A few notes on experiences with the Hameg 203-7 Scope.

[David G4EBT]

Given that lots of forum members have bought Hameg scopes over recent months which ‘Mark in Manc’ has rescued from the skip to raise money for Christian Aid, I thought some comments on the 203-7 scope that I bought from Mark earlier this week (faulty, for spares or repair), as a back-up to my existing 203-7 scope might be of interest.

Firstly, there’s a useful video on the EEVBlog of Davy Jones in Oz, looking into a Hameg scope he bought at auction for $19 AU, which he later donated in a free raffle on his forum:

http://www.bing.com/videos/search?q=...3FD6&FORM=VIRE

On that scope (not a 203-7 but very similar), the V/Div controls weren’t working and he was unable to effect a repair. It’s a major strip-down to get at the pots and they’re a custom design. Both of the V/Div controls on my scope were also known to be not working – the knobs just twizzle round and round so it isn’t possible to calibrate the scope with the internal calibrator, which provides a 2V and 0.2V square wave for calibration purposes.

At 40 mins into the video, the shaft in the plastic boss at the rear of the pot can be seen slipping around. It’s secured to the shaft with two allen screws, but in looking at my scope, it’s evident that the Allen screws don’t simply work loose – the plastic boss cracks due to fatigue over the years, (which another forum member alluded to in another thread). Were it possible to easily get to the two pots, the boss could be repaired by fitting a metal sleeve over it to hold the fractured boss together. However, the fault only affects the accuracy of V/Div calibration, which isn’t a critical factor – certainly not for my purposes. That said, by gently pressing on the knob and turning it while observing the trace height, I was able to line it up.

I’ve attached a (not very clear) pic of the right hand pot and hopefully, the crack in the white plastic can be seen. (I’d managed to turn the boss with a dental probe to be able to see the grub screws and the crack). Maybe someone who owns a Hameg scope which exhibits this fault and is more adventurous than me, will dive in and discover how to remove that PCB to get to the two pots? No guts no glory!

At the 43 mins stage in Davy Jones's video he comments on the component tester not working. The fault was simply a duff 50mA fuse on the component tester board. The tester in my scope wasn’t working either, so I checked the fuse. It wasn’t open circuit, but it measured 150 Ohms for some reason. The smallest rated fuse I had to hand was 200mA so I fitted that for now, and the tester works fine. (The op-amp in the component tester circuit is just a socketed DIL 741, should it be duff).

I’ve attached a few pics, which I hope may be of interest.

The first pic shows the cracked in the plastic boss at the rear of one of the two V/Div pots.

The second pic shows the traces before the upper trace (channel 2) was ‘tweaked’, and it will be seen that it’s about 1.8V/Div. The lower trace was the correct 2V.

The third pic shows that by tweaking the pot, the upper trace came into alignment.

Given that this is a 20 MHz scope, I thought I’d check its capability. The fourth pic shows a 30 MHz sine wave with the x10 Mag button pressed in, so the scope exceeds what might reasonably be expected of it.

I’m quite a fan of Hameg scopes and really very chuffed with the 203-7 - it does all that I need or expect of a hobbyist scope. Easy to see why in their day, they outsold all other scopes in Europe.

In another post I’ll add some pics of the component tester traces.

Hope these notes are of interest to fellow Hameg owners.

Happy delving!

[David G4EBT]

Some pics of the Hameg 203-7 component tester in action.

The first is of a 1N4148 silicon diode.
Second is an OA90 germanium diode.
Third is of a 7V5 zener diode.
The last pic is of a resistor.

These are just four of the 20 component tests can be carried out, and illustrated in the Hameg User Manual, including mains transformer primaries, transistor, caps, diodes, including rectifiers, short circuits, and in-circuit semiconductor tests. Admittedly it isn't a facility that I often use, and most of the tests can be made on the cheapo Chinese 'multi-testers, but even so, it's a nice feature to have. Useful to identify types of diodes of doubtful provenance for example.

Hope that's of interest to someone.

[SiriusHardware]

The component tester is also good for low to medium value electrolytic capacitors which will show a vertical oval if they are happy, but an oval or a straight line slanted to the right if they have baked dry or leaked. The more the oval or line is slanted to the right, the worse the capacitor is.

It's not so useful for very large value electrolytics which will indicate a straight up and down line when healthy (same as a short-circuit) but that's because large value electrolytics -are- essentially a short circuit to the low frequency AC used by these component testers.

I have a standalone Hameg version of this component tester (use with any scope with X-Y inputs) which has three switchable levels of current limit rather than the fixed current limit used by the scope's internal tester - it allows useful results with larger and smaller value capacitors.

We have a small fleet of similar Hameg scopes in my department at work and we all shun newer models in favour of the old Hamegs, primarily because they have this useful analyser on board.

They are especially useful for obscure PCBs for which you don't have a diagram but you do have a known working spare board - join the 0Vs of the two PCBS and one probe of the analyser together and then go around looking at the same points on each PCB with the other probe - when you get to the area where the two PCBs have significantly different 'pictures', you're getting close.

[Lloyd 1985]

I used to have 2 of these, I gave the better one away to another forum member a few years ago. That left me with the rather dirty and battered one! It worked in as much as it could display a trace, but it was distorted when viewing a square wave, the tops of the wave were curved! That turned out to be dirty contacts in the X5 switches.

All the switches and pots needed cleaning. I also had a problem where the trace would wander off the screen to either the left or right, and it was really difficult to centre it, this was a bad connection on one of the internal ribbon cables, which responded to a good clean and re-seating. It also suffered from the broken pot shaft couplings! I have managed to get them out and repair them, I just melted them with a soldering iron! I do remember there is quite a bit to take apart to get to them. I also removed the handle from mine, as it got in the way where I had it stacked with 2 power supplies on a shelf.

These scopes are also good for testing line output transformers using the 'ring' test to show if there are any shorted turns.

Pic 1 shows the distorted trace, pic 2 showing my bodge repair to the pot couplings!

Regards,
Lloyd.

[Radio Wrangler]

The waveform looks like mis-adjustment of the HF compensation networks in the amplifier, or a bust component in one. Check it's the same on all attenuator settings before digging any deeper.... there are correction capacitors in the attenuator, too.

David

[Lloyd 1985]

That's just a pic showing what it was like, cleaning the X5 switches cured it completely! I was expecting it to be a bigger problem than it was. Trace looks fine now, I just forgot to take a picture of it afterwards.

Good scopes these are

Regards,
Lloyd

[David G4EBT]

Originally Posted by Lloyd 1985

It also suffered from the broken pot shaft couplings! I have managed to get them out and repair them, I just melted them with a soldering iron! I do remember there is quite a bit to take apart to get to them.

Well done on curing the trace fault and gaining access to the dodgy pots Lloyd.

Can you recall how far you had to go in dismantling the scope to get to the PCB please?

For example, did you have to remove the front of the scope, with all that entails? I can't see how the PCB can be removed without doing that. I'm not asking for a blow by blow guide - just your best recollections of how much dismantling you had to do. Once access is gained, the fault can easily be remedied permanently by making a metal sleeve to slip on the broken plastic boss and secure it with epoxy glue, leaving holes in the sleeve for access to the two grub screws. It's rather tantalising to be able to see the part but to not be able to get at it!

For now, I'm not going to tempt fate as the scope is working nicely. It warms up much quicker than my other (main) 203-7, on which the traces takes about 40 secs to appear, whereas this one comes to life in about ten seconds. Maybe there are some tired electrolytics which could be the culprit?

[Lloyd 1985]

Hi David,

The front does have to come off, it's not too bad, just have to take off all the knobs by picking the little coloured caps off then undoing a screw in the end if the knob to release it from its shaft, then I think it was 4 screws to remove the front panel, plus a bit of wiring needs disconnecting, nothing major. Can't quite remember, but I think the bnc sockets are attached to the front. I was taking mine apart as it needed a good scrub! I could do a blow by blow guide to stripping it down for cleaning and repair!

I do like the idea of a metal sleeve fitted over the top of the plastic thing, much better than my attempt at re-moulding the plastic with the soldering iron.

Regards,
Lloyd

[David G4EBT]

Thanks Lloyd - that's really helpful - perhaps not as daunting as I imagined! The boss on the RH pot that I can see is cracked in both places, and doubtless the LH one is the same, so I think that anything short of fitting a sleeve would be unlikely to produce a lasting repair. Not due to misuse - Just deterioration of the plastic with age, and I guess many such scopes exhibit the same problem.

[McMurdo]

I have the stand-alone Hameg component tester that can be added to any scope, in my case a modern Hitachi. I use the tester every day and don't know how I managed without it. It's found several obscure faults such as noisy diodes and resistors, leaky capacitors and tests mosfets and unijunctions properly.
I used to work for a company servicing scopes among other things and I fell out of love with Hameg after they went surface mount. The switchmode power supplies used to fail and we'd order a new board from Hameg only to find them faulty out of the box.

[Nickthedentist]

...but the ones David is talking about pre-date this by some way

[WaveyDipole]

Interesting that in component tester mode your images are centered on the screen. On my HM605, the image is slightly shrunk and off-centre. I couldn't find a tweak for this so I assumed it was normal until I just saw your images.

I hadn't previously looked at this topic, but over the weekend I had the idea to see how far in terms of frequency I could push my HM605 and found I was able to display traces up to 90Mhz from my RF1U after which the image faded out. The trigger mode had to be set to HF to get a clean trace, but I didn't think to try the x10 mag button though. As you observed with your 203-7, I am quite pleased with its ability to perform beyond its limits.

A while back I wondered whether a component tester could be made standalone to work with another scope but didn't pursue it. I hadn't realised that Hameg actually made one! Searching for 'Hameg component tester' I found some information on how to make a simple one here:
http://www.qsl.net/g4usp/Component%2...%20adapter.pdf

There is a video of something similar here:
https://www.youtube.com/watch?v=Gwo3pEH7hUE

There is even a kit you can buy:
https://www.quasarelectronics.co.uk/...mponent-tester

A circuit diagram of the actual Hameg one is available on the Radio Museum Website:
http://www.radiomuseum.org//r/hameg_..._hz65_3hz.html

[dave cox]

Does that 1st linked design really put ~ 19V peak ac (via 1K) across the tested component ? I would want to be a bit selective with the components I was testing at that level of applied voltage / source resistance! Are the Hameg designs a bit more gentle ?

For example, one thing I was undecided on is driving a B-E junction into reverse breakdown, my gut feeling is that this is not a good idea even with a small current but I didn't find much to back this up ...

dc

[David G4EBT]

The component tester in Hameg scopes is a 'nice to have' aid, useful for such things as identifying whether an unmarked diode is germanium, silicon or a zener, but really, it's a feature which - with the passage of time - has I feel been largely been rendered redundant. I say that, because it doesn't measure the value of components such as resistors and capacitors, the gain of transistors, or the ESR of electrolytic capacitors. For some time now, those dinky little 'bare bones' Chinese multi-testers have been around and can currently be had on e-bay for just £7.61 post free.

They automatically detect NPN and PNP transistors, N-channel and P-channel MOSFET, diodes, resistors, capacitors and inductors.
Automatically test the pins of a component and displays them on the LCD.
Measure the gate threshold voltage and gate capacitance of MOSFETs.
Measure bipolar transistor current amplification factor and base-emitter threshold voltage.
One-button operation, and auto shutdown to avoid unnecessary battery drain.

True, they come with an annoying ZIF socket, but with care, that can be removed and the unit boxed up with test sockets and test leads on a front panel. I've had two for about 3 years now, use them often, and they're both still on the same Poundland PP3s as they auto shut-off about 15 seconds after the readout. Much better than my aging Atlas transistor tester at ten times the price, which despite claiming that it does, won't test MOSFETs.

I won't bang on about them - they've been mentioned elsewhere and this thread is about Hameg scopes, but as the Hameg and other component testers have been mentioned, I thought it relevant to compare and contrast the scope display with that of the little digital tester jobbies, so have shown a couple of readouts below.

[Ambientnoise]

I am sure you are correct about reversed Vbe. We used this technique in the 70s to obtain very low current zener diodes using BC109 types, but the transistors were permanently degraded afterwards in a more standard configuration. They had lowered gain and high noise. It may well be a function of the manufacturing process of course.

Ken

[WaveyDipole]

I tend to agree and I have one of those gizmos myself. They are very useful and, as you say, tend to render the oscilloscope tester obsolete. I did find it interesting though, that an oscilloscope could be used, among other things, to test components in this way. I would probably only experiment with the above as a matter of interest rather than for any practical reason, but I have found myself using the tester on the Hameg sometimes.

Out of curiosity I checked the output from the Hameg tester on the HM605 using the TQ D61a (which is currently undergoing repairs although still reasonably accurate on trace height) and I got almost exactly 20v ptp. The DMM showed that the current was limited to about 15mA. I expect this voltage level would be concerning. Why couldn't a lower voltage be used?

Thanks a very nice box BTW.

[newlite4]

The experiences that I have found with HM203-7 faults have mainly been mechanical. Two weak areas are the weak plastic bellows couplings from the time/div control shaft to the wafer switch and the fragile edgewise trigger source switches. Regards the former, the plastic coupling can be replaced with a new brass coupling (which may need drilling out to accept the shaft diameter). In the latter case, the trigger source switches have a bell crank rod coupling to a slide switch on the TB board, if these have broken it is difficult to repair, I have scrapped a 203-7 because of this.
On the plus side, the component tester is a very quick method of testing passives, actives and pots and switches. When I have a batch of 500 1N4148 diodes to test (quite often!), I reach for the Hameg every time as the visual result is instant rather than having to wait for digital test gear to reset after every single test.
Neil

[Billie the Boss]

I acquired on of these from "Mark in manc" recently. Works a treat from what I can see.
I am new to the scope so Learning. I have a HZ154 probe but I would like to source two additional probes for it. Any suggestions.?

Also. Although I have no problem with the above mentioned issues, Can anyone post the said Boss measurements shaft diameter etc. Maybe I will get ahead of the posse and make a brass replacement or sleeve as suggested, " to have it on hand"

Your suggestion of a blow by blow strip down would be interesting Lloyd. By me anyway.
Maybe a video. Hah, Lloyd they say NEVER volunteer.

Regards.

Billie.

[Radio Wrangler]

Scope probes?

Look right by the BNC input connectors, it should say something like "1 megohm 20pF"
The capacitance varies somewhat from scope to scope. You want a 10:1 ratio probe which states that it will work with a capacitance range which includes what your scope says on it.
The scope end of the probe will have a little hole to access a trimmer capacitor which is used to correct the HF response of the probe to match your scope. You use the scope's calibrator output.

The world is awash with cheap switchable probes which do both 1:1 and 10:1 ratios. This sounds great. But the performance on 10:1 is compromised to be able to do this, and you rarely need a 1:1 probe anyway.

Check the voltage rating on whatever probe you are considering is enough for what you intend to do.

It's always worth having two or three matching probes. Most scopes have two channels you can use at once to compare things and sometimes you use a third probe on the trigger input when you want to trigger on something other than one of the traces.

David

[Billie the Boss]

Thanks for that.

Yes its 1.meg and 11-25pf. The HZ154 probe is spec,d at 18/45pf so how does that work in terms of matching or is it critical.

I am considering something like these.


Mouse over image to zoom

2pcs-P6100-Precision-Oscilloscope-Probe-14cm-1X-10X-100MHz-Test-Probe-UK-40LL

Specifications:
Band Width: 100MHz
Rise Time: 3.5ns
Attenuation Ratio: 1X / 10X
Input Resistance: (1MΩ/10MΩ)±2%
Input Capacitance: 1X: 70pF-120pF 10X: 13-17pF
Maximum Input: 1X: 200 Working Voltage(Vp-p) 10: 600 Working Voltage(Vp-p)
Compensation Range: 10-35pF
Operating Temperature: 0-50°C
Operating Humidity: 0-80%RH
Item Length: 14cm.

Amazingly cheap at under 6 quid. They say you get what you pay for so thoughts on these would be most appreciated.

Best wishes.
Billie.