half a screen help

[kjn4685]

I have a elenco oscilloscope 30 mHz oscilloscope model #s-1325. I was testing a 5v power rail. An then I noticed that the scope had a half a screen. I have tested everything I know how.
Can anybody help me figure out what's going on.
Lou I would appreciate any help
Sorry they out of order.
 I have a problem the silk screen on the board and the parts list are different. Does someone have some ideas what's going on.

[tautech]

I have a elenco oscilloscope 30 mHz oscilloscope model #s-1325. I was testing a 5v power rail. An then I noticed that the scope had a half a screen. I have tested everything I know how.
Can anybody help me figure out what's going on.
Lou I would appreciate any help

Pics required.
Do you have a manual or schematic?

[Psi]

Maybe you've lost one of the deflection coils.
Either bad connection or blown driver.

[tautech]

BUMP
OP has attached a pic and schematics.

[vk6zgo]

Maybe you've lost one of the deflection coils.
Either bad connection or blown driver.

It is Electrostatic deflection---guess "coils" was a typo!

[mij59]

Hi,

The horizontal and vertical amplifier are affected, could be a short in one of the output transistors of the h-amplifier, affecting  the +160V  power supply rail .

[tautech]

I have tested everything I know how.

You must first ensure all PSU rails are to spec.
As you have a trace, I would overlook the HV (2KV) supply for now.

Then refer to P53 onwards in the Troubleshooting your Oscilloscope pdf
Your schematic 6 shows the horizontal output amp and often 1 transistor will fail.
This is were I would suspect the problem is.

But to eliminate a further possibility, the sweep should also be checked for correct triangular wave output.
Normally you need another scope for this, however a slow timebase setting and a moving coil meter might do for a rough functionality check.

[christopher iles]

Hello,

I had EXACTLY the same fault with my Gould OS300 oscilloscope. It turned out that there are 2 transistors (look like voltage regulators, think the outline is TO-72) each of which do half of the trace. One of the transistors had a minute hole in the insulating washer and had shorted the case to ground. I took that transistor out and put the other transistor in its place. The trace then shifted to the other half of the screen which proved that that was the problem.
As the transistors were only £1 each I bought 2 new ones, fitted them and now I have a full trace!
I know my scope is a different make to yours but they all work the same basically.
The transistors in my scope are bolted to the chassis side by side, they're in the horizontal amplifier output. When you locate them, with power off do a quick ohms check for open or short circuits.
I'm sure you're aware but there is an awful lot of high voltage (2.4kV in mine) in oscilloscopes so they demand respect! Keep one hand in your pocket when poking around EHT as my teacher used to tell me!

I hope this is of help, please let me know how you get on.

Regards,

Chris.

[kjn4685]

I have another problem the silk screen on the board is different than the parts list in the manual. The printout is different and the the numbers don't match. I don't know what to do now. I am going to put a copy on the forum.

[christopher iles]

If you can put as much information as you have on here I'll take a look.

Cheers,

Chris.

[kjn4685]

here is the parts list and broad

[christopher iles]

Check the four transistors on the right of the H-FINAL circuit.

I suspect one or more of those have failed and that's where the fault is.

Also check the voltages as per the circuit diagram to make sure that they are all there.

Good luck!

Regards,

Chris.

[kjn4685]

I would like to explain about the transistors that are on my board are different than what I have in my service manual. In the service manual you'll see it's a 2sc 945 and of course on the board is 2sc 838.  The silkscreen layout of the pins is different than the datasheets. If you look at the picture that I sent you of the board you'll see a c838 transistor and if you look at the data sheet on this particular transistors it's different than what  the silkscreen says. The silkscreen says from right to left BC E and datasheets says from left to right you will see  cbe. I hope I'm not confuse anybody If I do I'm sorry but I am confuse myself there has to be an explanation of this procedure. I hope I explained this enough for everybody to understand. For more information the rest of the transistors on the board says from left to right BCE. So if anybody can help me out I would really appreciate.
Confused:
KJn 4685
   

[tautech]

Close examination of your problem reveals the 838 much inferior to the 945. The pinouts are also different as you say and if no allowance was made for this the circuit will not work as intended.
Is there evidence that somebody has made a previous repair on this scope?

Replace with the correct 2SC945.

[kjn4685]

No the was new I bought myself. What about the silkscreen has anyone ever run across this problem. I have a bad switch on the magnifier times 10. So I have to find one of those. I am going to a pic on here and see if anyone would have one.

[tautech]

No the was new I bought myself. What about the silkscreen has anyone ever run across this problem.

No wonder you are confused with components that do not match the schematic and wrong silkscreen.
But if you bought the scope new and it has been working until recently, we should not change any "working" components.
I believe your problem lies in the H-Final amp in your scan 6 of the schematics.
As has been posted before, very likely a failed transistor.
Usually one of the 4 output transistors as christopher iles has said.
Can you post those 4 transistor part numbers?

Do you have a multimeter with a transistor tester?
Check each transistor datasheet for Hfe and test that each transistor falls within the datasheet Hfe range.

[kjn4685]

here is the transistors numbers. do you guys think that I can use c945 instead c838 or . If c1907. Because I have c945 already. This would save me money.
Again thank you
lou

[tautech]

That does not look right.
There are 2 PNP and 2 NPN in the schematic for the H-Final output stage.
Normally 2 matching pairs.

[kjn4685]

I am sorry you are right. The q650, is npn 2sc945 q651 is a npn 2sc945 q652 pnp is 2sa1015gr accourting to the service manual q653 is 2sa1015gr the same as the other transistor. Now the board the q650 is c1907 q651 c1907 q652 a1015 q653 a1015 q654 c1907 q653 c1907 q656 c1907 q657 a838 now are you guys confused.
Lou

[tautech]

here is the transistors numbers. do you guys think that I can use c945 instead c838 or . If c1907. Because I have c945 already. This would save me money.
Again thank you
lou

2SC945 has a different pinout to 838. But if you can make it fit yes.
Not ideal, but good enough for a trial, then get the 838 later.

You can test the "diode" action of a transistor as a quick test. Google it.

BTW I nearly missed your edit to this post, you should point us to an important edit. 

[kjn4685]

ok I will try everything you have shared.
again I thank you very much and I will let you know how it turns out.
Lou

[christopher iles]

I should check the transistors even though they are different, manufacturers do change parts without notice sometimes. I would test all of the transistors in the x amp area and also check the voltage rails, particularly the 5v one as you may have accidentaly blown a regulator when you were checking the 5v rail.

Hope this helps,

Chris.

[kjn4685]

I changed the transistor c838 to c945 and it still does not work. I still wrestling with the slikscreen pin destination witch is on the board reading even at q657. The rest of the board has the same. Can anyone help me. I also have a bad switch I have pics does anyone have one of them. the value is B10ka

[tautech]

Can you test the transistors?
What test equipment do you have?

[kjn4685]

DMM with hfe tester and I have a kit I built transistor tester. can I still test my scope without this switch.