EPE June 1993 - Maplin mini-lab article - Page 1
Forum section: electronics / general

author: cowasaki
author_rank: Frequent Contributor
timestamp: February 03, 2019, 12:36:33 am
content: I'm trying to restore the first decent sized project I ever built which is the Maplin mini-lab. The actual circuit board from Maplin was pretty poor quality and my soldering technique, at the time, was equally poor. I really could do with a copy of the circuit diagram from the original article if anyone has a library of old EPE magazines or knows of where I can find such a thing. A scan of the article would be perfect.It might also be in volume 12 ?? OR a Maplin magazine of similar vintage??Several of the PCB tracks are broken due to the track being barely wider than the drill holes which added together with some other strange design decisions is causing me a bit of a headache.

author: Macbeth
author_rank: Super Contributor
timestamp: February 03, 2019, 12:51:51 am
content: You might find something here:https://www.americanradiohistory.com/Maplin-Electronics.htm

author: cowasaki
author_rank: Frequent Contributor
timestamp: February 03, 2019, 12:53:26 am
content: Quote from: Macbeth on February 03, 2019, 12:51:51 amThanks, but no June 93 :-(But it does state in the volumes 1-15 bit in the bottom left that its in volume 12 number 66 page 12. It doesn't show the volumes though :-(

author: tsman
author_rank: Frequent Contributor
timestamp: February 03, 2019, 02:10:31 am
content: The Mini Lab project in June 93 is based on the original Mini Lab project from Sept 83 which is on the American Radio History site. The 83 project uses Veroboard though so no PCB but it does give you the schematic + component details.

author: cowasaki
author_rank: Frequent Contributor
timestamp: February 03, 2019, 10:57:18 am
content: Quote from: tsman on February 03, 2019, 02:10:31 amBrilliant, I will start looking there. IF you have a link it would be appreciated but if not I'll find it. I want to restore this to how it was then maybe design and build a version for this decade with 16 bi coloured LEDs to detect either state, current limiting, volt and amp meters adjusted square wave generator rather than two speeds etc with arduino control. It might be an interesting project and once up and running might be a good project for this decade's beginners.

author: tsman
author_rank: Frequent Contributor
timestamp: February 03, 2019, 12:38:23 pm
content: Sounds like a fun project to update. Looking at the photos of the finished Mini Lab, I do remember reading that issue of the magazine. Unfortunately it is long gone now so I can't help you with that.I'm not sure if they'd appreciate a direct link to the PDF. It is just the September 1983 magazine at the top ofhttps://www.americanradiohistory.com/Maplin-Electronics.htmIt is PDF page 18 onwards.http://www.chatzones.co.uk/discus/messages/7/16629.htmlhas a short thread about your 1993 project. The photo of the first page shows that Maplin did alter the project as it mentions specifications were improved. Not sure how easy it would be to get in touch with the person that received that PCB + magazine but it might be an option if the 1983 version is too different.Hopefully nothing too major was changed as the 1993 edition of the magazine is elusive. The Mini Lab in the projects book #3 is 1983 version so that is a dead end as well.

author: cowasaki
author_rank: Frequent Contributor
timestamp: February 03, 2019, 04:41:36 pm
content: This is its current state. The only modifications I did were to add banana sockets to the back of the case for the variable out and two 2mm? sockets on the front for the same thing which was to plug in a multimeter.I also built the volt meter/ammeter and electronic fuse projects into another case just the same which worked quite well. The quality of their PCBs was shockingly poor and together with my poor standard of soldering back then I have some work to do!!!

author: cowasaki
author_rank: Frequent Contributor
timestamp: February 03, 2019, 04:47:07 pm
content: Just downloaded it, BRILLIANT!!!!This is just what I needed. A lot of the tracks have cracked so it's a little difficult to see what they are doing. I replaced the 12v and 5v regs and one of the bridges and the 12v reg got so hot it burnt me so must be shorted somewhere. The negative power outputs DID work and it worked a few years ago so should be fixable.Once fixed it will just be an ornament to be honest but I do fancy designing and building something in the same vein as a project......EDIT.............The Maplin kit is not quite the same as the original. The transformer is a dual tap type with 2 x 20v AC output rather than 17v. There are 2 bridge rectifiers in the Maplin version as well so they are clearly doing something else differently as well. I'm going to probably map it out using fully again. The TTL circuits appear to be the same.

author: tsman
author_rank: Frequent Contributor
timestamp: February 03, 2019, 05:40:04 pm
content: Quote from: cowasaki on February 03, 2019, 04:47:07 pmAh. That is a shame.

author: cowasaki
author_rank: Frequent Contributor
timestamp: February 03, 2019, 05:54:21 pm
content: Quote from: tsman on February 03, 2019, 05:40:04 pmNo seriously I just think that Maplin had made a few minor changes so this was more than helpful.

author: philpem
author_rank: Frequent Contributor
timestamp: February 04, 2019, 03:03:21 am
content: If it'd help any, I've got a fairly large (dead tree!) collection of Maplin magazines and could probably scan the article -- assuming I have it.Drop me a PM to remind me

author: Chris56000
author_rank: Frequent Contributor
timestamp: February 04, 2019, 01:40:01 pm
content: Hi!I'll get rooting thro' mine tonite – I KNOW I have it because I won a small lot of 'em (88–102!) last year, so as soon as I find it I'll get it scanned!Chris Williams

author: philpem
author_rank: Frequent Contributor
timestamp: February 04, 2019, 06:27:48 pm
content: Found my copy and I'm scanning it as we speak!It's a "2nd Time Around" article, i.e. a re-do of the original with some minor tweaks.It includes mechanical drawings for the case, the schematic and the PCB track pattern and silkscreen.

author: philpem
author_rank: Frequent Contributor
timestamp: February 04, 2019, 07:23:03 pm
content: Scanned -- enjoy!https://www.dropbox.com/s/pwibcbmprv6z5yj/Maplin_Jun1993_Minilab.pdf?dl=0

author: tsman
author_rank: Frequent Contributor
timestamp: February 04, 2019, 08:57:18 pm
content: I see what you mean about the traces on the PCB. The schematic is drawn a bit strangely due to the limited space.

author: cowasaki
author_rank: Frequent Contributor
timestamp: February 09, 2019, 10:21:58 pm
content: Well, it's been a mad repair job!The list of replaced components:5 Tantalum caps1 Diode bridge1 switch4 voltage regs3 resistors3 electrolytic capsI remember I had to take it apart after I had built it because one of the LEDs didn't work. I found that I'd missed a link although I did get it working back in the 80s by wiring the LED to the points it needed to go to using wire.

author: floobydust
author_rank: Super Contributor
timestamp: February 09, 2019, 10:46:20 pm
content: Six voltage regulators but not one protection diode...I would add 1N4004's from O/P to 0V for each regulator, to prevent reverse voltages from damaging things.i.e. if you short -5V to +5V one of the regulators will lose and fail, or on power-up a load between a + and - reg can cause latchup.You can put the diodes at the binding posts.If you charge batteries, I would add a bunch of 1N4004's from O/P to I/P for each regulator i.e. if you connect battery when supply is off, there is no backfeed charging filter caps through the vreg.

author: cowasaki
author_rank: Frequent Contributor
timestamp: February 09, 2019, 11:00:44 pm
content: Quote from: floobydust on February 09, 2019, 10:46:20 pmIf I was re-building it to use I would probably modify it but.....To be honest I think it is more to do with Maplins mechanical build more than electrical! The main circuit board has most of the regs attached to the main board and the base of the case. They saved a few pence by using a single sided board and making the person who put it together solder on the component side! There are, for example, two 2200uF electrolytic caps hovering 2cm above the board because you have to solder on the same side as the component which is ridiculous. Due to poor original soldering (It was a long time ago and I had to teach myself to solder) there were lots of issues. In order to get it working at all, I had to remove every component from the power side and clean up the board. Whilst trying to fix it I had a 7812 and LM317 literally explode! I would have binned it after removing a few components if it hadn't been the first kit I ever builtI'm only restoring it for sentimental reasons BUT I quite fancy designing and building a mini-lab for the 21st century adding - current limiting, bi-colour LEDs to detect GND or DC out, ability to change the voltage of the 8 outputs, add a voltage and current display, replace the 15v output with 3.5v, fuse on the secondary side, use soft buttons for the 8 outputs rather than switches and add a header to connect to an Arduino which could optionally control all the outputs. With Chinese PCB manufacturers, the boards could be less than a tener and it would be a great project for newbies now like the mini-lab was back then.

author: cowasaki
author_rank: Frequent Contributor
timestamp: February 13, 2019, 12:13:49 am
content: Well I had a few issues, the biggest one being a mistake in the component list which had a component wrong and I only found it when one of the regs got very hot! Spotted it in the circuit diagram but checked every connection after that. It's actually been quite a task getting it working as I've effectively rebuilt the thing, only to have it on the shelf after I've finished. Next repair is hopefully going to be something on a more modern PCB where the tracks are not all lifting off and components soldered onto the copper side of a single-sided board!! Cheapskates!!