Yihua 948 suction upgrade - Page 1
Forum section: electronics / repair

author: GRFixedGear
author_rank: Contributor
timestamp: February 09, 2024, 02:17:31 am
content: Working on some stuff recently I got very annoyed that the Yihua 948 solder sucker doesnt suck hard enough. I've seen posts related to putting holes in the side of the thing to exhaust the air more directly. I've seen posts related to changing out the vacuum pump. I took a slightly different approach to it.When studying the circuit layout, I arrived at the attached schematic. Its not quite accurate but more about that later.Gripe #1 about the circuit: The 500 ohm resistor and the small sot-23 NPN transistor are fighting each other whenever the pump isn't running. The 500 ohm resistor is mean to provide the base current for the Darlington when the pump is running, but all other times the 30-something milliamps through that resistor are going straight through the tiny transistor. Wasteful and making that little transistor hot hot hot.Gripe #2 about the circuit: Lots of voltage drop from the supply through the Darlington, yielding only ~10.2V at the pump. Not great when we've got 16V available on the board. I tested the pump from a bench supply from 10 up to 17V and it seemed happy enough and had much more chooch at the higher voltagesSchematic problem #1: I depicted the small-ish electroytic cap on the board across the supply rail. Thats not where it lives. The one on the board goes across the motor terminals. Probably for handling some of the noise from the brushed motor?Schematic problem #2: The black diode body shown still on the board in the "parts removed" photo is a Zener that was apparently limiting the base voltage in the original. I ended up removing that too as it will interfere with the Gate voltage of our P-channel replacement going all the way high and shutting off the transistor.So the approach:- remove the 500 ohm resistor- remove the small NPN transisor and bridge the two terminals to pass the signal from the opto directly to the gate of our P-channel- remove the zener diode- remove the NPN darlington transistor- remove the heat sink to give room to work and put the P channel FET on caddywumpus- LEAVE the 100K pullup on the output of the opto / gate net. This is the shutoff for the P channel- Place a P channel FET of appropriate ratings in place of the darlington - but you have to reverse the source and drain terminals. I crossed them over but I suppose just as easy would be install those backwards and bridge the low-current gate signal around to the through hole that originally held the Base of the Darlington.- I added a 470 and 10uf cap on the supply side of the 500 ohm resistor that was removed and tied the ground side to the low terminal on the opto just next door - This is probably optional but I liked the idea that we wouldnt be completely losing the voltage on the output with every cycle of the 120hz diode bridge output. 500-ish uF may or may not be enough to accomplish that goal. Circuit sims suggested 1mF or more would be better.Two photos attached of the after condition. One from off the edge of the board looking in at the transistor. The other looking outward from the center of the board to the output side of the opto where the caps were added.Testing on a live project still pending. Also, long term durability of this is TBD since I just finished the mod, but wanted to share with the group.Happy tinkering -Jason

author: GRFixedGear
author_rank: Contributor
timestamp: February 12, 2024, 04:24:16 pm
content: Rework pending to add more capacitance (and a NTC for inrush limit) and less-hokey soldering in of the FET. Will post an update when that stuff is done.

author: mikerj
author_rank: Super Contributor
timestamp: May 09, 2024, 04:22:18 pm
content: Just been given on of these and found this thread. How did this work out in the end, did you keep the magic smoke within pump motor? The Zener diode is the main limit for the motor voltage, it's forming a simple shunt regulator and the darlington provides current gain. Just removing the zener should give a significant increase in motor voltage.

author: aiyiadam
author_rank: Newbie
timestamp: July 05, 2024, 07:51:40 am
content: I have a 948 III. This thing seems to have a much better quality then the other alternatives and there is a lot of space inside for some mods.. I haven't tested it much, but the suction power could surely be improved. The shape of the spring in the gun could also be lowering the suction a bit.. It has a linear power supply and the transformer seems to be a bit tiny for the soldering iron, gun and the vacuum pump...Anyways.. I was thinking about installing a 12V SMPS just for the pump and use the 10V to switch on a power relay.

author: aiyiadam
author_rank: Newbie
timestamp: July 08, 2024, 05:37:00 pm
content: Done.. I have installed a 2.1A 12V Meanwell and set the voltage at 13V (At 13V the maximum current seems to be ~0,8A.). Now this sucker really works much better.

author: jpanhalt
author_rank: Super Contributor
timestamp: November 29, 2024, 08:09:28 pm
content: Yes, this is an old thread. Let me chime in.I bought a Yihua 948 a few weeks ago. Suction was poor. I measured only about 10.5V open circuit at the terminals to the pump and was considering adding a DC supply switched by an N-channel mosfet driven by the 10.5V. Then the switch on the "gun" failed. Of course, the link to Yihua was helpless, so I returned to the seller for a new unit. It seemed to work better overall. The most noticeable thing with the new unit was the suction was greater. I opened it, and the OCV was 11.8 VDC.Advice: Go by whether it works, not what you have read. I can't see any internal differences from the first version. Maybe it is due to device tolerances or maybe Yihua modified the code. I don't have a clue.

author: F4
author_rank: Contributor
timestamp: November 30, 2024, 01:16:30 pm
content: I have 2 Yihua 948s each with a different problem out of the box.Unit 1: cannot find a way to wake it up from sleep mode. I need to power it on and off every time.Unit 2: Iis super heating and making the gun tip red hot while very slow to "heat up" according to the display reading, and never reaches "working temperature" with the beeps despite being red hot. I have 2 guns, so tried the 2nd with the same result. The problem is inside the housing and something seems amiss in the temperature sensing.Can anyone that has opened one of these point me in the right direction to debugging either issue?

author: F4
author_rank: Contributor
timestamp: December 01, 2024, 12:19:26 pm
content: Following up on the overheating unit...Since the large chip is socketed I swapped them out between the two units and the problem went to the working unit, the broken unit now worked so it's this chip.The chip is a SAM88RCRI (S3F94C8E22-DK98)Datasheet:https://pdf.datasheetcatalog.com/datasheet/SamsungElectronic/mXrttxq.pdfInstruction set:https://datasheet.octopart.com/S3F9454BZZ-DK94-Samsung-datasheet-17925212.pdfDoes this chip have programming on it, or is its memory just to store settings like C or F, sleep timers, etc? If no programming, I can buy a new one. If it does have proprietary code, can I clone the known good chip onto a new SAM88RCRI? I am unsure what the options are.

author: F4
author_rank: Contributor
timestamp: December 01, 2024, 01:38:01 pm
content: Quote from: F4 on December 01, 2024, 12:19:26 pmAfter digging a bit more online, turns out there is a temperature calibration that can be performed. I tried it just in case and it worked. Hold down the up and down buttons at the same time for 2 seconds, the current set temp will then have dots next to the numbers, adjust the temp to what the nozzle actually reads, then press up and down again to set.I ran it first time and jacked it as high as it would go hoping it would stop the red hot overheating, and it did.Afterwards, I ran my FLIR One on the iron tip, measured about 30 degrees C off, after the adjustment, the unit is working correctly.Note on the FLIR One... there are 2 temp ranges in settings, you need to use the higher one as the other goes to like 200 C which is not high enough.

author: jpanhalt
author_rank: Super Contributor
timestamp: December 01, 2024, 01:44:15 pm
content: That chip is apparently similar to if not identical to Zilog as discussed here:https://www.eevblog.com/forum/microcontrollers/samsungzilog-s3f94c4-programming/http://www.zilog.com/docs/PS0315.pdfIt's an 8-bit MCU, but I have no experience with that series. The instruction set is pretty simple. It is likely to be read protected. Section 13 of the second link describes programming modes. If a special tool is required, the cost of that tool may be more than the cost of the Yihua 948.

author: Poroit
author_rank: Frequent Contributor
timestamp: December 02, 2024, 06:07:38 am
content: G'day All,All the replies to the OP's post relate to the electronics.Have you taken into account O-Rings, Seals etc in the Gun and Pump that can degrade over time?

author: jpanhalt
author_rank: Super Contributor
timestamp: December 02, 2024, 11:20:11 am
content: You are correct, these comments have focused on initial performance and quality. That was their purpose, just as it seems to be for most product reviews.As the initial product includes several spare parts, I suspect they are wear items. Amazon currently lists many of them individually. The gun is about $30. Who knows what availability will be in a few years? I wouldn't count on much. It was a bit of a surprise even to see replacement parts available today.

author: Poroit
author_rank: Frequent Contributor
timestamp: December 03, 2024, 07:20:56 am
content: G'day All,Attached is what I would like to see a teardown of.There should be a diaphragm and valves inside that will affect the suction as parts degrade.Is there a brand or model on the top of the pump?Are there any internal filters in the Suction Hose?

author: jpanhalt
author_rank: Super Contributor
timestamp: December 03, 2024, 11:57:31 am
content: So far as I can tell, everything having to do with gas flow control and filtering is in the gun. The instruction sheet shows what's user serviceable. The main unit has an air pump that is clearly visible in the pictures posted before my original post (light blue cylindrical thing with inlet and outlet). There's a large transformer and wires from the 12-V winding go to the main board. That voltage is rectified and switched to control the pump. Apparently, there is some voltage control that the 8-bit MCU may have a part in. That last assumption is based on my measure of the OCV on two different units. Yihua has mentioned "improved" units, a part of which may just be upgrades of the firmware as virtually every review of the earlier units mentions poor suction.I considered reversing the hose connections to the pump and making it a pressure rather than suction gun. Generally speaking when cleaning, I use vacuum. However, pressure works at a greater distance and is more effective at removing dust and drying stuff.

author: DBaje
author_rank: Newbie
timestamp: May 28, 2025, 09:58:05 pm
content: Wouild you happen to have the full schematic for this unit? I can't get my pu,p tp stop running and it's not the switch...

author: jpanhalt
author_rank: Super Contributor
timestamp: May 28, 2025, 10:47:33 pm
content: I do not have the schematic. If you are sure it's not the gun, then I don't know what the problem may be. Amazon sent a second unit and that works fine so far as is. One thought I had, but did not investigate further was blowing, rather than sucking.

author: the Chris
author_rank: Regular Contributor
timestamp: June 13, 2025, 08:07:22 pm
content: After the replacement of all input encoders on my LC584, I was fed up enough with a manual pump to buy one of these until budget allows for a Hakko. As described before, suction power leaves room for improvement and my pump measured only 10.15V on its terminals. I combined the suggestions of jpanhalt and aiyiadam and installed a Meanwell RS-25-12 driven by a Vishay IRFP240 NMOS asa) it takes 1A without a sweatb) works great with 10V gate voltagec) can be mounted directly to the case floor via one of the unoccupied holes using an M3 screw and a bit of thermal pasted) I had one left lying aroundI went with R1k for gate current limiting and R82k as pulldown, latter just because I found it quicker than the 100k ones. There should be nothing critical regarding timing so I just went by rough approximation.The pistol works a lot better now, certainly worth the time and money for the upgrade. I still have to build a proper holder for the PSU, but that should not pose a problem considering the large free space inside the Yihuan.

author: jpanhalt
author_rank: Super Contributor
timestamp: June 13, 2025, 08:33:53 pm
content: That approach worked fine for me, but the new one from Amazon worked out of the box with anything that was not a tight fit, as 0.025" sq headers are. I haven't bothered to add the Meanwell supply and NMOS yet. That seems like the simplest mod.