Tenma 21-147 soldering station repair - Page 1
Forum section: electronics / repair

author: crazyjim30
author_rank: Contributor
timestamp: April 02, 2016, 03:46:48 am
content: I was given a Tenma 21-147 soldering station. The unit turns on but the iron doesn't heat up at all. I'll start the repair by seeing if there is power to the iron. If so, time for a new iron. If not, further troubleshooting will be required.I would like to see the schematics for the unit. My Google Fu has failed to produce a set. Does anyone here have a copy?Sent from my SM-G900V using Tapatalk

author: crazyjim30
author_rank: Contributor
timestamp: April 03, 2016, 01:26:39 am
content: Well. I guess the Tenma gets no love. Oh, well. Moving on to repair report #1.Step 1 was opening the case.Step 2 was tracing the power from the cord through various cables to make sure there's power to the iron. There is. I was quite surprised to find that the voltage is full bore 120V. I thought that iron would be powered through one of the boards. How did I figure out the voltage , you ask? I slipped with a probe, briefly shorted two of the contacts, and made pretty sparks.?After finding out that there's power to the iron, I moved on to the pot that the temperature knob turns. Its a 1K pot that almost, but not quite, out of tolerance. I'd call it pretty good for something that was installed in the early 80's.The connector from the transformer to the main board is loose. I guess I'll be replacing that cable at some point.Conclusions so far: I need a new iron to get the unit working to the point where I can decide if the loose connection is worth worrying about or not. Parts on order. On to pictures!Main board of the unit, with the transformer out of the case and partially in the picture at the bottom.Sent from my SM-G900V using Tapatalk

author: Seekonk
author_rank: Super Contributor
timestamp: April 03, 2016, 07:13:31 am
content: Is the transformer 24V? Element still have continuity? Those replacement Hakko clone heads aren't bad for $3 even if under powered. A nice pencil point. Always good to have a second iron.

author: stj
author_rank: Super Contributor
timestamp: April 05, 2016, 10:55:25 pm
content: made by ZHONGDI.http://www.china-zhongdi.com/it's a ZD-929Bthat's a 24v iron on those, i made a schematic years ago of the digital version. (ZD-929C)these may help.

author: Hydrawerk
author_rank: Super Contributor
timestamp: April 05, 2016, 11:36:38 pm
content: Is there a zero-crossing circuit?? I do not see any!

author: stj
author_rank: Super Contributor
timestamp: April 06, 2016, 12:14:50 am
content: Quote from: Hydrawerk on April 05, 2016, 11:36:38 pmno, no snubber or anything either - just the essentials to make it work!

author: crazyjim30
author_rank: Contributor
timestamp: April 06, 2016, 06:59:42 pm
content: Thanks for the responses. My new iron has arrived and that has resolved the issue. VICTORY IS MINE!!!!!Sent from my SM-G900V using Tapatalk

author: stj
author_rank: Super Contributor
timestamp: April 06, 2016, 09:36:43 pm
content: good.one thing to keep in mind - those units bake the electrolytics in them - at some point you will need to re-cap it with 105' caps.

author: crazyjim30
author_rank: Contributor
timestamp: April 06, 2016, 11:43:13 pm
content: Good point. I'll keep that in mind.Sent from my SM-G900V using Tapatalk

author: Hydrawerk
author_rank: Super Contributor
timestamp: April 07, 2016, 04:25:08 pm
content: Are these Solomon soldering stations also made by Zhongdi?http://www.soldering.com.tw/Did Zhongdi buy the licence or what?

author: stj
author_rank: Super Contributor
timestamp: April 07, 2016, 05:39:51 pm
content: Solomon may be clones - licensed or otherwise.or resellers.looking at the Sorny Roong link you osted, some of those stations look like a copy of old zytronics and other designs.