Hantek DSO-2150 Repair

[EduardoLM]

Hello people, I hope someone here can help me.

I got a broken Hantek DSO-2150, which had the ADCs tampered with. After replacing both ADCs, the device came to live (both channels working), but with an intermitent problem: most of the time, I get the red led blinking forever, with a quick green after the first 3 reds, like this:

POWER ON .. red .. red .. red .. green .. red .. red .. red .. always red from here

But if I power off, flex the board slightly and power on again, it usually works, with green led blinking and readings on the software. But if I tap the board, even slightly, the red blinking starts again, software freezes and I have to power cycle again to make it work.

Well, it looks like a bad joint / bad trace somewhere, and it seems to be around the Cypress chip, but here's my first question:

1) What should I be looking for? What does RED RED RED GREEN RED RED RED means? Power problems? USB not communicating? Could you please help, giving me some pointers on what may be failing and causing this behavior?

I already did a blind reflow on most components near the USB PCB end, both sides, but the problem persists, so no bad solder on these. So here's my second question:

2) May I have a broken trace on the board? Or may I have a bad component too, with something broken inside? Is it a good idea to replace the Cypress MCU? Or the symptoms really indicate a bad trace somewhere?

Any help on this will be greatly appreciated! Thanks a lot!

Eduardo

[tautech]

Welcome to the forum Eduardo.
I do not like the sound of your problems and could not advise you more that that you have done.
tinhead is our Hantek specialist, PM him and point him to this thread, he may have some advice.

[EduardoLM]

Thanks for your reply, tautech! I PM'ed him, now I'm waiting for a reply, I hope he can help me somehow!

I have a small update: I noticed the device works if I press / flex the PCB near the FPGA too. I thought the problem was around the Cypress chip, because flexing there used to solve the problem, but flexing around the FPGA works too, so I'll reflow it and every component around it.

Since the PCB looks to be 2 sided only, I think my chances of fixing the thing are good!

Thanks again,

Eduardo

[tautech]

Since the PCB looks to be 2 sided only, I think my chances of fixing the thing are good!

Looks can be deceiving.
Hold in up to a bright light and check for internal layers to be sure.

[EduardoLM]

Good news! Reflowing the FPGA / CPLD worked! Probably a bad solder in one of the tiny pins. Now the device is rock solid, no more freezes.

However, now I would like to ask another question: I noticed each channel have 4 tiny trimmers underside the PCB, and most of them are damaged! I can see a small disk broken under the adjustment screw of all of them. Turning the screw makes the broken bits move an fall off. This scared me at first, but the scope is working ok, with just some noise.

So I would like to ask: what are these trimmers for? Is it worth to replace and calibrate them? If so, how to calibrate them?

Thanks a lot!

Eduardo