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Repairing Trimble Thunderbolt GPSDO

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ThBltOpnMy quest for a solid 10Mhz signal finally took it’s penultimate step recently, when I purchased a Trimble Thunderbolt GPSDO off eBay.

The unit arrived packed well, and in good shape. It even came with a power connector, which I had not expected. After rewiring it properly (it seemed “off”), I hooked up my Rigol DP832 for the ±12V supplies, and +5V supply, and powered the unit up. Everything looked okay except the +5V rail was drawing about 3x what it should. Oh, and the 10Mhz output being “out” by +26Hz (I wondered if this was because the unit was still powering up, so it didn’t bother disciplining the oscillator yet).

Hooking up a serial connection got no output, and probing the serial connection with the scope showed very low level signals (less than 1Vpp). Opening the unit, I found that the RS232 transceiver (a 232IBE, which is now called a ICL232, or any other number of MAX232 derivatives) was HOT. Everything else looked good for the unit, so my assumption is the chip was damaged. I clipped the leads and replaced the chip with a MAX202 made by TI. It’s pin compatible, but has much better tolerance for ESD and Latch-up (which seemed to be what was going on with the failed chip).

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FTDI, and why I’ll never trust them again

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ft232rlI recently purchased an inexpensive 3D printer from a colleague who had upgraded to a larger model. The printer is a Tinyboy, or Mini Fabrikator 3D. It’s a great little printer, with one unknown flaw… it uses a fake FTDI USB-to-UART chip. FTDI pretty much makes THE USB-to-UART controller, and they know it. The problem (everyone’s problem) is that some Chinese companies have decided to make counterfeit chips, or chips that show up as an FTDI, so they can use the FTDI driver, but aren’t actually FTDI chips.

Now, back in 2014, FTDI released a driver that detected that detected these chips, and reset some identifiers on the chip to basically “brick” the chip. Sure, those that knew how, could go in and fix the chip, then downgrade the driver to one that didn’t do this, but you had to know what you were doing, and it was a huge pain. After enough outrage, FTDI admitted they were a bit overzealous, and pulled the driver. And that was that. Or rather, it was. Then, just late last week, they pushed out another driver, which got into Windows Update (for at least Windows 7), that didn’t brick the chip, but instead injected “bad” data (“NON GENUINE DEVICE FOUND!”) into the USB serial stream. This prevented anything expecting valid data (everything) from working. And it did this relatively silently. The driver installed, loaded, and then just sat there throwing bad data. I quite literally spent four hours screwing with everything I could think of trying to get this working, only to figure out the following.

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Repair MOTU 828mkII

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MOTU 828 Mk IIDad dropped a “new” (new to him, that is) MOTU 8282 Mk II off with me a few days ago complaining that it was rebooting randomly. A quick Google search turned up this is a relatively known issue, and that the LM1117-3.3 (3.3V regulator) basically starts to flake out after a few years, and causes issues.

I opened the unit, and indeed, the PCB around the LM1117 was brown from heat. After the unit running for a while, the LM1117 was over 90C. They’re feeding about 9V into the regulator (which is pretty high for a 3.3V regulator), and apparently drawing a fair bit of current to get it that hot. Before replacing the regulator, I wanted to confirm the failure. Knowing it was intermittent, and the reboot only took about 5 seconds, I set up a webcam in front of the unit with motion tracking software, and had it email me anytime the screen changed. Within a few hours, I’d captured half a dozen reboots. Once it starts rebooting, it rarely lasts more than 10 minutes without rebooting again.

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