Repairing a Tektronix 465 (power supply, z axis amplifier, vertical pre amplifier issues)

Here are some pics of my new Tektronix 465 and how I had repaired it. It was bought on ebay and did not work. There have been several issues to solve, but finally I got a working 465. I found problems in these units:

  • power supply
  • z axis amplifier
  • vertical pre amplifier (channel 2)
  • Broken kobs
  • Volts/DIV Lamps/Bulbs are broken/do not work

About Tektronix 465

The 465 is a legendary product from Tektronix. Tektronix is said to be the company who invented the oscilloscope (in 1946, with model 511). As you can see in the image, they had a oscilloscope beam tube and a scope sinus signal display as part of their trademark.

As far as I know, the 465 came to the market in the early 1970-ties. It was a general-purpose analogue scope with a (for that time) large bandwidth of 100Mhz and two time bases for a price at that time of ~3500$. Tektronix sold the 465 very well and it is also said to be the most frequent scope in the world.

There are different models starting with 46?:

  • 465: The original one, 100Mhz bandwidth. Implemented mostly using transistors, only a few ICs are used in the design.
  • 465B: A version that came up some years later, specs were the same as for the 465, but the technology used inside the scope was newer. It uses e.g. ICs in the pre amps.
  • 465M: version with a digital multimeter (named DM44) mounted on top.
  • 468: A scope with digital storage, based on the 465B design. The digital scope part is based heavily on IC-technology. It has only 25Ms/s.
  • (also 475 with 200Mhz bandwidth, 475A with 250Mhz bandwidth, 485 with 350Mhz bandwidth, …)

Because the 465 uses only very few integrated circuits, it can be repaired relatively easy. It is said that the 465 was the last of the tektronix devices based (nearly) completely on discrete components. There is a big load of documentation in the internet including service manual and complete schematics. In many cases it is possible to replace tektronix parts (for example tektronix transistors) with todays standard transistors if the original ones break.

Devices that use many ICs, often sold only by tektronix itself, can be repaired only if you know from where to get replacements for the ICs if they are broken. Today’s scopes are of course all built using heavily ICs.

State how I received it

These are some pictures of the state of the device as I received it from ebay seller.
My Tek 465 was manufactured in Netherlands. PCBs are stamped with year 1971, but I believe its newer (serial number is 710090).

Hint: you can click on all images below to enlarge them!

Frontplate Check:
Volts/Div Knob at Channel 2 is broken.
Someone replaced it with an own solution. The red „VAR“-part
is still there and the scale is also there.
A Trigger Level Knob is also broken, but still there and usable.
If there were lights at Volts/Div Knobs, they do not work anymore.
Device came dirty.

Switched it on and hooked on some sinus signal at Channel 1.
In the back, my Tek 2432 shows how the signal really looks like.
The Tek 465 does display something, but very different from actual waveform.

That’s left from CH2 Volts/Div Knob.


At first some some random pictures from the inside of the Tek 465.

Delay Line can be seen below the display tube.

Channel 1 Input Attentuators

Interface Board (Bottom of device; HV cover removed.The big black cap at the lower right is not original and located there for testing)

With the scope came this probe.
It’s a P6006 (10x, 35Mhz) Probe, equipped with a banana tip.
More Info in this Probe can be found here.

Trying to repair it

At first I fixed one small problem at input of channel 1. A resistor-pin was detached from its target. This did not improve the overall result.

After opening the case and pressing around at PCBs and components, I got sometimes an improved display (see below). But it was not stable in any way. I noticed that hitting the big cap (5500µF) at the +15V voltage leads to big changes in display.

So I decided to change this cap. Infos about the 465 show that these caps are often failing after 30 oder 40 years…

I got this after pressing around at the PCBs and hitting on the big
poser supply cups…

Channel 1 Input. One Resistor pin is detached from input line. I solder it
to the input line.

After Cap replacement, I switched on the device. Immediately, the fuse F1419 broke. I replaced the fuse with an Ampere meter and measured a large current (10,5 Ampere). Despite switching the device on for only some seconds, the main fuse broke. Something smelled bad because it was getting hot, but I could not find that thing.

My conclusion from that was: When replacing the cap, some solder fell into the Tek 465 and created a shortcut on the interface board. I did not notice that and when switching the device on, the fuses broke (this conclusion was wrong, because another cap had a shortcut, I found out this later…see below).

I removed the interface board and cleaned the backside because I thought there is solder that produces shortcuts. I re-inserted the interface PCB afterwards.

Without F1419 the device could be switched on. I checked the power supply. I found several issues here:

  • Q1556 (5V regulating transistor) was broken
  • U1554 (Op-Amp for 55V regulation) was broken.

I replaced both parts.

Q1556 (a MSPS3414) was broken (no connectivity between the three pins). I replaced it with a BD677.

U1554 was also broken. I replaced it with a LF353 (it will be replaced with a NE5532 as soon as I have one)

After this, I could insert F1419 without shortcut and got back some beam traces like at the start of my repair try.

But suddenly there was the shortcut again. Now I saw whats happening, because the HV-shield was removed. A Cap (47µF, C1419) went very hot and even some smoke came out of it. I took it out and measured a resistance of about 50 Ohms. No capacity. I replaced the cap and for the first time, the power voltages look good, except the +15V.

I also noticed that the fan board was using to much load and removed it from 15V supply. 15V now got better, but was not totally stable and still ~1V below it’s should-be value.

Bad Cap C1419 (left) and its replacement (right).
The bad cap still looks nice!

The beam traces were still not good.

A sinus signal, very blurred and distorted at the right side

A rectangle signal, looking very bad.

I checked the vertical preamps for both channels. At channel 1, the signals are close to these mentioned in the service manual. At channel 2, a large ripple voltage (100Hz) is added to the test signal.

This image shows the test signal (~975Hz). To the test signal, another low frequency signal (ripple voltage) is added, resulting in the diagonal baseline.

Here the ripple signal can be seen, it has 100Hz. The ripple amplitude is much larger then the test signal.

The ripple comes from +15V supply. I checked the other power supplys, they have a very small ripple of some mV. The +15V supply has 990mV ripple, which is more than 6% of 15V.I wonder why the ripple is a triangle waveform (I expected sinus)

The signal displayed at Tek465 seems to be related to the ripple, compare the next two images:

This is what 465 displays on channel 2. Input signal is a rectangle signal.The rectangle signal result in two dashed parallel lines. Without rectangle signal, there is only one line and no dashes.The ripple is added to the rectangle signal. Because the ripple is so large,
the resulting signal crosses the whole screen.

This is the signal measured in the path of channel 2. The big ripple signal can be seen (~170mV). On top of it the test signal (very small, maybe 5mV) is added. (The smaller ripple curves in the middle seem not to carry the test signal)

The following pictures show that the signal is very blurry.

This is the test signal. Sinus, 1000Hz and 500mV amplitude.

Tek465: channel 1: signal blurred, but amplitude and frequency and look ok.

Tek465: channel 2: signal blurred, amplitude/frequency ok. Signal display is very unstable, see next image…

Tek465: channel 2: signal display jumps frequently to something like this

Tek 465: displaying both channels with CHOP mode. Blurred. Because the intensity knob does not work, I can not make it brighter than this.

After testing around and by Help of people from the Tek Group at Yahoo Groups, I understood that something is still wrong with the +15V power supply.

I checked the driver transistor (Q1544) and the foldover detection transistor (Q1548) and found both defect. These are 2N2222, I replaced them with BC547B which I had in my component boxes and for the first time I got really 15V (14,998). And the interesting thing, the ripple voltage completely disappeared.

Replacement of Q1544/Q1548

Meanwhile I had also replaced C1220 (a large cap which went warm, it still worked but to be sure I replaced it).

I could also replace the „Interim“-Op-Amp LF353 (which replaced a MC1548) with a NE5532. The other MC1548 (which is ok) was also replaced by the technically improved NE5532.

I also checked the display illuminance section and found both lamps defective and also the driving transistor MSPS3414. I replaced lamps and transistor (BD677 as a replacement). Now illuminance is ok again. (to be honest, I tried first to replace the lamps with 3 LEDs and a 470 ohms resistor. But the result was not bright enough and I replaced that again with real lamps).

Display illuminace lamps are hidden in this white box.

This was the first time I tried to improve the look of the signals which looked very blurred. I was able to make signals look much better. Both channels seem to be display the waveforms fully correct now.

Fixing the Z axis amplifier

At this state the following issues were left:

  1. Intensity knob has no effect
  2. Beam return is not hidden (I can see the beam returning)
  3. Volts/Div Knob at Channel 2 is broken.
  4. „A Trigger Level“ Knob is broken
  5. Volts/DIV Lamps/Bulbs are broken/do not work

1. and 2. were related to the Z Axis section of the device, so they seem to be related.

The beam return signal is not suppressed and can be seen on the screen. See the two following pictures.

Displaying rectangle waveforms, looking good on both channels.

The visible beam return can be seen on the following image:

Sinus waveforms look good on both channels. Here the visible beam return  can be seen. Its the dashed line starting at the right end of the screen and going to the left start of the screen (in fact, left start is outside of the visible area of the screen). Something is wrong with beam return.

After searching for the problem for some days I identified a shortcut between the collector and the emitter of a transistor in the z axis amplifier (at Q1472) as the source of the problem.

PCB, z axis amplifier section, Q1472 is removed, the pin holes can be seen. On this side of the PCB, there is no shortcut. It must be on the backside…

To remove the shortcut, the interface board has to be removed again.

Just to probe my suspection, I isolated the shortcut by removing all components from the PCB that were connected with Emitter of the transistor and wired everything together with some wires. For the first time, I could vary intensity and the beam return signals were not visible anymore. Z axis amp worked again!

Sticking all components desoldered from the PCB together in the air using some wires for a test

Intensity knob works again and the beam return is suppressed on the display as it should be! My 465 works!

After this, I tried to calibrate the scope. Calibration is described extensively in the service manual.

During calibration, I noticed that I could not calibrate the channel 2 amplitude. For 300mV in the 100mV-Range, I only get 2 graticules amplitude on the display, correct would have been 3 graticules. So there was another error, obviously in the channel 2 vertical pre amplifier.

I started exchanging transistors between both channels with no result. All were good. The problem seems to be in a passive component around the second amplifier stage.

Transistors, even pairs of them, can be exchanged easily on the old teks, because they are not soldered but stick on the PCBs

Close to the solution: The interesting thing is the 150 ohms resistor in the middle of the picture. It looks optically well. On its left pin I have a signal that I do not have on the same resistor pin at the other channel. Measurement at this resistor pins reveals a value of ~12KOhms. There is something wrong with that resistor. I decided to desolder it for further checks.

When touching the resistor during desoldering, I found that it was broken in two parts that stayed close together, looking as if its still ok, but without electric function anymore!

After repair, nice looking signals on both channels. Unit was also cleaned 🙂

And these are all parts I replaced: The big cap from the power supply, another cap that went warm for no reason (black one), the op-amp from the power supply, the cap C1419 with an internal shortcut (blue one), two small transistors and a bigger one from power supply, and a bigger transistor from the screen illumination section, from there also two light bulbs. At the bottom the broken resistor from the vertical pre amp.

Replacement of Volt/DIV – lamps/bulbs

The Tek 465 autodetects 1x and 10x probes (if they provide a readout for that). For those different probes, two light bulbs behind the transparent Volts/DIV-Knob shows the valid settings on both channels. At my scope, all four lamps were broken.

To replace the lamps, the complete vertical pre amp has to be detached from the scope. The removal is well described in the service manual, but it lasts some time.
I replaced the lamps with LEDs, because LEDs last much longer than ordinary bulbs.

Hint: I was informed by one of the readers of this document that simply replacing the bulbs with LEDs did not work in all cases. My Tek 465 is a newer one that can handle without changes the different (i.e. reduced) load from LEDs. Older Tek 465 devices (below S/N B250000) will not work as expected. It is possible to modify the scheme from the old  version to the new version by adding one resistor (R392/47K) and by removing another one (that connects base of Q392 and Collector of Q396). I haven’t tested this.

The detached vertical preamp. On the left, the two light bulb cabins made of white plastics can be seen

Each LED gets a 220 ohms resistor, so I have a LED current of about 15mA.

After removing the old bulbs I soldered LED+resistor together, adjusted the pins as good as possible and inserted the new lights into the white cabins. There is very few space to solder. The polarity of the LEDs has to be taken into account. + is always at the outer left and right end of the cabin, the two pins that are already soldered together are the – pin for the LEDs.

After putting everything together, I noted that the 465 always thinks that it has a 10x probe in channel 2. A quick test shows that the driver transistor Q392 was defect. I replaced it with a BC550B and everything is fine now.

These are the lights after putting everything together again. (Note that the channel 2 knob is not yet replaced with a new one.)
I like the green lights!

After all, I have now a nice second scope on my work bench!

I was also able to buy a completely broken 465 in ebay for less than 20 Euro and could combine the best knobs and switches from both devices, so I have no broken front knobs anymore. The completely broken 465 came in parts and as far as I could see, it was complete except the CRT tube. So I keep the parts, maybe I can get some cheap CRT someday. The 465 CRT with Tek Part No. 154-0676-10 comes from Tektroniks itself. I read from internet sources that also the tek CRTs 154-0731-00 (for 465B) and 154-0861-00 (e.g. for Tek 2235) can be used as an replacement (no guarantee for this).


Yahoo Tek Group

Tektronix Forum at Tektronix
Tektronix Parts Shop – Site with Docs for many old measure devices – (german) hints for repairing old tektronix devices (hints are for 7000 mainframe series, but usable anywhere)
Barrytech – Site with many infos and photos from Tektronix devices
Tek Gallery ( – (german) Nice gallery of many tektronix devices
Reprise Tek Site – Many infos on Tek devices by two tek employees
Helmut Singer Elektronik – (besides other trademarks) used tek devices in germany

Der Logik-Analysator Tektronix 1241

Geräte dieser Art waren in Forschung und Entwicklung der 80ger Jahre, besonders Entwurf von Logikschaltungen, sehr verbreitet.

Der Tek 1241 bietet bis zu 72 Kanäle, 2 Zeitbasen, einen farbigen Touchscreen und eine Bandbreite von 100 Mhz synchron und 50 Mhz asynchron. Er hat zusätzliche Slots für RAM- und ROM-Bausteine sowie für ein GPIB oder RS232-Interface. Er kann eine Tiefe zwischen 257 Bit (Aquisition mit Glitches mit einer Karte) und 4×512+1=2049 Bit analysieren (Acqisition ohne Glitches mit 4 Karten)

Mein Gerät hat ein 64KByte RAM-Baustein 12RS02, 2×9+2×18=54 Kanäle und zunächst leider kein GPIB-Interface. Dies habe ich später nachgekauft, leider war es zunächst defekt. Hier die Beschreibung der Reparatur des GPIB COMMPACKS 1200C02.

Beim Gerät sind 6 Pods (Probes) vom Typ 6460 dabei. Dies sind Probes mit „Variable Thresholds“, d.h. die zu verwendenden Werte für HI und LO können bei diesen Probes vom 1241 aus bequem eingestellt werden, Wertebereich -6.35..+6.35 V.

Handbücher zum Gerät sind im Internet zu finden.

Unterschiede 1240 und 1241: 1241 bietet ein farbiges Display. Die Geräte sind ansonsten wohl praktisch gleich, was ich daraus ableite, dass beide Typen dieselbe Firmware nutzen.

Glitches: Glitches sind kurzzeitige Signalunstabilitäten. Ein Signal, dass „eigentlich“ logisch 1 ist, kann -wegen Signallaufzeiten in beteiligten Gattern o.ä.- für sehr kurze Zeit auf logisch 0 gehen. Dieses Verhalten ist sehr unangenehm, weil es in anderen Logikbausteinen, die dieses Signal aus Input besitzen, zu Zustandsänderungen kommen kann, die nicht gewünscht sind. Wenn das Störsignal deutlich kürzer ist als der Takt des Logik Analysators und so zwischen zwei Sample-Zeitpunkten liegt, sieht der Logik Analysator diese Zustandsänderung nicht und zeigt sie auch nicht an.

Um diese besondere Situation mit einem Logik Analysator dennoch zu unterstützen, besitzt der 1241 eine „Glitch Detection“ Logik. Diese ist zwischen den Zeitpunkten aktiv, zu denen ein Sampling stattfindet. Die Logik prüft, ob eine Signaländerung zwischen den beiden Zeitpunkten stattgefunden hat (ohne das dies zu einem echten Signalübergang geführt hat). Wenn dies der Fall ist, wird der Übergang als Glitch im Diagramm dargestellt.

Der 1241 kann Glitches bis hinunter zu einer Länge von 6ns erkennen.

Demultiplexing: Auf einem Bus werden typischerweise zu verschiedenen Zeitpunkten verschiedene Arten von Daten transportiert: z.B. Daten und Adressen (Multiplexing). Der 1241 ist in der Lage, bei entsprechender Konfiguration diese unterschiedlichen Datentypen wieder aufzutrennen und z.B. in verschiedenen Gruppen in zeitlich korrekter Reihenfolge darzustellen. Diesen Vorgang nennt man Demultiplexen und er erfordert die Nutzung zweier Zeitbasen.


Bedienungselemente vorn

Dialog Operation Level: Es wird der aktuelle Level sowie die Slotbelegung angezeigt. In meinem Gerät sind zwei 9-Kanal und zwei 18-Kanal-Einschübe in den Slots. Das ist eine ziemlich gute Ausstatung.

Dialog Memory Configuration. Hier wird pro Probe die zu nutzende Zeitbasis, der Trigger/Signal-Theshold etc. eingestellt.

Dialog Trigger Specification. Hier wird auf das einmalige Auftreten des Wertes ‚0xff‘ an der Probe 0 (GRPA) gewartet.

Ausgabe der State Table nach Start der Akquisition und Eintreten des Triggers. Die Rote Linie(=CURSOR1)  zeigt den Triggerzeitpunkt an. Die roten Rauten zeigen Glitches im Signal an.

Ausgabe der State Table. Es wurde zum Zeitpunkt t=3,06 Mikrosekunden nach Triggerereignis gescrollt. Zu dem Zeitpunkt lag das Datenbyte ‚d7‘ an.

Ausgabe des Timing Diagramms zum Zeitpunkt t=3,06 Mikrosekunden nach Triggerereignis. Es werden 12 Datenleitungen dargestellt.

Ausgabe des Timing Diagramms zum Zeitpunkt t=3,48 Mikrosekunden nach Triggerereignis. Zu dem Zeitpunkt lag das Byte ‚b2‘ an.

Die 4 Slots des Geräts. Ganz oben der Ausgang des Testgenerators, unten das eingesteckte RAM Pack. Mittig die beiden 9-Kanal und die beiden 18-Kanal-Karten.


Ansicht von hinten. Ganz rechts das eingesteckte GPIB Modul


Trigger Aus- und Eingang.


Im folgenden einige Innenansichten des Geräts.

Auch ohne Gehäuse gibt sich der 1241 sehr geschlossen 🙂





Im Inneren lässt sich ein an Scharnieren befestigter kompletter Block -nach Lösen einiger Schrauben- herausklappen. In diesem Block stecken alle Einsteckkarten des Geräts.


Blick auf die Karteneinschübe.

Im obigen Bild kann man von oben nach unten sehen:

  • Control Processor: Haupt-Prozessor Karte mit 8088
  • I/O – processor: IO-Karte mit Z80
  • Display: CRT-Karte
  • 2x 9 Kanal Aquisition Karte
  • 2x 18 Kanal Aquisition Karte
  • Trigger Karte

Eine grobe Durchsicht der Produktionsdaten der Chips auf den Platinen zeigt, dass die neuesten Chips aus der 31. Woche von 1988 sind.





Prozessor Karte

Prozessor Karte


EPROMs auf Prozessor Karte


Die Batterie fürs Non Volatile RAM „Catalyst Research. Solche langlebigen Batterien haben eine garantierte Haltbarkeit typischerweise 30 Jahren. Mein Gerät ist von 1988, es würde also bis 2018 halten…
Ein Ersatztyp für die „Catalyst Research B-600“ (Lithium?, 2,8V?, 650mAh?) ist noch zu bestimmen


Der 8088


Aufnahmeplatz für RAM Pack


Unterseite Prozessor Karte


Die I/O Karte


Der Z80


Schönes Handlöt-Detail


EPROMs auf der I/O Karte


Rückseite I/O Karte


Die Display Karte


EPROMs auf der Display Karte


Rückseite Display Karte


Die 18 Kanal Karte






Rückseite 18 Kanal Karte


Die 9 Kanal Karte


Tektronix Custom Chips


Rückseite 9 Kanal Karte

Die Trigger Karte




Rückseite Trigger Karte

Pod 6460

Im folgenden einige Bilder einer geöffneten Pod 6460. Diese Probe hat 9 Dateneingänge sowie einen Clock/Qualifier-Eingang für synchronen Betrieb. Zur Pod gehören „Lead Sets“ unterschiedlicher Ausführung, um die Pod an das Gerät unter Test anzuschließen. Die Lead Sets haben z.B. Mini-Krokodilklemmen. Es gibt auch spezielle Diagnostic Lead-Sets zum Anschluß an den eingebauten Test Pattern Generator des Tek1241.

Die Pod 6460 erlaubt die Einstellung des Thresholds für die Differenzierung von HIGH und LOW vom Tek 1241 aus.

geschlossene Pod


Pod von oben


Das Lead Set (rechts) und die Verbindung zur Pod


Geöffnete Pod von unten. Rechts ein größerer Custom Chip von Tektronix.


Bei dieser Platine (auf Keramik aufgebaut?) handelt es sich vermutlich um einen komplexeren Attentuator für 9+1 Kanäle, um die variablen Thresholds einzustellen.


Stecker  Richtung Tek1241, 2×17 polig

64KByte RAM Pack 12RS02




Auch hier besorgt die „Catalyst Research B-600“ die Langzeit-Spannungsversorgung der RAMs.