Help Identifying Part - Page 1
Forum section: electronics / repair

author: Generalquark
author_rank: Contributor
timestamp: September 04, 2021, 02:32:55 pm
content: Hi,I recently hooked up voltage backwards on something I was working on and smoked this part. I have having trouble finding out what it is. Could one of the component experts help me out? Code is HMBUA Thanks!

author: fzabkar
author_rank: Super Contributor
timestamp: September 04, 2021, 10:07:55 pm
content: It's a switchmode step-down converter, but I guess you already knew that.If we could see the rest of the PCB, perhaps the other ICs might give us a clue. Designers often use the same manufacturer for several ICs.

author: amyk
author_rank: Super Contributor
timestamp: September 04, 2021, 10:14:26 pm
content: HM8119A?

author: Generalquark
author_rank: Contributor
timestamp: September 05, 2021, 01:05:19 pm
content: That HM8119A could be the correct part. I am not 100 percent sure yet. I took readings on a good one and here is what I got on a DMM. If that is the correct part I am having a hard time tracking down a replacement.Pin 1 19.45VPin 2 0 VPin 3 .616Pin 4 9.71VPin 5 19.46VPin 6 0Vhttps://html.alldatasheet.net/html-marking/1245137/HMSEMI/HM8119A/509/2/HM8119A.html

author: DavidAlfa
author_rank: Super Contributor
timestamp: September 05, 2021, 02:08:39 pm
content: Probably they used an existing pinout from a common part.0.8V reference, 45V max input, 500mA output, doesn't seem so strange.Microchip's MCP16331 seems an exact match, same specs and pinout.Just do some parametric search: sot23, 6 pin count, and check what's avaliable, ex.RS

author: fzabkar
author_rank: Super Contributor
timestamp: September 05, 2021, 10:08:23 pm
content: Quote from: Generalquark on September 05, 2021, 01:05:19 pmIt would appear that the "good" device isn't regulating. I would think that the voltage measured at pin#6 would be a little higher than the output voltage. I would measure the voltage on the load side of the inductor.

author: Generalquark
author_rank: Contributor
timestamp: September 06, 2021, 05:28:00 pm
content: I checked again today with a scopePin 1 has a switching pulse to a max of 40.9VdcPin 2 0VPin 3 960mvPin 4 9.52V steadyPin 5 19.5V steadyPin 6 has nothing.I checked the input to the inductor and it has the 40.9Vdc switching signal on the one side and the other side had around 19.5vdc steady signal. Does this seem correct?DavidAlfa, I don't have the component substitute experience. Would you say I should be good swapping in the MCP16331? I saw most of the specs seem very close, but the switching frequency was 850 vs 500. That won't cause any issues?Thanks for all your help guys!

author: fzabkar
author_rank: Super Contributor
timestamp: September 06, 2021, 07:32:13 pm
content: Quote from: Generalquark on September 06, 2021, 05:28:00 pmIt appears that I was wrong. It now looks like the IC is a boost converter. You will probably find a steady 40VDC on the cathode of the Schottky diode ("SF"). Is this the supply for a LED string?This part (unknown marking) has the correct pinout, but wrong FB voltage (0.6V):http://hmsemi.com/downfile/HM1535.PDFThis part (wrong marking) has the correct pinout, but wrong FB voltage (0.6V):http://txsemi.com/Upload/TX9710_V13-10192938183.pdf

author: Generalquark
author_rank: Contributor
timestamp: September 07, 2021, 12:11:20 am
content: I checked the Diode marked with Red. 28V stable on the other side. It is not a string of LEDs. There are strings of Asics on the board, but I am unsure how this ic would interact with them.

author: DavidAlfa
author_rank: Super Contributor
timestamp: September 07, 2021, 06:36:57 am
content: Adjust the feedback resistor network, usually only 2 resistors

author: fzabkar
author_rank: Super Contributor
timestamp: September 07, 2021, 10:22:53 pm
content: Can you confirm the voltage on pin #3?Can you tell us what device you are working on? Is it a laptop/netbook/tablet?

author: Generalquark
author_rank: Contributor
timestamp: September 09, 2021, 03:00:54 am
content: I'm actually working on a board out of a Asic Crypto Miner.Checked Pin 3 again with a Scope and DMMWhen the board has power but is not enabledDMM .615VdcOscope 52-54khz signal with the Vmin at .590 and the Vmax at .800 with a small pulse. See capture.When the board has power and is enabledDMM .615VdcOscope 41.7khz signal with the Vmin at .590 and the Vmax at .800 with a small pulse. See capture.Thanks!

author: fzabkar
author_rank: Super Contributor
timestamp: September 09, 2021, 03:09:20 am
content: It looks like 0.6V is the FB voltage. I would measure the frequency of the PWM pulses at the inductor. If it is 1.2MHz, then either of those previous candidates could be a good substitute.Alternatively, you could search for other subs from ON Semiconductor, Texas Instruments, Monolithic Power, etc. These would be more likely to be stocked by Mouser and Digikey.

author: Generalquark
author_rank: Contributor
timestamp: September 11, 2021, 03:02:42 am
content: I'm not following why your looking for 1.2Mhz at the inductor. I just checked the Inductor on both sides. One of the sides is connected to the part, and that one has the pulsed signal. The other side is straight DC. I checked it with the unit powered but not enabled first, then with the unit enabled. On the other side of the inductor voltage is the same in either on or off mode. I'm no good at figuring out which component would be a good fit with this information. Is there a way to know for sure with this information. Thanks Again for persisting with me!

author: fzabkar
author_rank: Super Contributor
timestamp: September 11, 2021, 03:40:23 am
content: The voltage at the output is controlled by pulsing the inductor with a varying duty cycle at a fixed frequency (Pulse Width Modulation, PWM). This frequency influences the selection of the inductor and filter capacitor.

author: Generalquark
author_rank: Contributor
timestamp: September 11, 2021, 04:07:13 am
content: I somewhat understand, but not fully. Are you confident which part this is based on the scope captures by chance?