix 7904 scope and realized that something is wrong with horizontal input B.
Horizontal input A works fine but I got no trace on input B. If I press “Beam finder” slightly I see dots for each inputs that are activated in the vertical slots and if I press the “Beam finder” harder I see bigger dots. I only see the dots when I press “Beam finder” otherwise the screen is blank when horizontal input B is activated.

Any suggestions where to start? I’ve measured the voltages on the Z axis-PCB but nothing alarming there. Since the horizontal Input A works something might be bad on the “Trigger B”-PCB? Or where should I start?

Here’s a video showing the problem:
https://youtu.be/KuPenOSkyJg

I’ve been exercising the switches and cleaned the input slots for the plugin.
Thank you in advance!

Best regards,
Henric




--
Dennis Tillman W7PF
TekScopes Moderator

Tektronix 7904, no horizontal trace on input B

Hermansson Amplification
 

I just bought a Tektronix 7904 scope and realized that something is wrong with horizontal input B.
Horizontal input A works fine but I got no trace on input B. If I press
“Beam finder” slightly I see dots for each inputs that are activated in the vertical slots and if I press the “Beam finder” harder I see bigger dots. I only see the dots when I press “Beam finder” otherwise the screen is blank when horizontal input B is activated.

Any suggestions where to start? I’ve measured the voltages on the Z axis-PCB but nothing alarming there. Since the horizontal Input A works something might be bad on the “Trigger B”-PCB? Or where should I start?

Here’s a video showing the problem:
https://youtu.be/KuPenOSkyJg

I’ve been exercising the switches and cleaned the input slots for the plugin.

Thank you in advance!

Best regards,
Henric

TDS3012B NVRAM

Ferenc Rózsa
 

Good afternoon for everybody,

I've got such a Tektronix TDS3012B scope and
run out the CR2032 coin cell in the NVRAM.
The type of the NVRAM is DALLAS DS1742W-120
So this is a 3.3V VCC, 2 KByte, JEDEC paralell programming NVRAM. Where can I buy it or which is the replacement type of this ?
This is 24 pin EDIP type.
Thank you very much for you help: Ferenc

Wanted: DPO7000 series probe pouch

 

Looking for a black, snap in place, probe pouch that goes on top of a DPO7000 series scope. Must be in very good condition.

Manuel

Large set of Tektronix parts for sale

Jamie Ostrowski
 

I ran into this ad. I am not associated with the seller in any way. I just saw this ad and thought that someone may be interested...

Location is Milton, NY. $1000 for all:

https://www.facebook.com/marketplace/item/2423409567986774/




to much to list here is some of it
The following is a list of electric parts for sale

5 201-0013-00
3 310-0600-00
3 311-0431-00 Tektronix Potentiometer Dual Concentric 50 K / 50K $8.50
Potentiometer Dual Concentric 50 K / 50K Tektronix Part # 311043100 3 [hidden information] Tektronix Trigger Level Slope Control 15.00 This is a replacement for the trigger level/slope switch control used on many Tektronix oscilloscopes, including the 400-series. These pots frequently become noisy, or the shafts are bent, or the slope switch stops working.

This is part number [hidden information]. It is a replacement for part number [hidden information], except that the bushing is 0.375 inches (3/8) long instead of 0.250 inches (1/4). Washers or a nut must be added behind the panel so that the bushing exposure on the front of the panel is the same as the original. There must also be an additional 1/8 inch clearance behind the pot. This clearance is present on many instruments, but please check your instrument for clearance before ordering.
5 309-0109-00
3 311-0258-00 Clarostat 100 Ohm 5.00
1 311-0283-00 1 311-0450-00 Potentiometer Hi Voltage 1 Meg Tektronix Part # 311045001 4 311-0026-00 Clarostat 100K Potentiometer 5.00 used
1 311-0297-00
1 311-1311-00 Bourns 81C1DE24BA0324 1k 16.00 6 [hidden information] Tektronix Trigger Level Slope Control Replacement for P/N [hidden information] This is a replacement for the trigger level/slope switch control used on many Tektronix oscilloscopes, including the 400-series. These pots frequently become noisy, or the shafts are bent, or the slope switch stops working. 15.00
8 290-0310-00 Capacitor, Fixed, Electrolytic Capacitance Value per Section: 2000.000 microfarads single section
Terminal Type and Quantity: 1 tab, solder lug Body Style: 2B W/twist tab mtg, terminal(s) on one end
1 281-0036-00 3 307-1023-00 TEKTRONIX 307-1023-00 DUMMY LOAD NEW IN BOX 10.00
4 311-1558-00 20K 1 311-1311-00 Tektronix VARIABLE RESISTOR 311-1311-00 S 8.00
1 311-0088-00 Resistor, Variable, Nonwire Wound
1 311-0285-00 Resistor, Variable, Nonwire Wound
1 311-0218-00 Resistor, Variable, Wire Wound, NON
1 310-0602-00 Resistor, Fixed, Wire Wound, Nonind
4 285-0749-00
1 310-0544-00 Resistor, Fixed, Wire Wound, Induct

1 308-0535-00
5 311-0066-00 pot comp 500 3.45
3 309-0103-11 res
5 309-0090-00 res 1 307-1011-00 Attenuator 4x NOS 5.00
3 309-0168-00 res
4 308-0176-00
3 308-0266-00 res
3 309-0180-00 res
5 309-0115-00 res
3 309-0049-00 res 1/2 w
6 309-0086-00 res
1 309-0030-00 res
3 309-0191-00 res
1 310-0537-00
5 309-0193-00

425 Allen Bradley resistor GB 1045 1 watt 100K OHMS 5.00 each .
500 Allen Bradley resistor GB 1035 10,000K OHMS 8546 1.50 each
2000 Allen Bradley resistor GB 1055 1 watt 1.0 Meg OHMS 8548
780 Allen Bradley resistor GB 1035 10,000K OHMS 8549 1.50
1000 Allen Bradley resistor GB 1045 1.0 Meg OHMS 8631 5.00 each
500 Allen Bradley resistor GB 1045 100K OHMS 8012

2 308-0315-00 Resistor,Fixed,Wire Wound,Inductive 5 283-0575-00 CAP MICA .01 UF 5.00
3 309-0196-00 Res
2 309-0199-00 Res
3 309-0245-00 Res
5 309-0181-00 Res
3 309-0197-00 Res
3 309-0125-00 Res
3 309-0194-00 Res
4 309-0195-00 Res
5 310-0596-00
5 308-0018-00
3 310-0537-00
1 307-1013-00
5 309-0182-00 Res
6 309-0114-00 Res
2 310-0611-00
3 309-0007-00

1 260-1037-00
1 262-0595-01
8 262-0417-00
1 262-0561-00

200 EB 1015 Allen Bradley resistor 1/2 Watt
100 EB 1045 Allen Bradley resistor 1 Watt

20 1802C Wire Bound Resistor 20 Watt 3.00 OHMS











2 311-0386-00 control Potentiometer Precision 10 Turn 2K 5% Lin = .1% - Tektronix Part # 311038600 Potentiometer Precision 10 Turn 2K 5% Lin = .1%
3 311-1670-00 Potentiometer Dual Concentric 10K / 100K with Long Shaft - Tektronix Part # 311167000 Potentiometer Dual Concentric 10K / 100K with Long Shaft $23.50
1 311-0431-00 control Potentiometer Dual Concentric 50 K / 50K - Tektronix Part # 311043100 Potentiometer Dual Concentric 50 K / 50K 8.50
1 311-0189-00 control
15 311-0190-00 control
1 311-0426-00 Potentiometer 300 KOhm With Switch - Tektronix Part # 311042600Potentiometer 300 KOhm With Switch 8.50
2 311-1701-00 control
3 311-1558-00 control 1.05
1 311-1273-00 control .70

Re: 7844 power supply

Peter Gottlieb
 

I looked again and one of the switcher transistors failed again so replaced that. Now back to burst operation.

The switcher shutoff is coming from the control chip. It seems to be triggered by large spikes coming in on the balance input and those seem to be coming from the current sense on the HV side. This might be caused by a shorted HV diode or the multiplier. I am hoping it is not the HV winding as that would likely mean scrapping of this otherwise mint scope, but the indication is promising (at least right now).




Peter

On Nov 18, 2019, at 12:50 AM, Ed Breya via Groups.Io <edbreya=yahoo.com@groups.io> wrote:

The last time I fixed a 7844 PS, it was fortunately just two or so rather large (100 or 220 uF 20V) Ta caps shorted, on the pre-regulator supply board, for the +/- 15V inside the PS module - the one inside the cage, just below the outer, upper, linear regulator board. It's a PITA to get to, but doable - if you take enough stuff apart, you can run it while opened up and make measurements. The fix is fairly straightforward, but there's very little space, so you'll have to get creative with alternative cap arrangements. I manged to do all the work from the component side, avoiding having to remove the board, which is even more a PITA.

If it's not those or something else like another Ta cap in the scope circuits, it could be the dreaded HV winding failure on the main transformer. Hope for the lesser grief.

Ed


Re: 7844 power supply

Ed Breya
 

The last time I fixed a 7844 PS, it was fortunately just two or so rather large (100 or 220 uF 20V) Ta caps shorted, on the pre-regulator supply board, for the +/- 15V inside the PS module - the one inside the cage, just below the outer, upper, linear regulator board. It's a PITA to get to, but doable - if you take enough stuff apart, you can run it while opened up and make measurements. The fix is fairly straightforward, but there's very little space, so you'll have to get creative with alternative cap arrangements. I manged to do all the work from the component side, avoiding having to remove the board, which is even more a PITA.

If it's not those or something else like another Ta cap in the scope circuits, it could be the dreaded HV winding failure on the main transformer. Hope for the lesser grief.

Ed