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RC Test Equipment

For fault finding, trouble-shooting etc

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Dave Cooper 306/10/2018 15:44:53
51 forum posts

Hello All - I'm new to the forum and hope this is in the right section !

I'm just starting to delve into RC electronics - mainly 27 and 35 MHz at present, fault-finding and trouble shooting existing gear etc.

Regarding test equipment, I have a good, reliable multimeter and one oscilloscope on the way. I have a few questions you may be able to assist with :-

1. Does the 'scope need dual trace, alternative triggering and any special probes ?

2. What would you recommend for a signal generator /frequency analyser etc ?

3. Current faults involve Rx I/F selectivity stages and ESC /BEC switching - anything especially useful here ?

4. Reasonable cost power supply sources ?

5. Sources of old Futaba (and 'compatible' Service Manuals etc

Home /DIY kit projects especially interesting...will shortly be upgrading to the '2.4' equipment, so anything different here test-wise is of interest.

Thanks for your patience with the above !

Regards,

Dave

Edited By Chris Bott - Moderator on 08/10/2018 17:50:51

Geoff Sleath06/10/2018 16:10:31
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2941 forum posts
243 photos

I assume you're familiar with general electronics and how superhet receivers and transmitters work as well as FM discriminators (I don't think TRF (tuned radio frequency) has been used for RC control for some time (I've only been involved with RC since the mid 90s but with electronics all my life ie 70+ years). I built my own transmitter and receivers

Any 'scope you buy would certainly need to be dual trace with suitable triggering with at least 100Mhz b/w. When I worked anything other than a very expensive Tektronix would be judged against that sort of standard but I've been retired over 25 years and things change.

A spectrum/frequency analyser would be a 'nice to have' but they're quite expensive or certainly were and probably not essential. Obviously you need a signal generator that will work at the frequencies you're interested in.

You could probably manage without a bench power supply and use batteries. I've never seen any service manuals but I suppose there must be some. The kit you're dealing with is all quite old so perhaps there are some available s/h.

With 2.4gHz you're in a different range altogether. First the technology and systems used for the spread spectrum frequency hopping modern radios use is different (and probably confidential) for each manufacturer. Then then most of the components are surface mount which are a nightmare to replace (I've tried it!) and moreover a lot of the integrated circuits are unique and really are not repairable - or even worth repairing in many cases.

Those are my thoughts but Pete Christy on here knows a lot more than I do so he may have a different take.

Geoff

Edited By Chris Bott - Moderator on 08/10/2018 17:53:06

Piers Bowlan07/10/2018 06:34:27
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1470 forum posts
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Welcome to the forum Dave. Don't worry, one of the moderators will be along soon to sort you out devil! wink 2

You could always PM Peter Christy too, to find out what you need to know.

Edited By Chris Bott - Moderator on 08/10/2018 17:54:36

Chris Bott - Moderator08/10/2018 18:15:26
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Thread all sorted thumbs up

Dave I think you'll find an oscilloscope useful but not at all essential. It will help you understand PPM and PWM signals etc.

Most RC equipment is very modular and the innards of the modules are inaccessible to us. That is apart from vintage RC gear. If you're interested in that then pop over to see Phil Green and Shaun Garrity over on **LINK**

For modern equipment I'd say that the electronics interest is in telemetry systems and multi protocol transmit modules along with Video feeds from FPV and heads up displays / head trackers etc. All of this is again modular and you might find more interest in the programming/software side than anything else.

I hope to have a number of arduino R/C based articles in the magazine soon, although just when, is up to the editor.

Peter Christy08/10/2018 18:57:48
1091 forum posts

Dave,

If you want to PM me your email address, I'll send you my phone number and we can have a proper chat!

--

Pete

Dave Cooper 309/10/2018 20:05:14
51 forum posts

Hi All - thanks for the very warm welcome !

Geoff : I'm familiar with superhet (and super-regen) principles and did a little FM detection /discrimination during my City & Guilds studies (early 70's) but this is a bit rusty now ! The 'scope is coming via an ex-BBC radio engineer, so I'm hoping will be quite good. I too used Tektronix gear whilst at Hewlett Packard. It was generally regarded as the "Rolls-Royce" of 'scopes. Laterly, I worked mainly with Analogue <> Digital computer stuff - clock boards, disk controllers and the like.

Piers : I will be pm'ing Pete C quite soon - I'm sure I can learn something new from him...

Chris : Many thanks for sorting out my earlier 'scrambled egg' thread and for the guidance on current equipment etc !

Pete : PM on it's way soon.

Dave Cooper 319/10/2018 20:21:35
51 forum posts

First oscilloscope arrived today - a Tektronix T912. Quite an old CRT model but with dual trace, storage and 10MHz bandwidth.

Next on the shopping list will be some good meters eg AVO 8 (analogue) plus a quality digital one. To follow, a spectrum analyser and frequency counter if anyone is 'unloading' ? These may have to come via kit construction if I can't afford a ready-made commercial unit.

As a first RC project, I quite fancy a single-channel valve Tx /Rx pairing. If anyone has a suitable circuit diagram, valves, pcb, instructions etc to assist with this I would be interested to hear from them...

Dave

Denis Watkins19/10/2018 20:56:44
3133 forum posts
144 photos
Posted by Dave Cooper 3 on 19/10/2018 20:21:35:

As a first RC project, I quite fancy a single-channel valve Tx /Rx pairing. If anyone has a suitable circuit diagram, valves, pcb, instructions etc to assist with this I would be interested to hear from them...

Dave

Unbelievably, there were 2 shops in Manchester thriving in the 1960s, providing us lads with sheet aluminium, and all the components to make a Tx/Rx,combo

The ally sheet was folded up into a girder fom to mount the components, as some of you already know

The Rx was suspended within the model on elastic band dampers

The Batteries were huge Ever Ready

I will have a look for diagrams

Robert Cracknell19/10/2018 21:08:53
122 forum posts
2 photos

Dave

For circuit diagrams of most of the 35Mhz gear you can look here...**LINK**

If you explore the site there is lots of info on troubleshooting.

Geoff Sleath19/10/2018 22:42:22
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2941 forum posts
243 photos

An AVO 8 is pretty old technology. Mine must be 60 years old and weighs a ton! We had new AVO 8s at work which were much lighter for some reason (mine dates from the days when we lived at the family Radio/TV business). I almost never use it as my little digital meter is so much easier to use - and that's over 20 years old!

You can't go wrong with Tektronix 'scopes. The only problem might be a knackered crt which might be almost impossible to replace - especially a storage one. If it's as old as needing valves, they were quite big and needed a trolley.

Good luck

Geoff

Dave Cooper 320/10/2018 10:34:33
51 forum posts

Thanks for the info' folks. Will follow up all leads as suggested.

Denis : Yes, I remember diagrams and photos of the Rx's suspended in a sort of cruxiform from each corner in the "radio compartment".

Robert: Thanks, looks like a first class link - I have some 35MHz fault-tracing on the go now.

Geoff : My 'scope came free within the family, so if the CRT goes....Yes, at Rediffusion years ago I remember our Avo's being replaced with more modern one's. I should have grabbed one then before it went into the skip !!! The 'scope is a bench top model and not too heavy to move about. I think I spotted a manual for it on ebay....will have to investigate.

Dave

Chris Bott - Moderator20/10/2018 16:04:11
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Dave rather than an old Avo, why not look for a modern multimeter? (Somehow I think you'll already have one).

A very quick look on Amazon and there's loads at all sorts of prices. ?25 should get you a true RMS meter that also measures the usual plus component values, temperature and frequency up to say 60Mhz.

Edited By Chris Bott - Moderator on 20/10/2018 16:04:31

Dave Cooper 320/10/2018 16:43:30
51 forum posts

Hi Chris, Yes I already have a 'pocket' multi-meter that will do ohms, ac and dc voltage, light current etc. But one that would do RMS values, temp's and frequency etc. sounds very useful...we have a Lidl and an Aldi opening up in our area shortly so, will pop along and see what's on offer.

Dave

gangster20/10/2018 18:37:59
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797 forum posts
7 photos

For fault finding old gear 27 &35 you don’t need elaborate test gear generally. A scope is useful but if you are just looking for the 1-2 ms pulses any scope will do. You can hear the pulses from the modulator on an earphone even and by waggling the stick cam tell which is missing. How do you measure the centring and pulse width. Well you need a special device called a servo. Is the RF working well a simple diode probe is a wonderful tool simply a diode and a decoupling capacitor plenty info on the web. Rf output and modulation time an ordinary FM radio and it will hear the modulation flick the switch’s and you will hear the pulse width change Power output ? Well your FM radio will give a clue as will the diode probe and of course a range check. So an analogue meter and FM radio together with a diode probe and you can find most faults on 27/35 am and fm gear. 2.4 well that’s a whole new ball game uses a technique called PFM. If you don’t know what that is you best not ask (the mods won’t like it. I can email you some diagrams for home brew radios of the 70s and 80s

Dave Cooper 320/10/2018 20:11:46
51 forum posts

Thanks for your reply Gangster - I like simple solutions /methods, so there is definitely some food for thought here ! However, I suspect my current faults (dual conversion, 35MHz) may lie in the two IF stages ie signal in but no signal out. The hope here is that I can use the 'scope to trace where the signal path is lost.

BTW is your picture an actual Ripmax Gangster of certain vintage ?

Dave

gangster21/10/2018 19:13:48
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797 forum posts
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boutHi Dave. Yes I would agree a scope would be easier but in the absence of one a diode probe would test the two crystal oscillators

As far as the avatar no that is not a vintage Gangster but a Gangster 63 light which as far as I know is still available in kit form directly from Mick Reeves lovely model mine flys on about 650watts electric it is designed for a 40 2s I have some pictures somewhere of 52 and 63 that I owned back in the day might put one of those up

Dave Cooper 323/10/2018 21:50:53
51 forum posts

All, just been reading up on some RC theory - especially, Superhet Tx and Rx, AM and FM material. Many of the diagrams were a mixture of 'black box' IC's and discrete components, and, I was able to follow most of it.

However, in the concluding section on superhet Rx's it stated that the tuneable coils (Inductors) are quite fragile. The circuit diagram outside of the main IC 'block' contained an RF amp, Mixer transformer and an IF amp all with tuneable coils. It occurred to me that as my non-working Rx came out of a crashed fuselage (it hit a road in a vertical dive), one or more of these coils could be u/s resulting in no signal output ?

Now to the test.....would a simple continuity check across the coils' contacts on the pcb suffice to say if it is ok or not ? Would further tests be necessary eg a 455kHz IF injection at an appropriate point. What about the second IF stage (the Rx is dual conversion), or, perhaps, a check on the fixed Xtal maybe (I don't know how fragile these are) ?

Bit of a teaser for me - thanks for any pointers.

Dave

ps Got my 'scope working now. It would be good to use it to help solve this one !

Peter Christy24/10/2018 17:38:33
1091 forum posts

Dave,

A continuity check across the coils will tell you that they are not not OK, if you get my drift! If they are open circuit, they are definitely dead! However, if they show a short, they are *probably* OK. Those little coils are pretty tough!

More likely candidates are the crystals (two of them, remember in a double superhet) and the ceramic filters. Worth checking the socket on the plug-in crystal, too.

Its also worth checking the PCB for cracks or failed joints after a heavy impact, though again, my money would be on the crystals or filters.

1st IF is generally (but not always) 10.7 MHz, and the second is almost always 455KHz. Insertion loss though the filters is usually around the 3 to 6dB mark.

It should be straightforward enough to trace a strong signal through the chain, and see where it disappears. Even a 10MHz scope should be good enough for that, but use a X10 probe to avoid loading anything.

Good luck!

--

Pete

Dave Cooper 324/10/2018 19:09:42
51 forum posts

Thanks for the info' Pete - I'll get checking !

I'll dig out my old magnifying glass to check the PCB - have already tested the plug-in Xtal but will now check the fixed one too.

I got a X10 probe with the 'scope and I found an instruction manual on the internet.

Will call for a chat soon (I'm bound to miss something important !).

Dave

gangster25/10/2018 08:57:04
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797 forum posts
7 photos

Dave My advice would be to start by thinking simple . Start with a magnifying glass closely inspect the track all over. are ant components crackedDo some simple DC tests. Is it drawing any current at all. As Peter has said the crystals and the filter are the most susceptible After that get your scope out and see where the signal gets to. Those IF transformers ain’t particularly tender you can do more damage doing unnecessary tests and removing components. Keep it simple chances are the fault is something basic

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