Aaron BS-310S CRO Mini teardown

[tautech]

I scored a pair of these little cuties recently.
Dainty wee things, 115mm high (41/2") (Case & feet removed) by 225mm wide (83/4") by 360mm deep.
Massive 3 inch 95mm display. 
Specs 15 MHz  Max input 300V DC+AC peak or 600V p-p

Long looked for manual with schematics: 
http://www.download-service-manuals.com/download.php?file=Aaron-8331.pdf&SID=p7q2q1u430i6ltslu975m7r9d4
41 pages 2.8 Mb

See following post for manuals specific to NZ models that were mostly ex NZ Navy:
https://www.eevblog.com/forum/testgear/aaron-bs-310s-cro-mini-teardowm/msg3828221/#msg3828221




So in keeping withe the EEVblog motto, I didn't turn it on, I tore it apart. 

The controls are set out just like a traditional CRO and include nearly all  except AC trigger coupling and graticule illumination.
No Dual or Delayed timebase.



They both came with nice little vinyl overcoats with a few dozen perferations on each side to match the case holes, but not so many in number.
Obviously cooling is not a problem with these units.
Off with the jacket and a few screws later the case and carry handle just slide off the rear. Easy.
Imagine my suprise when I spot this yellow 12V NiCad battery pack. 



10 "sub-C" cells, there's a spec for the battery on the base of the unit: 2A...guess thats 2 A/hr
Multi volage 120 or 240 VAC internal switch.
Circuitry layout is simple and neat, inputs down the LH side terminating at the vertical amps...all on one PCB. Nice.
Timebase, sweep and Horizontal amp on the RH PCB. Also nice.
There is a botton PCB, full width and ~ 2/3 the length of the scope. It is the only SS PCB.
It is mainly PSU, battery charging, main PSU (single 30V linear) and the CRT HV supply housed under the Ali cover below the CRT.

All componentry is facing inwards and with the outer cover removed all PCB traces are easily accessable for measurements.
Componentry is all through hole, IC's 4000, 74LS and the like. There are no hybrids that I could see, the bulk of the work done with BJT's with the exception of a 2SK228T (6 lead Dual Fet?) and a HA1127 DIP14 (5 Transistor array) IC in each of the channel inputs.
All preset trimmers are semi sealed types. 




So time to turn it on....



You little beauty.

Bit of a fiddle and all seems to work as it should.....except the battery.
So time to hunt out why, nackered or just not charging.

AND the other thing missing ....a MANUAL......anybody? Found. 

So what will I do with these little beauties..... just might give them to newbies plus the cost of probes.... but not until I find a manual first.

[SeanB]

Nice little scope there. Battery will very likely be a dead short on all cells, and even if you zap them open it will not hold charge, and will have vented a lot under that yellow jacket. Replace with a new pack, either from a local battery repacker, or use without.

[tautech]

Nice little scope there. Battery will very likely be a dead short on all cells, and even if you zap them open it will not hold charge, and will have vented a lot under that yellow jacket. Replace with a new pack, either from a local battery repacker, or use without.

Yep, they are little cuties and nicely built Japanese units.
Had 1 of them running for a few hours now, (low intensity of course) rock solid. 
Even though the display is small, it's nice and crisp and resolution with both traces is excellent.

The batteries are another project, simple to build a pack with tagged cells but I'll probably leave this to the beneficery of these scopes. The added cost of replacing them will only appeal to those that need a portable unit.

But I don't want to offer them until I have at least a users manual for them. 

[tautech]

Well I powered the other one up tonight, seems that it functions OK except the Intensity control is at full despite any setting adjustments.     
Focus works fine so I reckon the Intensity pot or a resistive divider is open.
Done a bit on CRO's in the past, so it'll be a "just one foot after the other" type fix. 

Trouble is the pot shaft goes all the way under the CRT into the encased HV section seen in previous photos. 
This may take a little while, when I have it all open I'll post some pics and report on the fix.

Bugger not having a manual, I like to see what I'll find before I go looking. 

[tautech]

Well a little more progress.
Hauled out the NiCad battery pack to check the charge circuitry and with the pack disconneted and scope on the battery LED goes green, good, seems as one would expect. 
Probably best I also check the charge cut-off voltage, that should be ~ 14.5 V for 10 "C" cells

Lets see if this scope really does work from a battery supply.
  connect up a 12V SLA and a DMM in series and another DMM to monitor voltages.
  500mA draw with one trace on, 550mA with 2 traces.
~ 220mA charging falling away as battery freshens up. It was fully charged to start with.

The battery pack was a Sony 12V 1200mAh which would suggest ~ 2hrs run time for the scope on battery power. Enough to get a job done you would think.

Next step is to get this one off the bench....its seems fine, then concentrate on the other with the non-responding Intensity control.

OOOHHH for a manual.

As Arny says "I'll be back".

[Kevin Pearce]

Hi tautec.

I'm new to the forum, so please bare with me if I get any protocol a bit out of whack.

I have spent the majority of my working career in the test & measurement field, with experience in a range of mostly Philips and Fluke equipment.

I have read with interest, your comments and findings of the tear down of the Aron BS-310S scope.

I recently purchased one of these second (or 3rd, 4th, or even 7th) hand. I opened it to set the mains voltage to 230V (New Zealand mains), but it would not function.
I found a blown fuse which I replaced (2A). Now the power light comes on, followed soon afterwards by a component burning smell and no trace of a trace. I think it is emanating from under the main PCB metal supply covers. Like you I have no circuit diagram of the instrument, and getting to remove the 2 top covers looks to be a mission, as there is minimal clearance below the CRT.
I may need to remove the rear panel to gain access to what lies within the metal box.

I will keep the forum updated as and when I make the necessary breakthrough.
Until then I follow with keen interest,

Cheers all.   
Kevin.

[tautech]

Welcome to the forum Kevin.

The PCB with the covers drops out the bottom after de-soldering some wires and removing screws and plugged leads.
My second unit is still on the bench waiting for some rainy days to finish it.

I'll post some photos of this PCB with the cover removed.

If you're near AK maybe we can get together, check my website for contact details.

Got to fly now, will try to do that tonight. 

[tautech]

After some tracing and checking components to assess the cause of the over-bright traces the only thing I found was a trim pot in the HV path was set to max.
Now set to mid point and ready for reassembly to check if the trace and be brightness adjusted. 

The bottom PCB contains all the HV circuitry for the CRT, the main single supply PSU (bridge next to the pair of glass fuses), several 78L** regulators, battery charging control and the 3 main CRT adjustment pots for Focus, Intensity and Trace rotate.
All 4 DIP IC's are 4011, from 3 different manufacturers  Motorolla (UB)x2, Texas (BN) and RCA (BE).(IC suffix)
All litic's are...... is it Marcon? 105C.
Big red transformer has been dipped for insulation, being the CRT HV supply. Dated Aug 84.


Interestingly the Intensity pot shaft extension coupler grub screws had been rubbing against the windings of the choke positioned between 2 of the pot shafts. While the extension shafts are non-conductive composites, the pot shafts aren't and the pots are secured to one wall of the shield housing that is GND'ed. 
As far as I can tell it has not caused any damage,    the choke is in series on one of the PSU LV rails to pins that supply to another PCB.

Not sure when I'll get back to this, but I will.........

[tautech]

Well after all this time there's been some of these Aaron BS-310S scopes for sale on our local online sales thing Trademe.
Cheekily I asked the seller if he had manuals for the 2 units he had for sale. 

Available online was his reply..... not when I last looked. 

Well damn me there are and with schematics      

Link added to the OP and specs updated too:
http://www.download-service-manuals.com/download.php?file=Aaron-8331.pdf&SID=p7q2q1u430i6ltslu975m7r9d4

[mission]

Hello,
I have recently acquired the same oscilloscope and would like to use it to learn and understand new side to how circuits work. My issue is that it came without probes. in the manual it says 10:1 though when i went to look for probes I found that there is a mass of different ones and i don't want to buy something that may not give me the best out of it.

Can anyone please suggest what would be the best probe to buy for this oscilloscope?

many thanks

[tautech]

Hello,
I have recently acquired the same oscilloscope and would like to use it to learn and understand new side to how circuits work. My issue is that it came without probes. in the manual it says 10:1 though when i went to look for probes I found that there is a mass of different ones and i don't want to buy something that may not give me the best out of it.

Can anyone please suggest what would be the best probe to buy for this oscilloscope?

many thanks

Hi mission, probes like these ones on our local Trademe are most likely P6100 units and can be found heaps cheaper on eBay or Aliexpress.
http://www.trademe.co.nz/electronics-photography/radio-equipment/amateur-radio/auction-1290353577.htm

For low voltage signals you can use just a bit of wire while you're waiting for something to turn up.
To learn with and what offers some versatility just get P6100 1x, 10x switchables but force yourself to use them on 10x attenuation to give better protection for your scope.

[mission]

Thank you much for the info. 

[sharow]

Hello.

I really need HELP!

I got BS-310S few month ago. looks very good (except battery). but no trace. Current draw is under 50mA. so I suspect something wrong with PSU section. and yes! Q13(2SA886) was found dead. I replaced to Toshiba TTA008B. ... then PSU consume over 2Amps(2A is my CC limit) ! some bad noise from L2 choke. no smoke but smell like magick smoke .

hmmmm something wrong with this section. that causing to kill Q13.
few days later, I found something. R22 is 47k ohm in schematic. but my board soldered 47 ohm!!!!

Question! which is right? 47k Ohm or 47 Ohm?
in theory, 5V / 47 ohm = 100mA. it's too high for 78L05 output.(wrong, 4.7k in series...)
I want to see high-res picture of this post: https://www.eevblog.com/forum/testgear/aaron-bs-310s-cro-mini-teardowm/msg675699/#msg675699
That save my life.

of course I can replace to 47K and see what happen. but I need put back choke, capacitors, diode, registers ... everything I desoldered .
so, I want evidence for now.

PS>
My unit is Application Brand (not Aaron).
same as this picture: https://www.radiomuseum.org/r/aaron_oscilloscope_bs_310s.html
my unit using many tantalum capacitors, 4011 is all RCA, little bit different.

Cheers

[tautech]

few days later, I found something. R22 is 47k ohm in schematic. but my board soldered 47 ohm!!!!

Question! which is right? 47k Ohm or 47 Ohm?

Welcome to the forum.

47 ohm.
My units, just one checked for you: Yellow, Purple, Black, Gold......47 Ohm, 5%.
Original soldering so it should be correct.

[sharow]

thank you tautech!

so, wrong value in schematic  .
I'm going to suspect another.
maybe I should check to see Q14, Q15 is alive.

this is only place for the BS-310S owners.
Thank you.

[sharow]

Finally!


Tantalum capacitors, that it.
C22 broken and dead-short. then kill D17 D18 and Q13 .
I replace all tantalum-cap in PSU.

another problem is `free-running state`. manual(page 4) say

the sweep is set in free-running state even when no input signal is applied, with trace line displayed on CRT.

trigger is OK, but my unit behave like no free-running state.
Still many tantalum-cap in Vertial-Amp unit and Horizontal unit.
I'll replace all of them.

Anyway, I'm happy now

Thanks

[tautech]

Good progress. 
There are some differences in the componentry between your unit and mine, not that it should matter much:
Yours:


Mine:


But note the grub-screws in the pot shaft couplers, they can contact the windings of that inductor, glue the bugger down so that they won't !

[peteb2]

I have had one in my pile of hoarded gear and today i had a small play.... It works!... quite well but there is no cal 5V and, well loads of noisy switches....

The reason i put it on the bench is i have a real use all of a sudden for a small display 'scope (already have an old-school 4 channel TDS 420A Tek and on my drool list is a 4 channel MSO... one day) but then i noticed a some-what shocking problem.

The entire front diecast that holds just about everything has completely and utterly "LET GO" as in swollen up and deformed everything.... Input BNC sockets are all a kimbler at weird angles and the 5V cal has tuned over so far as to short to GND ...effectively.

So effectively the entire casting is crumbling into bits! I initially thought that the front had been smacked and beaten in over its life thanks to some rough as hell previous owners. The rechargeable battery is missing so that's good news on the chances it would have leaked and the chemical goop eaten everything so because i want a wee analog 'scope and i like a good hiding of a challenge i might make a new front casting... I am assuming here that its unlikely i will find another of these units even in an not going state that i can make into one working, rebuilt, refurbished unit.

It could be a good 3D printer project but it needs to be really conductive material and really strong. It's more of a milling operation i'm thinking.... (All i need is a machine to punch out some extra time because i sure do not have much of that right now).

[tautech]

Now you've got me  that mine might fall apart too but no they're in good shape. 

Most of these that came available here in NZ around the same time were from military sources  so I wonder if a few are ex Navy and had their fair share of salty air which is good for nothing except fish.

Being part Scots (deep pockets, short hands) I'd be getting some Ali plate and quietly drilling and filing away until I bashed something into shape as a substitute front panel.

[peteb2]

I am already measuring up so as to make something. The main label escutcheon has come back from the gloom of being bent in places and coated in what i can only describe as fly-poop after a huge clean with soapy water. Its actually quite readable now. 

I picked up the escutcheon/front chassis and was attempting t remove the BNC sockets when.... the photo shows it. I need to take a few measurements before the thing turns into a pile of rubble....! Interesting these were sold into military use in NZ. If this one has been at sea that could certainly explain the rot in the diecast.

I rescued this wee 'scope from a rubbish bin quite a few years ago, it has a black plastic cover-all and it's sat in the dark in a box in my 'junk' room for around the last 8years! I'd a brainwave needing an analog 'scope with XY input and almost bought the Oscium unit that ties up your iPad but at the last minute saved a few $s remembering that old little scope had hoarded away....

Nothing better than doing the 'hobby thing' with electronics on a summers Sunday Evening...

[Chris56000]

Hi!

I know it's a bit of a long shot, but if I came across that my idea for restoration/rebuild would be to obtain one of those instrument enclosures that houses front/rear panels in slots moulded near the front and back, with front-panel dimensions larger than, but still as close to the original front-panel overlay dimensions as possible.

I would then use illustrator/cad s/w (or a front panel designer) to make a border on plain colour background that just fits round the original panel overlay, whose outside dimensions fit the new case, place the overlay on the border sheet and secure it to the overlay sheet with light adhesive (Evo-Stik etc.). A new Aluminium or thin steel panel to fit the new case can be cut and drilled for the original switches, BNC connectors and other fittings.

The new case can then be screened internally with copper foil and/or spray-on copper EMC shielding, the PCBs fitted to the case bottom - if the original scope used a separate chassis this can be reused.

If you can get a full Heathkit IO-4505/IO-4510, etc., complete Assembly Manual with illustrations this will give you an idea of the method of rebuild I'm thinking of!

I'm thinking of the construction used in a lot of pieces of 1970s/1980s Heathkit T & M equipment by the way - a lot of their oscilloscopes (IO-4505, IO-4510, etc., etc., were built this way!

I have to admit I'm amazed die-cast metal can disintegrate like that by the way!

Chris Williams

[wolfy007]

Did you ever find a solution for the replacement front plate?

[peteb2]

I have drawn up something that I plan to mill out of a lump of ordinary alloy.. I’ve gone as far as squaring up a piece of scrap plate but as my home mill is totally manual, things have stalled for now with Life generally getting in the way.... I need to make it a priority, the little scope is a handy wee thing...

[wolfy007]

Must admit, I found one on Gumtree, looked like a pretty cool little scope and bought it on a whim. Thought I better learn more about it, as I mostly collect Tek and BWD scopes.  Came across this thread looking for a manual (with tautech's link), then saw your story and had to know how it turned out! 

[tautech]

Must admit, I found one on Gumtree, looked like a pretty cool little scope and bought it on a whim. Thought I better learn more about it, as I mostly collect Tek and BWD scopes.  Came across this thread looking for a manual (with tautech's link), then saw your story and had to know how it turned out! 

Note
The manual in the OP is close for the units I have but 'not quite' correct.
Particularly for the center PCB that handles the HV. Layout and componentry is a little different. 
Shelved project that I need to get out of the pile. 

[wolfy007]

Thanks for the heads up, will be interesting to compare.

[wolfy007]

Well it came in the post and sure enough it works. But seems to be slight signal 'filtering' on channelB and the cal signal is warped badly so pull apart time (and check caps). Ill post pics of the inards if I notice any differences.

[zl2tpq]

Thanks for the blogg.
I got one at a computer auction, I don't think most of the punters knew what it was. I couldn't see it working, so I bid on it for the case value to me.
It was with  a lot of computers from Reuters and I don't think was used. The brightness control shaft was slightly loose and you could only turn the control down and it slipped when it was wound up. Easy fixed.   No dirt dust scratches. That was at least 15 years ago and because of its size, it is my bench scope of choice until I need the features of the Tektronix units (rarely)   I'm about to check if I can brighten up the trace.
Thanks again for all the info.
 

[tautech]

Thanks for the blogg.
I got one at a computer auction, I don't think most of the punters knew what it was. I couldn't see it working, so I bid on it for the case value to me.
It was with  a lot of computers from Reuters and I don't think was used. The brightness control shaft was slightly loose and you could only turn the control down and it slipped when it was wound up. Easy fixed.   No dirt dust scratches. That was at least 15 years ago and because of its size, it is my bench scope of choice until I need the features of the Tektronix units (rarely)   I'm about to check if I can brighten up the trace.
Thanks again for all the info.
 

Welcome to the forum.

If you check the manual linked (and it's not quite right for my units) on P39/41, VR10 is listed as Int Adj that I strongly suspect is the bias adjustment for the main intensity control, VR8.
Have a squiz at the manual for the trace intensity adjustment procedure that normally goes something like: the trace should just be invisible with the main intensity control set to minimum.
Let us know how you get on.

[Bravo]

Hi all,
I acquired the 2 scopes from tautech, & managed to repair the faulty one which had high intensity. The fault was repaired by replacing IC 1 on the PSU board, which is a 4011, used as an adjustable duty cycle oscillator feeding the HT adjustment transistor. My life was made a lot easier by be able to obtain manuals with fully readable schematics. In addition some calibration notes & the mods which were done for the units used by the NZ Navy. Hopefully I will succeed in attaching them.

[tautech]

Thanks G and pleased you now have them both sorted out. 
As per our emails lucky finding that just a faulty 4011 was the root cause of no Intensity control.

OP updated with a link to your post with the manuals attached.