Author Topic: Help Needed - BK Precision 2160 / Elenco S-1360 Oscilloscope Repair  (Read 2915 times)

0 Members and 1 Guest are viewing this topic.

Offline ilcaccillo

  • Contributor
  • Posts: 18
  • Country: pt
Hello
My oscilloscope is in desperate need of repair.
I work mainly in pro audio electronics and have no experience in oscilloscopes repair. So it would be great to have some of you help, if you can spare the time.

My unit is branded UniVolt OS-3062, although I was able to find it's just a re-brand and it's the same unit as the BK Precision 2160, Elenco S-1360 and Pintek PS-605.





There's diferent BK Precision 2160 models, theres the 2160, 2160A and the 2160C.
I guess my unit it the 2160, as I was able to get some service docs for the 2160A and the PCB's layouts and component numbering are different.

The unit powers up, but there's only a fixed Dot in the middle of the screen.
I guess that means that both the Horizontal and Vertical circuits are not working properly.

I would like to start by checking the PSU voltage rails but without the schematics or service manual it's a bit hard since I dont see any test points or voltages silkscreened on the PCB's.

Does anyone have the Service Manual for the  BK Precision Model 2160?

Tried to contact BK Precision, Elenco, Pintek and the only Univolt supplier I found online and got no response. Also I searched quite a bit on the Web for service manual/servicing info and schematics for these models and had no luck.

I guess I will have to try to measure the voltage rails using the 2160A schematic hoping that the schematic is similar.

Any tips and thoughts are welcome.

Thank you
« Last Edit: December 06, 2017, 10:00:09 PM by ilcaccillo »
 
The following users thanked this post: john_p_wi

Online tautech

  • Super Contributor
  • ***
  • Posts: 9968
  • Country: nz
    • Taupaki Technologies Ltd.
Re: BK Precision 2160 Oscilloscope - Repair
« Reply #1 on: May 12, 2016, 09:57:10 AM »
My oscilloscope is in desperate need of repair.


Any tips and thoughts are welcome.
There maybe other models in this series that have different bandwidths yet their construction is similar so try this one for a 2120.
http://elektrotanya.com/b_k_2120_oscilloscope_sch.pdf/download.html

Wait for the "processing" to change to "Get Manual"
Avid Rabid Hobbyist & NZ Siglent Distributor
 

Offline ilcaccillo

  • Contributor
  • Posts: 18
  • Country: pt
Re: BK Precision 2160 Oscilloscope - Repair
« Reply #2 on: May 13, 2016, 08:14:37 AM »
My oscilloscope is in desperate need of repair.


Any tips and thoughts are welcome.
There maybe other models in this series that have different bandwidths yet their construction is similar so try this one for a 2120.
http://elektrotanya.com/b_k_2120_oscilloscope_sch.pdf/download.html

Wait for the "processing" to change to "Get Manual"

Thank you so much I got that manual and also the BK 2125 Service Manual that is available on the same site and the PSU's dont match my unit.
I also got a Schematic for the Pintek PS-605 and is doesn't match my unit but it matches the BK 2160A. (this PSU uses 7812, 7912 and 7805 regulators)

I was able to get the Service Manual from BK Precision for the "2160" unit and although it's an 1993 schematic it also doesn't match my unit. This a nice  and detailed Service Manual,

I got the Service Manual for the older Elenco S1360 and finally the PSU schematic corresponds to my Oscilloscope. Unfortunately this Service Manual is the worst of the bunch I got. No parts Lists, some small mistakes, Schematics dont show values for components and theres no parts list to identify them. Anyway it's much better than nothing so with this I was able to start tracing.
 

Offline ilcaccillo

  • Contributor
  • Posts: 18
  • Country: pt
Re: UniVolt OS-3062 / Elenco S-1360 Oscilloscope - Repair
« Reply #3 on: May 13, 2016, 08:28:25 AM »
here is the PSU Schematic:



I Measured all the voltages at the transformer secondary and every value is spot on.

Replaced all the PSU Electrolytic caps with new Panasonic 105ยบ

Replaced BD901 and BD902 Bridge rectifiers

Replaced IC's U901 and U902, these are MC4558 opamps

Unsoldered Q901, Q902,Q903 and Q904 and verify them with my Atas DCA Pro, all the transistores measured good. Soldered them back on

Tested all the PSU diodes, all tested well

Problems:

After the BD901 regulator I'm measuring +-15v instead of +-18.
Collector of Q902 I'm measuring +1.7v instead of +12v.
Collector of Q903  I'm measuring -0.9v instead of -12v.

All the other circuit boards are disconnected from the PSU board.

Any idea of what might be causing this?
the only thing that I didnt had time to do today was measuring the resistors one by one because I have to lift one leg up, visually they look fine.

theres one strange thing with the DB901 bridgr rectifier. I measure it with the + and - legs in the air so it was not connected to the rest of the circuit. I have 16VAC coming from the transformer, after BD901 I'm measuring + and - 14VDC, thats really strange shouldn't the votage after rectification go up by an 1.414 ratio? I changed the Bridge Rectifier for a new one and the same happens.

thanks

 
« Last Edit: December 05, 2017, 11:27:22 AM by ilcaccillo »
 

Online tautech

  • Super Contributor
  • ***
  • Posts: 9968
  • Country: nz
    • Taupaki Technologies Ltd.
Re: UniVolt OS-3062 / Elenco S-1360 Oscilloscope - Repair
« Reply #4 on: May 13, 2016, 12:44:34 PM »

Problems:

After the BD901 regulator I'm measuring +-15v instead of +-18.
Collector of Q902 I'm measuring +1.7v instead of +12v.
Collector of Q903  I'm measuring -0.9v instead of -12v.
Double check transistor pinouts and C902/3 polarities are correct.
Check P901 is completely home and making contact on all pins.
Avid Rabid Hobbyist & NZ Siglent Distributor
 

Offline oldway

  • Super Contributor
  • ***
  • Posts: 1821
Re: UniVolt OS-3062 / Elenco S-1360 Oscilloscope - Repair
« Reply #5 on: May 13, 2016, 03:40:16 PM »
Seems to be an overload on the +12V rail.
 

Offline ilcaccillo

  • Contributor
  • Posts: 18
  • Country: pt
Re: UniVolt OS-3062 / Elenco S-1360 Oscilloscope - Repair
« Reply #6 on: May 13, 2016, 07:05:44 PM »
Double check transistor pinouts and C902/3 polarities are correct.

Checked, Correct

Check P901 is completely home and making contact on all pins.

Do you mean Q901?
if so checked
 

Online tautech

  • Super Contributor
  • ***
  • Posts: 9968
  • Country: nz
    • Taupaki Technologies Ltd.
Re: UniVolt OS-3062 / Elenco S-1360 Oscilloscope - Repair
« Reply #7 on: May 13, 2016, 07:16:26 PM »
Check P901 is completely home and making contact on all pins.

Do you mean Q901?
if so checked
No.

Your schematic shows an interconnect P901 between the mains transformer and the bridges.
Check continuity.
Avid Rabid Hobbyist & NZ Siglent Distributor
 

Offline ilcaccillo

  • Contributor
  • Posts: 18
  • Country: pt
Re: UniVolt OS-3062 / Elenco S-1360 Oscilloscope - Repair
« Reply #8 on: May 13, 2016, 10:35:12 PM »
Thanks,
Yes theres continuity between all the the transformer secondaries and the pcb pins. All the BR are receiving the correct AC voltages
 

Offline ilcaccillo

  • Contributor
  • Posts: 18
  • Country: pt
Re: UniVolt OS-3062 / Elenco S-1360 Oscilloscope - Repair
« Reply #9 on: May 15, 2016, 10:26:53 PM »
Hello I was not getting anywhere with the +-12V rails problem so I decided to convert this rails to use the 7812 and 7912 regulators like in the updated revisions of this PSU.

here is the present PSU schematic



The +-12 rails are spot on now.
Voltages on the other 2 rails are a bit lower than the correct value

I'm measuring 117V instead of 145V and 3.6V instead of 5V

Something is strange with the "High Voltage multiplier" of the Second Anode Supply (the one that has the suction cap and 12Kv), this is a Black rectangular plastic box with some sort of Red epoxy potting material.
As soon as I power the unit this box makes some crackling noise, when I turn the power off the box still crackles for 1 to 3 seconds and then stops.

here are some pictures and symbols of the component in question, the red wire that come out of it it's the wire that has the suction cap in it's end and connects to the second CRT anode.





What might be the cause of the crackling noise? arching inside the multiplier box? Excessive voltage on the multiplier's input?
The multiplier is shot?

« Last Edit: December 05, 2017, 11:32:13 AM by ilcaccillo »
 

Offline ilcaccillo

  • Contributor
  • Posts: 18
  • Country: pt
Re: UniVolt OS-3062 / Elenco S-1360 Oscilloscope - Repair
« Reply #10 on: May 15, 2016, 10:29:57 PM »
HV Generator Circuit Schematic

« Last Edit: December 05, 2017, 11:33:03 AM by ilcaccillo »
 

Online tautech

  • Super Contributor
  • ***
  • Posts: 9968
  • Country: nz
    • Taupaki Technologies Ltd.
Re: UniVolt OS-3062 / Elenco S-1360 Oscilloscope - Repair
« Reply #11 on: May 16, 2016, 04:39:35 AM »
Hello I was not getting anywhere with the +-12V rails problem so I decided to convert this rails to use the 7812 and 7912 regulators like in the updated revisions of this PSU.

here is the present PSU schematic



The +-12 rails are spot on now.
Voltages on the other 2 rails are a bit lower than the correct value

I'm measuring 117V instead of 145V and 3.6V instead of 5V
Fix those rails too ^^^^



Quote
Something is strange with the "High Voltage Rectifier" of the Second Anode Supply (the one that has the suction cap and 12Kv), this rectifier visually is a Black rectangular plastic box with some sort of Red epoxy potting material.
As soon as I power the unit this box makes some crackling noise, when I turn the power off the box still crackles for 1 to 3 seconds and then stops.


What might be the cause of the crackling noise? arching inside the rectifier box? Excessive voltage on the rectifiers input?
The rectifier is shot?

CRT still works even with this noise going on, although I only turn it on for some seconds because Im afraid at the moment that I might be damaging something else.
Maybe, but until the other rails are correct overlook it for now.

Another thread that may be of interest:
http://www.eevblog.com/forum/repair/tek-7704-pops-and-clicks-image-compressing-for-a-moment/
Check all the links within.  ;)
Avid Rabid Hobbyist & NZ Siglent Distributor
 

Offline ilcaccillo

  • Contributor
  • Posts: 18
  • Country: pt
Re: UniVolt OS-3062 / Elenco S-1360 Oscilloscope - Repair
« Reply #12 on: May 16, 2016, 08:24:53 PM »
The +-12 rails are spot on now.
Voltages on the other 2 rails are a bit lower than the correct value

I'm measuring 117V instead of 145V and 3.6V instead of 5V
Fix those rails too ^^^^

Thanks,
will do that first.

I checked it already, Transistors measure good, all caps replaced, all resistors replaced, OPamps replaced, Diodes replaced, and still the output voltages are lower than the schematic values. I guess I have to change resistor values to increase voltage.

Could you help me in letting me know in both rails what resistors could I change the value so that I could bring voltages up?

 

Offline ilcaccillo

  • Contributor
  • Posts: 18
  • Country: pt
Re: UniVolt OS-3062 / Elenco S-1360 Oscilloscope - Repair
« Reply #13 on: May 18, 2016, 07:40:01 AM »

I would like to ask if changing the resistors R909 in the 145V  rail and the R970 in the 5V rail would allow to vary the output voltage?

Thank you
 

Offline ilcaccillo

  • Contributor
  • Posts: 18
  • Country: pt
Re: BK Precision 2160 / Elenco S-1360 Oscilloscope - Repair
« Reply #14 on: May 19, 2016, 10:54:18 PM »
Hello ,
could someone help me out?

thank you
 

Online tautech

  • Super Contributor
  • ***
  • Posts: 9968
  • Country: nz
    • Taupaki Technologies Ltd.
Re: UniVolt OS-3062 / Elenco S-1360 Oscilloscope - Repair
« Reply #15 on: May 20, 2016, 09:21:56 AM »

I would like to ask if changing the resistors R909 in the 145V  rail and the R970 in the 5V rail would allow to vary the output voltage?

Thank you
Yes of course.

Here's some study of how to do it:  ;)
http://people.eecs.ku.edu/~callen/501/LinearRegulators.pdf

Google: series voltage regulator using op amp for more clues.
Avid Rabid Hobbyist & NZ Siglent Distributor
 

Offline ilcaccillo

  • Contributor
  • Posts: 18
  • Country: pt
Re: BK Precision 2160 / Elenco S-1360 Oscilloscope - Repair
« Reply #16 on: May 20, 2016, 10:03:18 AM »
Thank you so much,
will learn that.

Regards
 

Offline KG6FDM

  • Newbie
  • Posts: 1
  • Country: us
Re: BK Precision 2160 / Elenco S-1360 Oscilloscope - Repair
« Reply #17 on: September 27, 2017, 07:01:43 AM »
Hello, Sorry to hear of your oscope problem, they can be difficult.   I have several Elenco 1360 scopes and other test equipment that I will sell for giveaway prices if you have any interest contact me at 813 737 3190,  Jerry, KG6FDM
 

Offline ilcaccillo

  • Contributor
  • Posts: 18
  • Country: pt
Re: BK Precision 2160 / Elenco S-1360 Oscilloscope - Repair
« Reply #18 on: December 05, 2017, 11:04:16 AM »
Hello, Sorry to hear of your oscope problem, they can be difficult.   I have several Elenco 1360 scopes and other test equipment that I will sell for giveaway prices if you have any interest contact me at 813 737 3190,  Jerry, KG6FDM

Hello Jerry, thank you so much for your offer. I located in Europe.
I will send a pm to you to see if it's possible to contact you over email

thank you so much
 

Offline ilcaccillo

  • Contributor
  • Posts: 18
  • Country: pt
Re: BK Precision 2160 / Elenco S-1360 Oscilloscope - Repair
« Reply #19 on: December 05, 2017, 11:18:47 AM »
Hello everyone,
I'm still trying to fix my scope, unfortunately photobucket removed my photos from this thread, but I will try to fix the picture links using another pic hosting site.

I was finally able to fix all the voltage rails.
I was able to get a another schematic of the PSU that has the components values written (the old one didnt have) and one resitor had the worng value. Replaced that and the 145VDC rail is fine now.

So I have +12V and -12, 5V and 145V all spot on.

I connected the unit and at least the CRT doesn't work, so the scope circuit may be working or not but it's impossible to tell without the monitor.

When I turn the unit on there's crackling audible noise coming from the CRTs voltage multiplier.
The voltage multiplier is a sealed circuit a plastic box filled with a kind of epoxy.



I'm afraid of damaging more stuff, so I didnt leave it on for long.

I will have now to ask help locally to someone experienced with CRTs because of the High voltages presented there.

Any suggestions or advice are welcome

thank you all so much
« Last Edit: December 05, 2017, 11:21:15 AM by ilcaccillo »
 

Offline ilcaccillo

  • Contributor
  • Posts: 18
  • Country: pt
Re: BK Precision 2160 / Elenco S-1360 Oscilloscope - Repair
« Reply #20 on: December 05, 2017, 11:33:33 AM »
Fixed the picture links in this thread
 

Offline ilcaccillo

  • Contributor
  • Posts: 18
  • Country: pt
Re: Help Needed - BK Precision 2160 / Elenco S-1360 Oscilloscope Repair
« Reply #21 on: December 06, 2017, 10:01:20 PM »
Going to meet a TV tech locally to see if he can provide some help.

Do you guys have suggestions or tips to sort out this problem?

Thanks
 

Offline ilcaccillo

  • Contributor
  • Posts: 18
  • Country: pt
Re: Help Needed - BK Precision 2160 / Elenco S-1360 Oscilloscope Repair
« Reply #22 on: December 11, 2017, 03:18:17 AM »
I met the TV Tech, he had a nice HV probe. We are all to measure all the voltages above 1KV.
All those voltages were fine. Even the 12KV voltage going to the CRT suction cap.

The 145V rail measures 145v when not connected to the circuit but when I connect it to the circuit it drops to 26V.
So I have to check whats going on there.
Maybe there's a problem with the circuit that load that rail.
I have to check now whats going on there, maybe if I fix that the Scope is back to work again.

I'm just happy that we were able to measure all the HV and that concluded that part of the circuit is working as expected.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf