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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 28th May 2014, 10:35 am   #1
Phil G4SPZ
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Default Servicing PCBs compared with wired chassis

Split from this thread, a discussion has started up about the relative ease of servicing PCB-based radios compared with those using the conventional point-to-point hard-wired chassis.

Before becoming involved in vintage radio I did lots of repairs on printed circuit boards, in TVs, radios and general electronics. In the last 10-15 years though, I have worked almost exclusively on conventional chassis, but a few recent opportunities to repair PCB-based sets and test equipment has reminded me how relatively easy it is to effect an 'invisible' repair by changing components on a circuit board compared with a hard-wired chassis.

I admit to taking my time when replacing a component on a PCB. I usually snip out the component on the top side, then unsolder the stubs of wire from the board. I also use a solder sucker, good quality desoldering braid, and a variety of soldering irons of appropriate size and wattage, and I take care to clean out the hole thoroughly. I rarely if ever have problems with lifting tracks. I also ensure that the leads of the replacement component are pre-bent to exactly the right spacings to fit the holes, and clean and/or tin the leads before attempting soldering.

This question isn't designed to be provocative, in the sense of a "hard-wired = proper vintage = good" versus "PCB = modern stuff = bad" argument. It's just that I find I can repair a PCB a lot quicker, more easily and end up with a neater-looking job than working on a conventional chassis, yet I enjoy doing both equally. I wonder if anyone else has any thoughts?

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Old 28th May 2014, 11:14 am   #2
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Default Re: Servicing PCBs compared with wired chassis

Very much concur with those thoughts. With the right tools, practice and good lighting, I found PCB work quick, rewarding and effective even with dense, DS boards. With care and a good post-scrub with one of the usual suspect cleaners, a repair could be pretty much invisible- I used to take a certain mischievous pride in being able to quickly change 28-40 pin ICs on through plated print and leave it on the edge of the bench so as to provoke the comment, "oh, you haven't got round to it, then?". There was something of a dogmatic divide with some as to whether braid or sucker was best but I found some jobs suited one best, some the other, at one point I even had the use of an expensive Pace desolder pump with paralleled foot/trigger switch. Luxury!

I'll concede that I was lucky in that I came to PCB work in the mid 'eighties when the art of PCB making was thoroughly mature, some older consumer stuff I've worked on was prone to lifting/bubbling without a quick but careful approach- it made me appreciate that it must have been a bit of a learning curve for those used to hard-wiring. As with any new technology, some thrive, others don't like it so much I guess.
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Old 29th May 2014, 12:36 am   #3
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Default Re: Servicing PCBs compared with wired chassis

I have had some success with mid 60's PCB's, certainly easier than trying to remove resistors and capacitors from a valve pin buried under other things.

Now SMD's on PCB's are something else, I recently tried to remove a micro USB connector, and utterly failed, I can't even see where the pins are connected to the PCB traces since some of them were though-hole to the other side of the board.

So in some ways the hard-wired stuff was more fun, that is until you broke a tag trying to unwrap a couple of resistors that were wrapped around the tag one and a half times per GPO requirements
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Old 29th May 2014, 9:50 am   #4
Peter.N.
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Default Re: Servicing PCBs compared with wired chassis

It depends on the age and quality of the hard wired equipment, some of the early TVs had flat tagboards with the components laid out side by side in a row, they were very easy to work on and a lot easier to fault find as well.

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Old 29th May 2014, 10:16 am   #5
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Default Re: Servicing PCBs compared with wired chassis

Hardwired is ultimately more rugged and durable than PCB, and on low component density sets more convenient to work on. Very often a PCB has to be detached to access the soldered side, unless an access panel is provided. Obviously as component count became high, hard wired became practically impossible so PCB is the only way. Some makers were better than others at PCB's, lots of Philips stuff was horrendous due to very thin traces which would lift and break even with routine component replacement, regardless of how careful you were. I hated them at the time! Valve PCB's need careful design as the heat and temperature change cycles can cause trace failure. This can be seen on a number of TV's where valve holders were changed from low profile to standoff types, and trace thickness increased on later versions when long term durability problems were revealed during a given sets production. Some hardwired equipment is a joy to look at and work on, Solartron springs to mind as an example. They persisted with hard wiring into the transistor era.
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Old 29th May 2014, 12:40 pm   #6
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Default Re: Servicing PCBs compared with wired chassis

I'm happier with vintage hand wiring in vintage equipment. It's different to the day job, makes doing a good job easier, and there's no fear of tearing tracks or having to cope with carbonised panels that have to be cut away. It's all part of the vintage experience. In the day job modern world, writing off very expensive burned pcbs is always a risk and the thought that they've probably never been touched (or loved) by a human being at any part of the production, and the fact they usurped hand-wiring as a time-and-cost-cutting measure detracts from a pleasurable repair.
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Old 29th May 2014, 2:05 pm   #7
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Default Re: Servicing PCBs compared with wired chassis

I've never liked working on transistor stuff but after doing a couple of late valve radios realise that it's PCBs that bother me far more than what's fitted to them.

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Old 29th May 2014, 2:28 pm   #8
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Default Re: Servicing PCBs compared with wired chassis

I agree that some hand wired sets can look very attractive. The Mayflower comes to mind, unfortunately this usually goes with very secure connections to tags. It makes fault finding easy but replacing components with very strong mechanical joint - threaded through eyelets then wrapping round the tag - followed by solder can be a pain. it is even worse when more than one component is secured to the same tag.

Most PCBs look very tidy on the component side but the solder side is a matter of taste. Replacing components neatly on the earlier single layer PCBs though is almost a pleasure. The problem of several components on the same tag does not arise. What I find irritating is service data that shows the component side all nicely labeled but no identifiers on the solder side. Some very thoughtful manufacturers though show ghost representations on the solder side with everything identified and this is fine.

I have a vague memory of a PCB with components identified on one side and the leads on the solder side bent so that they would not fall out. The tracks were not very robust either so changing parts on this was a bit of a challenge. In fact at the time I thought it was the worst of all worlds.
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Old 29th May 2014, 5:47 pm   #9
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Default Re: Servicing PCBs compared with wired chassis

I hate PCBs with component leads bent tight against the pads. Removal of the component often ends in tears with early boards, even when you use all the usual tricks that Phil mentions in post 1.
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Old 29th May 2014, 8:42 pm   #10
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Default Re: Servicing PCBs compared with wired chassis

Yeah, bent leads are a pain.

I quite like proper plated-through holes on double-sided or multilayer boards. You can work on them from either side.

Sometimes wick works better than a sucker, sometimes the other way round. The best suckers I found were the EDSYN Soldapullt.

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Old 29th May 2014, 11:17 pm   #11
turretslug
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Default Re: Servicing PCBs compared with wired chassis

I get the feeling that it took a while for manufacturers to gain confidence in the ability of the solder alone to have the strength to retain components- it's arguable (and it has been argued in previous forum threads!) that even with point-to-point hard-wiring that the "secure mechanical joint" lingered as a practice long after improving soldering techniques (alloys, fluxes, preparation) had rendered it frequently unnecessary. Conversely, unsupported/inadequately supported heavy components (notoriously LOPTs) on cheap, flexy single-sided SRBP boards didn't help the reputation of the PCB.

Some early PCB construction even had a loop or hairpin formed in the lead against the board for extra annoyance. In all bent-over cases, things like a fine hollow-ground watch-makers screwdriver and fine point dental spike are your friend- suck/wick the joint as dry as you quickly can, then carefully pry the hot lead away from the heated joint.
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