Metrix OX 709 oscilloscope repair.

[vari21]

Hello all.
I bought an old oscilloscope from the internet the metrix os709 , the oscilloscope was worked like a charms when i got it, i was testing the device by injecting signals to it no, problem chanel A chanel B works after that i ve injected a signal from a mini AM battery powered AM radio to chanel A ? and then chanel B stops working but chanel A still working perfect. here are the symptoms when i select chanel B i have no trace, but when i trim chanel B volt division slowly the trace appears and i can bring it up or down but as soon as i trim volt division again to set the right voltage it disappear time base division works fine, vertical trimmer chanel B works.i dont know from were i can start , i searched the shematics for this model online but could not find it no were.
i attached a picture of chanel A and chanel B circuit , i can attach other pictures.
i appreciate any help thanks in advance.

 

[danadak]

Sounds like V/Div switch needs cleaning, maybe even the pots. Also look
at solder joints if those switches are soldered to PCB.....

DeOxit D5 great but pricy stuff, use sparingly, will last you a long time.


Regards, Dana,

 

[vari21]

thank you so much daadak for the clue, i will try to clean it up with dioxit , yes the joints are directely soldered to pcb.

 

[vari21]

Thanks again daadak i ve used a contact cleaner and the problem is gone i have both chanels working now.
But it sill have some problems , this oscilloscope can work on battery i opend it and found battery compartment empty , i just need to know what voltage and amps it requires? on what voltage

 

[vari21]

I ve noticed inside the unit an empty compartiment i think its for the battery ,also a two wires plug red and blue as you can see i think its for to plug a battery but im not sure, im wondering what type,voltage,amps of battery it requires to work if anyone can help it would be appreciated.

 

[danadak]

You need manual, if some how you can find it. Go to their website and
see if a help forum exists to ask for a copy....

 

[rjenkinsgb]

The label mentions external power "10 - 36V"

From the size and age, I'd guess that the battery could have been a sealed lead-acid type, with a connector so it could be removed for recharging externally.

My first thought for a simple alterative is an 18V (20V) power tool battery with a connector plate, if the battery bay is large enough?

You can get connectors for several of the major tool makers batteries on amazon or ebay etc.
I use the Aldi 20/40V batteries for various things, with connectors I 3D print.

 

[vari21]

Thank you rjenkinsgb for the informations , just for a confirmation so using a 20v battery will be enough to operate the oscilloscope and will not to damage it?. Also i want to know if i can make a battery pack from 18650 batteries type like the ones we find in laptop batteries, 3.7v X 6 =22.2v please it it possible or not powerful enough to operate the tube.
Thanks again for your precious time and help.

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[vari21]

Another question please, The label mentions external power "10 - 36V"please were it can be plugged(what connector should i use to plug this DC supply) , is it using the same AC 220v/120v plug? .
sorry i dont have a knowledge, and im new to these equipments.

 

[rjenkinsgb]

It looks like the external DC socket is somewhere at the bottom of the rear panel - that area is hidden by the mains cable in the photo? The marking imply a Roca / coaxial style connector; it's definitely not the same as the AC connector.

If the 10 - 36V DC input range is correct as shown, a 12V or 18/20V battery should be fine.
(Five cell lithium packs used to be labelled 18V, but the advertisers decided 20V looked better..)

18650 cells should work, if they are good quality.

The problem with those is safe charging and over-discharge protection; series connected lithium cells must have under and over voltage protection, plus "balance" charging. You can get protection + balance PCB modules to make battery packs.

They also need precisely regulated charge voltage with current limiting; any overcharge to any cell in the series chain can cause it to burst or catch fire.

A commercial battery and charger is far simpler and safer!


You could use individual cells fitted to holders and a separate charger.
Some cells have internal protection - those cannot be used in built-up packs as the protection module can prevent the balance function working.

These are some three cell packs I've assembled, with the essential protection/balance PCBs.
You still need an appropriate charger.

 

[vari21]

Very nice build, im getting confused on the back panel as you can see on the picture bellow there is only a hole for coaxial cable , and one for the main connector , the wired red /blue connector inside the unit shown in the picture post n5 is for the battery, i do need a manual anyway.
Ok in my case i will need 18v battery 5x18650 + the protection balancing module like this one on the link bellow.

https://fr.aliexpress.com/item/1005002958700474.html?spm=a2g0o.productlist.main.1.25d22dcfyt56wh&algo_pvid=5afec37b-3e36-4ce4-964c-7eaac4b8afd3&algo_exp_id=5afec37b-3e36-4ce4-964c-7eaac4b8afd3-0&pdp_npi=4%40dis%21EUR%214.01%213.57%21%21%214.21%213.75%21%402103856417149080243918671e5dc9%2112000037756155153%21sea%21FR%210%21AB&curPageLogUid=ShKwGkPIcLDh&utparam-url=scene%3Asearch%7Cquery_from%3A

is there any wiring diagram on how to wire things.
thank you.

 

[rjenkinsgb]

It looks like the translucent disc may be a blanking plug?? Possibly the socket has been damaged at some time.

 

[vari21]

Ok, i see.
do you think using only 5 bateries of 18650 type would be enough to operate the tube??

 

[rjenkinsgb]

A set of five in series would definitely give a voltage in the range marked on the scope, from 21V full charge to around 17V when flat.

Whether a single string could supply enough current depends on the cell type and the scope power requirements?

Power tool batteries are generally rated for high current loads, but not all cells are.