TDS 500 600 Series (and TDS 820) Monochrome CRT Horizontal Linearity

I have a batch of TDS 620A which everything looks shiny new, but the display will stretch vertically and eventually gone unstable after turning it on continuously for a long time.

Turns out there’s a specific batch of flyback transformer (120-1841-00) on the monochrome CRT driver board (640-0071-06) that has quite a bit of infant mortality. The newer the unit looks (of the CRT tube looks shiny new without burn-in), the more likely it’s a victim of the bad batch.

The transformer is almost impossible to source (other than getting another CRT driver board), but I was able to find a Chinese supplier who makes it. It was usable, but it’s a nightmare to get it on because it’s really done with the stereotypical Chinese (PRC) manufacturing caliber.  When I received the unit, it’s a WTF moment! Leave me a comment if you want me to write about it.

The replacement transformer is only pin and functionality compatible, but it’s not a drop in replacement (not even geometrically). The characteristics are different and I had to adjust the trimmers all over the place.

I was able to get the screen width I want by adjusting the variable inductor (L105, HOR SIZE) by nearly pulling ferrite rod out, but the horizontal linearity was way off (the left side is very squeezed):

I looked into the TDS520B Component Service Manual (Same CRT board circuit diagram) and found this:

But L100 looks like this, which doesn’t seems trimmable:

The right hand side is the same L100 choke I extracted from a CRT driver board (same model) that I’ve disposed of. I saw two suspicious pieces of metal-like objects strapped on the choke on the left (installed) which I haven’t seen in other identical boards. 

Thinking that by changing the magnetic property of the core, I can adjust the inductance of an otherwise non-adjustable inductor. I took a few bits of magnets sitting on my bench and swing it around the L100 choke, the horizontal display widens/narrows depending on which pole of the magnet is facing the L100 choke.

After a few trial and error, I picked the right amount of magnet discs to correct the horizontal linearity so the squares have roughly the same width:

I guess I cracked the code! Here’s the result of correction by magnet:


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RTC / NVRAM in Test Equipment

HP Infiniium Series Atlas III Motherboard (Oldest generation Infinium oscilloscopes still branded as HP):

  • [RTC. There’s no exposed batteries] bq3287AMT = DS1288

Tektronix TDS Series (500, 600, 700, 800)

  • Older TDS (without alphabet suffix): Dallas DS1245Y
  • Model number that ends with ‘A’:  Dallas DS1650Y

The NVRAM in TDS series only contains the options data. Since I can reprogram the options, I can start with a blank NVRAM without reprogramming it). 

Will keep updating this page when I came across more test equipment.

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Agilent 54830 Infiniium Digital Oscilloscope Repair / Service / Upgrade 54830B, 54830D, 54831B, 54831M, 54831D, 54832B, 54832D

As time goes by, it seems like there’s quite a few small problems with the very well engineered 54830 series oscilloscope. These are all manageable (not core) problems and I believe I got the details down.

Models supported: 54830B, 54830D, 54831B, 54831M, 54831D, 54832B, 54832D
‘D’ means it’s a Mixed-Signal oscilloscope (comes with logic analyzer)
‘M’ is the military versions that’s exactly the same as ‘B’. The ‘M’ batch is for sure shipped with Windows 98.

I also support upgrading any Windows 98 based unit to Windows XP Pro.

I also have plenty of units and parts to get your problems fixed.

If it doesn’t power or boot, it might be a less severe problem than you think. Evaluation is always free. 

Trade in for a guaranteed unit

Serviced units (Motherboard corrected, replaced mechanical HDD to SSD, replaced CD-ROM with DVD writer, comes with LS-120 drive, Windows XP Pro installed, 2 years repair/exchange* warranty):

  • 54831M[$2999]: 600Mhz, 4GS/s
  • 54831M modded to 54832B [$3499]: 1GHz, 4GS/s.
  • 54832B [$3999]: 1GHz, 4GS/s
  • 54832D [$4499]: 1GHz, 4GS/s (Mixed Signal Oscilloscope with Logic Analyzer)

If your decaying unit is frustrating you, you can swap your it with the worry-free, fully serviced units by paying a $1500 difference to enjoy all the upgrade and peace of mind. 

* I’m likely to have a replacement unit for immediate exchange to get you up and running. In the unlikely event I run out of units, I’ll pay you $100/week delay if the repair takes more than 1 week, up to the full amount you’ve paid.

NOTE: This (swap) deal does not apply to units with a genuinely failed Acq board (like analog signal path/cal/trigger problems) or I confirmed that it has a failed power supply unit.

Parts cost (they are taken from fully working units, so there’s sacrifice):

  • Corrected VP22 motherboard [$699]
    [Subtract $200] if you trade in a defective VP22 (4 PCI slots).
    [Subtract $300] if you trade in a working M880 (3 PCI slots).
  • Old style interface card [$699]:
    [Subtract $200] if you trade in your working GPIB combo card.
    Old style interfaces works across the board. The combo only works on the latest acq boards.

Labor/Repair cost (all service guaranteed for 2 years). No cost if not successful:

  • Front-end problem (cannot calibrate) [$599 for first channel + $199/channel]. Parts included.
  • Cannot power up [$199]. Parts NOT included. Not charged if no actual repairs were made.
  • Boot problems [$199]. Waived if parts were bought to solve it.
  • Oscilloscope program hangs / BSOD [$199]. Waived if parts were bought to solve it.
  • Replace motherboard [$199]. Parts NOT included.

Upgrade / service cost

  • Upgrading from Windows 98 to Windows XP Pro [$499 for DIY, $699 for full service]: SSD included. This covers the self-calibration.

    If your unit comes with licenses, you will need to provide the license number (can easily do it yourself) to enable them. Can ask Keysight to look it up for you.

  • Modernize the unit [$299, $149 when combined with any repair/service/parts above]: migrate hard drive to SSD, replace CD-ROM with DVD drive, replace FDD with LS-120 drive (if applicable).

The prices are negotiable if more than one part/service is needed. 

Call me at 650-804-5024. I’m located in Irvine, CA. You’ll be responsible for all shipping costs for anything that’s not my fault.

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Test instrument repair services (Specific models only)

There are a few used test instrument models that I’m familiar with the common problems. I moved onto the higher end, big ticket items so I wouldn’t bother acquiring them anymore.

Nonetheless, it hurts to see a piece of good equipment going to landfill. I’d be happy to repair the following models at a moderate rate (materials included, no fix no pay) below if anybody is interested:

  • HP 6515A power supply: $400 for a problematic unit, $300 when you send in a good one for preventative recapping (the capacitors are from 1970s! They are dying.).
  • HP/Agilent 54600 series oscilloscope: display got squeezed ($200), unit losing memory/time ($200), blown input channels due to excessive voltage ($300 for 1 channel + $100 per extra channel), unstable/cannot trigger ($500).
  • HP/Agilent (Older, non-Megazoom) Infiniium series: replacing OS hard drive ($250), cannot calibrate certain channels ($400 for 1 channel + $100 per extra channel).
  • HP/Agilent Infinium 5483X and above: refer to 54830 series post.
  • TDS 500, 600, 700 series oscilloscope: SPC fail without other symptoms ($500), Acq/Attenuator fail ($600), Proc board fail ($400), Color screen bubbled ($500), Cal initialization failed ($300), upgrading all possible software options ($200, free with any other service).

Contact me at 650-804-5024. All units must be delivered to Irvine, CA for service (and shipped back/picked up) at requester’s cost.

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Tektronix S1001 DIP switch: Open pin 3 to boot for fast self-test (TDS 744, 744A, 684A, 784A)

Normally for most TDS 500 series oscilloscopes, the DIP switch (S1001) typically all closed for normal operation. The only described use in the service manual is opening pin 6 and 7 to reveal the hidden composite test pattern screen for display adjustment.

However, I got a TDS 744 scope that boots very slow. Almost 5 mintues! To the extent that it’s unbearable. Initially I thought it’s just the non-A type booting slow. Nonetheless, I got a chance to open up another TDS 744A with boots much faster (in half a minute) with calibration seals on, and I noticed the pin 3 of S1001 is opened. Initially I thought it was out of place so I closed it again. Guess what? A slow 5 minute boot sequence!

I suspected opening pin 3 of S1001 puts the oscilloscope in the quick boot mode. I experimented with the pin 3 opened and manually initiating the full blown self-test (utility menu). Turns out I was correct! The full self-test is 5 minutes!

Since it was the settings from the calibration house, I looked up the TDS 744A/684A/784A service manual and noticed that the factory default is with pin 3 opened, while the old TDS 544A manual says pin 3 is closed. I suspect that the self-test for the new models 744/744A/684A/784A is unbearably long that the Tek decided to have it disabled for boot-up self-test.

In any case, try opening pin 3 to have the scopes boot faster!


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Agilent Infiniium (Motorola VP22) Motherboard USB Pinouts for DOM SSD

The Motorola VP22 motherboard used in a variety of modern Agilent’s Infiniium series oscilloscope (the ones with Megazoom) and logic analyzers has a 5-pin USB port that’s not quite the same as the standard headers on most motherboards.

The reason I needed the pinouts of the USB port is because I have a 40-pin DOM SSD to replace the old clunky mechanical hard drive, which needs 5V for power.

I don’t want to modify/resolder the original wire harness (for the LS-120 and CD-ROM drive) nor I have the molex connectors to make a power splitter. Luckily, I found somewhere that I can safely tap a 5V for low power devices: the internal USB header. Here’s a picture with the DOM SSD module wired:

VP22 USB Power Tap

This post serves as a reminder to myself that the ground is the second pin to the left and 5V is the rightmost pin. The pinout diagram as follow:

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(Front-end) Attenuator Autopsy of HP 54616B Digital Oscilloscope

One day I got a call from a friend saying that he accidentally fed high voltage signal (line voltage) and broke one of the channels.

My hunch is that since he didn’t feed kilo-volts into it, the damage is limited to the (front-end) attenuator (an expensive part). I had an extra unit lying around so I just swapped it for him so he can get it up and running.

Once I got the time, I opened it up the broken unit to see the damage. My hunch was correct:

Fried 1NB7-8303 54616B Attenuator Block

The 500Mhz attenuator used in 54616B, 54615B, 54520A, 54540A, 54503A and early Infiniiums 54810A, etc. are all the same: 1NB7-8303. The resistive trace was blown open circuit (charred), so bad that it spot welded the metal casing.

I took a good attenuator and measured resistance that the blown open ‘trace’ should have been. Turns out it’s a little less than 1Ohm so I used 4-lead Kelvin sensing from my Agilent 34401A multimeter. I calibrated that meter using my Data Precision 8200 reference and agreed with my Fluke DMM, so hopefully I wasn’t way off.

I could have put a small SMD resistor matching the resistance of the blown trace, but since I have a few back up attenuators lying around, I’d rather not risk the signal integrity by doing so, since I cannot guarantee the temperature specification if I just replaced it with a resistor. The scope was up and running in perfect condition after replacing the attenuator.

Now you know what happens when you feed line voltage to a scope. The damage is usually limited, but the front-end (attenuator) is the most expensive RF part that makes a scope truly a scope (see Dave’s rant on EEVblog). The ADC hybrid can get just as expensive, but usually the attenuator takes the hit before your input gets to fry the ADC.

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Agilent 54641D (Mixed Signal) 54642A (Digital) Oscilloscope Fan Mod

Agilent 54641D has a ADC hybrid (1NB7-8394) converter that runs very hot. The heatsink does a very good job extracting the heat from the chip, but there’s nothing to carry the heat away from the heatsink. The heatsink is actually hand-burning hot when passively cooled. Even with the case, the bottom of the unit gets so hot that it actually warms up the instrument below it.

For longetivity, I decided to give it a tiny fan. But given the tight space at the bottom, how can I squeeze a standard 5mm fan? A squirrel cage fan might do the trick, but where am I supposed to secure it? Turns out there’s a screw hole for the fan and there’s only one place I can screw it down:

Fan for 54642D's ADC

I padded the fan with 3 plastic washers to create a surface level with the two ASIC chips the fan is sitting on.

Where should I get the power for the fan? It’s not a low-end 100Mhz scope, so I took extra precaution to not have a DC power line flying all over the circuit board to generate noise. I twisted the power wires together just to lower the EMI and follow the same holes Agilent designed to let the power cable go through.

It’s a little risky to steal power from the circuit board directly when I don’t have the schematics, but luckily I found a printer power port which nowadays nobody uses which I can steal the power from.

I could have tapped the 12V fan power from the power module for the power supply fan, but I noticed the printer power port is even better: it’s around 7~9V:  I don’t want the noise from running it at full speed (squirrel cage fan are typically noisier).

54642D Printer Power


Finally I made an internal terminal for the printer power so the fan can be easily detached. Weakly wrapped it in a clear heat shrink tube so it won’t get accidentally disconnected yet reminds myself that a connector was built instead of directly soldered on.

At last I tie-wrapped the power wire to the other power wires Agilent already secured so they won’t dangle during transportation.

54642D Tie-wrapped

Self-calibration expects the temperature to be stable, so the oscilloscope needs to be warmed up before a cal would register. That means before the fan, it’d take a long while for the ADC to heat up to a guaranteed temperature.

With the new fan, the calibration needs to be done again because it’s much cooler now. Even better, it takes nearly no time to warm the oscilloscope up for calibration because the steady temperature isn’t high anymore.

Of course this mod works for 54641A, 54641D, 54642A, 54642D as well. Technically you can put it in any 5462X oscilloscope, but since they are 100Mhz, you don’t need to cool the ADC down that much.

I recently tried it on a 54642A, which doesn’t has only one stream instead of two, so one chip with glued heatsink and one ASIC (1821-5733) is gone. Looks like I can use the screw hole on the top left (the one with a red condom over it). Unfortunately, since the only way to use that screw hole is to flip the fan over, it became an inferior choice because

  • The suction part came from the bottom of the case instead of the board. That means I’m blocking ventilation for some components.
  • The fan’s power line is now close to the board, creating potential signal integrity issues (might not be material, but why mess with EMI issues when there’s no real advantage anyway?)

In other words, even if it looks tempting to deviate from the solution above, there’s no good reason doing so.

Now that I have a seek thermal camera module, here’s the thermal picture after the fan compared to the board:

You can see from the picture how effective the heatsink is. It took only a very weak breeze to carry the majority of the heat away. The 12V squirrel cage fan running at ~7V is pretty quiet, and I don’t feel the wind speed coming from the fan, yet it cool the ADC hybrid down to near room temperature.

The real reason why I did this fan mod is because I had some units (like 54641A) bought from the used market that after powering it up for 30 minutes, the signal displayed just went nuts and jumped all over the place. I opened up the ADC and the metal bracket holding it down had a lot of heat stress pattern on it (the golden bracket looked purple-rainbowish). The unit was fixed after swapping the ADC hybrid from a donor unit, but now I know the ADC hybrid really needs to be kept cold to ensure longevity.

By the way, if you need a replacement ADC hybrid (1NB7-8394), I have 2 pcs at $660/ea.

First come first served. Call me at 650-804-5024 if you suspect it’s the ADC hybrid that needs to be replaced.

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