Budget workbench. - Page 1
Forum section: electronics / testgear

author: Rx7man
author_rank: Regular Contributor
timestamp: June 23, 2019, 05:03:15 am
content: So I am trying to get at least the basics covered, I won't be doing any RF work nor any high accuracy work.. Mostly audio and analog automotive circuit design, test and troubleshooting.Here's what I've gotKeysight DSO 1052B scope, 2ch, 50mhz, 1Gs/s (200 USD)KKmoon FY6800 waveform generator, 2ch, 20v, 20mhz (90 USD)https://www.ebay.com/itm/KKmoon-FY6800-60MHz-Digital-Function-Signal-Generator-Counter-Frequency-Meter/132689072999?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l264910A 30V power supply.. For $9 USD with free shipping, I couldn't pass it up.. how bad can it be?https://www.ebay.com/itm/10A-30V-DC-Power-Supply-Adjustable-Dual-Digital-Variable-Precision-Lab-Grade/362675214578?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649853D 3 in 1 soldering station ($70USD)... OK, this I have some comment on.. Seems like the hot air gun and iron work well, but the auxiliary power supply is GARBAGE.. I got 2 of them and they both died, one died on first power up, LOTS of magic smoke came out of it... the PCB is very poorly fastened..https://www.ebay.com/itm/3-in-1-853D-SMD-DC-Power-Supply-Hot-Air-Iron-Gun-Rework-Soldering-Station-Welder/381253195679?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649I have an assortment of multimeters, cheap handheld scope, inductance/capacitance meter.. Just picked up a vintage Hioki AC analog meter, wish it did DC.. still want to find a good DC analog meter.So for $500 or less, you think this is a good start?

author: bob91343
author_rank: Super Contributor
timestamp: June 23, 2019, 05:37:25 am
content: Looks good to me. However I am suspicious of that $9 power supply. Did you receive it, and if so, how does it look?

author: maginnovision
author_rank: Super Contributor
timestamp: June 23, 2019, 05:46:14 am
content: The power supply is absolutely not worth 9$ unless you're going to be adding your own TVS or other voltage limiting components to everything you hook it up to. They have severe overshoot(at turn on and attaching a load) and it's not a short amount of time. They are also typically poorly calibrated so the number on the displays are rough estimates. Those can be somewhat tuned/calibrated though.The 853D I've also unfortunately used. The hot air is fine enough but the iron is not good and as you know the power supply is bad(although, when working, less overshoot than the 9$ unit).Otherwise it looks fine.

author: bob91343
author_rank: Super Contributor
timestamp: June 23, 2019, 06:05:27 am
content: Thanks for the heads up on the power supply. That is so cheap I can't see how they can even ship it for that.However if the design is flawed perhaps it could be reengineered. After all, there is a power transformer and rectifier and digital displays and heat sink to work with.I have a similar unit that goes to 18V and 2A and it seems fine. But 30V and 10A are tempting.

author: windsmurf
author_rank: Frequent Contributor
timestamp: June 23, 2019, 06:08:13 am
content: The power supply is most likely a scam...

author: bob91343
author_rank: Super Contributor
timestamp: June 23, 2019, 06:29:06 am
content: That was my immediate reaction. I am not sure which way to go.I fell for a scam some time back and ebay made it good.

author: Rx7man
author_rank: Regular Contributor
timestamp: June 23, 2019, 07:12:48 am
content: Ebay usually does go good on scams.. There was another item unrelated to test equipment I couldn't pass up, 7" android 1DIN touchscreen head unit for a car, navigation and all, $13..I'll have a scope so I can see what the overshoot on the power supply is, ordered it a few days ago, won't be here for some time.. Adding a decent cap on the output should significantly reduce the amount of overshoot shouldn't it without any ill effects. Most of the stuff I'll be powering will have it's own regulation anyhow.. time will tell, if I get it!Quote from: maginnovision on June 23, 2019, 05:46:14 amWhat didn't you like about the iron? I used it a bit and while no doubt it's not a Hakko, I didn't have any issues with it, I do have better tips thoughI got this little iron and quite like it as well, heats up nice and fast and feels pretty goodhttps://www.ebay.com/itm/Electric-Soldering-Iron-LCD-Digital-Thermostat-Adjustable-60W-110-220V-US-EU-/202311957982?var=&hash=item2f1abb7dde

author: MosherIV
author_rank: Super Contributor
timestamp: June 23, 2019, 10:05:37 am
content: Hi.Do not worry about getting everything before you start. Get things as you need them.Re the power supply. I doubt a simple capacitor will fix the issue.At supposid 10A output, I doubt it is a linear, more likely a smps.In a 10A linear psu, the transformer alone would be bigger than the whole unit!Additionally, linears have to convert unused voltage/current into heat, so 30V at 10A is worst case 300Watts of heat to get rid of.That means, the psu is definitely a smps of some sort.So, no transformer and no heat sink. Case, displays, knobs yes.Can you get a smps for $10? Probably a really cheap nasty one.So, yes a psu is probably on its way to you.Will it work? Probably, but for how long.Will it have overshoot? Personally I have no idea but I would guess yes due to the price.Try it out when you get it.Do a tear down for everone here.For a learning project, let everyone here guide you on how to modify it to work properly.It is still made with cheap part. You may even be able to replace them for good ones.It is worth the effort? No, not for a working psu but maybe yes for the learning.Keep an eye out on ebay for old used linears. In USA, lab/test equipment is more available than in Europe, especially at bargin priceses.

author: Arhigos
author_rank: Regular Contributor
timestamp: June 23, 2019, 11:38:46 am
content: 1) Keysight scope is good2) Waveform generator is good too.3) Power supply is 100% scam. If you need budget adjustable power supply go and get lm2596 and connect it to any laptop power supply.4) Soldering station is ok, but you can get same functionality if you buy cheaper 852d+ for $50. Or hot air and T12 iron separately.

author: Rx7man
author_rank: Regular Contributor
timestamp: June 23, 2019, 03:08:33 pm
content: While lacking a higher voltage capacity, what about an ATX power supply.. a few banana plugs on it for a few of the common voltages, -12, 3.3, 5 and +12 should be fairly accurate, could add an adjustable output as well..One thing I've noticed about stuff from china is they often move the decimal points around on you, 1.0 becomes 10 all of a sudden... had some batteries that were at about 1/10 the advertised capacity and such

author: Microcheap
author_rank: Frequent Contributor
timestamp: June 23, 2019, 03:28:51 pm
content: Just be aware that the power supply is a scam, there are plenty of threads in this forum with similar cases.I myself tried the lucky once and posted ithere.You probably will get your money back as you are protected by ebay and paypal, but it doesn't worth the hassle to try.

author: Rx7man
author_rank: Regular Contributor
timestamp: June 23, 2019, 04:21:52 pm
content: Yeah, I'm thinking there's a whole pile of hacked/scam accounts out there...This one looks really badhttps://www.ebay.com/sch/yewg770-4/m.html?_nkw=&_armrs=1&_ipg=&_from=

author: windsmurf
author_rank: Frequent Contributor
timestamp: June 23, 2019, 04:33:12 pm
content: Quote from: Rx7man on June 23, 2019, 04:21:52 pm$3.99 30V 10A Power supply shipped free from China!

author: MosherIV
author_rank: Super Contributor
timestamp: June 23, 2019, 04:43:17 pm
content: QuoteI would advised not using ATX PSUs as a substitute bench psu.The main problem is lack of current limit.The 3.3 or 5V rails will deliver the full rated current into what ever is unlucky enough to be connected.While this might be amusing to some, be a boon to some.For first time power on of circuits, it is very foolish.If you have a spare lying around and budget forces you into it. Ok but if you have a choice - avoid it.In another thread someone mentioned using a wallwart and a LM317.This will be quite easy for first project and the current will be limited to what ever the wall wart is limited to.

author: jjoonathan
author_rank: Frequent Contributor
timestamp: June 23, 2019, 04:54:28 pm
content: One time I popped the MCU on a $200 prototype on account of a "quirk" in a $15 power supply.https://www.eevblog.com/forum/testgear/cheap-power-supply-pitfalls/msg1319146/#msg1319146After that I swore off the "bare circuit board" tier of power supplies and bought a couple TP3005T. They haven't let me down

author: Rx7man
author_rank: Regular Contributor
timestamp: June 23, 2019, 05:04:49 pm
content: Looking at other power suppliesAgilent 6227B, looks a little rough but 2x 20V 2A with current limiting seems like a reasonable unit to start with, Little rough around the edges, $60Elenco, can't remember the model number, 4 output, 3 fixed -12, +5, +12V and one variable 20v 2AHP 6236B, +/- 0-20V 2.5A, and 0-6V 1A looks like a fairly versatile unit as well... Shipping is always the killer on these old bricks though.I do have a transformer from an old stereo, I think it had +/-50V rails and some lower voltage ones as well, I could probably make something from it.. a couple fixed outputs with LM series regulators.. Again, as you say, unless I'm going to get a bit fancy with it I'm not going to have current regulation, and I do value that!

author: MosherIV
author_rank: Super Contributor
timestamp: June 23, 2019, 07:19:36 pm
content: Get a proper PSU when you NEED it.If you have transformers to use and are confident with building mains, by all means throw something together.Instead of building the biggest most powrrful thing you can, try buildinb for what you need.If you all doing low powered circuits, try building a psu which can only supply 200mA, that way the worst that can happen is that you fry some compononet with 200mA instead of with 3AOnce you are happy with fixed or even variable voltage (lm317), try workinb out how to do current limit.

author: Rx7man
author_rank: Regular Contributor
timestamp: June 23, 2019, 08:22:08 pm
content: Fried is fried right? lolI'll start a thread in the right place when/if I get serious about it, but here's the transformer I have in mind, I think it's about 250-350 va, I can't remember exactly what stereo it came from, Just hooked it up and did some measurements on it, the center tapped windings are a decent gauge, non center tapped ones are light gauge.. there's a part number I can't read anymore on it.

author: tautech
author_rank: Super Contributor
timestamp: June 23, 2019, 08:28:44 pm
content: Yummy !That should make a nice PSU but a little bit of thinking will be required to relay switch all those windings so to not have too much dissipation losses in the regulator circuit.......good future project !

author: Rx7man
author_rank: Regular Contributor
timestamp: June 27, 2019, 04:34:58 pm
content: Well, That power supply was a scam, Ebay removed the item and refunded me... Seems to be a lot of those items (all stuff I want) being scam items right now.. Usually buyers have been there less than a year and have less than 100 items sold... There were some Baofeng 2 way radios for $5 each that were scams too.

author: Old Printer
author_rank: Frequent Contributor
timestamp: June 28, 2019, 07:43:26 pm
content: When starting my bench I pickup up a few of the old HP 6216As on eBay. Found most in nice shape for $40-60 each shipped. Built like a tank, easy to work on and HP wrote an excellent service manual which is easy to find online. They stack nice too.

author: bsudbrink
author_rank: Frequent Contributor
timestamp: June 28, 2019, 07:47:50 pm
content: Uh, the electrons are all gonna fall out.

author: Old Printer
author_rank: Frequent Contributor
timestamp: June 28, 2019, 09:14:59 pm
content: Quote from: bsudbrink on June 28, 2019, 07:47:50 pmThat was weird

author: bsudbrink
author_rank: Frequent Contributor
timestamp: June 28, 2019, 09:17:41 pm
content: My cell phone camera does that all the time. You look at it on the phone, fine. You upload it somewhere, upside down.Those are nice little supplies, BTW.

author: Rx7man
author_rank: Regular Contributor
timestamp: June 29, 2019, 07:08:13 pm
content: I have been seeing those old HP units on fleabay.. I may get one, but I still kinda want to build my own and see how it performs as a learning project.

author: Old Printer
author_rank: Frequent Contributor
timestamp: June 30, 2019, 03:16:30 pm
content: Quote from: Rx7man on June 29, 2019, 07:08:13 pmA great project and you would learn a lot, but I would buy a working unit with a good service manual first, to have one to study. There are so many vintage, serviceable pieces out there pretty cheap. A couple years ago I ran across a guy on ebay that had a bunch of the BK 1651 analog triple output supplies from the ITT sales. I got them for about $45 shipped each, but one was a dud, so he let me keep it and sent another. Tektronix had rebadged the same unit as their CPS250 and put out a great detailed service manual with schematics, which was obsolete and easy to find. I studied that thing for a month before I tracked down a bad 10 cent diode, but learned a ton in the process. Even a mid-level PS like that is a very complicated circuit, way beyond my ability to design anything close.

author: Rx7man
author_rank: Regular Contributor
timestamp: June 30, 2019, 04:25:17 pm
content: Quote from: Old Printer on June 30, 2019, 03:16:30 pmI had a Marantz 2275 with a bad cap that caused a hum.. found it without a manual, but found a manual since..I will keep an eye out for non working units.. Do you have a favorite site to source manuals? I think I found most of my Marantz ones on eserviceinfo.com

author: Old Printer
author_rank: Frequent Contributor
timestamp: June 30, 2019, 08:16:00 pm
content: In general the BAMA Boat Anchor Manual Archive is stop one, though Artech sells a lot of TEK & HP scanned to PDF for a very fair price. Other than that, ebay and Google are your best friends. Honestly, look for a working one first, they are pretty close in price to the non-working units. Make sure you can get the manual before you buy and make sure it is a good service troubleshooting manual. Makes all the difference in the world.

author: Rx7man
author_rank: Regular Contributor
timestamp: July 06, 2019, 06:00:28 pm
content: Well, i got my Keysight DSO1052B and signal generator in the mail yesterday WEEEE!!... Scope was listed as a used item but is absolutely mint, no probes with it but has calibration sheet... Was there a firmware hack for this model?So I've ordered some probes, clips, and whatnots.. I have a few odds and ends around anyhow.Meanwhile, for the power supply, I was in a surplus store and found a 8V/10A or 16V/5A (or 8+8V and 5A) transformer that would be a better starting point for a power supply than the one I pictured earlier.