Velleman LABORATORY POWER SUPPLY (0-30 VDC + 5 VDC + 12 VDC) WITH ANALOGUE DISPLAY PS603
Specifications:
input voltage: 230 Vac ± 10 %
output voltage: 0-30 Vdc / 12 Vdc / 5 Vdc
corrente de saída: 3 A / 1 A / 1 A
limited current: 10 mA – 3.2 A / 1.2-1.6 A / 1.2-1.6 A
ripple and noise:
constant voltage: max. 2 mV
constant current: max. 5 mA
voltage indicator deviation: max. 10 mV
current indicator deviation: max. 5 mA
fuse: F1.5AL 250 (order code FU1.5N: FUSÍVEL 5 x 20 mm LENTO 1,5 A (10 unids/caixa) )
working time: 8 hours uninterrupted without overload or short circuit
dimensões (Lg x Al x P): 150 x 145 x 300 mm
peso : 4.5 kg
protection: current limitation and short circuit protection

The used power supply I got had a problem with current readout and I needed to find the problem.
The basically same power supply is known as Velleman PS603 when it has analog meters and as PS613 when it has digital meters. The same power supplies are also sold with other brand names like Altai, Electrovision, Auto-Tech and Manson. Those power supplies seem to be imported from China and come with just basic English/Chinese instructions. It’s a simple case of “Badge Engineering”, in accordance to the importer/distributor’s requirements.

Power supply circuit details

Manson, Velleman, etc, PS 613 bench power supply repair – Schematics needed discussion at
https://www.eevblog.com/forum/repair/manson-velleman-etc-ps-613-bench-power-supply-repair-schematics-needed/ says:

In the same family of these re-labelled bench power supplies:

Manson EP-601, analog panel meters, 0-30VDC 2.5A
Manson EP-603, analog panel meters, 0-30VDC 2.5A, Aux 5V 12V 0.5A
Velleman PS-603, analog panel meters, 0-30VDC 3A, Aux 5V 12V 1A

Manson EP-611, LCD panel meters, 0-30VDC 2.5A
Manson EP-613, LCD panel meters, 0-30VDC 2.5A, Aux 5V 12V 0.5A
Velleman PS-613, LCD panel meters, 0-30VDC 3A, Aux 5V 12V 1A
Circuit Test PSA-2530D, LCD panel meters, 0-30VDC 2.5A, Aux 5V 12V 0.5A
Jaytech MP-3082, LCD panel meters, 0-30VDC 2.5A, Aux 5V 12V 0.5A

Manson EP-3050 ?, LCD panel meters, 0-30VDC 5A, Aux 5V 12V 1A
Dick Smith Q1760, analog panel meters, 0-30VDC 5A, Aux 5V 12V 1A

The 5A and 2.5A are the same design, just beefier pass-transistors. I also have schematics for the one’s with a fan.

Mastech HY-3010D, HY3005 is a bit different circuit design, also missing protection diodes and blows up just as easily.

Circuit diagram
https://www.eevblog.com/forum/repair/manson-velleman-etc-ps-613-bench-power-supply-repair-schematics-needed/?action=dlattach;attach=479027;image

https://www.eevblog.com/forum/repair/velleman-ps603-power-supply/ discussion says:
Same schematic PS603 (analog meters) or PS613 (digital panel meters).
They are not very strong or well made and need a lot of repairs.

LABORATORY POWER SUPPLY (0-30 VDC + 5 VDC + 12 VDC) WITH ANALOGUE DISPLAY
https://www.velleman.eu/products/view?id=13880

Specifications

input voltage: 230 Vac ± 10 %
output voltage: 0-30 Vdc / 12 Vdc / 5 Vdc
anto: 3 A / 1 A / 1 A
limited current: 10 mA – 3.2 A / 1.2-1.6 A / 1.2-1.6 A
ripple and noise:
constant voltage: max. 2 mV
constant current: max. 5 mA
voltage indicator deviation: max. 10 mV
current indicator deviation: max. 5 mA
fuse: F1.5AL 250 (order code FU1.5N: FUSE 5 x 20mm SLOW 1.5A (10pcs/box) )
working time: 8 hours uninterrupted without overload or short circuit
dimensions (W x H x D): 150 x 145 x 300 mm
paino: 4.5 kg
protection: current limitation and short circuit protection

Links to more information:

https://www.eevblog.com/forum/beginners/manson-ep-613-dc-power-supply-troubleshooting

https://www.eevblog.com/forum/repair/velleman-ps603-power-supply/?action=dlattach;attach=1858798;image

Meter repair

The main problem with the power supply I had was that the analog meters seemed to be stuck so that they did not move well. I had to do some repair and cleaning. And after it I had to check after fixing that the meters worked correctly and accurately.

Here are some information on analogue meter repair that I found useful:

https://bbs.homeshopmachinist.net/forum/general/59343-ot-meter-repair discussion says:

9 times out of 10 a few good blasts of dry air will fix it fine.
Gently hold the needle and try to avoid blowing the spiral spring too hard.
I use one of those rubber squeeze bulbs and direct the air carefully.
Some people use small strips of scotch tape to remove particles from inside the works.
I was always to uncoordinated to do that.
If the meter has been dropped or bumped too hard or the needle has been slammed, the needle may be bent and rubbing.
Also, if it’s a plastic face it may have a static charge, use anti static fabric softener to clean.
If the Meter is really old the jewels may be broken or missing or if your lucky the pivot bearings are loose and need tightening.
There should be a very slight lateral movement ( like a couple thou at most ) at the pivot points.
Too Much play? Tighten them, but, Don’t, Do Not! Never Ever! over-tighten! I’ll tighten the screws about 20 degrees at a time.
As an end note, do not use oil.

Tuner cleaner would be my first choice, it cleans out any dried oil and gunk and leaves behind a very light, non conductive lubricant.
Cheers,

There is a little coil of wire on the “tail” of the needle, which is supposed to counterbalance the needle. If it does not, then when vertical, it will not be in balance, but when horizontal, it will be fine, the uncounterbalanced weight has no effect.

One major cause of what you mentioned is corrosion of the magnet faces. Whiskers of corrosion may get trapped in the works and cause random problems. Allowing the coil to move around, as when one bearing is loosened or removed, may crush the whiskers and free it up again. If the particles are not magnetic, they can fall free after being crushed.

Obviously any magnetic material will cause big problems.

It’s possible for sticky bearings to cause random needle stoppage, but, I think, less common than crud in the magnet/coil assembly..

When working on Old Radios, TV’s and such, I mostly need to use a 1000 “ohms per volt” Analog Meter.
Schematics contain Voltage data based on these type meters.
Today’s Digital meters often are several meg-ohms total load and will give a higher than normal reading because of the lighter load on the circuit under test.
This is especially critical when testing sensitive equipment.
In a pinch, a proper size series resister can be used with a DVM.

Links to more information on old meters repair:

https://www.rfcafe.com/references/qst/rejuvenating-old-meters-feb-1943-qst.htm

https://www.eevblog.com/forum/testgear/analog-multi-meter-needle-freaks-out-when-i-clean-(rub)-the-meter-(needle)-cover/

International Repair Day is an annual celebration for everyone who makes repair happen in their communities around the world. Be part of the global movement calling for The Right to Repair.

People are celebrating the power of repair to bring our communities together, reduce our impact on the planet, learn new skills and so much more. Repairing things isn’t always easy – especially with electricals and electronics!

International Repair Day was established in 2017 to promote the value and importance of repairing. International Repair Day is organised by the Open Repair Alliance, an international group of repair organisations collaborating to make electronic products more durable and easier to repair.

https://openrepair.org/international-repair-day/

https://openrepair.org/international-repair-day/2024-events/

https://communityrepairnetwork.org.uk/get-involved/

https://therestartproject.org/campaigns/international-repair-day/

https://www.positive.news/society/public-enthusiasm-for-fixing-revealed-international-repair-day/

Here are links to information I used in the repair problems.

Xbox One Wireless Controller Repair
https://www.ifixit.com/Device/Xbox_One_Wireless_Controller

The Xbox Wireless Controller, manufactured by Microsoft, is commonly used with the Xbox One and Xbox Series consoles, but the controller can also be used on a PC. This includes repair information for model numbers 1537, 1697, 1698 (Elite), 1708, and 1914.

Xbox One Wireless Controller (Model 1697) Repair
https://www.ifixit.com/Device/Xbox_One_Wireless_Controller_1697

Xbox One Wireless Controller 1697 Bumpers Replacement
https://www.ifixit.com/Guide/Xbox+One+Wireless+Controller+1697+Bumper

Repairing An Xbox One Controller
https://www.youtube.com/watch?v=LHNnPK2uleE

Repairing An Xbox One Controller
https://www.youtube.com/watch?v=LHNnPK2uleE

How to Fix Trigger & Bumper Buttons on Xbox Controller | LT RT RB LB Shoulder Sticking Stuck Repair
https://www.youtube.com/watch?v=-AdymLCSqxU

HOW TO FIX XBOX ONE CONTROLLER JOYSTICK
https://www.youtube.com/watch?v=ANTbgghBVS0

NEW XBox One controller tear down, fix, and repair video.
https://www.youtube.com/watch?v=Vx1xAhaYdKA

Any repair tips or recommendations for a good replacement (I want one with light and sound measurement built in).

RIFA is Swedish and stands for RadioIndustriernas FabriksAktiebolag, which translates into The Radio Industry’s Manufacturing Incorporated. In German vintage audio forums, these RIFA caps are known as “Knallfrosch”, which translates to firecracker. This is a common problem with vintage computers. Especially in the power supplies. Just get an old machine, turn it on, and boom! Magic smoke! The PME labeled caps were used extensively in older Tektronix switching power supplies. RIFA PME capacitors is pretty much the electronic version of Surströmming. Both come from Sweden, and both explode and stink.

Evox Rifa Metallized Paper X2 Capacitors PME271M
https://www.hificollective.co.uk/components/evox-rifa-pme271m.html
They are classified as X2 capacitors. X2 capacitors are used in positions where a failure of the capacitor would not expose anybody to danger of electric shock.

Failing RIFA safety capacitors
https://www.youtube.com/watch?v=GDTuHDsHHFA

RIFA AC Filter Capacitor Blowup
https://www.youtube.com/watch?v=njbwdbcfXjc
An attempt to capture the failure of a RIFA AC filter capacitor in a TRS-80 Model II Microcomputer.

Rifa Capacitor Fun
https://www.youtube.com/watch?v=8YhS-k1TRFA
In this video I demonstrate why I ALWAYS replace Rifa capacitors when I am repairing vintage machines.
Do not watch this video if you have a nervous disposition.

RIFA capacitor Blows up! while playing Revox B790
https://www.youtube.com/watch?v=YtGdWZ93-uQ
An old RIFA capacitor blows up while playing a record on Revox B790.

Why Do Rifa Capacitors Fail?
https://hackaday.com/2023/04/01/why-do-rifa-capacitors-fail/

Anyone who works with older electronic equipment will before long learn to spot Rifa capacitors, a distinctive yellow-translucent component often used in mains filters, that is notorious for failures. It’s commonly thought to be due to their absorbing water, but based upon [Jerry Walker]’s long experience, he’s not so sure about that. Thus he’s taken a large stock of the parts and subjected them to tests in order to get to the bottom of the Rifa question once and for all.

Rifa Capacitor Fun Follow Up
https://www.youtube.com/watch?v=TB5FL3vziko

EEVblog #1183 – RIFA Madness (Schaffner Repair)
https://www.youtube.com/watch?v=XAbrU17hLTM&t=548s
Repairing the Schaffner NSD200E Mains Interference Simulator.
And the dangers of bad mains filters capacitors, and RIFA brand in particular.

How ironic! They were advertised as a very safe capacitor type once.

Ohhhhhh this did NOT age well.
A bit like the Rifas themselves.

Now there is even joke:
RIFA = Random Interval Fire Autostarter

Ah Rifa madness. To think some reputable suppliers still have them.

How to fix a device with failed or soon failing RIFA filter capacitor between mains wires:
Replace it with a newer (not Rifa) X2 capacitor of the same capacitance and equal or higher voltage rating.

And it is not only the paper capacitors that fail when they get old…

EEVblog 1486 – What you DIDN’T KNOW About Film Capacitor FAILURES!
https://www.youtube.com/watch?v=ikp5BorIo_M
You might think you know how film capacitors fail and degrade in capacitance over time – self-healing due to surges, right? WRONG!

Metallized Film Capacitor Lifetime Evaluation and Failure Mode Analysis
https://cds.cern.ch/record/2038610/files/45-56-Gallay.pdf

It looks like to be the same as this VGA Signal Generator – 15 Selectable Signals that is advertised as
“Simple and compact color generator.for testing and adjusting VGA/SVGA/XGA display devices such as monitors, projectors, etc
15 selectable Modes covering common Resolutions, Frequecies, & Sync. Polarity. With LED Mode Display & Power switch”
The device support four most common VGA resolution modes: 640×480, 800×600, 1024×768 and HV8-1,HV8-2,HV8-4 and HV8-8

Here is the operation instructions and supported video modes list from the manual:

One day it did not work. The colors on the monitor were off and I could not see all colors. I found out that one RGB component (R) was missing. I did debugging and found out that where was bad soldering on the one PIC 16F84 microcontroller pin (the one on the corner). Re-soldering it made the unit to work well again.

Links for DIY PIC processor based VGA signal generator projects:

16F84A VGA Test
https://www.instructables.com/16F84A-VGA-Test/

16F84A VGA Test – How to Connect a Computer Monitor to PIC16F84A
https://www.youtube.com/watch?v=pcXeEb4dy60

VGA Tester using PIC Microcontroller
https://www.eeweb.com/vga-tester-using-pic-microcontroller/

VGA output with PIC Microcontroller
http://www.toughdev.com/content/2011/02/vga-output-with-pic-microcontroller/

16F84A VGA Output
http://embedded-egypt.blogspot.com/2010/07/16f84a-vga-output.html

PIC 16F84 Microcontroller VGA interface
http://tinyvga.com/pic-vga

The Acer Nitro 5 is a budget gaming laptop. This model was just around 4 years old. This computer was hit with two problems: the computer does not turn on and the screen hinge was broken.

Open the laptop by removing the bottom of the computer. It had many small screws that I had to remove.

For computer does not turn on problem I found the following links:

https://community.acer.com/en/discussion/567979/how-to-fix-acer-nitro-5-nitro-5-an515-51-black-screen-that-wont-start-up

https://www.ifixit.com/Answers/View/754153/Nitro+5+refuses+to+turn+off+on+after+charge.

FREE BROKEN Laptop – But Can I Fix It? Acer Nitro 5 No Power (Gifted From A Subscriber)
https://m.youtube.com/watch?v=C4S6QL4keOQ

ACER Nitro 5 gaming laptop repair – Not coming ON, not charging board repair
https://m.youtube.com/watch?v=uohBIm59MY0

https://onlinecloudsecurity.com/acer-nitro-5-will-not-turn-on/

https://www.geekbuffalo.com/computer/acer/how-to-fix-the-acer-nitro-5-laptop-that-wont-turn-on/

I did not manage the laptop to boot with any easy tips. A repair shop looked at it, but did not get it to boot as well. The problem was not in battery (did not start without battery). The end result was that that motherboard was broken (which means too expensive to be worth to fix).

Because computer could not be made to work, it was not worth to try this hinge repair tip (which I would have done if the computer would boot):

How to Fix BROKEN SCREEN HINGE on Acer Nitro 5 Easily!
https://m.youtube.com/watch?v=BYDJRoJMZ1s

I have had a HP ENCY 17 laptop for many years. It has worked well. But just some days ago it started to make strange noise and became slow. After rebooting it showed fan not working error.

So I decided to open my laptop in the plan to fix the fan to work again. It could potentially need just cleaning or I would need a new cooling fan. Fortunately I found this very helpful video

Good video how to open and clean fan

and also this How to replace fan useful repair video.

After watching those videos I wan convinced the that opening this laptop was a good idea. Fortunately this “old school” laptop PC was built so that it could be opened reasonably by opening screws (not everything glued and taped together). After removing tens of screws I finally got the PC open.

The fan had some packed dust and some small plastic particles in (the computer has taken some hits over years to could be caused by that).

This is the fan after cleaning. It worked well and I did not need to replace it.

The HP 54645D (also known as Keysight 54645D) mixed-signal oscilloscope was designed for embedded systems developers. This Mixed-signal oscilloscope focuses on 8-bit microcontroller applications was released to market in 1996. This product was discontinued in March 2001.

It was specifically designed to cost-effectively address the testing and troubleshooting needs of the many engineers designing with 8-bit microcontrollers, but was powerful enough also for many 16-bit embedded applications.

The Keysight 54645D 100-MHz 200-MSa/s Mixed Signal Oscilloscope seamlessly integrates logic channels into an oscilloscope to offer new measurement capability for designers of combined analog and digital systems. Analog and digital on one display, aligned in time, to help you isolate cause and effect in complex circuits.

The 54645D was selling for under $5,000 ($4,995 stock), which was cheap at the time when you consider what features it offers.

The HP 54645D is a two-channel, deep-memory oscilloscope integrated with a 16-channel logic analyzer. It features the ability to trigger on any or all of its 18 channels and to observe and measure the relationship of the analog and logical operations of a circuit under test on a single display screen.

Specifications:

Scope Channels: Ch. 1 and Ch. 2. 
Bandwidth (3dB): dc to 100 MHz @ >= 10 mv/div (> 75 Mhz @ < 10 mv/div), ac Coupled: 1.5 Hz to 100 MHz. 
Rise Time (calculated): ~ 3.5 ns @ > 10 mv/div (< 4.6 ns @ < 10 mv/div). Input Resistance: 1 Mohm. 
Input Capacitance: ~13 pF. 
Maximum Input: 400 V (dc + peak ac). Range: 1 mV/div to 5 V/div. 

Digital channels: 16 channels (0-15) in two pods of 8 channels each 
Maximum Input Voltage: ± 40 volts peak. 
Threshold Range: ± 6.0 volts in 50 mV increments. 
Threshold Accuracy: ± (100 mV + 3% of threshold setting). 
Sweep Speeds: 50 s/div to 5 ns/div main and delayed. 
Accuracy: ± 0.01%. Horizontal Resolution: 40 ps. Trigger Modes: Auto, Autolevel, and Normal. 
Holdoff: ~ 200 ns to ~ 25 seconds. 
Polarity: Rising or falling. 
Minimum Pulse Width Setting: 8 ns. 
Maximum Sampling Rate: 400 MSa/s on one pod, 200 MSa/s on two pods. Maximum Memory Depth: 2 MB samples per channel on one pod, 1 MB samples when both pods are used.

Display: 7-inch raster monochrome CRT. 

The two scope channels of the HP 54645D are each 100 MHz and 200 megasamples/s, and feature 1 Mbyte of memory. The logic-analysis channels run at 400 Msamples/s and 2 Mbytes of memory on eight channels, and 200 Msamples/s and 1 Mbyte of memory on 16 channels.The scope supports simple edge, pattern, and advanced triggering capabilities, including a glitch triggering feature.

Because the MSO is an two channel digital oscilloscope, you works for everyday use with its simple edge triggering. This has the familiar scope triggering mode and it is the one that will solve most of problems that you have with electronics circuits. In addition to analog channels, you can view the 16 digital states and use them as triggering source.
You can trigger on a rising or falling edge on any of the MSO’s 18 input channels. Pattern triggering is provided to allow you to set up a pattern of high, low and don’t-care levels across any or all of the MSO’s 18 channels.

The 54645 was the first of the digital oscilloscopes with MegaZoom so it has 4 megapoints memory both on analog AND digital combined. MegaZoom technology that is a multiprocessor/parallel-processing architecture that enables the HP 54645D to combine the deep memory capability associated with some high-end DSOs with the ease-of-use, high update rates, and responsiveness usually found only traditionally in analog scopes. Megazoom is , apart from the large memory, basically a huge resampling ASIC that resamples the ‘slot’ you define in the memory and creates a 540 pixel wide image to screen. I have to admit that MegaZoom works well.

While the HP 54645D is not the first instrument to combine oscilloscope and logic-analysis capabilities, its ease of use, versatility, and price combine to set a new standard.

Digital Oscilloscope Set Up and Tutorial using HP 54645D Digital Storage Oscilloscope video shows how to set up and use the HP 54645D digital oscilloscope.

HP 54645D Pushed to the MAX! video demonstrates how responsive and capable a vintage (1998) digital HP scope (HP 54645D) is. This video also demonstrates FFT function from the Measurement module (that I don't have).

There is a "easter egg" game in this oscilloscope. It can be started by pressing first "Print Utility" and then two buttons below screen together (buttons 2 and 3 from left to right).

You get this snake game:

Another hidden feature:

HP 54645D Manuals
https://www.manualslib.com/products/Hp-54645d-2960596.html

Keysight product page with manual downloads
https://www.keysight.com/us/en/product/54645D/100mhz-200msas-mixed-signal-oscilloscope.html

Sources:

Mixed-signal oscilloscope focuses on 8-bit microcontroller applications
Posted on January 1, 1997 by Electronic Products
https://www.electronicproducts.com/mixed-signal-oscilloscope-focuses-on-8-bit-microcontroller-applications/

Old logic analyzer and probe cables
https://www.epanorama.net/newepa/2022/07/05/old-logic-analyzer-and-probe-cables/

Keysight (Agilent) 54645D CALIBRATION and Keysight (Agilent) 54645D REPAIR
https://custom-cal.com/ModelInfo.aspx?kn=3465&m=Agilent_54645D&srv=Calibration

54645D 100-MHz 200-MSa/s Mixed Signal Oscilloscope
https://www.keysight.com/us/en/product/54645D/100mhz-200msas-mixed-signal-oscilloscope.html

Should I sell my 54645D for a new Rigol?
https://www.eevblog.com/forum/testgear/should-i-sell-my-54645d-for-a-new-rigol/

HP54645D print screen via RS232
https://www.eevblog.com/forum/testgear/hp54645d-print-screen-via-rs232/

Playing Tetris On An Oscilloscope
https://hackaday.com/2014/04/26/playing-tetris-on-an-oscilloscope/

The Tektronix 2235 is a 100 MHz dual-trace, dual-timebase portable scope.
Tektronix 2235 has two channels and delayed sweep.

This is still a pretty decent analogue oscilloscope (if you are looking for an analogue oscilloscope) with Large, Bright CRT screen. This oscilloscope has the U shaped handle that has detents which allow it to double as a stand.

Tektronix 2235 100 mhz Oscilloscope- When Only Analog will do….

The manufacturing of this scope model started around 1983 by Tektronix, Inc. In 1984 the price was $1,650 ($4,300 in 2021 dollars). It was also sold to the military under the model name AN/USM-488.

It was then advertised with features like: Tektronix 2235 ensures measurement quality and reliability while reducing instrument cost. Tek started with the innovative architecture of the 2200 Series: fewer boards, fewer mechanical parts, less cabling and electrical connectors. This approach, plus advanced circuit design and a focus on essential features, has led to a scope that is more accurate, more reliable, lighter and more serviceable-and simpler to use-than any other 100 MHz scope. Features like rugged design, light weight and easily learned front panel make the 2235 an ideal service scope.

The 2235 delivers 2% vertical and horizontal accuracy in normal operation. Accuracy of 3% or better is maintained across a wide range of environmental extremes.

This oscilloscope has 100 MHz bandwidth, which is a quite good bandwidth and also the vertical voltage goes down to 2m volt. With oscilloscopes like these, Tektronix specifies the bandwidth at the probe tip when the proper probe is used. The quoted bandwidth is given at -3dB (http://www.ens-lyon.fr/DSM/AGREG-Physique/oral/Notices/N036-003.pdf) to be (at least) 100 Mhz from 5mV to 5V/div and 90 Mhz at 2 mV/div… And it also deacreses by 10 Mhz when the ambient temperature rises above 35 degrees celsius. If you can accept some measurements errors, you can do some measurements event at higher frequencies. The 2235′s 100 MHz will cover enough above and beyond 108 MHz if you have probes that will go well above 100 MHz.

The input capacitance of this oscilloscope is around 20 pF.

You also get delayed sweep with the 2235. Delayed sweep is a technique that adds a precise amount of time between the trigger point and the beginning of the scope sweep. When the scope is being used in the sweep mode, the start of the horizontal sweep can be delayed. In some applications it can be useful, but you probably won’t end up using much.

The calibration adjustment are done with pots, that can change their position slightly due to mechanical vibrations for example. Service manual is still available on-line.

Manuals:

2235 Oscilloscope Operators Instruction Manual
https://www.tek.com/en/oscilloscope/2235-manual/2235

2235 Service Manual
This manual contains information to check performance, adjust, and service the 2235 oscilloscope.
https://www.tek.com/en/oscilloscope/manual/2235-service-manual

Tek Wiki 2235
https://w140.com/tekwiki/wiki/2235

Videos:
Tektronix 2235 – 100Mhz Dual Trace, Dual Time Base Oscilloscope
Affordable Portables Tektronix 2200 Series Oscilloscopes 1986
Tektronix AN/USM-488 2235 Oscilloscope repair and calibration 1 of 7
Tektronix AN/USM-488 2235 Oscilloscope repair and calibration 4 of 7

Links to sources and more material:
https://www.computerhistory.org/collections/catalog/102733015
https://www.eevblog.com/forum/testgear/tektronix-2235/
http://www.linear.com/docs/4138
http://circuitslab.case.edu/manuals/Probe_Fundamentals-_Tektronix.pdf
https://www.antiqueradios.com/forums/viewtopic.php?t=147362
https://www.testequipmentdepot.com/usedequipment/tektronix/oscilloscopes/tek2235&2236.htm
https://accusrc.com/product-Tektronix-2235-3929