Help troubleshooting Elenco FM-88K radio kit - Page 1
Forum section: electronics / beginners

author: dennisEEV0
author_rank: Contributor
timestamp: May 25, 2025, 12:28:47 pm
content: Hi,I just started soldering electronics for the first time and am putting together the Elenco FM-88K radio kit whose manual is attached. I have reached the point in instructions where it asks me to put in a new 9 volt battery and turn the volume control / power knob on to see if the LED (diode D3) lights, but it does not light and there is no indication it is getting any power. I think the problem may be bad connections due to a soldering iron that doesn't heat up properly but wanted to show you photos of what I've soldered so you can point me in right direction.

author: PA0PBZ
author_rank: Super Contributor
timestamp: May 25, 2025, 12:43:39 pm
content: There:You should really improve your soldering, if you think it's the iron get another one.

author: dennisEEV0
author_rank: Contributor
timestamp: May 25, 2025, 07:28:13 pm
content: Thanks, I will try resoldering the part.

author: BillyO
author_rank: Super Contributor
timestamp: May 26, 2025, 03:48:34 am
content: You really need to get a better iron. There are a lot of joints on that board that look like they need a bit of TLC.There are probably a thousand videos on YT showing how to make a proper solder joint. I can only assume you have watched a few of them. If your iron won't do what you see in those videos it needs replacement.

author: watchmaker
author_rank: Unknown
timestamp: May 26, 2025, 12:35:58 pm
content: I have not looked at that kit; but I have gone line by line thru the Elenco manual for the 108 CK (Discrete AM/FM) which I will use for a stem course.That manual has incorrect test instructions and incoherent explanations. It looks like it has been assigned to new employees to "improve" over the years who attempted "cut and paste" revisions to say they got it done; but no one checked the work. I asked Elenco about this and they said that was pretty near the case and asked me for my lab manual and lesson plans when I complete them.So in addition to the soldering videos, try to find some videos of doing the complete project. I think the kits fill a niche, but the manuals for the 108ck often lead to frustration.OTOH, the FM radio of the 108ck is quite good.

author: dennisEEV0
author_rank: Contributor
timestamp: May 28, 2025, 04:41:13 pm
content: Update on problems with the FM-88K kit. I was trying to remove the red LED D3 since I think I soldered it in wrong direction, using soldering braid and a new iron. But one of the leads on that LED completely broke off and I am left with one lead for LED D3. Is there any way to make it still work or will I need a new D3 LED? Photos are attached.On the plus side, I proceeded with the other tests per the manual and was able to get the speaker to click repeatedly by shorting the bottom and mounting pins of the potentiometer / volume control on the foil side with my finger. Does this mean I should have a working radio regardless of the lack of a working LED light?

author: BillyO
author_rank: Super Contributor
timestamp: May 28, 2025, 04:52:30 pm
content: It won't work without that LED. It is not only a power on indicator, it is being used in conjunction with D2 and R1 as a voltage regulator for the receiver IC. Any 3mm red LED can be used to replace it.You can continue on until page 12 in the manual (Testing - Section 2) but you will need to replace the LED before you do those tests.

author: dennisEEV0
author_rank: Contributor
timestamp: May 28, 2025, 05:10:10 pm
content: Thank you for your help. I am ordering new LED now. May I ask if there is correct way to desolder using soldering braid? The reason I accidentally broke the LED is because I was having problems removing all the solder from the LED while reinstalling it, even after carefully applying the braid to the solder, the iron to the braid, and heating the iron past 350 Celsius. The remaining solder still hardened around the lead.

author: BillyO
author_rank: Super Contributor
timestamp: May 28, 2025, 06:04:23 pm
content: On a single sided board, what I normally do is use the soldering iron to melt the solder and extract the part. Once the part is out I'll clean up with the solder braid.It looks like you have lifted a few traces. You'll need to fix those. Get yourself some very thin wire awg-22 or even awg-30 to make bodge wires.

author: PA0PBZ
author_rank: Super Contributor
timestamp: May 28, 2025, 06:07:01 pm
content: I was just going to mention the damaged copper traces, you need to fix those:Maybe it wouldn't be such a bad idea to find an old pcb where you can practice your soldering/unsoldering skills before doing more damage to your project?

author: dennisEEV0
author_rank: Contributor
timestamp: May 28, 2025, 08:15:41 pm
content: The copper traces are needed to conduct current through the parts, right? Can I fix the damaged traces by applying more solder over the damaged parts with copper exposed? I don't understand how awg-22 wiring will help.

author: dennisEEV0
author_rank: Contributor
timestamp: May 28, 2025, 08:20:02 pm
content: Honestly the FM-88K kit is so cheap I wonder if it is better to just order a new kit and use this broken one to practice until I get it right.

author: BillyO
author_rank: Super Contributor
timestamp: May 28, 2025, 08:29:07 pm
content: Sounds like a good idea.

author: MathWizard
author_rank: Super Contributor
timestamp: May 31, 2025, 02:56:22 am
content: Hey Dennis, do you have separate electronics flux to apply, besides what's in the solder ? I can remember my early soldering days, without flux, and once you've tried it, you'll never want to run out. There's different types, but a basic and cheap 'rosin flux' will do, it's often mixed with wax. And then you just dab some onto the surfaces to be soldered, and it basically reacts with some of the oxides that build up on the solder. Depending on the flux and solder, sometimes you have to clean it away after, with Isopropyl alcohol. And especially between tight places, I use my SMD tweers to scrap out gunk.Sometimes before I use the iron, I'll use fine sandpaper to clean old dirty solder joints, like on some old vaccum tube radio.To fix the traces, I would probably cut away the loose part, then scratch off some of the coating of the trace, and then solder in some piece of wire or resistor lead, from the trace to the part lead. Bend it to the shape you want, then put some flux on it, and it will hold it in place before soldering too. And anytime you are joining stuff like this, it's always nice if the both surfaces are tinned 1st, so I'd tin the exposed trace, and maybe the end of the wire/jumper to be used, and then when they are laid on each other, especially with added flux, you can heat the edge of a solder joint, and both tinned surfaces will melt and snap into place.A little piece of wire, can all too easily, get stuck to the soldering iron, or move in a way that you don;t want. So that's why I might pre-shape the wire, and pre-tin the surfaces, and then carefully melt one end, sometimes just enough to tack it, then solder the other end. And depending on the job, you might let it all cool down for a moment, before touching up and reflowing each end again.

author: dennisEEV0
author_rank: Contributor
timestamp: May 31, 2025, 03:13:07 am
content: I've been practicing soldering and desoldering on the old board and I think my problems with burning the board and breaking components is getting worse. As seen in photo, I've completely destroyed the battery holder leads and traces so the battery can't even be fitted anymore. I think the problem is how I'm using the iron. This the second iron I've purchased, and it has variable temp control (https://www.amazon.com/dp/B09TZVLCC7?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1), but I am getting same problem of oxidizing / burning the tip as I did before. Photo of damage is attached.I can't figure out how I'm doing it wrong. I am wiping the still hot iron with a wet sponge every few joints, then adding a few drops of solder to tin the tip. (Using tin rosin core solder included with project). The project soldering guide says to it is recommended to use 700 F or 371 C, I started out using 325 C temp but ended up cranking the heat up to 400 C because I couldn't get the solder attached to board to melt using either direct application of the iron or solder braid.I just got flux and tried dipping the hot iron in the flux to see if it helps remove the oxides, I don't think it helps. I am trying tip cleaner tomorrow, as I've heard trying to scrape the black stuff off with sandpaper destroys the tip.I've been watching a couple videos on soldering starting with this one,and following the instructions as best as I can, but am still wrecking irons. Willing to try anything at this point.

author: MathWizard
author_rank: Super Contributor
timestamp: May 31, 2025, 03:28:43 am
content: No don't put the iron in the flux, IDK how good/bad the tip is, but if it's really burned up, you could use some fine sandpaper on it. But normally just wiping it on scrub pads and keeping it tinned when not in use for more than a few minutes or less, is what I do.What kind of solder and flux do you have? IDK the best temp, but I use 660F all the time, and even that seems a bit high for the flux I use. I'd try 650F and see how that goes, you should notice less flux get burned away, and it takes longer to brown up the iron, and PCB.

author: dennisEEV0
author_rank: Contributor
timestamp: May 31, 2025, 12:36:27 pm
content: I use LF-99 lead free solder (99% tin with 0.031" dia rosin core), and SRA flux # 135, a rosin paste flux. Question about tinning process, do you need the solder to flow over the entire tip for tinning? Because when I do it beads of solder just stick to the tip where I applied it, like in the photo of of my iron I showed you.

author: MathWizard
author_rank: Super Contributor
timestamp: June 02, 2025, 04:58:05 pm
content: Yeah that tip looks horrible, lots of burnt stuff on it, it should be silver. And at least with leaded solder, you shouldn't have much trouble coating the last 1/4" of it all the way around. No wonder you had a had time soldering with it, it would have worse heat transfer too, or maybe that was mostly from dipping it in the flux, but still.I would clean the iron with fine sandpaper, like 600grit. You will sand off some of the good metal, but that's it. Or try scrapping it clean with a knife. The whole thing should be nice and silver. And then try some tip cleaner.I gave up using a wet sponge, I much prefer the scrub pad types for wiping the iron, I find they do a better job too, the water tends to cool the surface to the point the results are inconsistent.

author: BillyO
author_rank: Super Contributor
timestamp: June 02, 2025, 08:09:33 pm
content: I this your new iron?What temperature are you using it at? I've had tips that don't look that bad after 5 years.

author: dennisEEV0
author_rank: Contributor
timestamp: June 03, 2025, 02:33:04 am
content: Yes, that's the new iron I started using a couple days ago. Normally use it at 325 C but I tried increasing the temp to 400 C after I started having problems desoldering using solder wick. I wipe with wet sponge after a couple joints, but the same damage that made me throw away my old iron is appearing on this one. I am now using tip tinner to see if that helps, but I tip tinner only cleans the very tip of the iron, for some reason it does not affect the part of the cone below the tip.

author: BillyO
author_rank: Super Contributor
timestamp: June 03, 2025, 02:35:53 am
content: It could be the solder. Can you show a picture of the label on the solder?

author: dennisEEV0
author_rank: Contributor
timestamp: June 03, 2025, 02:44:55 am
content: I have used two types of solder. First I used the one in the tube that came with the radio kit, then when i ran out the green spool one that came with the new iron.

author: BillyO
author_rank: Super Contributor
timestamp: June 03, 2025, 02:52:44 am
content: Those solders are not beginner friendly, or even good. Even with over 55 years of soldering experience I would not enjoy using them. Not by a long shot.I highly recommend a decent solder. I suggest a 60/40 or 63/37 from either Kester, Mutlicore or MG Chemicals. Choose 1mm or thinner.

author: dennisEEV0
author_rank: Contributor
timestamp: June 03, 2025, 04:32:05 am
content: So I sanded the tip with sandpaper and was able to clean most of the gunk off except at the bottom of the cone. Then I applied tip tinner all around it. Attached a photo of the iron. Would you say it is now safe to use?Edit: forgot to wipe off tinner with sponge, I think it looks better now.

author: dennisEEV0
author_rank: Contributor
timestamp: June 03, 2025, 10:10:15 pm
content: I ordered new MG chemicals solder as suggested:https://www.amazon.com/dp/B071JHLT8Q?ref=ppx_yo2ov_dt_b_fed_asin_title. Hopefully this will fix my problems with desoldering and resoldering components. I don't want to pay for a new iron, but wanted advice on whether the $12 one I am currently using is good enough for a simple student project like this radio kit:https://www.amazon.com/dp/B09TZVLCC7?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1

author: BillyO
author_rank: Super Contributor
timestamp: June 04, 2025, 12:50:37 am
content: I've tested irons like that for friends and they are fine. I even have one around here somewhere. If you get going in the hobby you might want to upgrade, but these are super easy to get cheap tips for as they use the old style Hakko 900 series tips. A million people make them and you can even get NOS Hakko tips on the cheap.

author: dennisEEV0
author_rank: Contributor
timestamp: June 13, 2025, 04:24:14 am
content: I've tried it again with a new board and parts and ran into same problem, the LED won't light. I connected the battery, which I tested with a multimeter showing it has about 9V. I tried measuring the leads from the D2 diode to the D3 LED also with the multimeter, getting inconsistent results, sometimes 1.3V, but never more than 2, when manual says it should be 2.6V. I desoldered the D3 LED with braid and resoldered it after ensuring that the flat end is pointing in the direction the instructions indicate, same problem. Not sure what to do now. Attached photos of both sides of the board.

author: BillyO
author_rank: Super Contributor
timestamp: June 13, 2025, 02:03:24 pm
content: It looks like the LED is in correctly. However. The soldering is still very bad. I honestly do not know how to help you on this. I can only suggest you watch some YT videos on the subject and get some cheap strip board to practice on until you can get nicely flowed solder joints.For instance, those speaker and battery connections - the entire pad you soldering to needs to be flowed over with solder and the the joint should show the solder coming up to cover the attached wire in a smooth convex manner. Not a big Roundy blob. It looks to me like you are not heat the joints adequately to allow the solder to flow properly.

author: BillyO
author_rank: Super Contributor
timestamp: June 18, 2025, 11:30:26 pm
content: I just ordered this kit. I like a nice little kit once in a while. I'll do some pictures and possibly some videos of how it needs to be soldered.

author: radiolistener
author_rank: Super Contributor
timestamp: June 19, 2025, 02:24:35 am
content: Quote from: dennisEEV0 on May 28, 2025, 05:10:10 pmsoldering braid (desoldering wick) is not meant for component removal, it is designed to clean up residual solder after the component has already been removed. For desoldering components like LEDs, a solder sucker (desoldering pump) is intended. It allows you to quickly remove molten solder from the pads and leads.Also, it’s critical not to overheat the PCB. Exceeding iron temperature over 300 °C or maintaining contact with the soldering iron for more than 1 second can easily lift or burn the copper traces, especially on consumer-grade boards. When desoldering without a pump, it’s possible to remove components by heating all the leads simultaneously, quickly melting the solder, and gently pulling the part out, but again - avoid prolonged heat.Avoid keeping the soldering iron in contact with the PCB pad for more than one second.Before soldering, generously apply flux to the pad. If the pad is not pre-tinned, tin it first. Don’t skimp on flux - soldering without adequate flux leads to oxidation on the surface, which prevents proper wetting and results in poor solder joints.Similarly, pre-tin the component leads before soldering by applying plenty of flux and running a soldering iron with solder along the leads.After soldering, you can clean off the flux residue using alcohol (96% ethanol or isopropyl).Given the challenges you're experiencing with PCB soldering, it would be beneficial to first build up your skills by practicing on wire-to-wire soldering, without using a PCB. When I was learning, we had a dedicated soldering course where we practiced by creating wire frameworks and meshes using ~0.5 mm copper wire. These included loops and junctions to which other wires were soldered and branched out. This kind of practice helps develop precise soldering technique and better heat control before moving on to delicate PCB work.

author: radiolistener
author_rank: Super Contributor
timestamp: June 20, 2025, 05:16:52 am
content: Quote from: dennisEEV0 on June 13, 2025, 04:24:14 amFrom your photos, this doesn’t appear to be proper soldering - it looks more like random blobs of solder placed on the pads, and notably without any flux. It’s clearly visible that no real solder joints were formed - just solder drops sitting on the surface.Before moving on to working with PCBs, I strongly recommend practicing soldering with wires first. This will help you develop the necessary hand control and understanding of how solder behaves.Also, an essential aspect you’re overlooking is the use of flux. It’s absolutely critical for proper soldering. If you have solid rosin, dissolve it in 96% ethanol or isopropyl alcohol to make a thick flux solution, and apply it generously to the soldering area before soldering.Always ensure the solder fully wets the surfaces being joined. A proper solder joint should look smooth and flow evenly over the contacts, not sit on them like a loose droplet.