Replacing TRS 80 Model 100 rechargable NiCad CMOS battery.

I have a TRS 80 Model 100 and while doing a routine maintenance. I noticed the internal NiCad is showing sign of crystal forming. Before allowing it to leak and destroying the PCB, I ordered a 3.6V 60mA NiCad replacement from eBay to replace it.

I was planning to remove PCB to do it properly, however after the cover was removed. It seem like it can be done without removing the PCB.

Using the 40W solder iron, I heated each leg of the NiCad battery from the top side and gently removing each leg. Then I used the solder wick to clean up the solder points and install the new battery in it place. Afterward, re-solder each leg with sufficient heat to ensure  proper bonding.

Once everything is put back together, hook it up to external power adapter and let it charge. Now unless, one of these electrolytic capacitors start failing. It should extend the life of this laptop another 5+ years.

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Restoring HP 403B AC Voltmeter (10Hz – 2MHz)

The following instructions, document the process that I toke to restore the  HP 403B AC Voltmeter to working order.

Day 1

The unit was a bit dirty when USPS delivered it to my front door. The rechargeable battery pack is showing sign of corrosion.

First, I checked the meter movement and making sure that it is in good shape.

The moment is smooth and doesn’t appear to have any issue. With a 1.5V battery and a variable resistor, I checked the full-scale reading and a few other reading just to confirm the meter linearity.

A quick check of the voltage across the capacitor C21 and I am getting a steady 42.28V DC.

Next, I checked the battery +13, -6 and -13 supply voltage. I am getting +10, -6.5 and -13, this is because the battery is so old and some of the cell are dead and not evenly charged.

Even though the supply voltage are way off! The good sign is that the unit is fully working.

The battery is showing sign of corrosion and need to be replaced. So, it’s on my next to do list.

After a quick search, I found suitable replacement battery from eBay. The seller is trying to get rid of his inventory and selling a 25 packs of 3.6V 700mAh for cordless phone for only $0.99. The only catch is the $20.00 shipping.

The meter originally came with 4 x 6.0V 225mAh Nickel-Cadmium Battery but I am going to replace it with 8 x 3.6V 700mAh battery packs made for cordless phone.

The combined voltage will be slightly higher when it is fully charged, however, it doesn’t seem to pose any problem after everything is re-calibrated.

After tying them together and solder their leads in series connection to make 2 x 14.4V batteries pack.

 

I reconnect and the battery to the original +13, -6 and -13 leads and put everything back together.

NOTE:  Don’t solder the -13 lead just yet, as you will insert the amp-meter in series with it to adjust the charge rate later on.

I made some minor change to the orientation of these batteries after soldering them in place, so that the PCB will fit on top.

With the Amp meter connected in series with -13 power line, I adjust the pot to 6.5mA as suggested by  the manufacturer. You may set it to 11mA, if you plan to use it on battery regularly.

I let it fully re-charge over night before I return to work on it again.

Day 2

As I am going over the calibration procedures.

I notice that when meter is on, it never quite return to zero. It is alway 2 ticks higher.  Which kinda annoy me.

TODO: Investigate to find out which aging components causing this.

But for now, I just re-zero it with the zero adjustment screw. This will affect it accuracy a little bit. However, when checking the voltage indication on each range the reading track very closely to my HP 334A reading. So, for now it is not an issue for me at the moment.

The strange thing is that, on these HP AC Voltmeter. There is only mechanical zero adjustment. Unlike most VTVM that I had restored. Where you have to adjust  mechanical zero, AC and DC zero.

Day 3

While calibrating, I notice that on 0.01 and 0.03 range. The meter doesn’t work at all and it’s alway peaking.

It seem the meter is fully deflected when those range are selected.

At first, I though some resistors in the voltage divider network are bad. But after checking these resistors, switches and signal path. Everything checked out ok.

So, to diagnose this further. I connected the oscilloscope to take a peek at the signal at each stages.

After tracing the signal path on the diagram, the original input signal is amplified and then going into the resistor divisor network.

When I connecting the probe and observe the output at R20 and R22, There is 11mV p-p (.048us or 21MHz) voltage showing  on the scope.

In the 0.01 and 0.03 range, the original signal coming out of the voltage divider  is so small compare that with the 11mV p-p noise.

The noise is swamping the original signal and causing significant meter reading error.

NOTE: According to the manufacturer manual, this may be caused by a noisy transistor and need replacing.

But first, I wanted to try to fix it by adding a filtering capacitors.

After adding a 0.1uF 50V to +13V and -13V to ground, this seem to eliminate the noise.

To install the capacitors, I find some open space on the PC board and solder them in place.

This help to remove the noise and making 0.01 and 0.03 range working again.

As seen below the signal is much cleaner now.

Day 4

Spend a few hours calibrating the meter the best I can. Due to lack of a signal generator that can put out 30V 300kHz sine wave, I have to put off those calibration steps.

At the moment, the meter is track accurately from 1mV to 1V from 10Hz – 2MHz.

TODO:

• Recap
• Finish up calibration at 300kHz

 

Link to Service Manual:

Click to access HP-403B-Manual-SNprefix-403.pdf

Display a pop message at the end of a cron job.

Traditionally, when a cron job is finished. You will get a nice email indicating of its status.

Lately, I am quite annoyed by the amount spams that I am getting.

On my Linux laptop, I had it configured with a few cron jobs running in the background monitoring other activities.

Lately, it just flooding my in-box with messages and becoming unmanageable and hard to keep up.

Since, I am only interested to know if something interesting had occurred. There must be a better way than flooding my in-box with emails.

After, some research I found that the notify-send is included with every Linux-Mint installation. It’s quite simple to use and quite customizable and fit the bill perfectly.

Below is a sample on how to use it:

          notify-send –icon=/usr/share/icons/Mint-X/apps/48/gnome-gnibbles.png –expire-time 30000 ‘Oppa’ ‘You do have a life after work! So, go home!’

Free Online Virus Scanner

If you’re a vintage computer collector or someone enjoy using old computer like me. Once in a while you might, in inadvertently downloaded softwares from a questionable source which may contain virus/worm.

Overtime, I have taken many precautions to avoid such problem.  But, the idea of having to buy Virus scanner software and pay yearly subscription fee to me is ridiculous.

A better solution I found is to use a free on-line virus scanning services which will use multiple virus scanners to look for potential virus or worm.

Once such service, I found is https://www.virustotal.com, you simply upload the file in question and after while you will get the scan status report. After which you can rest assure the file virus free.

Installing Wings3D on Linuxmint 15

Recently I just upgraded my laptop with Linuxmint Mate 15 and found out the hard way that Wings3D is now broken and won’t install through the package manager due erlang-wx package is now no longer part of Ubuntu main due to the size foot print of wxWidgets library.

Anyway, here are the steps if you wanted to have the packe installed on your system.

1. Go to http://www.wings3d.com and follow the link to download wings-1.4.1-linux.bzip2.run.gz for Linux.
2. Unzip and run the installer

gunzip wings-1.4.1-linux.bzip2.run.gz

chmod +x wings-1.4.1-linux.bzip2.run

./wings-1.4.1-linux.bzip2.run

3. The installer will install wings3d under your home directory. Move the package to /opt

sudo mv ~/wings-1.4.1 /opt

4. Edit the bash script /opt/wings-1.4.1/wings so that ROOTDIR path is now /opt instead of your home directory and save the file.

#!/bin/sh
ROOTDIR=/opt/wings-1.4.1
…

5. Integrate it with desktop menu by right click on the menu and select Edit Menu.

• In Main Menu dialog, select Graphics under Application. Click New Item to create a launcher.
• Click on the icon and select /opt/wings-1.4.1/lib/wings-1.4.1/ebin/wings_icon_big.bmp
• Enter Wings3D in name text box.
• Enter /opt/wings-1.4.1/wings in Command text box.
• Enter “Wings3D Modeling Program” in Comment Text box.
• Click OK to save the launcher.

If you find this information helpful and would like to see more. Please show your support.

Scheduling Linux laptop to suspend and re-animate at scheduled time.

I recently created an automate script which search the internet for certain items and email me the search results. It’s currently running on HP Probook and I don’t want to leave the laptop running indefinitely.

So, I created a cron job to run this script to automatically suspend the laptop when there are no interactive user using the system. The script use rtcwake command to suspend the system in memory and it seemed to work pretty nicely.

To use this script, login as root and saving the following to a file /root/scripts/hybernate

#!/bin/bash
SLEEP_DURATION=1800
if [ $# -gt 0 ]; then
SLEEP_DURATION=$1
fi

# Put the laptop to sleep, if no interactive login and wake up later
if [ `who | wc -l` -eq 0 ]; then
/usr/sbin/rtcwake -m mem -s $SLEEP_DURATION
fi

Change the script permissions:

chmod 755 /root/scripts/hybernate

Then add the following line to root crontabs:

# m h dom mon dow command
* * * * * /root/scripts/hybernate 1800 2>/dev/null

Making a simple crystal tester

Remember from my previous post in Restoring Heathkit IT-17 tube tester? Where I mentioned that I got a box of tubes for $20 buck!

Well, under this pile of tubes there are bunches these little crystal modules that was made for WWII radios communication equipment.

I wanted to get rid of them on ebay but I need some way of assuring that they are working and the frequency is still as accurate as marked before I list them.

After some research on Internet, I found couple of plans which can be build quite easily. I wanted to make some modification to the circuit to use 2N3904 since I have bunches of them on hand. After fiddling with it for a while in LTSpice, I got a working circuit.

I then use KiCAD to draw the circuit and create a PCB layout from it and here is the final circuit and PCB:

Making the PCB

This time, I wanted to try the toner transfer method to create a polished and professionally looking PCB. However, my stupid Samsung laser printer keep on jamming and it is low in toner. The final laser printed PCB artwork has many flaws and some traces are spotty.

After transferring the toner to the copper clad, I have to manually use the permanent marker to cleanup these traces. After etching the PCB and installing the components, this is what I got.

Here the circuit is being used for the first time to test an unknown crystal, the green LED is lid to indicating that the crystal is working perfectly.

One down, plenty more to go. 🙂

Restoring Heahkit IT-17 Tube Tester

I acquired quite a bit of old test equipments lately and some of them are based on old vacuum tubes. Most of the time during the restoration process, I am able to get them working without the need of the tube tester. So, a tube tester is on my wish list but it’s not a high priority.

Out of a blue, I stumbled up on a Craigslist listing of 10+ test equipments at really good deal. The piece that I am really interested in buying was the Heathkit IT-17, the rest are nice too but I have no use for them at the moment.

The seller listed it pretty early in the morning, so the chance of it still available when I saw the ad was pretty slim. So, I decided contacted him late in the night anyway.

Early next morning, I got a response back and they are still available. I was so elated when I heard the news. I immediately arranged the time to drop by and drove 50+ miles to Oxnard to pick them up. While I was there he also offered to sell me a box of tubes at really good price.

The Heathkit IT-17

The unit was really an ugly duckling and disgustingly dirty when I pull it out of the box. The back cover is dirty and the paint are peeling. The good thing is that the front panel is still in pretty good shape.

Restoring

With the case opened, I quickly examined all the soldering join and looking for burned components. Everything looks good. I went ahead and replaced all bad carbon resistors that are out of tolerance and cleaned all switches and pots with contact cleaner.

I initially followed the IT-3117 instructions, since I can’t find the original IT-17 manual anywhere on the Internet. The only thing I found was the IT-17 schematic and the two are quite similar in design. I proceeded to check the continuity from the switch to all the pins on each socket, they are all good. The filament voltage, however, it is really off and the line test is off-center but the unit is functional.

Testing

With the tube tester semi functional, I decided to give it a test run. With a box of unknown condition tubes at hand, I tried to test some of them. After going through 1/4 tubes in the box I got 2/3 of the tubes are bad and 1/3 are good.

With 2/3 bad tubes start piling up, I started to question the tube tester functionality because who would keep a bunches of bad tubes???

Manual Testing

I decided to do manual testing on 6L6 which was tested bad earlier.

1. Connected pin 2 and 7 to external power supply the filament is glowing nicely at 6.3 DC. So, the filament is fine.
2. When connected to the socket on the test tube. The filament is not glowing at all, 0V is measured between 2 and 7.
3. When 6L6 is not installed, there is 6.3V between pin 2 and 7.
4. I decided to plug 6L6 tube back in and use the alligator jumper wire and connect pin 2 and 7 to corresponding wire on the switch bank. The filament start glowing nicely. This confirm the socket is making clean contact, but the wiring is possibly bad.
5. Measuring the resistant from the switch to pin 2, the wire has 50+ Ohm?? Note to self – Don’t trust the continuity beep!!!
6. After some tracing, it appears that the original builder missed one solder join on one of socket. After fixing that the 6L6 filament start glowing again and the tube tested fine now.

Calibrating Tube Tester

All original instructions assumed that all parts are new and working to spec. So, some of these assumptions are no longer valid since the meter is old and not that accurate. This is true at least in my case, when the meter is zeroed, the reading are way off.

I have to come up with alternative way of calibrating it and ensuring that the tube tester result are some what usable.

Calibrating Line Test Indicator

1. With no tube in any of the socket
2. Set all switch to center position, then set A to bottom
3. Set the filament to 110
4. Connect a voltmeter black lead on pin 1 and connect red lead on any other pin so we can read the filament voltage. This is important, since the during line voltage adjustment, the meter is connected to 110V tap on the filament winding. At 110V the meter should be reading 50 or .5mA. If not check the 1K and 75K resistor and make sure they are within tolerance.
5. Turn set line until the filament voltage reading is 110V RMS. Cut a piece of electrical tape in triangle shape and tape it to set line dial to mark this position. This is the correct line voltage for use with the tube tester.
6. When set line voltage is properly adjusted, the filament voltage reading should be 110V. At this point the meter should be reading exactly 50 or .5mA. This is assuming that the 1K, 75K and your meter are good. If 1K and 75K are good but the meter is not at 50, the meter reading is off. In that case,insert an amp meter in series with the panel meter to get the correct reading, it should be around .5mA. Then adjust the panel meter so that it’s indicating the same reading by turning the zero adjust screw on the panel meter. Once that is done, your set line switch and meter is properly calibrated to show proper line voltage. NOTE don’t adjust the mechanical zero from now on it will screw up the reading.
7. Next insert a known good tube and set the tube tester accordingly. Then the plate control is adjusted so that the meter is reading from 0 to 100, the measured value from amp meter still inserted in series with the panel meter is recorded at each point to produce a table and chart.
8. From now on, after testing using the original instructions. Take the reading and use the table to map it to actual value in mA or multiply that by 100 to get % scale.

If you find this information helpful and would like to see more. Please support my future project.

Building a simple Programmer for ATMEGA8

Woke up pretty late this morning and feeling bored, so I wasted an hour this morning building a simple in circuit serial programming interface for use with the PonyProg software to program the ATMEGA8 micro-controller.

I intended to use this programmer for ATMEGA8 micro-controller which I recently bough from eBay. For now, I need to create the interface and do some testing with PonyProg to see how it goes.

The circuit that I used is based on one published here which is based on one published on here with some minor modification.

It’s quite simple to build but the challenging part is fitting it in DB-9 hood.

Links:

http://electronics-diy.com/avr_programmer.php

http://www.lancos.com/prog.html

Julian’s collection of Tektronix oscilloscopes

Julian’s collection of Tektronix oscilloscopes

Julian @caltech.edu has huge collection of old Tektronix oscilloscopes in his collection. It’s interesting seeing the innards.