Date   

Re: 515A Trigger Cathode Followers (V410) Questions

Craig
 

I doubt that this pertains to your problem, but I had a recent issue with some 6922/6DJ8 tubes. This is a very popular tube in audio equipment and I recently had a problem with Tesla brand tubes in a Audio Research power amp. The tubes were breaking down with plate to grid shorts (visible sparking) when balancing the low level section of the amp. Switched out to Electro-Harmonix brand and no more problem.

This was a very specific circumstance because setting up the low level biases is done with no output tubes plugged in. As a result the high voltage (400V) remains for a long time after the power (tube filaments) is switched off. It was during this time when the high voltage was present and the filaments were off that the internal arcing in the tube happened.

These same tubes perform perfectly in less demanding preamp applications.

There are differences in the 6DJ8 tubes from different eastern european manufacturers.

Craig

- Both of the 6DJ8s, the recent failure and its replacement,
have the blue "sparks" when the scope is first
powered up. - They're made by the same company and were
bought at the same time so may be from the same batch. It
could be that they were both bad valves.


Re: 7834 readout problems

Albert Otten
 

Hi Ricardo,

This thread is not the proper place for your message. At the website click "New Topic", type a clever subject title and type your message. With e-mail I think there is a similar button.

Albert


---In TekScopes@..., <jeanious2011@...> wrote :

Don't know where to post this but I have a working Tek 465 in good condition ...


Re: 7834 readout problems

Albert Otten
 

Just some thoughts. The Match pots have most effect at the high currents and nearly no effect at the low currents. As I understand it, originally more readouts were shown than there were active channels selected. Was that perhaps due to a shifted 0 mA current, and missing a SKIP that way? After fiddling around with socketing the selected channels and the 0 became properly displayed. The +15V# and +15V* at the decoders are supplied, it seems, from the +15V at the data switch side (main interface board) via the braid of Peltola cables. These voltages at docoders pin 7 seem to serve as zero reference for the input voltage at pin 10. What would happen with the column decoder when pin 7 (+15V*) receives higher voltage than the supply voltage at pin 8 (+15V)?

Albert


Re: 7834 readout problems

Ricardo Flores <jeanious2011@...>
 

Don't know where to post this but I have a working Tek 465 in good condition (pretty clean, cosmetic and working) with the leather (or vinyl not sure but its original) along with the service and user manuals inside. Am wanting to sell it but don't know if there will be any interest in it. I don't want much for it but I know shipping is a good 35 bucks.

I also have a 468 in decent condition, works. The only problem I found on this one was that the Time/div knob is a bit crooked and when you turn it...it changes the "VR" knob.


If anyone is interested am in the DFW area in Texas....willing to ship (will pack very carefully with plenty of bubble wrap and cushion). These can be used or used for parts (don't know why they are working pretty darn good). Email jeanious2011@....

On Wednesday, September 17, 2014 3:26 PM, "David @DWH [TekScopes]" <TekScopes@...> wrote:




On 17 Sep 2014 12:53:41 -0700, you wrote:

David is right, R3409 & R3419 let the current change be sensed as a voltage change by the column decoder. I may jump in a resistance decade box to see if I can't persuade those voltages in the right direction. What do you think?
I considered suggesting this early on as it is likely to improve the situation
or at least reveal something but did not because I think it would fix the wrong
problem.

Adjusting the values of R3409 or R3419 will change the gain or scale of the
decoders' transfer curves while leakage affecting all decoded values is an
offset problem. I think it is worth trying because it is so simple but I do not
think it is the best or even a good solution.



[Non-text portions of this message have been removed]


Re: 7834 readout problems

 

On 17 Sep 2014 12:53:41 -0700, you wrote:

David is right, R3409 & R3419 let the current change be sensed as a voltage change by the column decoder. I may jump in a resistance decade box to see if I can't persuade those voltages in the right direction. What do you think?
I considered suggesting this early on as it is likely to improve the situation
or at least reveal something but did not because I think it would fix the wrong
problem.

Adjusting the values of R3409 or R3419 will change the gain or scale of the
decoders' transfer curves while leakage affecting all decoded values is an
offset problem. I think it is worth trying because it is so simple but I do not
think it is the best or even a good solution.


Re: 7834 readout problems

Paul
 

@ Ed - Thanks, I've seen readouts in the upper and lower channels, depending on what's selected. It's consistent with what I'd expect.

I've got a 7A26, it indicates that it's uncalibrated as soon as you pop the knob out. Right, sorry, the ">" is the uncal sign. So that's the only correct character being shown, and with the column select trimpot, I can get it to show the incorrect character (the delta), but ONLY on the 'uncal' character of the UPPER channel. All the other characters are still one column too low.

David is right, R3409 & R3419 let the current change be sensed as a voltage change by the column decoder. I may jump in a resistance decade box to see if I can't persuade those voltages in the right direction. What do you think?


Re: 7834 readout problems

 

On other 7000 series oscilloscopes, you can disconnect the connector P2118 going
between the readout board and the mode switches and force readout signals to
force all of the readouts to be active.

I have never before studied the detailed differences between the earlier readout
boards and the later ones like in the 7834. This game is fun.

On 17 Sep 2014 12:13:33 -0700, you wrote:

Also, be sure that the lower vertical channel is active on each one. The readout will be blank unless the channel is selected for display by itself, or in chop or alternate modes. Ed


Re: 7834 readout problems

Ed Breya
 

Also, be sure that the lower vertical channel is active on each one. The readout will be blank unless the channel is selected for display by itself, or in chop or alternate modes. Ed


Re: 7834 readout problems

Ed Breya
 

Actually, the ">" sign prefix is correct for vertical variable mode - not exactly sure what you meant by:

"I've re-socketed everything, and I did notice one thing:
with the column select trimpot I can now get the correct character on the first slot of upper channels of the vertical plugins - ie when variable knob is extended, I now get the delta, whereas I was getting the greater then sign. Both plugin slots, but only the upper channel. The numbers & suffix are still one off... weird. "

When the variable knob is in the detented "CAL" position, there should be no prefix on the V/DIV readout. Otherwise it should show ">" meaning it's more than the nominal V/DIV since gain is reduced.

Ed


Re: 7834 readout problems

 

On 17 Sep 2014 11:19:29 -0700, you wrote:

I've re-socketed everything, and I did notice one thing:
with the column select trimpot I can now get the correct character on the first slot of upper channels of the vertical plugins - ie when variable knob is extended, I now get the delta, whereas I was getting the greater then sign. Both plugin slots, but only the upper channel. The numbers & suffix are still one off... weird.
This is not unexpected. The decoders are not perfect and so there is some
variation from ideal for each signal level.

I need to study the manual more. I got my head wrapped around the .1ma steps, but don't fully understand the switching upstream yet. I'm suspecting either something in the neighborhood of Q3419, where I'm getting slightly different voltage readings (my earlier post), or Q3264 or the resistors around it.
The voltage at the base of Q3264 should be 3.1 volts.

I see what you mean about the diodes now, CR321x, right?
No.

The protection diodes, CR21 to CR56, are shown at the top of schematic 3 which
is the main interface board.

So could resistors R320x or R321x throw the current off as well?
I do not think so. There is no common problem there that could affect *all* of
the slots.

The CR321x and R32xx parts are the switching network which disables various
readout elements based on which plug-ins are used and which plug-ins are
selected via the mode switches. The force readout signal from the plug-ins is
used to prevent the mode switches from disabling a specific readout so plug-ins
like counters and multimeters do not need to be selected to use the readout.


Re: LCR Meter Recommendations Sought

David Gravereaux
 

It looks like Yahoo is stripping text attachments..
Save below as inductorTest.tcl


# inductor tester written by David Gravereaux <davygrvy@...> 4:26
PM 4/2/2012

package require gpib ;# http://gpib-tcl.sf.net/
package require tpscope ;# custom (my own) extension used for TiePie DSO
scopes and meters

set frequency 0
set lastrange 0 ;# an invalid value that is guarenteed to become updated

proc Freq {freq} {
global frequency
set frequency [tiepie::SetFuncGenFrequency $freq]
}

proc SetupTP {} {
tiepie::SetFuncGenDCOffset 0
tiepie::FuncGenBurst 0
tiepie::SetFuncGenSignalType sine
tiepie::SetFuncGenOutputOn 1
tiepie::SetFuncGenAmplitude 1.0
Freq 1000
}

proc SetupDmm {} {
global dmm

# open DM5010 (one with the readable lens)
set dmm [gpib open -address 16]
gpib write -device $dmm -message {acv; dig 4.5; rqs off; opc off;
monitor off; calc ratio; mode run}
CalculateCurrentMath
}

proc SetupAm {} {
global am

# open AM5030
set am [gpib open -address 5]
gpib write -device $am -message {bwlin on; cou ac; rqs off; amps 0.2}
}

proc SetupDist {} {
global dist

# open AA5001
set dist [gpib open -address 4]
gpib write -device $dist -message {func volts; rqs off}
}

proc CalculateCurrentMath {} {
global dmm am lastrange

# read AM5030 scale.
gpib write -device $am -message {amps?}
set range [expr [lindex [split [string trimright [gpib read -device
$am] {;}]] 1]]

if {$range != $lastrange} {
# change math in DMM to give direct (and correct) ampere output.
set adjust [expr {1/($range*100)}]
gpib write -device $dmm -message "ratio $adjust,0"
set lastrange $range
}
}

proc Setup {} {
SetupTP
SetupAm
SetupDmm
SetupDist
}

Setup

proc Test {} {
global dmm am dist frequency

# upload current probe range (if needed) to DMM for direct current
reading.
CalculateCurrentMath

# ask DMM to take a ACVRMS reading which is ratio'd to the current
in amperes
gpib write -device $dmm -message {send}

# ask DA to take an ACVRMS reading of volts across the inductor
gpib write -device $dist -message {send}

# should be using 'global execute trigger' above,
# but no such feature in gpib-tcl

# read current from DMM
set current [expr [string trimright [gpib read -device $dmm] {;}]]

# read voltage from DA
set voltage [expr [string trimright [gpib read -device $dist] {;}]]

# Xl = 2*Pi*F*L, solve for L in millihenries
set Xl [expr {$voltage/$current}]
set mhenries [format {%.5f} [expr
{1000*($Xl/(6.283185308*$frequency))}]]

puts "inductance = ${mhenries}mH and inductive reactance = &#92;
[format {%.2f} $Xl]&#92;u2126 @ [format {%.1f} $frequency]Hz"
}




--
David Gravereaux <davygrvy@...>


Re: LCR Meter Recommendations Sought

David Gravereaux
 

On 09/14/2014 08:39 AM, Bob Vines bobvines00@... [TekScopes] wrote:

What relatively affordable LCR meters do you guys (and ladies)
recommend for a hobbyists use at home? I doubt that I need a
NIST-certified or other high-end bench-top meter, just something
decent to give reliable enough measurements/tests for home/hobbyist
use -- a portable meter would fit my needs just fine, I think.

Somewhat off-topic, but interesting as a discussion...

I had to test custom wound inductors for speaker crossovers a while back
and put together a test set and automated it. Mostly Tek 5000 series
stuff, too.

- AM5030 with A6302 current probe
- DM5010 - A/C scaled current meter for the probe amp
- AA5001 - as an A/C voltmeter on the DUT
- TiePie HS3 - for the audio oscillator
- A rugged audio PowerAmp capable of 12 amperes at excessive power
factor loss

GPIB and scripting to the rescue. It was fun to see how the selected
frequency I would test the inductors at had little effect on the result
(as it should). I was expecting to measure some core saturation
artifacts at high current levels, but it wasn't apparent.

--
David Gravereaux <davygrvy@...>


Re: 7834 readout problems

Paul
 

yes, sorry off by one column.
I don't have a layout for that board in my manual either.
U3262 & U3232 were easy to reach on the main interface board once I slid the power supply out.

I've re-socketed everything, and I did notice one thing:
with the column select trimpot I can now get the correct character on the first slot of upper channels of the vertical plugins - ie when variable knob is extended, I now get the delta, whereas I was getting the greater then sign. Both plugin slots, but only the upper channel. The numbers & suffix are still one off... weird.

I need to study the manual more. I got my head wrapped around the .1ma steps, but don't fully understand the switching upstream yet. I'm suspecting either something in the neighborhood of Q3419, where I'm getting slightly different voltage readings (my earlier post), or Q3264 or the resistors around it.

I see what you mean about the diodes now, CR321x, right?
So could resistors R320x or R321x throw the current off as well?

thanks again!


Re: 7834 readout problems

 

On 16 Sep 2014 11:59:23 -0700, you wrote:

Does this happen with all slots?
yep, all slots, though I don't appear to be getting any readout from the left horizontal. The problem behaves identically on both the left and right vertical slots (ie off by one row).
I think that is actually off by one column and not one row.

R3407 adjusts the column matching but leakage could be causing a problem.
turning the pot shows no visible change, which is strange, no? What do you mean by leakage?
It is not uncommon for adjustment of the row and column match to have no effect.

The signals from the plug-ins are currents from 0.0 to 1.0 milliamps with a
fixed step size of 0.1 milliamp. The resistors in series with the row and
column match trimmers convert the currents to voltages (I think. I do not have
much data on what the decoders actually look for.) for the row and column
decoders which are 1 of 10 analog to digital converters.

Leakage anywhere along the signal lines and up to decoders U3429 and U3418 will
shift the column or row current but data switches U3232 and U3262 are
specifically vulnerable to damage because their inputs are exposed which is why
diode protection was added to their inputs.

Tektronix added a protection diode board to the signals from the main interface to protect U3232 and U3262 from damage. Does your 7834 have it?
That's an extra board with a few diodes on it? It doesn't appear that I have it. I can trace out the path between 3262 and the read-out board, and it looks like a straight shot via the ribbon cable.
My 7834 does not have it but since my other 7000 mainframes have protection
diode boards, I assumed the 7834 did as well but the schematics show that
Tektronix moved the protection diodes to the main interface board which makes
sense since the 7834 was designed after the diode protection boards became
standard on the earlier models.

Tektronix also moved the data switches from the readout board to the main
interface board which makes good sense.

U3232 may be swapped with U3262 and U3429 may be swapped with U3418 to see if the problem moves from the column matching to the row matching.
I swapped U3429 & U3418 - no change.
U3232 & U3262: I can see them behind the power supply under the CRT, just don't know what the disassembly steps are yet, have to dig through the manual a bit more.
Is there a layout for the readout board in the 7834 service manual? I
apparently am missing that page.

it is normal for pulses to be missing at pin 16 and for the negative part of the waveform at pin 10 to be shortened because of the display skip function.
Ah, OK, thanks. Have to dig deeper to really understand the skip function.
I studied the design in detail a while ago and remembered that there was some
kind of display skip function.

Removing Q3416 disables display skip and is handy for diagnosing the readout

board. It should then display two rows of 40 zeros each. Some of the service
manuals like the one for the 7904 recommend this as part of calibration and
adjustment.
Yep, I did try that and saw all zeros.

Thanks again - next up some judicious metering and figuring out how to get to U3262 & U3232
I am not even sure where they are on the board.

On 16 Sep 2014 12:46:42 -0700, you wrote:

U3232 & U3262 swapped, no change.
So the problem is probably neither the data switches nor the decoders.

Should I be suspecting Q3419?

2) The characters are all one column less then they should be based on the table on page 3-36 of the manual. '0S' should be '1V' and '4m' should read '5u'
So we are actually looking for leakage which lowers the current going into
column decoder U3418. Anything on the line between U3262 and U3418 which could
do that is suspect.

The gain of Q3264 could be low. I would swap it with Q3234 or just replace it.

Q3419 could have very high Icbo leakage or maybe it is not turning off
completely.

The gain of Q3406 could be low.

On 17 Sep 2014 07:43:01 -0700, you wrote:

update:
re-socketing a few of the transistors fixed the missing readouts on the right horizontal bay, and the upper/lower duplication I was seeing. Now every bay has it's readout, it's just wrong.
That is kind of weird but I should not be surprised given the complexity of the
design.

what's supposed to be +4.4v on pin 9 into column decoder U3418 is only +3.84v
I think pin 9 is a digital input so the absolute level has some leeway. If the
gain of Q3406 is low enough though which would pull current out of the signal
line causing the one column less issue, then maybe Q3416 is not receiving enough
drive.

what's supposed to be +14.5v on pin 10 is 14.8v
I do not really understand the signaling on the decoders. It seems like they
should accept a voltage input which is provided by the signal current through
the shunt resistance to +15 volts at their input.

ideas welcome!
I would at least replace Q3264 and Q3419 to see if either is the problem since
that is easy to do. Q3406 is a little more difficult to replace but I think a
pair of transistors with matched Vbe to within a couple millivolts would work. I
would epoxy a pair of 2N3904s together.

I always get suspicious when I find transistors with low gain in old equipment.
I had some fun playing with my curve tracer to test all of the transistors from
a DC505 after a couple turned up bad and found all kinds of interesting issues
with the working ones so I replaced them all.


Re: LCR Meter Recommendations Sought

K5MYJ <macklinbob@...>
 

I use a Heathkit IB-1A and a Heathkit QM-1.

They work fine for my needs!!

Bob Macklin
K5MYJ
Seattle, Wa.
"Real Radios Glow In The Dark"

----- Original Message -----
From: bonddaleena@... [TekScopes]
To: TekScopes@...
Sent: Tuesday, September 16, 2014 7:46 AM
Subject: Re: [TekScopes] LCR Meter Recommendations Sought



Hi, I do a lot of older radio and test equipment restorations. I have replaced thousands of caps. There are at least 3 different aspects to capacitor testing (at least in my small mind).
As I have said on this forum before, the small hand held VOMs (that also measure capacitance, Hz, etc) will probably be OK for testing for value.
In fact, I have a NIST traceable LCR bridge (works on 9 VDC) that gets a lot of use (mostly for identifying unmarked variable capacitors).
They won't tell you a thing about either 'leakage' or ESR.
A lot of the caps I replace are .01 uf, ,1 uf / 400 VDC etc. These caps will measure perfectly for value on the bridge. HOWEVER, when tested at the cap's RATED value (HV) they sometimes leak 300-400 VDC.
For ESR, I have 4 LCR meters (handhelds). My go to and favorite is the Peak.
It :
1. has Kelvin leads
2. automatically discharges smaller caps (although I always short them first)
3. shows the capacity
4. shows the ESR

For in-circuit work I like the Dick Smith clones including the one from Portugal........

regards
ron
N4UE

-----Original Message-----
From: 'Dennis Tillman' @Dennis_Tillman_W7pF [TekScopes] <TekScopes@...>
To: TekScopes <TekScopes@...>
Sent: Mon, Sep 15, 2014 10:11 pm
Subject: RE: [TekScopes] LCR Meter Recommendations Sought

Bob,

The question of L/C or L/R/C meters is one that comes up regularly on the
forum.

About a year ago I bought one of the L/C Meters which looks like the one
shown in current Ebay auction 170909706565 (I have no relationship to the
seller, etc.) and I reported back to the group on how well it worked. To
summarize: It was accurate for caps from 1uF to <1pF and for inductors from
10mH to <1uh. It was not reliable below 1uH. I did not test for other
values.

There are a lot of L/C or L/R/C testers on Ebay. Some look better than
others but they all probably do a decent job. If you buy one please let the
group know your experiences with it once you get it.

Dennis Tillman W7PF

>On 9/14/2014 10:39 AM, Bob Vines bobvines00@... [TekScopes] wrote:
>>
>> In many of the discussions by this Group, it is highly recommended to
>> test capacitors (and sometimes inductors) using LCR meters. I can
>> measure resistors with my DMM, but have no way (yet) to measure/test
>> capacitors and/or inductors.
>>
>> What relatively affordable LCR meters do you guys (and ladies)
>> recommend for a hobbyists use at home? I doubt that I need a
>> NIST-certified or other high-end bench-top meter, just something
>> decent to give reliable enough measurements/tests for home/hobbyist
>> use -- a portable meter would fit my needs just fine, I think.
>>
>> Thanks,
>>
>> Bob

------------------------------------
Posted by: David <@DWH>
------------------------------------

------------------------------------

Yahoo Groups Links

[Non-text portions of this message have been removed]


Re: 7834 readout problems

Ed Breya
 

You may want to try the same thing on all the ICs on the readout board - pry them part way up, but not all the way out, then push them back down fully into the sockets. Most of the older RO boards I have seen used TI brand sockets, which have a lot of contact problems. The TI sockets and ICs issue has been covered quite a lot here over the years, and not just for RO boards. Ed


Re: OT: high temperature automotive epoxy

Ed Breya
 

Some models have provisions and methods for bleeding air from the cooling system. This one apparently does not need that. I found an excellent post in a forum, that exactly addresses this issue. If anyone is interested it's at the url below - the answer is in the post called "update," near the end of the page.

http://forums.bimmerforums.com/forum/showthread.php?1946472-Help-with-2007-X5-4-8-coolant-leak http://forums.bimmerforums.com/forum/showthread.php?1946472-Help-with-2007-X5-4-8-coolant-leak

I'll find out more today - I'm taking it in for brake pads check and possible replacement - my mechanic friend said he will check if it needs air-bleeding too.

Ed


Re: 7834 readout problems

Paul
 

update:
re-socketing a few of the transistors fixed the missing readouts on the right horizontal bay, and the upper/lower duplication I was seeing. Now every bay has it's readout, it's just wrong.


what's supposed to be +4.4v on pin 9 into column decoder U3418 is only +3.84v
what's supposed to be +14.5v on pin 10 is 14.8v
ideas welcome!


Re: LCR Meter Recommendations Sought

n4mf_sc
 

Stay away from the DM4070 on flea-bay, It's poorly constructed, and the one I bought about 6 months ago worked for about a month before I started having problems with the range selector switch. It's now in the junk box..

73,
Mitch
N4MF


Re: LCR Meter Recommendations Sought

EJP
 

I use and recommend the Peak LCR meter, available in a neat case with their DCA (digital component analyser).