Hi Ed,
Yes I agree, it's possible with 2 transistors to do the job, I done it too in the past, but anyway, I find simplest to just change The IC.
My challenge now is to do it on my 2 SG503 witch use strange segment decoders.
|
Re: Tek 7854 Info, Repair, Restore
Hi to All,
Nice that Brian put some energy in contacting the buyer of the 7854 with the 067-0961-00 Diagnostic Memory Board.
In Post 62147 I copied a list of Fixtures to service a 7854 (see below):
" In the past I made some overview of 7854 dedicated Calibration Fixtures (7854 Service Manual: Maintenance Section 3-7/8/9):
067-0892-00: Tektronix Microlab 1 Mainframe (provides power for service package and in conjunction with the RS232 Compatible Terminal control over the 067-0961-XX Diagnostic Memory Board)
067-0911-00: Diagnostic Test Interface (serves as a interface between the Microlab 1 Mainframe and the digital portion of the 7854)
067-0912-00: Analog Test Board (used to isolate the analog circuitry from the digital portion) Plugs into A29-Display Board
067-0913-00: Extender Board 44-Pin (used with the A30-GPIB and A31-ROM Boards)
067-0914-00: Extender Board 80-Pin (used with the A27-MPU and A28-RAM Boards)
067-0915-00: Extender Board 124-Pin (used with the A26-Control Logic and A29-Display Boards)
067-0961-XX: Diagnostic Memory Board (contains a portion of the service package firmware, as well as 7854 specific troubleshooting stimuli and diagnostics)
070-2972-XX: Signature Tables (is a complete and cumulative (historical) document of the firmware in the digital portion of the 7854)
RS232 Compatible Terminal (In conjunction with the Microlab 1 provides control over the 067-0961-00, the A2-Test Processor Board and the 067-0911-00 Diagnostic Test Interface)"
I never saw on eBay or else the 067-0911-00 Fixture which is really needed to take advantage of the 067-0961-00 Diagnostic Memory Board. The 067-0911--00 and up Manual is on TekWiki and you must have access to both big Volumes of the "Test Procedures for 7854 Diagnostic Troubleshooting using the 067-0911-00 and up Diagnostic Test Interface"
Greetings and much succes,
Egge Siert
|
Re: Timebase and CRT Issues on Tektronix Type 545A
That kind of waveform is commonly caused by an open in the high
impedance vertical signal path before the first buffer. The
capacitance bridging the open circuit is enough when combined with the
high input impedance to make a high pass filter.
The output of the calibrator could be open causing the same problem
since it is looking into the high impedance input of the CA vertical
amplifier plug-in.
It also looks like the horizontal sweep is uneven.
toggle quoted message
Show quoted text
On 27 Mar 2016 22:42:35 -0700, you wrote: Albert,
The voltage divider was a good idea. I was able to see the voltage across R330 as a sawtooth-looking waveform. The trouble is I couldn't get any leads into where the tubes were because the pins are very hard to get at. I did however look at the voltage across the anode of V384A and it seems to be the culprit because there was 0 V across the points that the manual says should have +123 V (when the horizontal position is all the way to CCW) and +325 V (when the horizontal position is all the way to CW). No matter what the horizontal position was, the voltage was 0 V. So I figured the tube was the issue. I replaced the tube with an equivalent 6DJ8 and it seems to have fixed the half screen problem! However, the waveform shown is off. It could be due to calibration being way off so it might be an easy fix. But I am feeding Channel B the calibrator square wave and it looks very off. It doesn't look square first off and also, it has this spot in the middle that seems to be different than
the rest of the signal. Picture: Imgur: The most awesome images on the Internet
|
Re: Timebase and CRT Issues on Tektronix Type 545A
Albert,
The voltage divider was a good idea. I was able to see the voltage across R330 as a sawtooth-looking waveform. The trouble is I couldn't get any leads into where the tubes were because the pins are very hard to get at. I did however look at the voltage across the anode of V384A and it seems to be the culprit because there was 0 V across the points that the manual says should have +123 V (when the horizontal position is all the way to CCW) and +325 V (when the horizontal position is all the way to CW). No matter what the horizontal position was, the voltage was 0 V. So I figured the tube was the issue. I replaced the tube with an equivalent 6DJ8 and it seems to have fixed the half screen problem! However, the waveform shown is off. It could be due to calibration being way off so it might be an easy fix. But I am feeding Channel B the calibrator square wave and it looks very off. It doesn't look square first off and also, it has this spot in the middle that seems to be different than the rest of the signal. Picture: Imgur: The most awesome images on the Internet
Imgur: The most awesome images on the Internet Imgur: The most awesome images on the Internet.
View on imgur.com
Preview by Yahoo
But the display seems to extend all the way horizontally so I suppose this is a step in the right direction.
Thank you for all your help,
Alex Brinister
|
Re: 7904 plug-in connector pins
Hi Ed,
I believe they can be replaced individually. I once saw a Tek made backplane
connector repair kit for the 7000 series. At least I recall that is what it
was for.
What I wonder about is how you would go about aligning the pins perfectly. I
don't recall seeing any way to do that in the kit I saw.
Dennis Tillman W7PF
toggle quoted message
Show quoted text
-----Original Message-----
Sent: Sunday, March 27, 2016 9:18 AM
Subject: [TekScopes] 7904 plug-in connector pins
The recently fixed 7904 has no readout in the A-horizontal slot. I found the
likely obvious cause - some bent and broken off contacts near the top of the
plug-in connector. I believe that these contacts can be replaced
individually, in situ, but have never needed to do it, so not absolutely
sure. I have entire spare main interface boards, so could conceivably
replace the whole thing, but that seems like an awful lot to go through.
I could tell by looking at the spare parts, but they're at another location.
Could someone please confirm whether these contacts can be replaced
individually? I'm picturing turning the scope on its back and performing the
surgery all from the plug-in compartment side.
Ed
------------------------------------
Posted by: edbreya@...
------------------------------------
|
Re: Tektronix 576 577 Safety Shield cover for Curve tracers
Hi Raul,
Congratulations. The 577 is a wonderful instrument for anyone to own.
The cover IS NOT NEEDED on the two lowest collector voltage ranges: 6V and
25V. There are some setting combinations that will cause the yellow light to
flash so you should follow the "First Time Use" setup in the service manual
to be sure you have proper settings to get a good display of curves on your
577.
It is uncommon to need to test semiconductors on the higher voltage ranges.
But if you do need to do that there are two choices: My "front porch"
(another name for the 177) had a red push button on the front of it which
bypassed the safety interlock. It was factory installed but it was not
labeled. It was a "mystery pushbutton" and everyone who used the 577
understood its purpose. Eventually the Product Liability Lawyers or the
Liability Insurance Company at Tek found out and had it removed.
You can always put one in your 577, or you can do what a lot of other people
do which is to press a cue-tip down into the interlock hole and depress the
micro switch. It only takes light pressure. Just don't touch the transistor
when you are doing measurements on those higher voltages (don't ask me how I
know this).
The covers are extremely hard to find (and therefore very expensive) because
engineers immediately tossed them into the drawer on the curve tracer's cart
and forgot about them. I would not concern myself with trying to find one.
Instead learn how to use this incredibly versatile instrument.
Dennis Tillman W7PF
toggle quoted message
Show quoted text
-----Original Message-----
From: TekScopes@... [mailto:TekScopes@...]
Sent: Saturday, March 26, 2016 3:01 PM
To: TekScopes@...
Subject: [TekScopes] Tektronix 576 577 Safety Shield cover for Curve tracers
Hi All: I recently purchased a used 577 form eBay, It is in good shape
although I couldn't yet even plug it on. It miss the safety plastic cover
and recently the following appears in eBay:
Tektronix 576 577 Safety Shield cover for Curve tracers OLD STOCK
=STRK%3AMEBIDX%3AIT
Tektronix 576 577 Safety Shield cover for Curve trace...
=STRK%3AMEBIDX%3AIT US $150.00 New in Business & Industrial, Electrical &
Test Equipment, Test Equipment
I looked at other 577's photo's and this one looks similar but not the same,
it has a right shoulder that i did not see in other 577/76's and the
tektronix logo has the (R) for registered missing. Dimensions seems to be
right but for some reason I suspect this is not an original piece. My
specific questions for the group are:
1) Does anybody recognize this plastic as a Tek part?
2) If so to which equipment belongs and most importantly if it would work
on 577.
Raul
PD: The packaging for the 577 was great, I will later post the photos of it
in the context of tek packaging in this forum recently active.
------------------------------------
Posted by: martinez.raul.jorge@...
------------------------------------
|
Re: PS501 PS503A large Sprague Capacitors
Capacitors have gotten smaller but there has been a cost as well; with
less surface area, heat dissipation is less so ripple current ratings
are reduced. While it is not an issue in this case, it may be
necessary to use a higher voltage capacitors just to maintain the same
ripple current rating as the originals.
The wires are 18 gauge and the largest size which would fit in the
printed circuit board holes so they are very rigid and I did not feel
that they needed to be insulated. The original wires were thinner but
did have less distance to travel.
Notice that the wires are paired up but not in parallel. One of each
pair goes to the rectifier and the other goes to the following
circuits; this minimizes the capacitor ESR although this is not really
necessary. The original capacitors were wired in the same way.
After I installed the capacitors, I realized that it would have been
better if they had been longer which would have shortened the wire
length. This would have been easy enough to do by ordering higher
voltage units although at an increased cost.
toggle quoted message
Show quoted text
On Sun, 27 Mar 2016 20:09:24 -0400, you wrote: That example photograph is one of the best depictions of how much the technology has changed over the years.
I would have slipped a piece of Teflon tubing over the leads though.
Nice work.
I do not know of any and I would avoid NOS (new old stock) capacitors
anyway. Aluminum electrolytic capacitors do not age like fine wine
unless the wine turns into vinegar.
What I did was to find new replacement capacitors which have the same
diameter so they fit into the existing plastic mounts:
I could have used higher voltage capacitors so they would be
physically longer.
|
Welp. Not my proudest moment. don't de-solider angry. The frustration of de-soldering DIPs on multi-layer boards has probably chipped away months off my life, which is why there's a Hakko FR-300 now en-route to my office.
...
View on paulcarbone.com
Preview by Yahoo
On the plus side, there's one more good DC508A display out there, and one less functioning unit that needs it.
|
More came back. Another NPN with base driven from the BCD "2" input, and the collector tied to the upper segment output, will force it on in all states that include 2. Except for decimal 1 and 4 output, the others have it on anyway, so are don't-cares. When decimal 6 is called for, the BCD 2 will light the upper bar. So, another NPN and base resistor takes care of it.
Ed
|
Re: PS501 PS503A large Sprague Capacitors
That example photograph is one of the best depictions of how much the technology has changed over the years.
I would have slipped a piece of Teflon tubing over the leads though.
Nice work.
toggle quoted message
Show quoted text
----- Original Message -----
From: David davidwhess@... [TekScopes]
To: TekScopes@...
Sent: Sunday, March 27, 2016 7:58 PM
Subject: Re: [TekScopes] PS501 PS503A large Sprague Capacitors
On 27 Mar 2016 02:34:21 -0700, you wrote:
>I repaired two of these and on both the 3000 ?F resp. 4500 ?F (C10/C20 resp. C10/C110) Spraguelytics were the culprits. Exchanging them against some 35V types I had laying around in much smaller outline and larger capacity made the units work again.
>
>Only it doesn't look very nice and I would rather build in some devices that fit into these plastic holders.
>
>Are there still sources for these original Sprague capacitors?
I do not know of any and I would avoid NOS (new old stock) capacitors
anyway. Aluminum electrolytic capacitors do not age like fine wine
unless the wine turns into vinegar.
What I did was to find new replacement capacitors which have the same
diameter so they fit into the existing plastic mounts:
I could have used higher voltage capacitors so they would be
physically longer.
|
Re: PS501 PS503A large Sprague Capacitors
On 27 Mar 2016 02:34:21 -0700, you wrote: I repaired two of these and on both the 3000 ?F resp. 4500 ?F (C10/C20 resp. C10/C110) Spraguelytics were the culprits. Exchanging them against some 35V types I had laying around in much smaller outline and larger capacity made the units work again.
Only it doesn't look very nice and I would rather build in some devices that fit into these plastic holders.
Are there still sources for these original Sprague capacitors? I do not know of any and I would avoid NOS (new old stock) capacitors anyway. Aluminum electrolytic capacitors do not age like fine wine unless the wine turns into vinegar. What I did was to find new replacement capacitors which have the same diameter so they fit into the existing plastic mounts: I could have used higher voltage capacitors so they would be physically longer.
|
I think some of it came back to my brain. I think I used a couple of transistors gated from the input code or other segment codes, to add the extra segment pull-down states on the open-collector outputs. So, not as simple as I was imagining.
For example, for digits 8 and 9, an NPN driven from the BCD input MSB will be on for both, and can light the lower bar in both states. For all other decimal digits it doesn't matter. So, a base resistor and an NPN take care of the 9. I think the 6 fixer was similar.
Ed
|
Re: 2445a power supply repair
In your position, I would change all of the aluminum electrolytic
capacitors except maybe for the input capacitors which are less likely
to be worn out. The output capacitors for the switching power supply
are usually the first to fail.
The electrolyte is acidic (boric acid?) and water soluble so cleaning
the area using a damp swab should be sufficient. I might use window
cleaner which has ammonia in it since this will neutralize any acid
and then follow up with clean water. I would not soak the entire
board to clean it.
toggle quoted message
Show quoted text
On Sun, 27 Mar 2016 22:59:56 +0000 (UTC), you wrote: Hello, David,
Thank you for answering. Yes, I do have a few other scopes, but before I've started the real debugging, I've noticed that the aluminum caps had a high leakage current.When I've unsoldered them, they literally leaked out!!! The epoxy gasket cracked and electrolyte was spilled to the center of the board. Fortunately no corrosion yet. The scope doesn't have many hours clocked. Just old. All the other caps seem to be dryed out, but these 6 caps: four 250uF and two 180uF are dead. Before going any further I've ordered @ Digikey the new caps for the power supply.
I'll keep you posted once the caps are installed.
Thank you,
Maxim
|
I think there may be a simple way to get nice 6 and 9 digits including the upper and lower bars of the display, even using a regular old 7447. I did that years ago to make the display the way I wanted it. I can't remember exactly how, but it involved looking at the various decoded segment drive lines, and adding a little circuitry to light the bars. I vaguely recall that it only needed some extra resistors, and was simple because of some "X" states of the decoding. Could be wrong - it was long ago - maybe there was more to it.
Ed
|
Re: 2445a power supply repair
Hello, David,
Thank you for answering. Yes, I do have a few other scopes, but before I've started the real debugging, I've noticed that the aluminum caps had a high leakage current.When I've unsoldered them, they literally leaked out!!! The epoxy gasket cracked and electrolyte was spilled to the center of the board. Fortunately no corrosion yet. The scope doesn't have many hours clocked. Just old. All the other caps seem to be dryed out, but these 6 caps: four 250uF and two 180uF are dead. Before going any further I've ordered @ Digikey the new caps for the power supply.
I'll keep you posted once the caps are installed.
Thank you,
Maxim
toggle quoted message
Show quoted text
On Tuesday, March 22, 2016 12:51 AM, "David davidwhess@... [TekScopes]" <TekScopes@...> wrote: ? On 21 Mar 2016 04:00:34 -0700, you wrote: Hello,
I've got a 2445a, which was burned by the previous owner (he was debugging the mains power supply without an isolation transformer). After repairs, where I've changed the channel #1 hybrid, TL072, TL074 and MC1458, now it seems, that the scope can be calibrated.
Before starting the calibration, I've checked the voltages on the power supply connector. All are nominal for exception of the analog +5 and -5 volts, which read well before the minimum.
I've got 4.78 and -4.76 volts. Voltages don't drift. Ripple is within the spec. The scope traces are stable before and after the warmup.
I looked at the PSU schematics and +5VA/-5VA are sourced via the linear regulators from the rectifier/filter. Could it be that the C1115 and C1114 caps have "dried out"? I don't see any leaks. Checked the capacitance, seems ok. Don't have a possibility to check the ESR. It is very odd that +5VA and -5VA are both off by the same amount while none of the other voltages are. A single bad capacitor should not be able to cause this problem and all of the supply voltage rely on the same +10 volt reference. What are the voltages for +5V UNREG and -5V UNREG? If both C1114 and C1115 are bad, then the UNREG voltages into the regulators could be low enough to cause matching low output voltages. Can I substitute a different capacitors instead of 250uFx20V?
Can I use for example, 330uFx25V? Yes, the values are not critical. Do I have to use the "low ESR" caps, or I can buy the standard "heavy duty" caps? C1114 and C1115 should be low ESR to keep the ripple from the switching power supply down but "heavy duty" capacitors should at least work. They might not last as long. Thank you! If you have not already pulled or replaced C1114 and C1115, measure +5V UNREG and -5V UNREG with the old capacitors still installed. Then when you replace them, measure +5V UNREG and -5V UNREG for comparison. Do you have a working oscilloscope that you can use to measure the high frequency ripple on +5V UNREG and -5V UNREG? #yiv9138071348 #yiv9138071348 -- #yiv9138071348ygrp-mkp {border:1px solid #d8d8d8;font-family:Arial;margin:10px 0;padding:0 10px;}#yiv9138071348 #yiv9138071348ygrp-mkp hr {border:1px solid #d8d8d8;}#yiv9138071348 #yiv9138071348ygrp-mkp #yiv9138071348hd {color:#628c2a;font-size:85%;font-weight:700;line-height:122%;margin:10px 0;}#yiv9138071348 #yiv9138071348ygrp-mkp #yiv9138071348ads {margin-bottom:10px;}#yiv9138071348 #yiv9138071348ygrp-mkp .yiv9138071348ad {padding:0 0;}#yiv9138071348 #yiv9138071348ygrp-mkp .yiv9138071348ad p {margin:0;}#yiv9138071348 #yiv9138071348ygrp-mkp .yiv9138071348ad a {color:#0000ff;text-decoration:none;}#yiv9138071348 #yiv9138071348ygrp-sponsor #yiv9138071348ygrp-lc {font-family:Arial;}#yiv9138071348 #yiv9138071348ygrp-sponsor #yiv9138071348ygrp-lc #yiv9138071348hd {margin:10px 0px;font-weight:700;font-size:78%;line-height:122%;}#yiv9138071348 #yiv9138071348ygrp-sponsor #yiv9138071348ygrp-lc .yiv9138071348ad {margin-bottom:10px;padding:0 0;}#yiv9138071348 #yiv9138071348actions {font-family:Verdana;font-size:11px;padding:10px 0;}#yiv9138071348 #yiv9138071348activity {background-color:#e0ecee;float:left;font-family:Verdana;font-size:10px;padding:10px;}#yiv9138071348 #yiv9138071348activity span {font-weight:700;}#yiv9138071348 #yiv9138071348activity span:first-child {text-transform:uppercase;}#yiv9138071348 #yiv9138071348activity span a {color:#5085b6;text-decoration:none;}#yiv9138071348 #yiv9138071348activity span span {color:#ff7900;}#yiv9138071348 #yiv9138071348activity span .yiv9138071348underline {text-decoration:underline;}#yiv9138071348 .yiv9138071348attach {clear:both;display:table;font-family:Arial;font-size:12px;padding:10px 0;width:400px;}#yiv9138071348 .yiv9138071348attach div a {text-decoration:none;}#yiv9138071348 .yiv9138071348attach img {border:none;padding-right:5px;}#yiv9138071348 .yiv9138071348attach label {display:block;margin-bottom:5px;}#yiv9138071348 .yiv9138071348attach label a {text-decoration:none;}#yiv9138071348 blockquote {margin:0 0 0 4px;}#yiv9138071348 .yiv9138071348bold {font-family:Arial;font-size:13px;font-weight:700;}#yiv9138071348 .yiv9138071348bold a {text-decoration:none;}#yiv9138071348 dd.yiv9138071348last p a {font-family:Verdana;font-weight:700;}#yiv9138071348 dd.yiv9138071348last p span {margin-right:10px;font-family:Verdana;font-weight:700;}#yiv9138071348 dd.yiv9138071348last p span.yiv9138071348yshortcuts {margin-right:0;}#yiv9138071348 div.yiv9138071348attach-table div div a {text-decoration:none;}#yiv9138071348 div.yiv9138071348attach-table {width:400px;}#yiv9138071348 div.yiv9138071348file-title a, #yiv9138071348 div.yiv9138071348file-title a:active, #yiv9138071348 div.yiv9138071348file-title a:hover, #yiv9138071348 div.yiv9138071348file-title a:visited {text-decoration:none;}#yiv9138071348 div.yiv9138071348photo-title a, #yiv9138071348 div.yiv9138071348photo-title a:active, #yiv9138071348 div.yiv9138071348photo-title a:hover, #yiv9138071348 div.yiv9138071348photo-title a:visited {text-decoration:none;}#yiv9138071348 div#yiv9138071348ygrp-mlmsg #yiv9138071348ygrp-msg p a span.yiv9138071348yshortcuts {font-family:Verdana;font-size:10px;font-weight:normal;}#yiv9138071348 .yiv9138071348green {color:#628c2a;}#yiv9138071348 .yiv9138071348MsoNormal {margin:0 0 0 0;}#yiv9138071348 o {font-size:0;}#yiv9138071348 #yiv9138071348photos div {float:left;width:72px;}#yiv9138071348 #yiv9138071348photos div div {border:1px solid #666666;height:62px;overflow:hidden;width:62px;}#yiv9138071348 #yiv9138071348photos div label {color:#666666;font-size:10px;overflow:hidden;text-align:center;white-space:nowrap;width:64px;}#yiv9138071348 #yiv9138071348reco-category {font-size:77%;}#yiv9138071348 #yiv9138071348reco-desc {font-size:77%;}#yiv9138071348 .yiv9138071348replbq {margin:4px;}#yiv9138071348 #yiv9138071348ygrp-actbar div a:first-child {margin-right:2px;padding-right:5px;}#yiv9138071348 #yiv9138071348ygrp-mlmsg {font-size:13px;font-family:Arial, helvetica, clean, sans-serif;}#yiv9138071348 #yiv9138071348ygrp-mlmsg table {font-size:inherit;font:100%;}#yiv9138071348 #yiv9138071348ygrp-mlmsg select, #yiv9138071348 input, #yiv9138071348 textarea {font:99% Arial, Helvetica, clean, sans-serif;}#yiv9138071348 #yiv9138071348ygrp-mlmsg pre, #yiv9138071348 code {font:115% monospace;}#yiv9138071348 #yiv9138071348ygrp-mlmsg * {line-height:1.22em;}#yiv9138071348 #yiv9138071348ygrp-mlmsg #yiv9138071348logo {padding-bottom:10px;}#yiv9138071348 #yiv9138071348ygrp-msg p a {font-family:Verdana;}#yiv9138071348 #yiv9138071348ygrp-msg p#yiv9138071348attach-count span {color:#1E66AE;font-weight:700;}#yiv9138071348 #yiv9138071348ygrp-reco #yiv9138071348reco-head {color:#ff7900;font-weight:700;}#yiv9138071348 #yiv9138071348ygrp-reco {margin-bottom:20px;padding:0px;}#yiv9138071348 #yiv9138071348ygrp-sponsor #yiv9138071348ov li a {font-size:130%;text-decoration:none;}#yiv9138071348 #yiv9138071348ygrp-sponsor #yiv9138071348ov li {font-size:77%;list-style-type:square;padding:6px 0;}#yiv9138071348 #yiv9138071348ygrp-sponsor #yiv9138071348ov ul {margin:0;padding:0 0 0 8px;}#yiv9138071348 #yiv9138071348ygrp-text {font-family:Georgia;}#yiv9138071348 #yiv9138071348ygrp-text p {margin:0 0 1em 0;}#yiv9138071348 #yiv9138071348ygrp-text tt {font-size:120%;}#yiv9138071348 #yiv9138071348ygrp-vital ul li:last-child {border-right:none !important;}#yiv9138071348 [Non-text portions of this message have been removed]
|
Re: 7904 plug-in connector pins
Hi Ed, As I remember... changing individual contacts on the back plane is very easy. Remove the damaged contacts, put the replacement contacts in place and snap on the plastic side covers to locate everything before you solder the replacement contacts to the back plane. It is also not much trouble to exchange the entire back plane for a different one. tom jobe... On 3/27/2016 9:17 AM, edbreya@... [TekScopes] wrote:
The recently fixed 7904 has no readout in the A-horizontal slot. I
found the likely obvious cause - some bent and broken off contacts
near the top of the plug-in connector. I believe that these contacts
can be replaced individually, in situ, but have never needed to do it,
so not absolutely sure. I have entire spare main interface boards, so
could conceivably replace the whole thing, but that seems like an
awful lot to go through.
I could tell by looking at the spare parts, but they're at another
location. Could someone please confirm whether these contacts can be
replaced individually? I'm picturing turning the scope on its back and
performing the surgery all from the plug-in compartment side.
Ed
[Non-text portions of this message have been removed]
[Non-text portions of this message have been removed]
|
Re: 5440 low-voltage power supply
What did I write? I should have just eaten my easter egg and concentrate on *that*. -:(
Raymond
|
Re: 7854 RAM card upgrade only - any interest?
The Tektronix 7000 assemblies list (Tektronix7xxx_Assemblies.pdf in
the files section) says that the 7854 uses A18 670-5832-XX for the
vertical amplifier and that it is shared by none of the other 7000
mainframes.
The 400 MHz mainframes and the 7904 do use the same ICs though so
there are several potential sources for those.
toggle quoted message
Show quoted text
On 27 Mar 2016 06:45:29 -0700, you wrote: ...
It's quite likely that you can count me in for 2 of these RAM/ROM boards. I'm hoping I don't have to butcher the 2nd scope to resolve the vertical amplifier issue on my better 7854. I'll be going through a few manuals to see what scopes share the same vertical amp board so I can try to pick up a cheap board donor scope.
-Brian
|
Re: Timebase and CRT Issues on Tektronix Type 545A
Hi Alex,
So now you know that the problem is not in the B sweep generator.
A simple next step is to DMM measure the voltage just after the display switch, at the top of R330 (top in the schematic). Again with B sweep at very low speed, so that your DMM can follow the voltage. If OK, proceed with V353A pin 8. And so on, you can check all the voltage levels changes shown in the schematic. I wouldn't be surprised if you find that that one of the anode voltages , V364A or 384A, has insufficient swing.
BTW those 6DJ8 tubes are everywhere in your scope and plugins, so you might swap one with another (for instance against one from the A sweep generator). But try to judge that there is not another fault there that could (again?) destroy a tube.
It is normal that B386 lights up when you short the CRT deflection plates.
Don't you have a 10X probe for your USB scope? Even a simple 100X resistor voltage divider (say with 10 MOhm to 100 kOhm) would be of great help and protect your input (a heavy 10 MOhm is needed for safety, or a string of smaller resistor values).
Be careful measuring the plate voltages, these go very high. In general, be careful with those high voltages in tube amplifiers.
Albert
|
20+ years of various TTL work and I never learned about the 74247.
Thanks for bringing it up.
toggle quoted message
Show quoted text
On 27 Mar 2016 00:33:06 -0700, you wrote: Hello,
Yes, it may be the 7447, or more rarely a bad contact between the 7447 and the segments.
A suggestion, if like me you prefer well formed 6 and 9, you can replace the 7447 by a 74ls247.
I change it on all my tek plugin and the display is better.
You can see it on my website (sorry in French)
You can find 74ls247 on ebay
TM500
|
David Hess
Raymond Domp Frank