Repairing BWD 509B Oscilloscope

[vk2amv]

Hi all,

I need a bit of advice.

Firstly sorry for the long winded'ness of this.
I am just trying to include as much detail as I can.
Or you can read the summery at the bottom.

I have been repairing an old BWD 509B 10Mhz Single channel CRO, ($5 at a Wyong Radio FieldDay a few years ago)
I have attached the circuit diagram I have for reference.

I actually had 2 problems, one of which has been fixed.

First problem when I originally got it was a very weak trace even with intensity adjustment at max (Otherwise it worked fine), I had a look at it 2 years ago and the suspected problem then was the selenium diodes in the voltage doubler for the EHT supply were shot.
At the time I put the CRO on the shelf and it has sat there for 2 years since then.

I finally got around to making a high voltage probe this weekend past and pulled the CRO off the shelf to fix it.
My original diagnosis for the cause of the weak trace was confirmed when the EHT voltage measured 1.1KV down from the specified 1.5KV.
This was quickly fixed by replacing the 2 selenium diodes with 4x 1n4007's with 20k current limiting resisters in series.
The result is the EHT voltage is back up to a healthy 1.5KV.

Now it has developed another problem in the time it has sat on the shelf.
This time no trace at all.

I screwed around a little bit trying to find the cause, and eventually I found out that the Y plates are at massively different voltages, 50 volts for one and 186 volts, (which is nearly up to the 190V supply voltage) for the other.
Disconnecting the Y plate leads I get a nice solid dot right in the centre of the display on the Y axis so display is confirmed working fine.

After some more disgnosis and tracing back the voltage inbalance to it's source, it looks like one of the input FET's have died.
Q1 on the attached circuit diagram to be specific.
Following the signal I was putting into the CRO with my new Rigol DS1054Z I was getting a + DC Offset of 10 Volts on the drain of Q1, and + 3 volts on the drain of Q2.

Pulled the FET out and my ATMega tester is reading the Q1 FET only as a diode.
Testing the other FET it reads fine as a FET.
So I am confident I have found the problem.

Anyway I need a replacement.

The FET is MPF106 which is easy to get. (Listed as MPF106/2N5485 for $2.45 each at Jaycar)

But my question is this, in the manual it says the FET's were matched for gain and operating current in the factory.
Back when this old girl was made I imagine manufacturing tolerances between individual components were pretty ordinary so you had to individually match them for this usage.

Are tolerances much closer now for the same parts than in the 70's when this CRO was made?

Can I just buy any pair of MPF106/2N5485's FET's from Jaycar without bothering to individually match them and it will be all good without much more issue than a basic calibration?

Or should I just buy different/newer model FET's to better specifications than was originally used?

Just need some advice on this one

Many thanks


TLDR:
Need new input FET's for my CRO.
It uses MPF106's which were individually matched in the factory in the 1970's.
Are component tolerances close enough now that I can buy any two replacement FET's MPF106/2N5485 without needing to match them or should I buy newer model/better specification FET's?

[tautech]

Excellent post that makes it nice and easy for us to assist. 

You know for an old girl like this I'd do just as you propose and suck it and see. 
IME your analysis of tighter manufacturing tolerances these days is quite correct.
I've not studied the schematic yet but I would assume there is some trimming available in the input stages to tweak any discrepencies.

Other than that how does one match FETs?....time for some Google'ing. 

[vk2amv]

I've not studied the schematic yet but I would assume there is some trimming available in the input stages to tweak any discrepencies.

Thanks muchly for your reply.

You are quite correct.
Specifically the manual says.... the FET's were matched in the factory for gain and operating current and RV3 balance potentiometer provides the final adjustment to elimitate all line or signal variations on the DC rails.

So I am going to just grab a pair of 2N5485 FET's and keep my fingers crossed.
At the end of the day, for a 10Mhz CRO it should be pretty much close enough either way.

Honestly I have spent waaay more time and effort than really is worth on this old thing.
I more want to fix it simply because I hate to see any CRO, even an old one like this go to the big CRO junkyard in the sky.
Also BWD has a bit of Australian electronics history there as well so I would also like to fix it for that reason.
Plus it is a bit of a learning experiance for me poking around in this old thing with my DSO following the signals through the circuit.

[tautech]

I've not studied the schematic yet but I would assume there is some trimming available in the input stages to tweak any discrepencies.

Thanks muchly for your reply.

You are quite correct.
Specifically the manual says.... the FET's were matched in the factory for gain and operating current and RV3 balance potentiometer provides the final adjustment to elimitate all line or signal variations on the DC rails.

So I am going to just grab a pair of 2N5485 FET's and keep my fingers crossed.
At the end of the day, for a 10Mhz CRO it should be pretty much close enough either way.

Honestly I have spent waaay more time and effort than really is worth on this old thing.
I more want to fix it simply because I hate to see any CRO, even an old one like this go to the big CRO junkyard in the sky.
Also BWD has a bit of Australian electronics history there as well so I would also like to fix it for that reason.
Plus it is a bit of a learning experiance for me poking around in this old thing with my DSO following the signals through the circuit.

   
Just don't you learn sooo much when fixing scopes!

Warning, fixing scopes is addictive and with older CRO's always make sure you have a spare to fix the one that dies first. 

Do you have this link:
http://www.kevinchant.com/bwd.html

[vk2amv]

No I didn't have that link.
Thanks for that.

Anyway I have ordered a pair of FET's for $5.10 delivered for the pair.
I will report back here once they arrive (Fingers crossed before the weekend) and post back on the outcome of the repair.

And you are right, this has been kind of addictive.

Think I might have to buy a couple more old CRO's at the next Wyong Field Day haha. 

[tautech]

And you are right, this has been kind of addictive.

Think I might have to buy a couple more old CRO's at the next Wyong Field Day haha. 

The only risk doing that is you should first check to see the Service manuals are available.
Without one you will really battle unless it's a very simple repair.

Stick with older models of the main brands.

[vk6zgo]

I thought my 511 was similar to the 509B,but on looking at the circuit,you have FETs where mine has valves ,both in the input stage & the vert & horizontal outputs.

the 511 is a queer fish,though,as it has differential inputs which can be used in a similar manner to the "A" plus "B" connection sometimes used with two channel 'scopes.

They say in the book that "Common" is isolated inside the instrument,so it can be used across the Mains,(maybe why they went with the Hybrid design),
A link on the front panel allows it to be used with a single ended input.

The 511 had a triggering problem,which got progressively worse,until it stopped altogether.

I messed around,changing bits in the triggering circuit,until I realised that EXT trigger still worked,but not INT & there was only a switch contact difference between the two.

I gave up for a while,then purchased a little 10MHz Digitech from Jaycar,with the intention of finding the problem.
Well,I did-----very low level pulses coming  into the trigger circuit.

After much peering at the circuit,I found a voltage divider off the vertical output.
A 470k (R62) & a 100k (R80).with the INT triggering taken from the junction of the two-------R62 had gone very high in resistance.

As you will probably have found out,it is a bit of a nightmare working on that board under the tube,so I "put it on the backburner",where it remains-----I found the Digitech was OK for a lot of things.

Then I bought the Tek 7613,& the poor old BWD became even less likely to ever return.

Anyway,here's the point!
Quite a few single channel BWDs I've encountered have this trigger problem,so they probably use a similar source for the trigger.

Yours certainly does---------your divider is 470k(R32) & 220k (R31),so it might be a good idea to check R32 while you have it apart.

Maybe I'll drag the 511 out & have another go---it's a nice old beast!

[vk2amv]

Yours certainly does---------your divider is 470k(R32) & 220k (R31),so it might be a good idea to check R32 while you have it apart.

Thanks for that advice.

I did not have any triggering issues when I last used it 2 years ago, but I checked the resistor anyway as a preventitive measure.
R32 had gone high and was readiing nearly 600k.

So I replaced R32, as well as R31 just for good measure.
Now to go back to waiting for the replacement input FET's to arrive.
Hopefully Friday fingers crossed.

[vk2amv]

Just an update.

The new input FET's finally arrived today.
Took much longer to receive them in the mail than I expected.

Anyway I have them in place and I am now getting vertical deflection, as well as the expected Y plate voltages.

I need to recalibrate it now (Which I expected) as it is slightly unbalanced still, but at least I now have a trace.

Now onto another problem.
I am not getting a time base.

Something has failed in that section of the CRO.

When I turn the timebase switch on (set at at 100ms division) I get a single trace go across the display, and it stops at the end.
It doesn't seem to be resetting at the end for a new trace across the screen.

Back to the service manual I go.

X-Y mode does work so the CRT is being driven correctly, so I think the problem is just somewhere in the timebase circuit.

Hopefully something simple.
I will have a look at that to see how it works, and try and work it out later today or this evening and report back.

Time for lunch for now.

[TerraHertz]

It's a shame that for a historic Australian company, so little of the gear BWD made has manuals available now. [1]
vk2amv, are you going to post some photos of your 509B scope?

Growing up in Oz, seeing adverts in magazines for BWD scopes and stuff, I drooled over those things. Far beyond my means though, and it stayed that way through my early working life, raising a family, etc. By the time I could afford such things BWD were long gone. Also then I could get much more advanced 2nd hand test equipment, so couldn't justify buying any BWD things for sentimental reasons. Then a couple of years ago I got lucky and and acquired a BWD scope and power supply for free.

Here's a pic of my BWD 530A. It's mostly working, but could do with some adjustment. Unfortunately I've been unable to find any trace of a manual for it. I did find manuals for the BWD 521, 539, 539D and 540 oscilloscopes.


[1] No thanks to High Country Service Data, who years ago destroyed their entire huge library of physical service manuals rather than give them away or donate them to the national library. Seems to be a distressingly common practice. "Oh but we digitized them, who needs the old paper copies?"  Hey HCSD, please die in a fire.

[vk2amv]

Well turns out the CRO just needed recalibration after my work in replacing the input FET's and the resister divider for the trigger circuit.

It was just not triggering properly, after doing a calibration as per the service manual it came good.
At least at lower frequencies.

Triggering becomes unstable at higher frequencies, but I am not going to bother any more with it.
I have already spent enough time on this and I am going to call it, and have put it back together.

I really only want to use this CRO in X-Y mode for usage with my Hameg HM8028 Spectrum Analyser anyway and that works fine.
The analyzer doesn't have a screen itself, it uses the CRO as its display (I have a Hitachi 15Mhz Dual Channel CRO when I want to use an Analog CRO for chasing signals).

My two Rigol DSO's don't quite make it for the job with the Hameg Analyzer, and the analog CRO gives a much better display for that usage.

As requested I took a few photos this evening.
https://onedrive.live.com/redir?resid=7935293B544130EE!36935&authkey=!AEHYVcdvnJsOasI&ithint=folder%2c

First up is a photo of the old with the new.
BWD 509B in the foreground, with my nearly brand new Rigol DS1054Z in the background. (And my DS1052E which I bought after watching one of Dave's first reviews back in the single digits, is sitting on the shelf behind me when I took this photo)

Second up a close up of the BWD 509B.

Thirdly just for completeness is a bit of an overview of my work bench.
In the photo is

Far left WEP PS-3005D Variable Power Supply (Hmm made in China "to a price" quality....  lovely )

Middle bottom left Rigol DS1054Z (Bought after watching Dave's review on this DSO a month ago)
Middle top left Rhino Tools ZD985 Desoldering Station (Bought after being reviewed by Dave in EEVblog #542) and an old 6 Amp 13.8v Power Supply

Middle bottom right Marconi TF2015 10-520Mhz Signal Generator with matching Marconi TF2171 Digital Synchroniser for the Signal Gen.
Middle Top Dick Smith T2250 Soldering Station (Oldish but reliable, rebadged Xytronix 169D and takes Hakko 900M Tips so does everything I want)

Right bottom Anritsu MS62B7 1.7Ghz Spectrum Analyzer (Also sitting in front of it is a BK Precision 2709B bought after watching Dave's $100 multimeter shootout, one of half a dozen multimeters I have floating around)
Right middle Hameg HM8028 500Mhz Spectrum Analyzer with Tracking Generator and 898D+ SMD Hot Air Rework + Soldering station which I bought after watching Dave's review of the similar Atten 858 (It is also very handy to be able to have a second soldering iron running hot at times)
Right top Kenwood TS-2000 Radio, Power supply for that radio, and an old Dell laptop for looking up stuff while I am at my bench.

There does seem to be a bit of a pattern up there on some of my equipment after watching Dave Jones review certain pieces of equipment haha.

[georges80]

Good job on the repair.

My first scope was a bwd 509b. Saved many a penny of my allowance to purchase it back around 1976-77 (some time around there) when I was at uni. Lived in Perth at the time and that was a real backwater as far as electronics was concerned...

Sold the bwd scope to a friend 5-6 years later since I'd come to the US for work and picked up a nice hitachi 100MHz scope.

That bwd got me into digital electronics where I could observe/debug signals on the various 8080a and z80 based computers I was hand assembling (point to point soldered and then later wire wrapped).

I still have a remaining piece of BWD gear back in Perth, even last used it 9 yrs ago to test out a tacho of my 4wd. The BWD141 still worked fine and I even used my diy frequency counter to check things out. The 'good old days'

cheers,
george.

[vk6zgo]

Actually,there was a lot of Electronics going on in Perth back in the '70s,but most of the gear like Oscilloscopes was in Corporate hands--very few private citizens had them.

If you were lucky enough to work for Telecom Aust,or a TV Station,or whatever,it wasn't a major hassle,as they were very "enthusiast friendly" in those days,& would happily loan out equipment to staff,or turn a blind eye to a few "foreigners" done at work.
Oh for the days when such places were run by Engineers,instead of "bean counters"!

My first private Oscilloscope was a BWD 511 which I bought in the early '80s ---cost me $220,if I remember correctly.
I still have it!

There was a choice between it & a Philips CRO,but the latter had a tiny screen,& the BWD a nice large one.

TVW had a few BWDs which were rarely used by the 1980s----everybody automatically grabbed a Tektronix if they needed an Oscilloscope.

They were quite happy to loan the BWDs out,so I was pretty used to their peculiarities.
A lot of BWDs spent their lives languishing in equipment cupboards,due to the triggering problem referred to above.

[georges80]

I guess I'm jaded as far as electronics in Perth - versus what I found in the US...

After Uni I worked at a small computer company (they made their own z80 based system and we wrote ALL the operating system, utilities etc - business computer). It was fun and I learned a lot even though I was of course already building stuff at home. Funny thing is I can't even remember what test equipment they had there... Worked a couple of months in Sydney (eek - the big smoke) for the same company.

Couple of years working at the local Uni (UWA) as a staff engineer, that was fun. Lots of Tek and HP equipment etc of course.

Then moved moved to the US and worked for a few years here - what a different world when it came to electronics. Back to Perth for a year, then back to the US and this time Silicon Valley (nirvana) and been here a LONG time...

cheers,
george.

[vk6zgo]

As I mentioned,unless you were employed by one of the "biggies" like Telecom Aust,the ABC,STW9,TVW7,OTC,DCA or the like,fancy test gear was pretty thin on the ground.

Most TV Service places had one or more Philips CROs,Serviscopes,or the like.

I had an opportunity to forestall "Tech Rentals" in the '70s.

There was a lot of good Test equipment being sold off in the UK,& I figured  that even with freight,and import duties (not a lot on used stuff),I could have set things up & done OK renting the stuff out.

Everybody said "No-one will rent Test gear!",so I pulled my head in & didn't do it!

Along came Tech Rentals & did it,extremely successfully!

Still,I would probably have "stuffed it up"!

[ROAMER]

Hi all!!!

I found this post as I have BWD509b also that had trace issues that I repaired (well nearly there in reality). I also have dim trace problem. In normal daylight it's not even visible. Voltages that I have are as follows:
Cathose, pin 3: -1440 volts (intensity on max)
Focus, pin 4 - 1010 volts (best focus setting)
Astig, pin 11: +114 volts
Grid, pin 2: -1440 volts
So voltages seem good enough. Does anybody have any idea what might it be? I'm knowleageable in electronics, it's just this is my first time coming across cro tube, so I don't know what to expect.

Many thanks for your replies!

[amspire]

I have a BWD 509A that is working, and if you or anyone else wants it for the cost of transport (or free if picked up) you are welcome. It is different from the 509B though. It has a green screen rather then blue, so the tube is probably completely different. Also it is a valve/transistor hybrid and I think it was only 5Mhz rather then 10MHz. It was always a really nice scope to use. Triggering was always solid. Really nice waveform.

I have the original manual somewhere.

Richard

[MylesVK2ASS]

TerraHertz
In This you say you found the Manual for the 540 by any chance do you still have access to it
This is My first Oscilloscope and will be used for learning how to use a scope.
i paid $50 for it at ARNSW trash and treasure any help would be greatly appreciated
regards Myles

It's a shame that for a historic Australian company, so little of the gear BWD made has manuals available now. [1]
vk2amv, are you going to post some photos of your 509B scope?

Growing up in Oz, seeing adverts in magazines for BWD scopes and stuff, I drooled over those things. Far beyond my means though, and it stayed that way through my early working life, raising a family, etc. By the time I could afford such things BWD were long gone. Also then I could get much more advanced 2nd hand test equipment, so couldn't justify buying any BWD things for sentimental reasons. Then a couple of years ago I got lucky and and acquired a BWD scope and power supply for free.

Here's a pic of my BWD 530A. It's mostly working, but could do with some adjustment. Unfortunately I've been unable to find any trace of a manual for it. I did find manuals for the BWD 521, 539, 539D and 540 oscilloscopes.


[1] No thanks to High Country Service Data, who years ago destroyed their entire huge library of physical service manuals rather than give them away or donate them to the national library. Seems to be a distressingly common practice. "Oh but we digitized them, who needs the old paper copies?"  Hey HCSD, please die in a fire.

[TerraHertz]

TerraHertz
In This you say you found the Manual for the 540 by any chance do you still have access to it
This is My first Oscilloscope and will be used for learning how to use a scope.
i paid $50 for it at ARNSW trash and treasure any help would be greatly appreciated
regards Myles

Hi Myles. Yes, I still have the 540 manual, though only in pdf. It's 6MB.
Unfortunately I didn't make a note of the source URL. Just a list of places I'd looked. If these links fail you,
I can upload the 540 manual.

Edit to add: Btw, if you need to ask me about this, best to use the forum PMs. It's only by chance I happened to open this thread again. And, welcome to the forum!

BWD Manuals sources
-------------------

http://www.eserviceinfo.com/downloadsm/52708/BWD%20Australia_246A.html
http://www.kevinchant.com/uploads/7/1/0/8/7108231/bwd_242a_manual.pdf
http://www.kevinchant.com/bwd.html
https://groups.google.com/forum/#!topic/aus.electronics/CjI2zMjoxhI

http://bama.edebris.com/manuals/bwd/539     Closest they have.
http://isurplus.com.au/manuals/BWD%20539D%20Oscilloscope%20User%20Manual.pdf

http://techtv.com 
http://www.manualsplus.com/ 
http://www.ebaman.com   
http://www.eserviceinfo.com   
http://elektrotanya.com
http://www.mwrs.org.au/documentation-library/

https://www.eevblog.com/forum/repair/repair-documents-and-links-sticky-me-please-mods/msg594414/#msg594414
 tautech 
Re: Repair Documents and Links
Links for BWD instruments.

Some manuals: http://www.kevinchant.com/bwd.html
Thanks Kev. 

A recent thread:
  https://www.eevblog.com/forum/testgear/bwd-product-catalogues-(vintage)/msg590213/#msg590213
  https://www.eevblog.com/forum/testgear/bwd-product-catalogues-(vintage)/

https://www.eevblog.com/forum/testgear/bwd-112-sine-and-square-wave-generator/

20161017
https://www.eevblog.com/forum/testgear/help-find-information-of-very-old-bwd-oscilloscope/
  http://www.kevinchant.com/bwd.html

  IconicPCB
  I used to work at BWD in early eighties... Got to meet and work with the B in BWD .
Company was bought out by an accountant and renamed a few names since then.
Presently i think it i still in Mulgrave in Victoria.
I think it is now called McVan Instruments.
I think it is now  owned by ex BWD factory manager.
Chase them up and ask them if they still have any of that info.

   Radioman55
McVan Instruments Pty Ltd.
58 Geddes Street
Mulgrave, Victoria 3170
Australia
Phone +613 9582 7333

  tautech
Which seems to have morphed to:
http://www.observator.com/en/meteo-hydro/news/mcvan-becomes-observator-instruments/

  Radioman55
Great detective work, Tautech.   

Observator Instruments Australia
8 Keith Campbell Court
Scoresby, VIC 3179
Australia

T: +61 3 8706 5000

info.au@observator.com
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