Jaycar MP3098 20amp linear 13.8v - She dead. - Page 1
Forum section: electronics / repair

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: March 14, 2022, 06:07:18 am
content: Excuse the partially dismantled pics.PSU will output 13.8volts until any load is applied.A 100 ohm resistor load results in 8volts output.Apparently its meant to have short circuit protection, I suspect this has gone bad, but don't understand how this has been implemented.I suspected bad output transistors, hence the part that's freeballing.I also suspected bad rectifier diodes, they refused to measure in circuit.I've also replaced a handful of passive parts, which made no difference. (trimpot, the TO220 transistor on the controller board, and the resistor driving it (as it was discoloured) as well as the electrolytics on the controller board)HALP! - loads the part cannon

author: m3vuv
author_rank: Super Contributor
timestamp: March 14, 2022, 06:34:53 am
content: what is the to220 driver,tip 42 etc?,have you tested that out of circuit,is there only one 3055?

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: March 14, 2022, 06:42:37 am
content: Quote from: m3vuv on March 14, 2022, 06:34:53 amThat's what I was wondering. 20 amps seems ambitious.

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: March 14, 2022, 06:47:10 am
content: Quote from: m3vuv on March 14, 2022, 06:34:53 amIt was a 2SD313.I've replaced it with a TIP41.The TO220 transistor drives the single 3055, that drive the 4 MJ15003 that are all directly in parallel on the heatsink on the back (not pictured)Sorry I didn't make that clear to begin with.

author: m3vuv
author_rank: Super Contributor
timestamp: March 14, 2022, 07:09:40 am
content: with a load on the psu output,does the 2sd313 output drop to zero too?

author: m3vuv
author_rank: Super Contributor
timestamp: March 14, 2022, 07:10:44 am
content: looks like a discreet control board as cant see a 723 reg etc?

author: m3vuv
author_rank: Super Contributor
timestamp: March 14, 2022, 07:12:41 am
content: how did you kill it in the first place?

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: March 14, 2022, 07:25:47 am
content: Quote from: m3vuv on March 14, 2022, 07:09:40 am8ohm load on the output, drops the voltage to basically nothing.Collector has 28volts.E and B have ~200mv.

author: madires
author_rank: Super Contributor
timestamp: March 14, 2022, 11:10:34 am
content: Possibly TL431 based, i.e.classic power Zener circuit with a Darlington stage (2SD313 & 2N3055) driver for the pass transistors (MJ15003). The short circuit protection could be simply a shunt resistor plus a BJT which drains the base current of the Darlington stage or triggers a small SCR to do that. I'd check the TO92s.

author: floobydust
author_rank: Super Contributor
timestamp: March 14, 2022, 05:27:56 pm
content: This power supply resembles Samlex linear builds, there is overload protection that makes them confusing to troubleshoot and repair. There is no output current-sense using resistors in the traditional method.Instead, any output voltage sag or loss of mains AC, trips a one transistor latch and shuts down the DC output. To reset it, you have to remove AC power, wait for the filter cap to discharge. If the latch circuit has tripped, you can spend a lot of time poking around getting nowhere.There is no luxurious TL431 that would cost millions $.I drew a schematic of the Samlex SEC-14 13.8VDC 10A power supply here. OP check what your regulator board is about, it looks like a similar circuit.The Samlex RPS-1220 13.8VDC 20-25A(pk) power supply is the same control board and extra pass transistors.

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: March 15, 2022, 08:34:21 am
content: Quote from: floobydust on March 14, 2022, 05:27:56 pmThanks for the descriptive reply! Somehow, by searching for "Samlex", I ended up finding alternative branding for this power supply, and therefore, the schematic!(Turns out Jaycar also has the schematic attached to the product webpage for the 10amp PSU)I'm considering replacing all the passives on the controller board, and they're worth nothing anyway...

author: floobydust
author_rank: Super Contributor
timestamp: March 15, 2022, 11:40:37 pm
content: I forgot to mention the second trap with these power supplies.One, is they latch off if the output voltage drops, until you cycle power.Two, the main filter capacitors then stay charged up, there is no bleeder resistor so you can make sparks messing around with the pass transistors. They will have juice on them. So check the voltage on the filter capacitors and discharge them before going in.Also, for better regulation I think you could stuff in a TL431 in place of V31 and change the resistors/pot values accordingly.

author: jord4231
author_rank: Regular Contributor
timestamp: June 15, 2022, 11:52:25 pm
content: At least yours had the transformer output soldered to the board!

author: floobydust
author_rank: Super Contributor
timestamp: June 16, 2022, 12:07:41 am
content: I think these are assembled in some remote village. The power transformer looks like kids wound it.Similar soldering (think of all that solder saved!) but all filter capacitors took the piss on this Samlex. 4,700uF 25V parts running at around 23V but other caps spewed black goop, at least they did not vent. These are really cheaply built.

author: jord4231
author_rank: Regular Contributor
timestamp: June 16, 2022, 06:06:42 am
content: Did you end up getting yours going in the end?I just purchased mine last night and am going to do a full rebuild on it before use.

author: floobydust
author_rank: Super Contributor
timestamp: June 16, 2022, 05:48:24 pm
content: The same circuit is used in many brands and scaled from 5-50A supposedly. I had a Samlex and fixed it OK.To troubleshoot one, I would disable the protection latch. That transistor is normally on all the time, unless an overload or AC mains is lost, then it latches off. I lifted a leg on the 5.1k R3 that also goes to the diode to disable it. That way you can take measurements.I did swap in a TL431 for much better regulation. But these power supplies are not really short-circuit protected or suitable for charging batteries.If I had to do it again, I would change over to one of those cheap variable PSU board kits "0-30V 2mA-3A" to make a bench power supply out of it, toss the old control board.

author: Sandplough
author_rank: Newbie
timestamp: July 10, 2022, 02:24:01 pm
content: I am following to find out the outcome.I also follow jord4231's Youtube channel to see his repairs and mods, I purchased one a while ago for a pineapple ($50AUD for non Aussies due to colour) at Jaycar thinking it was just a clearance/return/discontinued etc, it had been dropped but nothing to important appears broken, I only found that out as I had to open it up as I could hear a screw rattling around, no external damage, one external screw torn out from voltage reg plastic bracket and rattle was another internal screw for voltage reg bracket, it managed to actually bend the transformers feet.I found this while googling,http://ct2ggx.blogspot.com/2016/07/restauro-e-repacao-da-classica-fonte.htmlKPS1330Looks like an old MP3099 (you can find a failed about them on an Aussie Ham radio forum), not much info on it, the brand name Kiotto looks like a piss take on Kyoto Denkiki power supplies, especially if someone told the noob like me to buy Kyoto and I misspelt as Kyoto on the search back when that was new.Search engines have improved a lot, I used to use Copernic as a necessity to find the obscure things I searched for (I miss the saved searches).Imagine search and see all the rebranded or slightly changed versions.https://www.akribis.co.uk/bench-hq-power-supply-ps1306https://www.velleman.eu/products/view/?country=es&lang=en&id=340477https://www.telectronics.gr/product/df-1765s/https://www.acdcpowershack.com/products/13-8vdc-20a-dc-regulated-switching-power-supplyEven mwave used to sell a rebranded version.https://www.mwave.com.au/product/138-volt-30-amp-dc-power-supply-aa82407I haven't had time to check this against Jaycar's schematic.

author: jord4231
author_rank: Regular Contributor
timestamp: July 29, 2022, 09:38:20 pm
content: Thanks for following the channelI will be doing another video on a crow bar and some mods soon

author: Ruthenium
author_rank: Newbie
timestamp: August 17, 2025, 01:49:11 am
content: I just finished repairing two of these with the exact same symptoms as the original poster. Posting here in case it helps someone else with the same problem. Just to confuse the issue further my version of the PCB has a different part identification numbering than the published circuit diagram, I have put the PCB identification (at least on my PCB version) in brackets.The over current relies on the voltage drop being detected and tripping V30 (V7) to turn off, when that happens current flows through R3 (R3) and V29 (V5) to the base of V31 (V8) and shuts off the output driver.The funny thing is that it will stay in this state until you power down completely to reset the latch.There remains a problem however, exactly how does the thing start up in the first place and turn on V30(V7)? There is a diode V19(V2) that feeds a 3.6V zener V20 (V3)via a 220R resistor and generates a pulse on power up that couples through C8(C6) that turns on the base of V30 (V7) via diode V21(V4), once V30(V7) is turned on the output stage can start to regulate.So the nett effect is a short delay on power up and maybe that stops the initial inrush current from overloading the array of 2N3055'sdunnoDownsides to the design are... running diodes in parallel is generally bad design practice, as is running 2N3055's without emitter resistors, but thereal killer for me is the lack of overvoltage protection. So I will be fitting crowbar protection.The fault symptoms were the output voltage was dropping with very light loads, a small current load would drop the output voltage to just a few volts. Same fault on both power supplies the fault turned out to be a bad transistor V28 (V9) had a bad base emitter junction. Replaced the 3DG9014 with a 2N3904 ( same pinout higher current). And now both are working again.

author: Ruthenium
author_rank: Newbie
timestamp: August 17, 2025, 03:50:45 am
content: jord4321 has a great couple of video's on his youtube channel about this power supply.https://www.youtube.com/@VK3ACUNow following jord4321's youtube channel and have ordered his crowbar PCB's from JLC. $3.60 for 5 including shipping...