Tektronix MSO4104B repair - Page 1
Forum section: electronics / testgear

author: michelg34
author_rank: Newbie
timestamp: March 14, 2025, 11:00:44 am
content: These days, my Tektronix MSO4104B was very very slow to start.After power-up, the fan go to full speed, very noisy, the splash screen take several minute to come, but it comes, and the fan speed decreases.Then after another several minutes, the scope displays it normal screen, seems fully functional and display all tests passed, in the test menu.Just by looking at every functions, it seems only the 4x USB host ports (2 front and 2 rear) do not work.After looking for such problem around the web, I find nothing similar. Just in this forum, there are some examples of faulty Tektronix 4000 scope, and repair advices.As I have solved and repair my scopes, I register and try to share my experience, maybe it could help somebody.1) the first thing I have understood is that Tektronix 4000 and 4000B series are different. The motherboard is no the same. So many post about 4000 (not B) serie doesn't apply to 4000B series.Once opened, following the easy to find "service manual", the MSO4104B looks like this:It is ready for debugging. When the power is plugged, beware of high voltage in the power supply. Put something above to increase safety.The fan need to be connected as the analog component below, with heatsinks, heat up a lot.

author: michelg34
author_rank: Newbie
timestamp: March 14, 2025, 11:25:29 am
content: Then I try to find where is the UART console to see the u-boot and linux start.At first, I have not easily found where it was in the forum, even if now I can find some post which explain it, herehttps://www.eevblog.com/forum/repair/tektronix-dpo4034b-stucked-at-tektronix-splash-screen/msg3537346/#msg3537346On the small communication board, I have seen a "MAX3221" IC which is a RS232 line driver/receiver which use 2 usually not used pins on the VGA connector.The pin 4 in TX (output from scope to PC) and pin 11 = RX (input to scope). And pin 5 is a ground.The speed is 115200,8,N,1.So I build a small adapter using a male VGA connector and a female DB9 RS232 connector.The grey wire is ground, VGA pin 5 <-> DB9 pin 5The white wire is TX from VGA pin 4 <-> DB9 pin 2 (RX of PC = DTE wiring)The blue wire is RX from VGA pin 11 <-> DB9 pin 3 (TX of PC = DTE wiring). I don't use it, the goal was not to try to interrupt and play with u-boot / Linux console.But my scope doesn't output anything from power-up to several minutes after when it comes ready.By chance, one of my colleague in my company also has a MSO4104B, and on his working scope, I can see all the startup sequence.I was very surprise to have my scope working after a very long time, but nothing on the linux console...

author: michelg34
author_rank: Newbie
timestamp: March 14, 2025, 11:34:46 am
content: Then I come back to the USB, to only problem I see after the scope has started.USB host port use an USB HUB from SMSC (Microchip), USB2514HZH (now obsolete in this 48pin version)The power switch use Micrel MIC2026-1YM delivering power to 2 port each.The 5V was not present on the USB host connector. But the MIC2026-1YM power switch was not driven by the USB HUB, so the problem doesn't come from the USB power switch (i read it was one of failure in previous tektronix 4000 serie, not B)The USB HUB use a EEPROM for configuration (U201, a 24C01B from Atmel), so should be independant of the main processor of the Scope.So I looked to power supply (good) and Clock on pin 45. Without a crystal quartz, an external clock should come to the chip, but the clock input pin 45 (via near the silkscreen C211) was quiet, no clock !!!

author: michelg34
author_rank: Newbie
timestamp: March 14, 2025, 12:04:25 pm
content: So I searched now for every clock. It should be something near 24 or 48MHz according the HUB datasheet.The HUB clock input comes from a 74LVC1G125GW logic gate (with OE permemently enabled, so used as a buffer) and the input of this gate comes from the motherboard...First all standard oscillators in 7x5mm package on the motherboard were working, but after a more carefull search, there was another oscillator, 48MHz in a black plastic 5x3.2mm package near the big processor (the power-pc).And this oscillator doesn't output any clock, no 48MHz at output.This is a 3V3 oscillator permanently enabled (EN pin 1 connected to 3V3)So I buy a new oscillator, in a 3.2x2.5mm package to keep room on the pads for manual iron soldering.1) desoldering and cleaning the pad with Sn62PbAg2 solder (more easy to solder than no lead...)For that, I use 2 iron solder (Pace TD100) one in each hand. It is much more cheaper than using desoldering tweezers... and I find this method also easier !A bit of flux (no clean, like MG chemical 8341), then I clean with isopropyl alcohol.2) soldering the new oscillatorEt Voilà !My Tektronix MSO4104B power-up exactly as before, USB port are working, and the serial port outputs the u-boot & linux starting.Very happy to keep this wonderful oscilloscope.

author: michelg34
author_rank: Newbie
timestamp: March 14, 2025, 12:06:57 pm
content: Here is the power-up trace on the RS232 serial link:boot_mso4104b.txt(4.61 kB - downloaded 20 times.)