Tenma universal test center 72-5085 - Page 1
Forum section: electronics / testgear

author: RJ
author_rank: Contributor
timestamp: November 20, 2016, 02:58:49 pm
content: Tenma universal test center 72-5085Has anyone owned one of these?I would like some thoughts on this unit for my CB radio work bench.Thank you.

author: saturation
author_rank: Super Contributor
timestamp: November 20, 2016, 04:47:17 pm
content: They were used in schools. If you bought each instrument separately and spent <= $100 each, each of those purchases would far exceed the specifications of that station's instrument. The main advantage of Tenma is having it all in one case. Tenma sold new for about $550.http://www.eham.net/reviews/detail/5875Teardowns:https://www.eevblog.com/forum/reviews/metex-universal-combined-test-instrument-systemsstations-a-look-inside/25/

author: RJ
author_rank: Contributor
timestamp: November 20, 2016, 04:56:10 pm
content: Quote from: saturation on November 20, 2016, 04:47:17 pmThanks for the link, I had read that link before and made me think its a good buy. Not much talk about these units in the CB world but did find a couple that spoke of them. I just bought one with hopes it will be in good shape and everything works on it. No manual and can't seem to find one online that does not have adware added to the download that my security shuts it down.Maybe someone on here owns one that will give some info about this unit for other lost souls like me to read.

author: saturation
author_rank: Super Contributor
timestamp: November 20, 2016, 05:14:04 pm
content: The link to eevblog archive has manuals and schematics to the Metex version, which is similar or maybe the same. Enjoy.

author: RJ
author_rank: Contributor
timestamp: November 20, 2016, 11:49:18 pm
content: Could not find the archives but did learn it is the same unit as Metex 9160. I downloaded both the manual and service manual for it.Asking around it seems there are mixed emotions on using this unit for a CB bench.1. The 13.8 Volts @ 3 amps max will limit what radios can be hooked up to it.2. The the max output on the signal generator is 10 MHz.The Universal System incorporates :1. Function Generator, capable of generating seven(7) forms of wave, ie, Sine, Square,Triangle, Skewed Sine, Ramp, Pulse and TTL level square in the seven frequency rangesourcing 1Hz to 10MHz2. Frequency Counter, capable of measuring the frequency ranges from 20MHz to 2.7GHz.3. DC Power Supply, capable of generating the voltage carrying with 5V/2A, 15V/1A fixedand 0-30V/3A variable.4. Digital Multimeter, capable of measuring DC/AC voltage up to 1000V DC/750C AC,DC/AC current up to 20A, Resistance up to 40M?, Capacitance up to 400?F, and Logictest(C-MOS/TTL). This section can be hooked into data acquisition system run on PersonalComputers, printers or pen-plotters, etc, through a USB interface connector

author: saturation
author_rank: Super Contributor
timestamp: November 21, 2016, 01:27:19 am
content: That's good news, then you have most of the schematics and operator's manual from the eevblog archives, that is the old posts.Just beware the published specifications may not be entirely true. What I recall the most was the function generator waveforms are unstable near 1MHz and yes you can reach 2 or 10 MHz but only as sine wave with a lot of jitter and amplitude instability. The units overall capabilities were never pushed to the upper end of its ratings, so its unclear what it can really do. You can read of the experiences of others in the archive posts. It does make a great student station, in class everyone got the same set of tools, the instructions applied to the whole station and its size and weight made in unlikely to fall off the lab bench or get stolen.Quote from: RJ on November 20, 2016, 11:49:18 pm

author: RJ
author_rank: Contributor
timestamp: November 21, 2016, 02:23:34 am
content: I found the correct user manual for the Tenma universal test center 72-5085. It is NOT the same as Metex 9160. This unit only goes to 2 MHz Not 10 MHz.After digging for hours to find the correct manual for this unit showed me I bought the wrong item for what I thought it was.Hope this will save someone else from making a bad choice like I did!I tried to upload the manual but site says it is to large so if anyone needs the correct Tenma universal test center 72-5085 manual send me a PM with your email address and I will send it to you.

author: Fraser
author_rank: Super Contributor
timestamp: November 21, 2016, 02:50:10 am
content: I owned four of the METEX versions. Paid £50 each for them in the UK. Sold one for £50, stripped one down to parts and gave the other two to the charity shop. They are just too heavy to pack for shipping for such a small return on them.My opinion of them is mixed. They claim to do much and they do work, to a fashion. Sadly I found that they did nothing particularly well. I would always go for the separate units that I would choose to meet my needs and they would likely be better quality. The power supply was decent enough and really the best part of the unit. the multimeter was pretty poor in terms of speed of response and it was very cheap in terms of design. Basic would describe it well. The function Generator and frequency counters were both built down to a price and so mediocre in terms of performance. I trusted neither in terms of accuracy. In my case they ended up piled up in a corner of the garage and made for pretty large space hoggers, hence why I got rid of them. People asked me to ship them all over the UK, and even overseas. I honestly do not think they are worth that effort and would likely disappoint the new owner.To be fair, I initially liked the design, if a little cheap and nasty in appearance. With time I realised that I just did not trust them enough to use them and so they were a waste of money. I would not risk a valuable bit of kit on the power supply and did not trust the other instruments enough to use them. For use in school labs they are perfect. Not too expensive and good enough for basic lab experiments. I still have the parts stripped out of the one I dismantled somewhere but I think I saved only parts that had some use, such as the LCD displays and frequency counter for its counter chip. The multimeter and function generator had little worth saving in them.Fraser

author: RJ
author_rank: Contributor
timestamp: November 21, 2016, 12:00:55 pm
content: Yeah it seems to be worthless for what I need it for and hope I can call the guy this morning before he ships it to see if I can get a refund. If not then I am stuck with a huge paper weight! I should have figured it out faster with such little info on the net about these units. Once I found this site from doing mass searches all weekend was really the only place where someone talked about them. Got my fingers crossed he will refund.Thanks guys for all your help. Glad to have found this site!

author: RJ
author_rank: Contributor
timestamp: November 21, 2016, 06:25:13 pm
content: Got lucky and got a full refund. Whew... Thanks again everyone for the help and info.

author: Fraser
author_rank: Super Contributor
timestamp: November 21, 2016, 07:57:49 pm
content: RJ,You 'dodged the bullet' well doneI recommend that you take a careful look at your specific needs and buy a selection of test equipment (used or new) that meets your nees. This will have the advantage of being far more portable as well.For CB radio work and similar (Ham Radio etc) I recommend the following:1. Digital Multimeter. It does not have to be a FLUKE ! Even a UNI-T unit will provide good service.2. Diode Probe for RF signal detection and measurement using a multimeter. FLUKE make one(FLUKE 85 RF) but you can easily make your own.3. Cheap Oscilloscope. I suggest you consider a used 20MHz analogue if cost is an issue. A 20MHz Hameg CRO still triggers fine at 30MHz. A DSO needs to have adequate bandwidth and sample rate to work at frequencies found in a 27MHz CB. I suggest a 1Gs/S/100MHz as a minimum.4. Simple RF signal Generator. A new or used RF signal generator can be expensive. Note that an RF signal generator is VERY different to a Function Generator. A cheap RF signal Generator often comes in the form of a simple analogue unit with a capability of around 100MHz, with up to 400MHz using harmonics. Yes, Harmonics are intended to be left unfiltered to gain higher frequency coverage. I own a couple of these signal generators and they are great for a quick RF source that produces a decent sine wave.Used units like this sell for around £50 to £100 in the UK.5. Cheap Frequency counter.You can buy new, use or a kit and yo need not spend a fortune on one for basic work. Kits are very cheap and usually use a PIC at their heart. The frequency counter is needed to check CB oscillator frequencies and also may be used on the analogue RF signal Generator to see exactly what frequency it is producing. The frequency counter does need to be accurate and I recommend one with a TCXO or better stabilised crystal oscillator. Buy a Frequency counter that covers the frequency range of interest. 50MHz will be OK for 27MHz CB's but I recommend one with 100MHz capability or better if possible. You used to be able to buy dedicated 'accessory' CB frequency counters but I advise against them. They often sample teh RF output and are not the type I would use on a test bench for general use.6. Power Supply unit. A variable power supply is an important part of a test bench. Sadly they can be expensive and you do tend to get what you pay for. Dedicated CB power supplies are normally set to 13.5V and can supply decent current. They are often pretty simple and you can build a fixed voltage supply relatively easily. CB power supplies in the UK are just a large 12V transformer with full wave rectifier, 10,000uF smoothing capacitor and a simple voltage regulator circuit. Such a power supply need not be very expensive.7. A decent set of trimpot and ferrite core trim tools. Do not make the mistake of using metal jewellers screw drivers on ferrite cores !Hope this helps a little.Fraser

author: RJ
author_rank: Contributor
timestamp: November 22, 2016, 12:05:14 am
content: Fraser,Yes sir that was a close one!Thanks for all the info. Its nice to see there is someone out there that wants to help newbies.Here is what I have so far:EXTECH EX520 MultimeterFluke 110 Plus MultimeterCheap Digital Multimeter that I hook my home-brew RF probe onAnti Static Non Magnetic Ceramic Screwdriver Set YR 034 105mm 4"Belden RG-174/U Miniature 50 ohm coax for making probes and suchRF Sampler 1-30 MHz SamplerLC100-A Digital LCD High Precision Inductance Capacitance L/C Meter TesterEZ Digital OS-5060A Analog Oscilloscope 60MHZ 45WP6060 1X 10X Probe Oscilloscope Probe Kit 60MHZ Oscilloscope Sonde TipFluke 1900A Multi-CounterSemiconductor Tester Model 72-9652in1 Soldering Station Rework Hot Air & Iron 852DWeller 45W Soldering IronMark IIB WattmeterPDC600 SWR/Watt/Modulation Test CenterAstron RS-50A Power SupplyKem Tron FC-50 Freq counter2 Micronta Fet Volt MetersSylvania SWR-Field Strength meter I converted to use as a RF probePDC1 SWR Meter1000 Watt Dummy Load2- 100 Watt Dummy loadsM328 DIY Kit Capacitance ESR Inductance Resistor LCR Meter Component Tester. Still waiting from Hong Kong.HP 8656B Signal Generator 0.1-990 MHzEdited to add a few things I missed and plus say my offer was accepted for the Sig Gen. Doing the happy dance

author: CJay
author_rank: Super Contributor
timestamp: November 22, 2016, 12:52:24 pm
content: More than enough to get you going, build a dummy load with diode detector to hook up to your DMM and you'll have a power measuring device capable of repeatable accuracy that's better than a lot of off the shelf power meters.http://k4eaa.com/dummy.htmlIf the sig gen offer falls through, until another turns up, you can get by with one of the cheap AD9850/1 or Si5351 boards and a programmed PIC chip/arduino, should cost well under $20. They're easy to AM modulate if you add a buffer stage (FM is *way* more complex).I found the cheap 6 and 8 digit eBay counters that sell for around £8 to be very usable and more accurate than the 'lab grade' bench counter I had (and sold), they agreed with my Racal counters (fitted with the oven option) to within a couple of Hz but you'll need to build an enclosure and work out a way of getting signal into them.

author: RJ
author_rank: Contributor
timestamp: November 22, 2016, 03:51:41 pm
content: Thanks CJay for the info.I edited my post to add 3 things I forgot to list. That is a cool trick on the dummy load. I done a DIY RF probe that hooks to the cheap DMM and works well but I like the idea of the one you posted.If all goes well one of those 4 generators will be mine by tomorrow. I will look into those cheap AD9850/1 or Si5351 boards you spoke of.Thanks again for your help.

author: RJ
author_rank: Contributor
timestamp: November 22, 2016, 10:35:36 pm
content: Few counter offers back and forth for the HP 8656B Signal Generator and she is now on her way to me