Date   

Re: 7904 Mainframe damaged

 

Hi JJ:
Your PSU Ok! Good!Did you connect the sens pins?
When my unit was normal . There is no spot on screen , when no plug-in installed.

Regard
Tony Cheung
Apr 17 2018


從我的 iPhone 傳送

JJ <jajustin@gmail.com> 於 2018年4月17日 上午9:54 寫道:

Hi Goran, I just got my power supply up - the voltages are reading within
1% at the output of the regulator board. I notice a square solid beam in
the middle of the screen (no plugins installed as yet) - I was wondering if
that is normal - or what could it be? Problem on main interconnect board?

Thx
John

On Mon, Apr 16, 2018 at 11:32 AM, Göran Krusell <mc1648pp@gmail.com> wrote:

Hi, MBD5300 is from American Microsemiconductor, Inc. This is for CR1311?
I used SR504 when I replaced CR1312.
Göran





Re: TDS210 repair help request

bobh@joba.com
 

Jack,

On page 6-39 of the service manual is a troubleshooting flow chart.  It takes you thru the following few pages of checking voltages on the power supply board and the connector to the main board.  This should help locate the problem.  The service manual is available here http://w140.com/tekwiki/wiki/TDS210

Be careful probing around on the power supply board there is 1200 volts present IIRC.

Check the connector pins on the back as they sometimes get bent and two contacting each other can stop the whole show.

Power supply failures have been common in the TDS 220 scopes I have had.  There are a couple YouTube videos on the TDS 210/220 scopes.

I haven't found a detailed schematic and I don't think Tek ever released them since this is a post component repair vintage scope.

Bob.

On 4/16/2018 3:05 PM, Vixen21 wrote:
I came across a TDS210.
Will not power up.
No signs of life when pressing power button.
AC Voltage is at Power supply input on pcb.
I dont understand how to troubleshoot this switching supply?
The repair manual is at pcb board swap level with no schematics .
Is there a common failure in these TDS210 scopes?
Or a schematic or troubleshooting guide available ?
Jack.
k0var



Re: 7904 Mainframe damaged

JJ
 

Hi Goran, I just got my power supply up - the voltages are reading within
1% at the output of the regulator board. I notice a square solid beam in
the middle of the screen (no plugins installed as yet) - I was wondering if
that is normal - or what could it be? Problem on main interconnect board?

Thx
John

On Mon, Apr 16, 2018 at 11:32 AM, Göran Krusell <mc1648pp@gmail.com> wrote:

Hi, MBD5300 is from American Microsemiconductor, Inc. This is for CR1311?
I used SR504 when I replaced CR1312.
Göran




Re: Darg-ON Off topic WAS (Re: [TekScopes] Adjustable Bias Mod Design Question)

Ed Breya
 

You're right Dave - this has hardly anything to do with Tek scopes other than tangentially, to maybe help some with general understanding of tube circuits, which are used in the old Tek scopes, so there's a remote connection. This thread has gone on for a while, so probably should be moved to an audio or tube group. I'd recommend the fun with tubes one, which may be appropriate. For anyone not familiar, this link should land you close enough:

https://groups.yahoo.com/neo/groups/funwithtubes/conversations/messages

I have no problem at all with occasional OT discussions, within reason - it's good to mix it up a little sometimes, which can lead to broader knowledge. I'm not a tube or audio guy at all, except for curiosity and maintenance of a few pieces of gear that use them. I had never heard of or cared about Boogie amplifiers and their issues, but I can't resist a good technical challenge, so had to put my one-cent's worth into the mix. I considered this a pleasant diversion from working on taxes (which I finally finished today - a whole day ahead of deadline - a record for me).

Thinking about different things is good. The positive feedback/runaway bias possibility occurred to me as I was writing my post, so I figured I'd share it, making it even longer and further off-topic. My unconscious dredged it up while trying to visualize the likely schematic topology of the subject amplifier, in order to understand more about this red-plating stuff. Way more fun than taxes.

Anyway, I have no more to say on this thread, except one last thing to the other Dave, the original poster. If the real issue is about trying to use non-selected, regular tubes in the "unchangeable" circuit designed for specific characteristics, why not just design a simple tube checker/matcher and/or provide the service, to sort through regular tubes for the ones that should work right? Could be a business opportunity if there's enough demand.

Ed


TDS210 repair help request

Vixen21
 

I came across a TDS210.
Will not power up.
No signs of life when pressing power button.
AC Voltage is at Power supply input on pcb.
I dont understand how to troubleshoot this switching supply?
The repair manual is at pcb board swap level with no schematics .
Is there a common failure in these TDS210 scopes?
Or a schematic or troubleshooting guide available ?
Jack.
k0var


Darg-ON Off topic WAS (Re: [TekScopes] Adjustable Bias Mod Design Question)

Artekmedia <manuals@...>
 

Gentlemen

At the risk of stating the obvious ...What does this have to do with Tektronix Test Equipment?
Asked and answered ...not a lot

Why don't you take this over to a more appropriate forum like EEVBlog or Esoteric_Guitar_Amps@ Yahoo.com

Flame Suit on
-DC
manuals@artekmanuals.com



On 4/16/2018 5:12 PM, Fabio Trevisan wrote:
Hello David,
Late hiker as well, I dub Ed (breya) in everything he said. He covered the technical aspect, but at the same time calling for attention that whatever you change in this amp, potentially changes its "sound"...
Emphasis on "potentially" because there's a high degree of subjectvism in this so-called "sound" which can be affected by the simple fact of the customer knowing that a change has been made.
Congrats as well to Ed's remark on the "runaway" condition... It's indeed a pitfall of this design...and I don't think that a protection circuit there would have any impact on the Mesa "sound" but, again, it's subjective.
The original amp equipped with Mesa sourced tubes may not need such a protection... But once the customer took that road of replacing tubes using other (cheaper) sources...he must comply that either he agrees to compromise on the "originality" of his amp (and still have a working amp to use), or he start buying tubes from Mesa again.
I
_*<SNIP>*_

--
Dave
Manuals@ArtekManuals.com
www.ArtekManuals.com


Re: Adjustable Bias Mod Design Question

Fabio Trevisan
 

Hello David,
Late hiker as well, I dub Ed (breya) in everything he said. He covered the technical aspect, but at the same time calling for attention that whatever you change in this amp, potentially changes its "sound"...
Emphasis on "potentially" because there's a high degree of subjectvism in this so-called "sound" which can be affected by the simple fact of the customer knowing that a change has been made.
Congrats as well to Ed's remark on the "runaway" condition... It's indeed a pitfall of this design...and I don't think that a protection circuit there would have any impact on the Mesa "sound" but, again, it's subjective.
The original amp equipped with Mesa sourced tubes may not need such a protection... But once the customer took that road of replacing tubes using other (cheaper) sources...he must comply that either he agrees to compromise on the "originality" of his amp (and still have a working amp to use), or he start buying tubes from Mesa again.
I also wanted to contribute but I had problems to find out an schematic (to understand what is the rest of the amp we were talking about).
So, I finally found one decent schematic, which helped. So, for the sake of others who may want to join the discussion, here is the link:
http://www.schematicsunlimited.com/m/mesa-boogie/mesa-boogie-dual-caliber-dc-3-schematic
Now, let's get hands on...
In considering only your question (how to change the bias circuitry) without changing Mesa designer's choices.. I understand your concern about changing the net resistance of the 120k resistor, as this could also impacts the phase splitter and...
Looking at the schematic, it indeed does... because it changes the negative voltage at the 220uF capacitor, and therefore, directly proportional to the tail current of the input's differential pair.
Soon enough I also realized that your idea, of acting upon the 33k resistor alone would take nowhere... not because your rational is flawed but because, in order to effectively change up to some 20% the bias voltage as you expect, even if you shorted out the 33k resistor, the negative voltage would still not get negative enough.
And that is simply because of ohm's law...The tube's grids don't draw or feed any current from the bias circuit and the only current going through the 33k resistor is the current drawn by the double path of 330k+220k+2M2 resistors, going to ground at the common node between the 2 x 2M2 resistors.
I estimate that each branch is drawing 5uA (11V/2M2) so your 33k resistor only have 0.33V of drop across it, and even if you short it out, the negative voltage at the output tubes' grids can only get 0.3V more negative (or so), so it's not enough for changing the bias voltage from -12V to -14V.
But, I think there's an equally minimal mod that can change the bias voltage, and not having the impact of changing the bias of the input differential pair...
If you cut the common connection of the 2 x 2M2 resistors to ground, and insert a trimpot of about 330k between that common node and ground, you can increase the negative voltage as much as 30%.
To avoid that extra resistance to have an impact on the input impedance of the output stage, you can just bypass the trimpot with a capacitor...
A quick calculation of what value such a capacitor could have... I got to 2.2uF.
This value would have a time constant of 1/20Hz for a trimpot "set" to a value as low as 22k and, since the idea of the trimpot is to add impedance to the 2M2 resistors and that, for that effect, the trimpot is very unlikely to be set to such small values... 2.2uF is more than enough.
If the trimpot is set to any value above 22k (which is likely), the time constant gets higher and higher and the frequency lower and lower than 20Hz, so, for every effect, irrelevant.
The average voltage across this capacitor is unipolar, up to some 3V max... so an electrolytic capacitor could do it.
The AC voltage across the same capacitor could be - in worst case - 15% of the p-p voltage at the output stage's input voltage (grids), not considering that most of the current increasing on one of the 2M2 resistors is being cancelled out by current decreasing on the other... so, there must be very little AC component at this node for all that matters, so confirming that an electrolytic capacitor would do just fine there.
Still, for purists... a 2u2 x 63V film capacitor would be impeccable, and and would not be too large either.
Rgrds,
Fabio


Re: GPIB using Win98 and a NI GPIB-PCII/IIA ISA card to talk to my TDS540B?

 

Can somebody tell me what is a working software combo for my card and maybe share the software if available?
If you look a little further on Tek's website there is a matrix of system requirements of various versions of Wavestar.
Obviously version 3 does not work on Win98 but version 2.8.1 should. Possibly also version 2.8.2 which I believe
is the last one before version 3.

I think you are right about GPIB driver v1.7 for your card and OS. NI has changed their website (to the worse). Before
you could easily find and download drivers for both current and obsolete cards and OS's. Maybe so still but I couldn't
find it with a quick check.

I have both of the above softwares on file so contact me off list if you want a copy.

/Håkan


Re: Adjustable Bias Mod Design Question

Geoffrey Thomas
 

What the hell, tell him to bin the Boogie and get one of these :

https://www.youtube.com/watch?v=G7qMVYf85sM

:)

Geoff.


Strange problem in TDS 620A

Jokken Feldhaar
 

Hi all,
i am repairing a TDS 620A that seems to defy my efforts to get it back to service again. To start, it had the "Electrolytic Disease", and I changed all of them and lots of corrosion on pins nearby. Now I have found a way to stop the two FAIL messages at startup, ATTN/ACQ.
But now I see sawtooth signals superimposed on the signals that should be displayed. The analog voltages generated by the AD667 and distributed via a set of 5 4051 ICs shows not a steady voltage on the 0,1 µF caps, but a sawtooth. Strangely, when I put a 4,7µF cap across the 0,1µF, thw sawtooth doen't even change. So there seems to be a GND problem, but I have spent two days looking for a clue, but without success.
Has anyone on this list experienced something similar and can recommend some treatmentor a way to work on the problem?
Regards, Jochen DH6FAZ


Re: Adjustable Bias Mod Design Question

Ed Breya
 

I'm late to this discussion, but after looking through the thread, I'd recommend a compromise that can protect the output stage without changing the basic design or its characteristics.

First, if fixed-bias must be used, with cathodes grounded, then a pot to tweak it makes sense. If no pot is allowed, then you'd have to resort to selecting and matching tubes to go with whatever bias it's fixed at, or selecting the bias string resistors (actually same as a pot, but tedious) to get the correct bias for the particular tubes. You have to choose among the options.

Without any other design changes, the most obvious protection is to fuse the B+ at somewhere just above the normal maximum current needed, to protect the tubes. Another thing to consider is what happens in the circuit that makes the tubes go from normal operation to red-plating. I'd guess that many of these failures are caused by insufficient or total loss of the negative bias voltage from the bias supply - resistor drift, rectifier or filter cap failure, etc. For protection against this, some circuitry could be added that monitors the bias supply to make sure it's right before the output B+ can be applied, and likewise disconnect it if bias is lost. This type of protection has been used in high power tube circuits, and is even applicable in solid-state, such as gate bias protection in power MESFET amplifiers with grounded sources (no degeneration).

I suppose that in consumer-grade equipment over the years, this sort of thing was not considered necessary due to the additional cost and complexity, and it was easier to just fix the failures: If the tubes get cooked, just change them out. If they get cooked again right way, then diagnose and fix the circuit and see what happens.

Now that a lot of this gear is valuable, expensive, and fancy, it may be worth adding some complexity to reduce risk and keep it going as long as possible. Assuring the bias is OK, and shutting down if not, would give some degree of protection without affecting the normal operating conditions - unless red-plating is considered "normal" sometimes.

One last thing. There can be a positive feedback mechanism in a typical tube amplifier system that can aggravate the fixed-bias/runaway situation. Depending on the specifics of the design, the fixed bias negative level may be proportional to the B+, allowing for positive feedback in certain fault conditions. Here's how: Let's say the negative bias supply is simply derived from one of the power transformer windings, from a rectifier and filter cap, then a resistive divider to set a nominal bias level for the grids. Now let's say that, for whatever reason, the tubes start drawing too much current, heading into red-plate territory. When this happens, the B+ will necessarily drop, as the load current increases. At the same time, all the other voltages will drop due to the power transformer regulation characteristics. So will the bias supply, so its negative value will decrease, allowing the tubes to draw even more current, loading the B+ even more - a runaway condition. One way to break this positive feedback is to regulate to bias supply so that is more or less constant regardless of the B+ load. A simple Zener shunt regulator would do, and as I recall, I've seen a number of tube amp circuits that do regulate the bias. If the amp in this discussion does not have regulated bias, then that would be a thing to to consider, but it may count as a "design change." In other words, if the bias is unregulated, thus affected by the average and low frequency B+ load, this characteristic may be part of the "tube" sound, while also being part of the red-plate risk. If it's regulated instead, the runaway risk is reduced, but this subtle bias feedback characteristic will be different.

Ed


GPIB using Win98 and a NI GPIB-PCII/IIA ISA card to talk to my TDS540B?

satbeginner
 

Hi all,

I happen to have a working Windows 98 Second Edition PC with 3x ISA and 3x PCI slots in a corner.
I also found an 8-bit ISA National Instruments card, GPIB-PCII/IIA @1991, assy-number 181065-01 in my stuff.

Now I am trying to get this up-and -running, just to see if it can talk to my TDS540B using GPIB, but for now I am stuck finding the right combination of NI drivers and Tek Software.

As far as I can tell I need a real old version of the NI software (V1.7 maybe?) or and old version of TekVisa, but these I cannot find.
I do not know if a newer version of Wavestar would work too?

I did find a Word-document on the Tek-site stating the support for Wavestar stopped, and for that reason they published a key to use it at full functionality. (WSTRO618650124)
The file is here: https://www.tek.com/support/faqs/wavestar-software-compatibility-win-7
This version will not install on Win98.... :-)

Here is a picture of my card: https://groups.io/g/TekScopes/album?id=44301

Can somebody tell me what is a working software combo for my card and maybe share the software if available?

Un saludo,

Leo


Re: DSA 602A Main Time Interpolator Died

kc0wox Leeper
 

Thanks for the update.
I'm getting ready to troubleshoot mine. It looks like maybe power supply but haven't looked with a scope yet. It seems to work but has a problem with vertical display.
https://groups.io/g/TekScopes/album?id=41301
Leonard


Re: 7904 Mainframe damaged

 

Hi:
I use my on hand replacements 200v 6 A , now can start up , but all voltage readings are not correct! May be send not connecting yet?
Rd
Tony


從我的 iPhone 傳送

Yiu On Tony C via Groups.Io <tonycheung_hk=yahoo.com@groups.io> 於 2018年4月16日 下午11:45 寫道:

Thanks !

From: Göran Krusell <mc1648pp@gmail.com>
To: TekScopes@groups.io
Sent: Monday, April 16, 2018 11:32 PM
Subject: Re: [TekScopes] 7904 Mainframe damaged

Hi, MBD5300 is from American Microsemiconductor, Inc. This is for CR1311? I used SR504 when I replaced CR1312.
Göran







Re: 7904 Mainframe damaged

 

Thanks !

From: Göran Krusell <mc1648pp@gmail.com>
To: TekScopes@groups.io
Sent: Monday, April 16, 2018 11:32 PM
Subject: Re: [TekScopes] 7904 Mainframe damaged

Hi, MBD5300 is from American Microsemiconductor, Inc. This is for CR1311? I used SR504 when I replaced CR1312.
Göran


SPAM ALERT Re: TDS 210 not powering ON?

 

SPAM / PHISHING ALERT

Do not respond to it.

This new member may be a spammer or a phisher.
This message has been permanently removed from the Archives.

Vixen21 is now being moderated to block future messages which may contain
dangerous, off-topic, or irrelevant links

Dennis Tillman W7PF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Vixen21
Sent: Sunday, April 15, 2018 7:19 PM
To: TekScopes@groups.io
Subject: [TekScopes] TDS 210 not powering ON?

TDS 210 not powering ON?

Where do j start with a volt meter?
Are there common problem with TDS 210 unit Not powering up?
Thanks
Jack

____________________________________________________________
Buckingham Confirms Unfortunate News
risingstarnewspaper.com
http://thirdpartyoffers.juno.com/TGL3131/5ad407fed5d9a7fd1232st03vuc




--
Dennis Tillman W7PF
TekScopes Moderator


Re: 7904 Mainframe damaged

Göran Krusell
 

Hi, MBD5300 is from American Microsemiconductor, Inc. This is for CR1311? I used SR504 when I replaced CR1312.
Göran


Re: 7904 Mainframe damaged

 

Hi Goran :
Is there any idea for the replacement of MBD5300 ? It is a fast recovery diode ! But I cannot find the data sheet ?
RegardTony CheungAPR 16 2018


From: Yiu On Tony C via Groups.Io <tonycheung_hk=yahoo.com@groups.io>
To: "TekScopes@groups.io" <TekScopes@groups.io>
Sent: Monday, April 16, 2018 9:49 PM
Subject: Re: [TekScopes] 7904 Mainframe damaged

Hi Goran :
I will purchase the resistor loads tomorrow . By the ways I find defective rectifier CR1311 and CR1312 are shorted !
RegardTony CheungAPR 16 2018

      From: Göran Krusell <mc1648pp@gmail.com>
To: TekScopes@groups.io
Sent: Monday, April 16, 2018 9:22 PM
Subject: Re: [TekScopes] 7904 Mainframe damaged
 
Tony, this is only 20W. You need at least 50W, I think. Can you add more load? Like 11 ohm to the -15V as well.
Göran


Re: DSA 602A Main Time Interpolator Died

Tom Norman
 

As luck would have it, a posting popped up on everyone's favorite auction site, advertising two "U400" hybrids with the 165-2078-00 Tek part number. The one I received, happily, was in working order, and it appears to be functioning correctly in the DSA. Wave forms display correctly up to the triggering capabilities of the scope, so I think this problem is fixed.

The service manual doesn't really discuss how this hybrid works, only that it is timing the difference between the sample clock and the sample strobe (probably using incorrect terms), and reports that delta to the sweep controller, which presumably tells acquisition where to place the sample data in the time record. To me, Siggi's explanation of how the TDS544A interpolator works makes perfect sense for this machine. Tek just decided to implement on a hybrid.

The hybrid itself is as you might expect, is just a chip with a few surface mount passives populated around it on a ceramic substrate. If I get some time, I'll post some pics of the little bugger...

I wish there was some way we could get Tek to release more information about these scopes. Every time I open one up, I just grin at the engineering that went into these.


Re: 7904 Mainframe damaged

 

Hi Goran :
I will purchase the resistor loads tomorrow . By the ways I find defective rectifier CR1311 and CR1312 are shorted !
RegardTony CheungAPR 16 2018

From: Göran Krusell <mc1648pp@gmail.com>
To: TekScopes@groups.io
Sent: Monday, April 16, 2018 9:22 PM
Subject: Re: [TekScopes] 7904 Mainframe damaged

Tony, this is only 20W. You need at least 50W, I think. Can you add more load? Like 11 ohm to the -15V as well.
Göran

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