Re: 485 super weak brightness control
The grid bias changes the voltage at TP1665 but does not have any visible
impact on the trace What voltage range do you see at TP1665 when you change grid bias. No need to re-measure, just ballpark numbers you remember. Especially the sign, positive or negative voltage. Ozan
|
Re: Tek 2225 that wont power up after a knock :-(
C914 reads as 12uF with an ESR of 1.2 - is that reasonable ???
It is a bit low in capacitance but it is not the reason for the failure. However, I would replace it anyway since you removed it and it was stressed by high voltage. Ozan
|
Re: 485 super weak brightness control
I thoroughly cleaned the entire HV area with IPA and now the 2950V is
steady while before it would drift slowly down to 2800 and even further
The grid bias changes the voltage at TP1665 but does not have any visible
impact on the trace
toggle quoted message
Show quoted text
On Wed, 17 Mar 2021, 15:54 Mlynch001, <mlynch002@...> wrote: On Wed, Mar 17, 2021 at 08:45 AM, Ondrej Pavelka wrote:
On Tue, 16 Mar 2021, 22:42 Ozan, <ozan_g@...> wrote:
I checked the DC recovery diodes in the HV supply as listed in other
thread
(all under the plastic cover and they are ok.
Any other suggestions? Note that checking the leakage of those diodes is important, just a DVM
diode check doesn't discover problems.
I would second this part of the post. I had a similar failure on a 475
and traced it to a bad restorer diode. The only way that I was able to
locate the problem was using a 5 On Tue, 16 Mar 2021, 22:42 Ozan, <
ozan_g@...> wrote:
I checked the DC recovery diodes in the HV supply as listed in other
thread
(all under the plastic cover and they are ok.
Any other suggestions?
Note that checking the leakage of those diodes is important, just a DVM
diode check doesn't discover problems.
I would second this part of the comment. I had a 475 with a similar
failure and symptoms. A simple DMM diode test showed the diode as ¡°good¡±.
When I removed it and tested it on the 576 curve tracer the problem
became apparent, as soon as I checked it on the CT, it exhibited a very
strange breakdown at higher voltages. So replacing the diode and
associated capacitor with a known good diode and capacitor repaired the
problem.
--
Michael Lynch
Dardanelle, AR
|
Re: 485 super weak brightness control
Behavior of your 485 is changing over time so some of these comments may not apply to current state of the scope but here is my feedback: If you look at pins 2 and 3 of U1624 what voltage do you measure (should
be essentially the same and close to 0V).
Pin 2 is zero pin 3 is 1.9V
This means the regulation loop (U1624) thinks HV voltage is too low and working as hard as it can to increase the voltage but can't increase anymore (railed). When you look at pin 6 do you see it railed (>10V)? In this condition HV supply is not regulated anymore. I'm not sure what's going on today I turned it on and I measure 2963V on
the HV spot. However, I also saw this post that now voltage is OK. Did pin 3 also changed to ~ 0V? Does the HV voltage change when you turn intensity knob? Maybe there is some interaction and when you change some settings HV voltage is changing. Or something might be baking and recovering ... The Z OUT DC can be controlled from -70 through -170 and finishes around -50 This should not be possible. If I am not missing a supply connection, minimum supply of that block is -5V. In normal operation "Z OUT DC" starts from ~ 14V and goes higher for lower intensity. What voltage do you see at the left side of R1792 (collector of Q1772)? Only possibility I can see is a DC path from the HV line, which would also explain why HV supply is low. Suspect components are C1684, C1664, C1663. You can also try cleaning the HV area more thoroughly in case there is some conductive residue. In almost all the "beam too bright" cases HV diodes were bad so it is a good idea to replace them all as a good measure. I am not an expert in HV DC restorers but if you look at past discussions UF4004 was recommended by Tom as a replacement. A random diode won't work. For time base issues, in the problematic 3 fastest settings how does the
"A Sweep" and "A gate" signals look? They are easily available at the back
of the scope with a BNC connection. Both if the signals don't change past the 10nS setting they stay the same for 5 2 and 1ns
I assume slower than 5ns you see a pulse at "A gate" and a triangle wave at "A sweep". In 5/2/1ns are they both flat? Flat at ground or some other voltage? Is the flat voltage same as the lowest point or highest point of proper signals (when sweep slower than 5ns)? Ozan
|
Re: I built a TM500 mainframe tester, and updated the design. Someone might find this useful?
Well, I'm glad it wasn't my design that was in error. :D
I'm interested in why the opamps popped too, I wonder if there is a bodge that can be added to existing units to protect the opamps from this issue, and maybe be added into the board layout for future board revisions.
I might add a suggestion to socket the opamps in the manual too. At least they are cheap parts to replace...
Jared.
|
Re: I built a TM500 mainframe tester, and updated the design. Someone might find this useful?
most likely the peaks on V+ ( or inputs)? exceeded max for the 741...had it happen a lot on equipment in implanters....we also had walking wounded which would sometimes work and well sometimes do funny things...PIA to find at times so down time and my time was expensive and the part cheap....shotgun approach worked...also adding mov to the supply rails helped.
¸é±ð²Ô¨¦±ð
toggle quoted message
Show quoted text
On 3/17/21 7:04 AM, ebrucehunter via groups.io wrote: I can only speculate why the 741s didn't like the unfiltered rectifier output as +Vs, but suspect the capacitor at the (+) input may have caused excessive input current as the device was violently cycled. As both 741s failed, there seems to be a weakness. A 741 Spice model might provide insight.
Now to investigate the DM502 and DM504 I haven't used in years and find a source for replacement capacitors.
Bruce, KG6OJI
-----------------
Why did the open filter capacitor destroy the 741s? Surely open filter capacitors is a problem the tester should identify and not itself fail from.
Best wishes,
Larry McDavid W6FUB
Anaheim, California (SE of Los Angeles, near Disneyland)Larry
|
Re: Very Inexpensive 7623A, but Problems
Ozan,
Thanks, that makes a lot more sense now.
I will run through and check all the connections from the LV regulator to the other boards (a nice, easy check that can be done with the power OFF).
I have not tried to adjust R881 at all. I've been coming at this backwards the whole time, mostly because I was distracted by the physical damage to the LV regulator in shipping. I need to be more methodical in my investigation and measurement.
-- Jeff Dutky
|
Re: 485 super weak brightness control
On Wed, Mar 17, 2021 at 08:45 AM, Ondrej Pavelka wrote:
On Tue, 16 Mar 2021, 22:42 Ozan, <ozan_g@...> wrote:
I checked the DC recovery diodes in the HV supply as listed in other
thread
(all under the plastic cover and they are ok.
Any other suggestions? Note that checking the leakage of those diodes is important, just a DVM
diode check doesn't discover problems.
I would second this part of the post. I had a similar failure on a 475 and traced it to a bad restorer diode. The only way that I was able to locate the problem was using a 5 On Tue, 16 Mar 2021, 22:42 Ozan, <ozan_g@...> wrote: I checked the DC recovery diodes in the HV supply as listed in other thread (all under the plastic cover and they are ok. Any other suggestions? Note that checking the leakage of those diodes is important, just a DVM diode check doesn't discover problems. I would second this part of the comment. I had a 475 with a similar failure and symptoms. A simple DMM diode test showed the diode as ¡°good¡±. When I removed it and tested it on the 576 curve tracer the problem became apparent, as soon as I checked it on the CT, it exhibited a very strange breakdown at higher voltages. So replacing the diode and associated capacitor with a known good diode and capacitor repaired the problem. -- Michael Lynch Dardanelle, AR
|
Re: PS 5010 troubleshooting (no negative, erratical display)
Third update: I made some experiments and found out that, once I let some current flow (200mA), the blinking stops and the display is steady.
Then I tested the module in may "Rack"-TM5006 frame, and to my surprise the display was fine there. Back into the other frame it.... still.... was.... fine!!
I decided to do some alignments and put the module back in the racked frame, this time in the high-power compartment at the right. Well, the display started acting up again, and remained so in both frames! Suspecting the hi-power switch on the module I did the same as I did to the front-back-switch, a lot of actuations. And indeed, that cured the fault.
So my conclusions are:
- the PS5010 is well built and rather precise power supply... :-)
- the linear switches used in many Tek equipments are prone to contact problems that can have all sorts side effects. Actuating all these switches should be the first thing to do when troubleshooting.
I didn't resort to cleaning the switches, just actuating seems to do the job, at least for a good while. If the supply acts up again I know what to do.
cheers
Martin
|
Re: I built a TM500 mainframe tester, and updated the design. Someone might find this useful?
I can only speculate why the 741s didn't like the unfiltered rectifier output as +Vs, but suspect the capacitor at the (+) input may have caused excessive input current as the device was violently cycled. As both 741s failed, there seems to be a weakness. A 741 Spice model might provide insight.
Now to investigate the DM502 and DM504 I haven't used in years and find a source for replacement capacitors.
Bruce, KG6OJI
-----------------
Why did the open filter capacitor destroy the 741s? Surely open filter capacitors is a problem the tester should identify and not itself fail from.
Best wishes,
Larry McDavid W6FUB
Anaheim, California (SE of Los Angeles, near Disneyland)Larry
|
Re: 485 super weak brightness control
On Tue, 16 Mar 2021, 22:42 Ozan, <ozan_g@...> wrote:
I checked the DC recovery diodes in the HV supply as listed in other
thread
(all under the plastic cover and they are ok.
Any other suggestions? Note that checking the leakage of those diodes is important, just a DVM
diode check doesn't discover problems.
It looks like the behavior of your 485 is different in different settings.
As the first issue are you debugging the intensity? Do you have too bright,
or too dim brightness, does intensity control make any difference?
HV supply voltage of 2000V is low. What is the impedance of your 1000x
probe? Looking at the schematic ¡°CATH REG¡± can only adjust ~ +/-100V so
this is outside adjustment range. Should be the first thing to fix since
everything else with intensity depends on it.
Feedback loop around U1624 uses +50V at the top of R1642B as the
reference. Is +50V correct?
If you look at pins 2 and 3 of U1624 what voltage do you measure (should
be essentially the same and close to 0V).
Pin 2 is zero pin 3 is 1.9V Once you fix the HV supply if intensity is still problematic:
There are multiple posts about DC restorer issues I recommend you search
"DC restorer" "Grid Bias" for useful information.
The ones I know well are: Topic #180156: Although different equipment,
this topic has some DC restorer debug. Topic #180235 is a 485 with
intensity control issues. In particular looking at the circuitry around
intensity control pots. If you review both chains from start there is some
relevant information.
For time base issues, in the problematic 3 fastest settings how does the
"A Sweep" and "A gate" signals look? They are easily available at the back
of the scope with a BNC connection.
Both if the signals don't change past the 10nS setting they stay the same for 5 2 and 1ns Ozan
|
Re: 485 super weak brightness control
On Wed, 17 Mar 2021, 14:32 Ondrej Pavelka, <info@...> wrote:
On Wed, 17 Mar 2021, 00:58 Ozan, <ozan_g@...> wrote:
I cleaned up the HV test point and I get now some 2800V. What makes me
little bit nervous is I don't know if the cause was just the contact
cleaning or if something else have changed. Nevertheless it changed in the
right direction. I think the whole section under the plastic cover needs
cleaning it's covered in black dust. It may be some conductive residue. HV section have some high M-ohm
resistors, any conductive residue will change things. 2800V is low (looking
at +50V supply and opamp inputs is still a good debug flow for HV) but
probably close enough for intensity debug. Too bright intensity is not good
for the screen so it is better to take care of it sooner than later.
I'm not sure what's going on today I turned it on and I measure 2963V on
the HV spot.
50V point measures 49.73V
I will de-solder the diodes in the DC restorer and measure leakage current.
Before you desolder the diodes, can you check if you can control
brightness with "GRID BIAS" adjustment (R1660)? Also, as you change
intensity knob, can you control the voltage at "Z OUT DC" test point
(TP1781), and at what range?
Grid bias control has no effect what so ever
The Z OUT DC can be controlled from -50 CCW through -170 and finishes
around -70 CW
Ozan
|
Re: 485 super weak brightness control
On Wed, 17 Mar 2021, 00:58 Ozan, <ozan_g@...> wrote:
I cleaned up the HV test point and I get now some 2800V. What makes me
little bit nervous is I don't know if the cause was just the contact
cleaning or if something else have changed. Nevertheless it changed in the
right direction. I think the whole section under the plastic cover needs
cleaning it's covered in black dust. It may be some conductive residue. HV section have some high M-ohm
resistors, any conductive residue will change things. 2800V is low (looking
at +50V supply and opamp inputs is still a good debug flow for HV) but
probably close enough for intensity debug. Too bright intensity is not good
for the screen so it is better to take care of it sooner than later.
I'm not sure what's going on today I turned it on and I measure 2963V on the HV spot. 50V point measures 49.73V
I will de-solder the diodes in the DC restorer and measure leakage current.
Before you desolder the diodes, can you check if you can control
brightness with "GRID BIAS" adjustment (R1660)? Also, as you change
intensity knob, can you control the voltage at "Z OUT DC" test point
(TP1781), and at what range?
Grid bias control has no effect what so ever The Z OUT DC can be controlled from -70 through -170 and finishes around -50
Ozan
|
Re: 485 super weak brightness control
Hi,
After having repaired several scopes (not only Tek's, but other brands also) with this symptom they invariably had leaky DC restorer diodes. Testing these diodes for leakage must be done at high voltages, because at normal DVM or component tester applied voltages they usually seems to be ok, but this is not true. Since the main work is to reach and remove the diodes, I would replace all of them, period.
This also applies to the focus circuit DC restorer if one is used. The symptom there is lack of control over the focus.? The way the DC restorers circuit operates may cause stresses in these diodes that make them to fail. I don't know the exact explanation.
Regards,
Ignacio EB4APL
toggle quoted message
Show quoted text
El 16/03/2021 a las 23:33, Ondrej Pavelka escribi¨®: Thanks so much for your reply, it makes it much easier to approach.
I cleaned up the HV test point and I get now some 2800V. What makes me
little bit nervous is I don't know if the cause was just the contact
cleaning or if something else have changed. Nevertheless it changed in the
right direction. I think the whole section under the plastic cover needs
cleaning it's covered in black dust.
I will de-solder the diodes in the DC restorer and measure leakage current.
The intensity is too bright
I'll get back to you when I follow up on the other measurements tomorrow.
The HV probe is labeled as HV-40 but can't find any manufacturer markings.
It's definitely from 80s or 70s
On Tue, 16 Mar 2021, 22:42 Ozan, <ozan_g@...> wrote:
I checked the DC recovery diodes in the HV supply as listed in other thread
(all under the plastic cover and they are ok.
Any other suggestions? Note that checking the leakage of those diodes is important, just a DVM
diode check doesn't discover problems.
It looks like the behavior of your 485 is different in different settings.
As the first issue are you debugging the intensity? Do you have too bright,
or too dim brightness, does intensity control make any difference?
HV supply voltage of 2000V is low. What is the impedance of your 1000x
probe? Looking at the schematic ¡°CATH REG¡± can only adjust ~ +/-100V so
this is outside adjustment range. Should be the first thing to fix since
everything else with intensity depends on it.
Feedback loop around U1624 uses +50V at the top of R1642B as the
reference. Is +50V correct?
If you look at pins 2 and 3 of U1624 what voltage do you measure (should
be essentially the same and close to 0V).
Once you fix the HV supply if intensity is still problematic:
There are multiple posts about DC restorer issues I recommend you search
"DC restorer" "Grid Bias" for useful information.
The ones I know well are: Topic #180156: Although different equipment,
this topic has some DC restorer debug. Topic #180235 is a 485 with
intensity control issues. In particular looking at the circuitry around
intensity control pots. If you review both chains from start there is some
relevant information.
For time base issues, in the problematic 3 fastest settings how does the
"A Sweep" and "A gate" signals look? They are easily available at the back
of the scope with a BNC connection.
Ozan
--
El software de antivirus Avast ha analizado este correo electr¨®nico en busca de virus.
|
Re: Help: unreadable listing from: 42W-4281-1 Measurement Variety. An Engineering Challenge Featuring the 7854
Thank yuou Clark, I will do.
Next week-end i'll try the complete program.
Max
|
Free 547 and plug ins (pick up in Boston area)
Hi folks,
I'm getting ready to move and need to find a good home for a 547 with 1A1
and B plug ins. Dusty, but stored in a low humidity storage area. It worked
the last time I powered it on a few years ago, but suspect it will need
some TLC. Complete, with power cord but no probes or cart. It originally
came from the EE dept. at MIT (stenciled on the side and property tag on
front). I need to have it picked up by 3/28, currently in Belmont, MA.
Please email me directly with any interest/questions.
Thanks!
--Chris (christopher.galbraith@...)
|
Re: Message from your fearless (foolish?) leader
Hi Dennis,
I'm glad to hear of Marian's success!!
I've had my knees replace 4 times (yes, I have only 2 knees) and both my shoulders replaced. In all cases, the operations were a success - it just took a long time to heal. Be as helpful as you can with Marian in her recovery regime but don't over help. I've gotten through 6 'replacements' and everything went fine.
larry
|
Re: Tek 2225 that wont power up after a knock :-(
Update :-
Q923 (TIP30C) is indeed a 3 pin short <1 Ohm in all 3 directions.
Also
Q913 (TIP31C) is essentially just a double diode with no gain
Q912 is OK
Q950, and Q960? (both TIP30C) are OK
C914 reads as 12uF with an ESR of 1.2 - is that reasonable ???
I have ordered replacements (+ spares) - probably not much more I can do until they arrive.
Thanks very much for the help so far?:-)
Regards,
Dave
toggle quoted message
Show quoted text
On 16/03/2021 20:29, Ozan wrote: I have identified that Q913 is short circuit between E,B&C and I also
suspect Q923, but until I get them out that's as far as I've got. Shorted Q913 could cause what you saw. However, did you measure it in place or after disconnecting from the circuit?
Someone suggested I check C914 - I know its 15uF but do you know the
rating ?? All component information is in the service manual. Section 8-9 (Page 113 in the PDF I am looking at) shows 15uF, 20%, 63V. I don't see why it would cause this issue after a knock but now all the components (including caps) did exceed their expected voltage by a large margin so they could be damaged. For example C971 is rated 50V but was stressed to 63V. Some components will survive brief over voltage, some may be damaged. In particular ICs may go into "latch up" and draw excessive current.
Ozan
Ozan
|
Type 576 curve tracer can capacitor IDs
All-
I have two 576s that I will be refurbishing as time permits and I am wanting to have parts on hand when I decide to dive in to the project - can someone confirm that the eight can type capacitors are the following (I am not where I can open everything up at the moment):
C707 200u 250v
C738 4200u 30v
C759 11000u 15v
C791 4200u 30v
C822 2000u 75v
C823 2000u 75v
C829 200u 250v
C850 100u 150v
Thank you,
Hal
|
Re: Tek 2225 that wont power up after a knock :-(
Yes, that is the one I found ... the one that refers to Q9070 which I cannot find on my schematic.
Dave
toggle quoted message
Show quoted text
On 17/03/2021 08:13, satbeginner wrote: Hi David,
here is the link to the original document made by Hakan (aka Zenith):
Hope this helps,
Leo
|
Jared Cabot
Mlynch001
Martin
ebrucehunter
Harold Foster