Shaun Merrigan's Information Pages



Hickok 209A VTVM Restoration Part 1

Posted by Shaun Merrigan in Electronics, Test Equipment. Comments Off on Hickok 209A VTVM Restoration Part 1

31st December

This is the first installment in a multi-part series documenting my restoration of a classic Hickok 209A VTVM. First a description and some images:

This is a Vacuum Tube VoltMeter (VTVM) with a nominal 12 Mohm input impedance and one of the largest mechanical meter movements found on commerical/consumer equipment (viewing area about 8.5 inches diagonal). It was produced from about 1947 (earliest direct evidence) to at least 1961 (catalog reference). One of the units I have has 03-09-55 written in grease pencil on the back of the meter movement. The cost in 1947 was (reportedly) $133 USD which is about $1500 USD in late 2018. In comparison, the HP 410A (a lab grade instrument) sold for $245 USD in 1948 or about $2500 USD in late 2016 dollars. So the Hickok 209A was not aimed at the laboratory … Read More »


HP 1340A Display Repair -2

Posted by Shaun Merrigan in Electronics, Oscilloscopes, Test Equipment, Troubleshooting. Comments Off on HP 1340A Display Repair -2

29th December

HP 1340A Display Repair


HP 1340A Display Repair – 1

28th December

I purchased a couple of HP 1340A XYZ Displays which I thought would be useful as troubleshooting aids and as graphical displays of CRT technology (oscilloscope clocks, and the like). Upon receiving them, they both worked, but careful visual inspection showed some potentially serious problems. I will document the repair process here.

HP 1340A Overview

HP 1340A Overview

HP 1340A Overview

HP 1340A Overview

HP 1340A Overview

HP 1340A Rear Panel, High Serial Number

Visual inspection of the units revealed the following problems:

Heat damaged A1R81 (both units)Heat damaged A2R13 (both units)Loose mounting hardware and corroded wiring on A2Q2 (one unit)

Heat Damaged Components

LVPS A2Q2 Damage

Heat Damaged Components

A2Q2 is mounted directly to the case for heatsink purposes. The hardware was loose, therefore the transistor effectively had no heatsink. I suspect that it had been running hot for quite some time because the PVC insulation … Read More »


HP 3562A CRT Replacement

Posted by Shaun Merrigan in Electronics, Oscilloscopes, Test Equipment. Comments Off on HP 3562A CRT Replacement

28th December

Based on my own observations and reading, the CRT in the HP 3562A is a marvelous piece of engineering. However, it literally fatigues over time and at some point the deterioration cannot be compensated for by the range of adjustments. The solution is to replace the ageing CRT display with a modern LCD. It turns out that SimmConn Labs has such a kit:

http://www.simmconnlabs.com/1401/2501.html

Terry at D-Lab Electronics did a good video on how to replace the original CRT with the LCD Kit from NewScope:

https://youtu.be/WKz7GYBON7g

Terry does a great job of documenting the replacement process, so I will focus on the before/after results. I will start with original CRT images, followed by LCD images and by split screen comparison images. Since I also purchased the RGB to VGA adapter cable from SimmConn, I will conclude with an … Read More »


600 Ohm Terminator Build

Posted by Shaun Merrigan in Audio, Electronics, Test Equipment. Comments Off on 600 Ohm Terminator Build

27th December

When doing work on older audio gear it is sometimes necessary to maintain a 600 ohm impedance from, for example, a signal generator to a DUT or a piece of test gear. An easy way to do this is with a 600 ohm terminator. The article will document how I built such a terminator.

First I want to acknowledge the work of ElPaso TubeAmps (David Beard) who covered this very subject several years ago:

https://youtu.be/tIB3U-U29wg

50 ohm and 75 ohm BNC terminators are relatively easy to obtain, but 600 ohm terminators harder to come by. The solution is to build one as follows:

Obtain a suitable 50 or 75 ohm BNC terminator . You need the type which can be opened. One clue is that it may have flats on the end of the barrel which were used during assembly.The … Read More »


HP 3562A ROM Repair

Posted by Shaun Merrigan in Electronics, Test Equipment. Comments Off on HP 3562A ROM Repair

26th December

Early in 2018, I purchased an HP 3562A Dynamic Signal Analyzer for an excellent price on Ebay. The display looked great and it was physically in good condition. However, the unit failed the power on self test as follows:

HP 3562A Error Message on boot

This error code indicates a ROM IC failure.

HP3562A Diagnostic LED’s indicate Hex code 4 4 (0100 0100)

This code indicates a failure of ROM Chip U105:

HP 3562A Rev B ROM board. The problem ROM chip is the fifth chip down in first column (U105)

HP 3562A ROM Board Rev B

This ROM board is an older version using 32kx8 chips in two groups (Low Byte & High Byte) of 18 chips each. I had access to a second 3562A, and swapping ROM boards confirmed that the ROM board was the problem. Now I needed to:

Locate a suitable set … Read More »


AC Line Voltage 34 Hour Log

Posted by Shaun Merrigan in Electronics, Time and Frequency. Comments Off on AC Line Voltage 34 Hour Log

26th December

AC Line Voltage 34 Hour Log


iPad Not Charging After iOS 12.1 Update

Posted by Shaun Merrigan in Electronics, Tech. Comments Off on iPad Not Charging After iOS 12.1 Update

23rd December

I recently updated my iPad Air 2 to iOS 12.1 only to find that it would no longer charge via my computer’s USB 3.0 port. Specifically, I had been using, for many months, a decent quality aftermarket cable to connect/charge the iPad to my PC. There were no issues with charging or connectivity using the same configuration prior to the iOS 12.1 update.

A bit of digging suggested a two-part solution:

Power off and restart the iPadUse a genuine Apple cable

Well, powering off and restarting (using the same aftermarket cable) did not work; the iPad still would not charge. However either changing to a genuine Apple cable or a different aftermarket cable together with a power off and restart, did work. The iPad is now charging normally from the USB 3.0 port on my PC. … Read More »


Site Updated to HTTPS

Posted by Shaun Merrigan in Site Updates. Comments Off on Site Updated to HTTPS

22nd December

I have completed updating this site to use HTTPS. Enjoy!

Update: Having a few hiccups after updating to HTTPS. The public facing site became unreachable after a day or so, while the backend was working fine. GreenGeeks support suggested that my Cloudflare configuration was the culprit and recommended a couple of changes to the configuration.

It looks like this was the case, because the site is now reachable again after making the suggested tweaks to Cloudflare. Another issue arose with some pages not loading/working I had to manually edit the code to point to the correct https source which fixed that problem .

Also this prompted me to get rid of a fragment of Adobe Flash code that was still running on the site (a good thing) but served no useful purpose.

As EDI said: “It … Read More »