9th Mar 2020, 1:54 pm | #161 |
Dekatron
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Re: Commodore PET 3016
No problem with the wire colours as long as you yourself know what they stand for. All the components are in the right place and oriented correctly - the soldering is quite rough but you have previously been quite frank about the fact that your soldering is beginner-level so we don't hold that against you. Everyone starts somewhere, and this was the ideal sort of project to start with.
I wonder if you are using lead-free solder - that won't help you very much if you are still at the beginning of that learning curve. Even people who have been soldering for years are generally not very fond of lead-free solder. Can you turn the PCB so the components are facing away from you and give the capacitor C2 a gentle wiggle to see if either of its leads is not properly soldered? One of the legs of C2 on the solder side has plenty of solder on it but I am not sure if it is soldered to the pad as well. If that capacitor is not soldered the amplifier may be unstable / oscillating, which could account for your problem. |
9th Mar 2020, 3:03 pm | #162 | |
Hexode
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Re: Commodore PET 3016
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The solder I am using does have a flux core - or at least that's what it says! I guess I'm just not very good - but I must practice more!! |
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9th Mar 2020, 6:07 pm | #163 |
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Re: Commodore PET 3016
I saved your images of your PCB so that I could load them into an image viewer and zoom in for a better look. What's noticeable is that the solder is largely confined to the component leads and has not really spread onto the pads very well.
I've noticed that if I hand a soldering iron to someone who has never used one before and ask them to solder something, what they will often do is put a generous blob of solder on the tip of the iron and then carry it over to the joint and try to deposit it on the joint. I suppose that's quite natural, because that's how you paint (and most people have tried painting). The technique for soldering is different, though - when soldering, you place the tip of a clean soldering iron so that it is touching both the component lead and the PCB solder pad and you keep it there for perhaps 4-6 seconds, then, still keeping the iron in contact with the lead and the pad, you dab the end of the solder wire onto the joint. The solder should flow onto the pad and around the lead, forming a nice cone shape with its base spread across the pad and its 'point' around the lead. Then you remove the soldering iron. The makers of your kit supply a very detailed construction sheet, obviously aimed at the education market. https://www.kitronik.co.uk/pdf/2165-...hing-notes.pdf Have a look at the soldering instructions on pages 14 and 15 of that PDF document, that's basically the method you need to try to follow. |
9th Mar 2020, 6:15 pm | #164 | |
Hexode
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Re: Commodore PET 3016
Quote:
So far so good with the PET - everything seems to be working - though with a 40 odd year old computer anything could happen - again thank you for all your help! Best wishes, John |
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9th Mar 2020, 7:36 pm | #165 |
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Re: Commodore PET 3016
I've just gone back over the information so far and I've realised that C2, the one with the bad connection, is the input series capacitor (not the one I thought it was). If that capacitor is not soldered then you will get little or no sound at all, which sounds a lot like the problem you are having. It will be interesting to see if it bursts into life once you've resoldered that capacitor.
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9th Mar 2020, 7:38 pm | #166 | |
Hexode
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Re: Commodore PET 3016
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10th Mar 2020, 1:23 am | #167 |
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Re: Commodore PET 3016
I would be tempted to buy a de-soldering pump and redo all of the joints on the amplifier board with leaded solder.
A dab of leaded solder on each joint may be all that is needed with any excess wiped off the iron may be enough to get it reliable. Do avoid trying to "save old solder" as this will not help at all. |
10th Mar 2020, 2:23 pm | #168 |
Octode
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Re: Commodore PET 3016
It looks like that lead free solder hasn't got hot enough to "flow" properly. Reasonable looking joints should be achievable with it with the right heat. You know its flowing when it goes very liquid like and has a "shimmery" look to it, rather than dull and "blobby". Try holding the heat to it a bit longer and you should see what I mean. Took me a while to get this myself in my early days of electronics
Leaded is better to work with overall, but you should still be able to achieve reasonable looking results with lead free |
10th Mar 2020, 2:32 pm | #169 |
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Re: Commodore PET 3016
I'm not sure but I think John may originally have been using the 'paintbrush' method of soldering I mentioned in #166 - if so, a simple change to the more established way of soldering should bring about a noticeable improvement.
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10th Mar 2020, 4:26 pm | #170 |
Hexode
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Re: Commodore PET 3016
Thanks everyone. I’m certainly going to practice on an old pcb to get the technique right. I probably need to invest in a half decent soldering iron too. Been told that one with a pointed end, rather like a pencil end? What do you reckon?
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10th Mar 2020, 5:23 pm | #171 |
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Re: Commodore PET 3016
If you can stretch to one, a temperature controlled iron is better, but not essential. Try to get one for which you can obtain two or three interchangeable tips, because different shaped tips suit different jobs better.
You should also consider getting some 'desolder wick' (also known as desolder braid) and a desolder pump as described earlier in the thread. Both are ways of removing solder but there are times when it is better to use one than the other so it's useful to have both. If your current roll or tube of solder has labels on it, what do they say? If it says something like 'Sn60/Pb40' then it is Lead-Tin solder which is the sort we rather approve of. It may alternatively say something like 'Pb-Free' (Lead Free) which is safer (less toxic) and that's why it has been introduced, but it isn't as nice / as easy to solder with as Lead-Tin solder. |
10th Mar 2020, 7:08 pm | #172 |
Octode
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Re: Commodore PET 3016
If you're buying soldering supplies, then consider getting a liquid flux pen (especially if using lead-free) as using a little extra flux can help soldering on old circuit boards or with old components. Some cheap solder can be a bit stingy with flux too, so some extra flux is always useful. If you really get into electronics their are several other types of flux available (gel, rosin etc) that have their application, but a basic flux pen is a good start and generally does no harm if you dont clean it off afterwards.
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10th Mar 2020, 7:41 pm | #173 |
Hexode
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Re: Commodore PET 3016
thanks guys for your advice - I will do some looking around and see what I can afford! I may be back to ask your advice again!!
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11th Mar 2020, 2:42 pm | #174 |
Octode
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Re: Commodore PET 3016
Look online for a "Quicko T12" solder station. Around £25, temperature controlled, its a Hako clone. Bits are cheap as anything, works brilliantly and for the money decent quality with a nice supple silicone lead and auto temperature cut to save bits, and also will cut off completely after a time. Great if you're absent minded like me!
I bought one last year and don't feel I need anything else, cant recommend it enough! |
11th Mar 2020, 8:39 pm | #175 | |
Hexode
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Re: Commodore PET 3016
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11th Mar 2020, 8:58 pm | #176 |
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Re: Commodore PET 3016
One thing though, if you buy one of those you will also need a DC power supply with output voltage somewhere between 16V and 24V and capable of supplying 3 Amps continuously.
If you have an unused laptop PSU (typically 19V) with the right sort of DC plug and the correct polarity on the end, that may do. |
11th Mar 2020, 9:03 pm | #177 | |
Hexode
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Re: Commodore PET 3016
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13th Mar 2020, 10:07 am | #178 | |
Octode
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Re: Commodore PET 3016
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13th Mar 2020, 1:12 pm | #179 |
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Re: Commodore PET 3016
I went looking, and many of the ones with a similar description are powered from low voltage DC 16V-24V - just have to be careful which version you buy.
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13th Mar 2020, 10:49 pm | #180 |
Hexode
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Re: Commodore PET 3016
Really interesting! I had no idea there were so many varieties of soldering irons!! It’s a mine field!
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