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Old 2nd Jul 2022, 4:25 pm   #61
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Default Re: Samsung 3 band radio cassette, model: STF55L

Oh forgot to mention when you solder that track after using super glue don't get yourself too near to it as the glue can give of cyanide gas, so do this in a very well ventilated area. We don't you having any issues from fumes. There are probably other suitable adhesives but whatever you use it wants to be a rigid repair and as strong if not stronger as the pcb material, and remember that a lot of glues will gas when hot.

Dave
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Old 2nd Jul 2022, 6:28 pm   #62
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Default Re: Samsung 3 band radio cassette, model: STF55L

Hi Dave, The area where the PCB is cracked was very difficult to push back together in place and now seems quite firm and rigid –so I did not glue it, does it need to be glued? I like the idea of the paint for the PR1, component side crack, what type of paint would silver loaded paint be? I’ll desolder the track side of the repair and do what you said re; solder a small wire across. I’ll try all this tomorrow (Sunday),

Cheers Dave… Malcolm
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Old 3rd Jul 2022, 11:06 am   #63
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Default Re: Samsung 3 band radio cassette, model: STF55L

Hi Malcolm, Yes ideally the pcb needs to be glued and they can be a little awkward to push back into their original position. The reason for glueing is twofold, firstly to keep the pcb stable at that location and secondly to prevent the crack from extending due to flexing. Temperature and movement of the complete radio cassette can both cause the pcb to flex thus causing the pcb crack to grow in length over time.

An unstable pcb crack will also cause the silver paint thats across it, to fail at some future stage.

You could try to let the glue go into the crack by capillary action after you've soldered the wire across the cracked track but it is usually better to put the glue in first for a better fix. You normally would flex the pcb to open the crack a bit and then put the glue in, then when it goes back into correct position after a little manipulation some of the glue will be pushed out of the crack. The excess glue can be wiped away.

Also the wire needs to be solid core and not flex. Solid core will also help to stabilise the break. In some cases where a crack has appeared it is possible to drill a small hole at the very end of the crack, this will stop any crack from spreading further. I don't think that your pcb will be suitable for the hole method though.

The paint is a special type as it is silver loaded conductive paint. It's usually sold in small quantities of 5mL and can be rather expensive, depending on where you obtain it from. Silver acrylic or enamel such as Humbrol is not suitable.

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Old 3rd Jul 2022, 11:53 am   #64
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Default Re: Samsung 3 band radio cassette, model: STF55L

Hi Dave, Well… the continuing saga of the Samsung continues… I looked at the crack and was concerned that if I opened it a little to put glue in it might split further (knowing my luck), so decided to leave well alone, and to leave the solder that was in place as that was helping to secure it. The crack really feels quite secure and rigid. I did solder a piece of wire over the crack on the track side OK. I might have over tightened that screw on the holder a little too much when I was looking at the plastic holder for the pulley wire weeks ago. Talking of the pulley wire in the process of unsoldering the VC1 pin, which went OK and the ohms reading is 1, I managed to catch the wire and it is now cut…. So if we, or perhaps I should say YOU, manage to get it working I will have to get another pulley wire.
So another task completed, what do you think Dave? THANK YOU very much for your help again.
Cheers… Malcolm.
PS. I will have another look at the crack to see if I can put some glue in it and about the paint I have some silvercoat reflective roof paint, that probably won't be any good either...would it be cheaper to buy that 330ohm resistor?
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Old 3rd Jul 2022, 12:02 pm   #65
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Default Re: Samsung 3 band radio cassette, model: STF55L

I've just had a look on amazon and they have some "Conductive Silver Glue Wire Electrically Paste Adhesive Paint Pcb Repair" a small thin hypodermic syringe for around £3... would that be any good as it would be a quicker repair, and probably cheaper?
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Old 3rd Jul 2022, 12:21 pm   #66
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Default Re: Samsung 3 band radio cassette, model: STF55L

That will repair the cracked silver paint track on the component side but not the solder side. Also you can't use it as a replacement for the glue needed to hold the pcb crack together. Don't put much on/in the top side crack and let it dry before going over it again. You can use a cocktail stick for applying the silver loaded paint. Once you've done the paint you can measure across it with the meter on ohms using both meter leads (one either end of the crack), you get a zero ohm reading which means that the paint repair was successful.

One thing to check though is that the paint is conductive through it's adhesive, as this paint is designed to put on a surface where there was no track previously. Personally I would look for the silver loaded conductive paint without the adhesive.

I don't think this will have aby effect on the short circuit readings that you have on the pcb as a crack would normally make an open circuit reading. It will however need to done to get the circuit tracks working on the component side of the pcb.

You still need to un-solder that corner pin of VC1, I reckon that once you do that and make sure that the pin is not touching the pcb track that the short circuit will disappear from the pcb but remain on the corner pin of VC1. This will confirm if VC1/TC1 is at fault or not. As it's a capacitor it should read open circuit on your test meter. Any lower resistance reading infers that VC1/TC1 is at fault. To measure that pin put the black meter lead to the metal switch body and use the red meter lead on the pin. Your meter should not change from the '1' for open circuit.

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Old 3rd Jul 2022, 12:54 pm   #67
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Default Re: Samsung 3 band radio cassette, model: STF55L

Hi Dave, Yes I did that on the VC1 corner pin and the reading was the same... 1 ...it didn't change. The paint syringe says conductive, I've checked and they all say the same. I was only thinking of the component side PR1 for the paint anyway and will try the glue on the track side. Cheers Dave, Malcolm.
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Old 3rd Jul 2022, 5:46 pm   #68
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Default Re: Samsung 3 band radio cassette, model: STF55L

OK Malcolm lets see what the situation is once you've effected all the remedial repair work. Just bear in mind that the adhesive in the paint might not be conductive, so you could get the situation where the paint top surface is conductive but the adhesive prevents the new paint from conducting to the original track. It might of course be perfectly OK and I hope that it is. I just don't want you being caught out and thought that I'd mention the possibility.

Dave
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Old 5th Jul 2022, 8:13 am   #69
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Default Re: Samsung 3 band radio cassette, model: STF55L

Hi Dave,
Hope you’re well. I’ve ordered the ‘silver paint’ (arriving in august Coming from China)…
(1) ”Conductive Silver Glue Wire Electrically Paste Adhesive Paint Pcb Repair 0.3Ml Multicolor”
But I noticed another which might be the one you were talking about…
(2) ”Universal Quick-drying Type High Concentrations Conductive Silver Paint Conductive Silver Paste Keyboard BGA Pad Repair”
Would there be any chance that you could check them out on Amazon as they have a description about them further down the page? I’m sorry to ask you but you seem to know about this paint. Thanks Dave very much. My best regards… Malcolm.
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Old 5th Jul 2022, 2:19 pm   #70
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Default Re: Samsung 3 band radio cassette, model: STF55L

Hi Malcolm,
The second (2) sounds the best choice between those, especially as it specifies keyboard BGA pad repair. Keyboard repair is like what you are doing with the radio pcb.

The problem with the adhesive type is that the adhesive sinks to the bottom and adheres to the substrate material but the silver paint floats on top and thus doesn't always conduct to the substrate below the adhesive, hence my concern.

Hope that helps.

Dave
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Old 5th Jul 2022, 3:24 pm   #71
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Default Re: Samsung 3 band radio cassette, model: STF55L

Dave, that helps a lot, many thanks, I will order that one (2) as the other one is already on it's way.

Best regards, Malcolm.
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Old 6th Jul 2022, 9:08 am   #72
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Default Re: Samsung 3 band radio cassette, model: STF55L

Hi Dave,
While I’m waiting for the silver paint to arrive I thought I might have a go at replacing the station indicator pulley string that I accidently cut while desoldering the pin on VC1(mentioned in post 64). Would fishing Braid line be OK, as we use it when sea fishing? It’s very strong and will not stretch, it has wire wrapped around the mono line. If not could you tell me where I could get some from as I’ve had a look online and could not see any? Any tips on putting the string on? I thought I would measure where the red station indicator is on the old one, mark it, and wait to glue it position once ‘we’ manage - hope - to get the radio back working on FM (fingers crossed). I have taken a few stills of the old installation to use as a reference.
Once again Thanks Dave, keep well…. Malcolm
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Old 6th Jul 2022, 9:43 am   #73
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Default Re: Samsung 3 band radio cassette, model: STF55L

Hi Malcolm,
That's a shame about the tuning cord. You could try the fishing line and other members have had some success doing this. The fishing line might slip if it is too shiny, really it's a case of try it and see if it works. Use the original cord to get the length for the replacement and remember to allow for the knots, perhaps an extra 1.5cm. If the original cord is still roughly in place make a note of where it crosses over itself at the end furthest from the large half pulley.

When you are fitting the fishing line follow the diagram on page 12 of the manual. I suggest that you study the radio chassis and compare it to the cord layout in the diagram very carefully. Also make some notes on paper to help you along the way as once the old cord is removed, you cn't refer to it.

I might be mistaken but it appears to me that the diagram is inverted left to right, so be careful. Don't be surprised if it all goes wrong on your first attempt, just keep trying until you get it right. Don't put too much stress on any of the pulleys as you don't want to end up with another problem due a broken pulley mounting.

Just take your time and think it through before jumping in.

Dave
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Old 22nd Jul 2022, 12:36 pm   #74
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Default Re: Samsung 3 band radio cassette, model: STF55L

Hi Dave,
Well I managed to do the silver paint on PR1 (component side, see attached photo 1.) as you suggested (via PM) I cleaned the surface with some of my photo lens cleaner that dries clear and solvent free. I put a tiny piece of paint on some paper and then used the syringe needle to apply it to ther PR1 crack. I have also attahced 2 more photos: (2) is the solder covering the crack (track side) with the solid core wire also covering the crack and (3) is the tuning pulley cord using the fishing braid - it works fine.... Cheers Dave... Malcolm.
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Old 22nd Jul 2022, 5:00 pm   #75
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Default Re: Samsung 3 band radio cassette, model: STF55L

Glad you finally got it all fixed, now you can look forward to using it properly and perhaps reminisce about your lost family.

Dave
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Old 22nd Jul 2022, 7:20 pm   #76
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Default Re: Samsung 3 band radio cassette, model: STF55L

Hi Dave,
Thanks for your reply... Wow I didn't think that was it I haven't checked it yet, I thought there were a few more checks to be done. I will try the FM tomorrow (once the paint has dried) and let you know the result... Fingers Crossed...Cheers Dave. Malcolm.
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Old 23rd Jul 2022, 11:02 am   #77
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Default Re: Samsung 3 band radio cassette, model: STF55L

Morning Dave,
Hope you're well. I've checked the FM signal and there is no sound or anything... but I'm now getting volts from the top of PR1.. 3.36 volts where as before there was nothing 0.0, and at the bottom there is 4.22 volts. Cheers Dave, Malcolm.
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Old 25th Jul 2022, 4:24 pm   #78
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Default Re: Samsung 3 band radio cassette, model: STF55L

Hi Malcolm, Let's re-do some voltage measurements, the pcb repair will have changed the previous readings. First go to IC1 and measure the voltages on all 7 pins, then do the same for IC201 16 pins. We need to see how they now compare with the service manual, as there will be changes after the pcb repair. You only need to quote the actual measured voltages.

Remember that the black meter lead goes to the centre socket on your digi meter and the red lead goes to the socket on the right. Select 20v dc range on the meter. Now clip the black meter lead probe end to the metal body of the waveband change switch of the radio. Of course making sure that the radio is in FM mode and switched on. Use the red meter lead to measure the voltages on the IC pins. Make sure that you get a good connection with the meter probes, as any loose contact will affect the voltage readings obtained.

Once you've done that we'll see where to go next.

Dave
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Old 26th Jul 2022, 10:49 am   #79
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Default Re: Samsung 3 band radio cassette, model: STF55L

Morning Dave,
Thanks again for your help. I have done the volts check and IC 201 seems to be roughly the same as last checked, but IC1 has more volt readings (apart from terminal 4 which is the same). I have attached a photo of the readings. Cheers Dave, Malcolm.
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Old 26th Jul 2022, 12:12 pm   #80
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Default Re: Samsung 3 band radio cassette, model: STF55L

OK Malcolm, those voltages look a whole lot better than before the pcb repair. I noticed that on all the 0v readings you have -0v. Does your meter do that with the red and black probes joined together when on the 20vdc range, or does it show 0v? Just wondering if something is oscillating due to a dodgy earth somewhere.

Next test is on ohms not volts, same 2 sockets on the digimeter. Connect the black meter lead to the switch body again and touch the red meter lead probe to pin 4 on IC1, you should have zero (0) ohms. Now do the same ohms test for pins 5 and 13 on IC201, again you should have zero ohms. The reason for this resistance check is to confirm that the 2 IC's are properly grounded to earth.

After that find a magnifying glass and take a good look at the tracks both sides of the pcb in the vicinity of the previous crack, just in case there are more breaks that got missed.

Dave
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