How do I replace this circuit board? - Page 1
Forum section: electronics / beginners

author: LeWidget
author_rank: Regular Contributor
timestamp: November 03, 2015, 07:55:19 am
content: Hey guys,Pulled apart an old analog multimeter to cleanup to try get working again, but the PCB doesn't seem too healthy. just wondering what would be the cheapest route if I wanted to replace it? I've had a quick google and cant find replacements.. then again it is about 25yrs old...looks like an old Dick Smith unit DSE Q1022Is it possible to 'make' a PCB board... similar in the way people make parts using a 3d printer?

author: tron9000
author_rank: Frequent Contributor
timestamp: November 03, 2015, 08:59:02 am
content: you could scan it, edit the image, print out a transparency and then expose, develop and etch your own PCB maybe?

author: LeWidget
author_rank: Regular Contributor
timestamp: November 03, 2015, 10:34:58 am
content: Thanks Tron,I've watched a few videos with people etching boards.. though I have to admit, Im clueless on the procedure and components required to pull of something like this.Is there anyone on Eevblog that does etching or homemade PCBs ?

author: rs20
author_rank: Super Contributor
timestamp: November 03, 2015, 10:41:38 am
content: You could also scan the design and regenerate it in a CAD package, and get it sent off to be made. Much cheaper than buying chemicals and equipment to do your own etching, unless you plan to go on to do more etching in the future.

author: krivx
author_rank: Frequent Contributor
timestamp: November 03, 2015, 10:44:11 am
content: If you want to use a rotating switch that contacts the board as in the original design you might need some kind of tinning or coating on the exposed tracks, bare copper might have problems with tarnishing.Personally I would try to replace any bad or missing traces before replacing the whole board. Another option would be to scan and recreate the original artwork but have it fabbed professionally. That would take care of the routing to get the exact shape needed, plus you could easily get spares in case something goes wrong during reassembly.

author: tron9000
author_rank: Frequent Contributor
timestamp: November 03, 2015, 11:18:43 am
content: ahh but where's the funyes you will get better results from a PCB fab house. Accurate drilling and of the cutouts. Where the rotatory contacts are concerned, I would go for a Hot Air Levelled (HAL) board.

author: tec5c
author_rank: Frequent Contributor
timestamp: November 03, 2015, 12:46:40 pm
content: Quote from: LeWidget on November 03, 2015, 10:34:58 amJaycar sell ammonium persulphate (about $15 IIRC) which is a simple and somewhat quick method to etch a board. They also sell a product called press and peel film, which is, IMO, overpriced though for a one off board it'd do the job. Alternatively if you have a laser printer you could use the toner transfer method while still using the ammonium persulphate.Different methods give different results so it all depends on final product that you'd consider acceptable.Where abouts in oz are you?Edit: Have the traces actually corroded off from the board or are they just heavily contaminated? It's a little hard to tell from the picture.

author: smbaker
author_rank: Regular Contributor
timestamp: November 03, 2015, 04:04:44 pm
content: I've had some success making my own PCBs over the years, but the ones I have manufactured sure are nicer to work with.I would suggest using 'Eagle' to layout the PCB, and use it as a learning experience becoming familiar with the software, but I bet the board is too big for the free version of Eagle.This board doesn't look in that bad of shape to me. Is repairing the traces an option? If a particular trace is damaged beyond repair, you could always tack some wire to it.

author: LeWidget
author_rank: Regular Contributor
timestamp: November 04, 2015, 10:57:40 am
content: Thanks guysI'll give scanning a shot and check out Eagle, see if i can replicate an image. How much would the etching materials cost roughly? the PCB is about 83mm x 121mm x 1.5mmQuote from: krivx on November 03, 2015, 10:44:11 amWould prefer to replicate it to original spec. Can I 'tin' the contacts with a layer of solder or does it require a specific layer ?What is 'fabbed'? I had a look online but all the manufacturers for PCBs seemed rather expensive.. probably alot more expensive then the Multimetre is worth :/The current traces seem intact.. but some sections seem not in good shape. one section in particular, in the centre circle area, the 'tin' has corroded and scratching that away leaves copper. Some areas are also bubbling.Being a multimeter, is it possible the condition of the traces / contacts could increase resistance and give false readings if trying to probe voltages ?Tec5c: Im located Hawkesbury - Sydney

author: tec5c
author_rank: Frequent Contributor
timestamp: November 04, 2015, 11:31:15 am
content: To etch a new board could be done for around $30. This is the cost of some copper clad board and ammonium persulphate from Jaycar. So you still need a way to transfer the circuit layout onto the board, which is where a laser printer can come into play. If you don't have a laser printer you can simply buy the press and peel film from Jaycar also.A set of calipers would be highly recommended to get all of the measurements right.I'd still consider trying to clean it up, just be careful to not wreck it any more than it already is so you can still get decent measurements from it if you need to reproduce the board.

author: krivx
author_rank: Frequent Contributor
timestamp: November 04, 2015, 12:04:28 pm
content: Quote from: LeWidget on November 04, 2015, 10:57:40 amOshpark are charging 5usd/square inch for an order of 3 boards. It's hard to tell the dimensions from your pictures but it seems like this would be comparable to the cost of etching one yourself.http://pcbshopper.com/will give you price comparisons.For tinning you could use solder, but you would want a very flat surface so that the switch contacts do not bounce or lift off the track as the switch rotates. This is why something like HASL might work better. If you are getting boards made professionally then a gold coating would probably also work.

author: krivx
author_rank: Frequent Contributor
timestamp: November 04, 2015, 12:10:39 pm
content: If you are trying to do this on a budget I would just buy a fiberglass brush from eBay and remove any soldermask from bubbled traces and tin with solder. Careful brushing on the center wheel should polish that up too. You will probably need to coat the copper, so a very thin layer of solder may work. Maybe try tinning it, then wicking off as much solder as you can you get a thin flat coating.

author: LeWidget
author_rank: Regular Contributor
timestamp: November 04, 2015, 12:11:48 pm
content: Thanks GuysIll checkout Oshpark and see how that goes. Dimensions for the board are83mm (3.2") x 121mm (4.6") x 1.5mmunfortunately I dont have access to a laser printer (though currently seeking one on gumtree and ebay).Regarding the Press 'n' Peel film.. is that stuff the same as transfer paper? The kind you print and transfer to clothing? ebay has some.. much cheaper.. not sure if its the same stuff though.Definitely trying to do it on a budget. I've already got a DMM, though this was something I wanted to do as a lil project, and maybe use the AMM down the track.. but not sure as you can get AMM from ebay for around $20 :/

author: mariush
author_rank: Super Contributor
timestamp: November 04, 2015, 03:01:41 pm
content: The traces are wide enough and the space between them is big enough that I think you'd be able to replicate the pcb by yourself.Get a semi-transparent sheet of paper or a plastic foil, put the plastic foil over the pcb, draw around the edges with a thin black permanent marker. If you want, simplify the design by avoidin round shapes or angles and mark the hole locations with a point.Cut a copper clad bare pcb in the form of this board, get some indigo paper and put it between the copper pcb and the foil, use something to apply pressure on the edges you've drawn on the plastic foil, so that you'll have the drawing on the copper. Now you should be able to use an exacto knife or something sharp to cut on the edges. Then use a needle or nail to start the holes then use a drill to make the holes.You'd still have to protect the copper from oxidizing which you could do by tinning the traces. Then use a multimeter to check for continuity between traces.