TDS6804B failed to power up repair

[pasta2018]

I'm fixing a TDS 6804B.The fault phenomenon is that the oscilloscope does not respond when the startup button is pressed. Sometimes when the power is plugged in, the oscilloscope starts and the fan turns, but the oscilloscope shuts down automatically in about 10 seconds.For now, I only keep P1 REAR PWR distribution plate, symptom does not change.I measured the voltage on P1 according to the service manual, and it was almost 0.I would like to ask if the voltage mentioned in the manual needs to be measured by oscilloscope in operate state, or could it be measured under standby state.Also, how to determine if the fault is due to a power failure or a fault caused elsewhere.

[calibrationfixture]

Hi pasta2018,

You also must read this:

https://www.eevblog.com/forum/repair/looking-for-tds6124c-os-restore-cd-(xp)/msg3850442/#msg3850442

Member/Poster noticed discrepancies in the Service Manual. The condition of the MB Battery has some influence about how the Power On/Off Button responds. That was the case with my TDS7404B (B02xxxx, same MB and PPC Board).

Calibrationfixture

[pasta2018]

Thank you for your information. I will refer to the voltage value he reported.Now my problem is that the oscilloscope does not turn on, occasionally turn on the power on (lasting for about ten seconds) and then automatically shut down. How to confirm whether the power supply voltage is normal in this state? I want to make sure it's the power supply or something.

[coromonadalix]

i would pull out the pc section  mobo and test it on a bemch,  sure it needs a psu ...  you would see about the coin cell battery state,  the capacitors state on the board  etc ...

 and check if they have the famous  nvram  dying battery ... on the power pc board  the board under the pc ...   

@ab1033 did a good investigation

[pasta2018]

I replaced the CR2032 battery on the motherboard, which uses intel865GLC.It is  clean, and no leakage capacitor was found.

PPC board is also relatively new, and its nvram is DS1245-100.

Next, I'm going to take care of the metal interface on the memory module.Because now plug in the power can occasionally start for a while, in most cases plug in the power indicator led on but the oscilloscope does not start.

[pasta2018]

Someone can tell me, under the standby condition of oscilloscope, will there be voltage at the power output interface such as P1?
If standby has voltage, it can be determined that mine is a power board fault, which saves time for other troubleshooting.

[calibrationfixture]

Hi pasta2018,

I think answers can be found on Page 4-21 of the earlier mentioned Service Manual (071-1798-00). The SMPS of your TDS6804B has 11! State Indicating LED's. Looking at an eBay Picture of the TDS6000B/C SMPS, I see many Ceramic Fuses. Another Area to look at.

Calibrationfixture

[pasta2018]

Yes, I noticed the description of LEDs in the manual. When I just plug in the power cord, these lights will light up for a moment and then go out.Then the DS10 Ds11 DS3 lights up green and red respectively and stays on.

[calibrationfixture]

Hi again,

" Then the DS10 Ds11 DS3 lights up green and red respectively and stays on. "  That's good.

I also noticed a Relais sitting right from the Big Black Caps. Does it click and when? The P1, P2 etc. Power Connectors must be inserted, before checking the Voltages.

Calibrationfixture

[pasta2018]

The chip on the right of Dallas is labeled Y540, which I guess is a crystal oscillator.

[pasta2018]

C1 of the P1 interface board is PW-on singal, short it to ground and the power can be started（All outputs of the power supply are now disconnected）
It is almost certain that the power supply is working properly.

Next, I need to find out whether the power supply is not started due to PPC ,MB or the acquisition board.

The 5V voltage connected to the acquisition board has a resistance value of about 8 ohms to the ground. I am not sure if this is normal.

[pasta2018]

I disconnect the motherboard from the power supply and set the C1 of the P1 board short to the ground, and the oscilloscope is not started. The motherboard should be no problem. The next step is to confirm whether the PPC or the acquisition board is faulty.

[pasta2018]

Then I install it like this, and then I boot it up. The oscilloscope still won't start. It should be that the acquisition board has a fault, and 5V is only about 8 ohms to the ground.

[pasta2018]

The good news is that when I disconnect all the outputs from the power supply, short-circuit P1-C1 and ground, and the power board does not start up.
At present, it should be the fault of the power board. The 5V power supply port of the acquisition board 8 ohms to ground may be normal.

[calibrationfixture]

Hi pasta2018,

I am confused and assume I missed something:

At Reply#10 you stated:

" C1 of the P1 interface board is PW-on singal, short it to ground and the power can be started（All outputs of the power supply are now disconnected）
It is almost certain that the power supply is working properly. "

And now it is not.

In addition when you Powered the Scope Up (with all interconnected) then all DS (LED's) light up. Then you know all Fuses are good.

Calibrationfixture

[pasta2018]

I was also very Confusion. At first, I left the power supply disconnected from anything, and the power supply could start up. But then I couldn't start it later. I suspect the power supply is unstable. It hasn't been repaired yet.

[calibrationfixture]

Hi pasta2018,

" The chip on the right of Dallas is labeled Y540, which I guess is a crystal oscillator. "

Y is indeed Tektronix nomenclature for a X-tal Oscillator. See for example page 9-58 from the 070-6863-01 2465B and 2467B Series Service Manual.

By the way U520 is a Dallas DS1245W-100. This is a 3.3V Device contrary to DS1245Y's.

Calibrationfixture

[pasta2018]

Thank you. The problem at the moment is that the psu does not start, there is no circuit drawing, and it is difficult for me to repair the power supply