HM5033 Repair

On Ebay I found this portable spectrum analyzer which was sold as defect.
I made a bid on the unit and to my surprise the bid was accepted.

When the unit arrived it showed no damage on the outside so I connected the main power supply and started to see what it was doing.

It was not working and only showing two horizontal lines on the display and further nothing.

I tried to search on the internet to see if I could find some schematics of the unit, but that was a fail, I only found an operation manual but that was not helping me much in this phase.

I opened up the unit and made an thorough visual scan to see if I could find anything suspicious.
I found the measuring points and decided to measure the voltages indicated on the printed board,
one showing 12 Volts DC and the second showing 5 Volts and a third 3,3 Volts DC

Measuring these measurement points showed that the 12 Volt and the 5Volt was present but the 3,3 Volt was failing.

That was a first start.

I further examined the board but did not find components related to the 3,3 Volt failure.

Not sure what to do I decided to build out the main board and see if there were components on the other side of the board.

After lifting out the main board I found another small board below the main board looking more like a power supply board.

I did also remove this board from the housing and suddenly I found on the housing a small black spot like something had burned at that place.
Looking at the power supply board on the same place opposite to the burned spot of the housing I also saw a burned spot which was a blown Mini SMD Integrated Circuit.

So the place of the defect was found, now I had to find out what the blown IC was.
Trying to look for a component type was not easy, I could see some indication on the burned and blown SMD component but it was not possible to read.
I took my microscope and looked at the blown SMD under large magnification. still impossible to read a full type number.

With a strong light moving from left to right I was able to read most part of the type number but that was still uncertain if it was correct.

I started looking on the internet if I could find a component with that type nr I read. After some search I found the component MAX1692EUB being a switched step down regulator

Still not convinced that this was the right component I tried to check surrounding components to see if these would fit to the typical operating circuit as shown on the data sheet from this regulator.
I found that most components surrounding the blown circuit were similar as shown in the typical operating circuit so I was almost convinced that this was the right component to replace.

I further investigated all boards if I could find more blown components because I did not have any clue why the MAX1692EUB had blown. After a intensive search I found nothing suspicious but off course one cannot be sure if the problem was caused anywhere else in the unit. I decided I would give it a try and see what happened if I replaced the blown MAX1682EUB

I started to look if I could buy this MAX1692EUB and found it at Farnell and ordered two of them.

A few days later they arrived and now it was time to unsolder the blown part and replace it with a new one.

That was a special thing because this IC was a mini SMD component and I did not have experience in soldering these.

I had to do this job using my Weller WECP20 soldering iron, a bit big for this work.

I first tried to unsolder the blown component which went quite well, cleaning up the solder tabs and then started mounting the replacement part.

With the help of the microscope I soldered the MAX1692EUB SMD IC into the board and after that I visual checked a few times if all pins of the component were correctly soldered. I did not thrust all soldered pins and resoldered a few again and again checked visual with help of the microscope.

I was happy with the result and remounted the power supply board in the housing and then the main board with all cables connected  and checked if all looked correct.

Then was the time to see if it was working or not, I connected the main power supply and pushed the on button. I heard a beep and saw the screen illuminating and responding with a spectrum analyzer display, woow it worked.

After that I did some first acquaintance on the operation of the HM5033 and it impressed me how nice it worked.
Charging the installed batteries learned that these were not very fine anymore so I replaced batteries also and then the repair of this unit was a fact.

Since then I did not have anymore problems with this Spectrum analyzer and it's working just fine.