Author Topic: My $50 scope (Hung Chang) Tenma 72-720 [Inside Photos!]  (Read 26103 times)

0 Members and 1 Guest are viewing this topic.

Offline edy

  • Super Contributor
  • ***
  • Posts: 1682
  • Country: ca
    • DevHackMod Channel
Re: My $50 scope (Hung Chang) Tenma 72-720 [Inside Photos!]
« Reply #50 on: August 15, 2013, 09:19:34 am »
Confirmed from seller.... It's in the mail. Should receive my JDR 2000 in a little while. Can't wait to try it out and pit it against my Hitachi which I bought at the same time (the JDR was an "accidental" ebay win since I actually got the Hitachi first and nobody bid again on the JDR so I was stuck with it). But for $20 (plus $30 in shipping), I didn't cry over it too much.

Will post pictures and video once I get it... I know it is a cheap low quality scope, but will be interesting to see!
YouTube: www.devhackmod.com
"Ye cannae change the laws of physics, captain" - Scotty
 

Offline Stonent

  • Super Contributor
  • ***
  • Posts: 3824
  • Country: us
Re: My $50 scope (Hung Chang) Tenma 72-720 [Inside Photos!]
« Reply #51 on: August 15, 2013, 04:32:22 pm »
Confirmed from seller.... It's in the mail. Should receive my JDR 2000 in a little while. Can't wait to try it out and pit it against my Hitachi which I bought at the same time (the JDR was an "accidental" ebay win since I actually got the Hitachi first and nobody bid again on the JDR so I was stuck with it). But for $20 (plus $30 in shipping), I didn't cry over it too much.

Will post pictures and video once I get it... I know it is a cheap low quality scope, but will be interesting to see!

50$ scope club!  :-+
The larger the government, the smaller the citizen.
 

Offline ddavidebor

  • Super Contributor
  • ***
  • Posts: 1012
  • Country: it
    • Fermium LABS website
My $50 scope (Hung Chang) Tenma 72-720 [Inside Photos!]
« Reply #52 on: August 15, 2013, 08:04:38 pm »
Not quite Won Hung Lo, but apparently also Hung Chang OS-620.

http://www.radiomuseum.org/r/hungchang_oscilloscope_os_620_depos.html


I've one!

Is the shietties shit i've ever seen. Looks like crap 80' consumer electronic inside
Davide Bortolami,
Fermium LABS srl
 

Offline edy

  • Super Contributor
  • ***
  • Posts: 1682
  • Country: ca
    • DevHackMod Channel
Re: My $50 scope (Hung Chang) Tenma 72-720 [Inside Photos!]
« Reply #53 on: August 15, 2013, 11:39:49 pm »
Still, if it works you can't complain too much. Even a cheap scope is an incredibly useful bit of kit, and I imagine you will keep it around for a long time even after you upgrade because sometimes you don't want to risk your expensive tools when checking some unknown device.

True, I'd much rather blow up the cheap scope while I'm learning. :-)

Another advantage is that with the schematics available and apparent use of cheap off the shelf components, one could possibly understand and fix it more easily. It is a basic design and being one-sided through hole you can follow all the traces and parts are large (none of that SMT stuff).
YouTube: www.devhackmod.com
"Ye cannae change the laws of physics, captain" - Scotty
 

Offline edy

  • Super Contributor
  • ***
  • Posts: 1682
  • Country: ca
    • DevHackMod Channel
Re: My $50 scope (Hung Chang) Tenma 72-720 [Inside Photos!]
« Reply #54 on: August 26, 2013, 11:31:31 am »
Finally arrived, Here's my $20 ebay win... JDR 2000, 20mhz rebrand of the Hung Chang. Works like a charm! And it came in original box, with 2 sets of probes with spring-hook tip options, some fuses and paper manual!

One question... Why is the square ref wave look ok with 1x on both of my probes, but has a capacitance issue when set to 10x? I played around with the screw on the probe but nothing changes when it is set to 10x... It overshoots and then settles for each square... As soon as I go back to 1x on the probe it looks nice (like the attached photo).
YouTube: www.devhackmod.com
"Ye cannae change the laws of physics, captain" - Scotty
 

alm

  • Guest
Re: My $50 scope (Hung Chang) Tenma 72-720 [Inside Photos!]
« Reply #55 on: August 26, 2013, 11:42:28 am »
See:

Your problem is probe compensation. The input of a probe is not just a 1 Mohm resistor, but there is some capacitance (in the order of 20 pF) in parallel. At higher frequencies (above a few tens of kHz or so), this capacitance becomes dominant. This does not matter for a 1x probe: it is 'just' a fancy specially engineered piece of screened coax. A 10x probe attenuates the signal by putting a 9 Mohm resistor in series, however. The capacitance in parallel with this 9 Mohm resistor has to match the capacitor in the scope (20 pF / 9 in my example). It becomes a capacitive divider at higher frequencies. Adjusting the cap matches the attenuation of this capacitive divider to the attenuation of the resistive part, so low and high frequencies are attenuated equally.

So turning the trimmer should allow you to switch the probe from undercompensated to overcompensated, with correctly compensated in between. Why doesn't this work?
- Maybe you're twisting the wrong trimmer. Some probes feature a LF and a HF compensation (ignore the HF compensation for now). Is there another trimmer in either the probe body and the part near the BNC connector?
- Probes are designed for a limited range of input capacitances. Maybe the input capacitance of your scope is outside this range? This is not likely unless the probe in designed for high frequencies well beyond 100 MHz, the probe is very old, or the scope has a capacitance much higher than 20 pF. You should be able to find the input capacitance of the scope either on the front panel or in the manual. You may be able to find the input capacitance of the probe in the datasheet if it's a brand name probe.
- The probe may also be broken.

What happens if you connect it to your other recently acquired scope and try to adjust it?
 

Offline edy

  • Super Contributor
  • ***
  • Posts: 1682
  • Country: ca
    • DevHackMod Channel
Re: My $50 scope (Hung Chang) Tenma 72-720 [Inside Photos!]
« Reply #56 on: August 26, 2013, 12:23:11 pm »
Thanks for your advice. Ok, fortunately I got a couple probes thrown in with my Hitachi and when I set them to 10x and adjust the compensation I see the curvature flatten out on my square... On BOTH scopes it works perfectly, either 1x or 10x setting.

However, the probes thrown in with my JDR 2000 appear to be broken at 10x setting. The little screw turns and turns with no resistance. If I press and bend the screw at the appropriate tongue angle I see the compensation curvature vary... But it doesn't stick. So these are going to be good only at 1x setting.

Meanwhile, I got a surprising goodie with the JDR...

- Original manual (different from what I've seen online)
- Original invoice (purchase date, price)
- Lots of schematics, full parts list
- JDR Microdevices San Jose flyer Sept 1987

These are worth a scan and upload for you guys.. It is hilarious.

PS - The attached picture shows a probe that actually WORKS (one of the two that came with the Hitachi which both work at 10x)
« Last Edit: August 26, 2013, 12:29:50 pm by edy »
YouTube: www.devhackmod.com
"Ye cannae change the laws of physics, captain" - Scotty
 

Offline edy

  • Super Contributor
  • ***
  • Posts: 1682
  • Country: ca
    • DevHackMod Channel
Re: My $50 scope (Hung Chang) Tenma 72-720 [Inside Photos!]
« Reply #57 on: August 26, 2013, 12:47:49 pm »
Here is the invoice and an exerpt from the manual (component tester). I thought that was interesting. It must work by doing some kind of sweep across the component and seeing the response. Looks like it is internally using the sweep to set X position while the component response becomes the Y. Otherwise you would have to use an external sawtooth to generate it. Is this correct?
YouTube: www.devhackmod.com
"Ye cannae change the laws of physics, captain" - Scotty
 

Offline edy

  • Super Contributor
  • ***
  • Posts: 1682
  • Country: ca
    • DevHackMod Channel
Re: My $50 scope (Hung Chang) Tenma 72-720 [Inside Photos!]
« Reply #58 on: August 26, 2013, 12:55:12 pm »
Excerpt from the manual.... What's a "regurator" ?  ;)
YouTube: www.devhackmod.com
"Ye cannae change the laws of physics, captain" - Scotty
 

Offline edy

  • Super Contributor
  • ***
  • Posts: 1682
  • Country: ca
    • DevHackMod Channel
Re: My $50 scope (Hung Chang) Tenma 72-720 [Inside Photos!]
« Reply #59 on: August 26, 2013, 01:09:23 pm »
One last set of images (divided over 2 posts)... A JDR microdevices Sept 1987 brochure. This was stuffed inside the JDR 2000 manual, next to the invoice.

Not bad for 1987... $350 for this scope. What was that in 1987 dollars converted to today?

Looks like JDR Micro and Dick Smith and scores of other electronics shops were able to import these and slap their name on it. Original box clearly says made in Korea. Wow it is 26 years old now.
YouTube: www.devhackmod.com
"Ye cannae change the laws of physics, captain" - Scotty
 

Offline edy

  • Super Contributor
  • ***
  • Posts: 1682
  • Country: ca
    • DevHackMod Channel
Re: My $50 scope (Hung Chang) Tenma 72-720 [Inside Photos!]
« Reply #60 on: August 26, 2013, 01:13:42 pm »
Here's the second half of the brochure. Worth a blast from the past.
YouTube: www.devhackmod.com
"Ye cannae change the laws of physics, captain" - Scotty
 

alm

  • Guest
Re: My $50 scope (Hung Chang) Tenma 72-720 [Inside Photos!]
« Reply #61 on: August 26, 2013, 01:32:16 pm »
Here is the invoice and an exerpt from the manual (component tester). I thought that was interesting. It must work by doing some kind of sweep across the component and seeing the response. Looks like it is internally using the sweep to set X position while the component response becomes the Y. Otherwise you would have to use an external sawtooth to generate it. Is this correct?
In generates a low frequency (usually mains frequency) sine that's fed through a resistor and the DUT. The scope plots the voltage against the current (voltage across the resistor). Search for octopus or Huntron tracker for similar equipment. Many Hameg scopes also feature a component tester.
 

Offline PedroDaGr8

  • Super Contributor
  • ***
  • Posts: 1252
  • Country: us
  • A sociable geek chemist
Re: Re: My $50 scope (Hung Chang) Tenma 72-720 [Inside Photos!]
« Reply #62 on: August 26, 2013, 02:33:50 pm »

Not bad for 1987... $350 for this scope. What was that in 1987 dollars converted to today?

that's about$720 now.

Sent from my EVO using Tapatalk 4

The very existence of flamethrowers proves that some time, somewhere, someone said to themselves, "You know, I want to set those people over there on fire, but I'm just not close enough to get the job done." -George Carlin
 

Offline Stonent

  • Super Contributor
  • ***
  • Posts: 3824
  • Country: us
Re: My $50 scope (Hung Chang) Tenma 72-720 [Inside Photos!]
« Reply #63 on: August 28, 2013, 09:37:55 am »
Notice the invoice made it sound like it was a warranty replacement for another scope.

My Tenma is the only one I've seen so far that doesn't have what appears to be a removable plate on top with the brand. 
The larger the government, the smaller the citizen.
 

Offline edy

  • Super Contributor
  • ***
  • Posts: 1682
  • Country: ca
    • DevHackMod Channel
Re: My $50 scope (Hung Chang) Tenma 72-720 [Inside Photos!]
« Reply #64 on: August 28, 2013, 02:35:48 pm »
Notice the invoice made it sound like it was a warranty replacement for another scope.

My Tenma is the only one I've seen so far that doesn't have what appears to be a removable plate on top with the brand. 

Yes I noticed that too. However, given that it was done in 1987 and I don't think these scopes were around for too many years, could be the first few models had problems and maybe died prematurely, and they needed to be replaced?

I had a look inside my "JDR 2000" and actually was surprised by how clean it looked! I wonder if they changed the internals along the way. My scope has only a few boards, few wires jumping around. I should post a picture so you can have a look. I somehow remember a photo previously in this thread showing a tangled mess, but I could be mistaken. It was actually fairly simple construction.

I attached a few photos here and in the next post (as file size exceeded).
« Last Edit: August 28, 2013, 03:52:53 pm by edy »
YouTube: www.devhackmod.com
"Ye cannae change the laws of physics, captain" - Scotty
 

Offline edy

  • Super Contributor
  • ***
  • Posts: 1682
  • Country: ca
    • DevHackMod Channel
Re: My $50 scope (Hung Chang) Tenma 72-720 [Inside Photos!]
« Reply #65 on: August 28, 2013, 03:26:54 pm »
Ok, so here are the guts of my "JDR 2000". I thought it was cleaner, but it looks the same. I see some Toshiba, Intersil?, Motorola? and Texas Instruments branded stuff in there, and other companies but I can't find the IC parts online (seem to be too old). Here's a page with logos in case for manufacturer chip ID: http://www.classiccmp.org/rtellason/logos/semiconductorlogos.html
« Last Edit: August 28, 2013, 03:31:54 pm by edy »
YouTube: www.devhackmod.com
"Ye cannae change the laws of physics, captain" - Scotty
 

Offline Stonent

  • Super Contributor
  • ***
  • Posts: 3824
  • Country: us
Re: My $50 scope (Hung Chang) Tenma 72-720 [Inside Photos!]
« Reply #66 on: August 28, 2013, 03:50:12 pm »
Aside from the picture tube, you could build one of these at Radio Shack / Tandy :P

Now that I got a new phone I'll need to take some better pictures of the insides of mine.
« Last Edit: August 28, 2013, 03:52:07 pm by Stonent »
The larger the government, the smaller the citizen.
 

Offline edy

  • Super Contributor
  • ***
  • Posts: 1682
  • Country: ca
    • DevHackMod Channel
Re: My $50 scope (Hung Chang) Tenma 72-720 [Inside Photos!]
« Reply #67 on: August 29, 2013, 02:09:53 am »
Looks like someone is selling one in Canada (near Toronto)... Here is the listing:

http://toronto.kijiji.ca/c-buy-and-sell-electronics-20-meg-dual-channel-oscilloscope-W0QQAdIdZ517202894

They want $275 for it. Wow.  And the image (can't make out the branding):

YouTube: www.devhackmod.com
"Ye cannae change the laws of physics, captain" - Scotty
 

Offline ddavidebor

  • Super Contributor
  • ***
  • Posts: 1012
  • Country: it
    • Fermium LABS website
Re: My $50 scope (Hung Chang) Tenma 72-720 [Inside Photos!]
« Reply #68 on: August 29, 2013, 06:43:04 am »
i'd like to pay like 8$ max only if the shipping is free and if 50% of the money go to some poor african kids
Davide Bortolami,
Fermium LABS srl
 

Offline edy

  • Super Contributor
  • ***
  • Posts: 1682
  • Country: ca
    • DevHackMod Channel
Re: My $50 scope (Hung Chang) Tenma 72-720 [Inside Photos!]
« Reply #69 on: August 31, 2013, 11:27:08 am »
Here is a "KB Electronics" branded version, being sold on Kijiji in Toronto, Canada for $200... Quick, somebody grab it before it gets sold!!!  :-DD 

http://ontario.kijiji.ca/c-buy-and-sell-electronics-KB-Electronics-Oscilloscope-with-Probes-Cash-or-Trades-W0QQAdIdZ516292376

KB Electronics Model 33330 Oscilloscope. I've attached an image.

Here's the tally so far:

Tenma 72-720
Elenco MO-1251
Hung Chang OS-620
Neotronics OS-620
JDR Model 2000
A-1 Electronics
AW Sperry 620C
Tenma 72-320
Dick Smith Q-1240
Aron BS-601
Degem System 112
Ramsey Model 2200
KB Electronics Model 33330
YouTube: www.devhackmod.com
"Ye cannae change the laws of physics, captain" - Scotty
 

Offline Stonent

  • Super Contributor
  • ***
  • Posts: 3824
  • Country: us
Re: My $50 scope (Hung Chang) Tenma 72-720 [Inside Photos!]
« Reply #70 on: September 02, 2013, 05:14:38 pm »
 :-+
The larger the government, the smaller the citizen.
 

Offline Ahyuan

  • Contributor
  • Posts: 5
Re: My $50 scope (Hung Chang) Tenma 72-720 [Inside Photos!]
« Reply #71 on: October 21, 2013, 11:25:14 am »
My physics teacher gave me one of these since it was broken and I fixed it!
An input filter capacitor failed short so the -9V rail was not working and another capacitor had caught on fire

The only capacitor in my very small parts bin happened to have the same value and I paralleled some resistors to get the 47 ohms and it works!

It's actually a very nice scope!

 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf