half a screen help - Page 1
Forum section: electronics / repair

author: kjn4685
author_rank: Regular Contributor
timestamp: August 05, 2014, 02:45:18 am
content: 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 helpSorry 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.

author: tautech
author_rank: Super Contributor
timestamp: August 05, 2014, 05:29:00 am
content: Quote from: kjn4685 on August 05, 2014, 02:45:18 amPics required.Do you have a manual or schematic?

author: Psi
author_rank: Super Contributor
timestamp: August 05, 2014, 05:49:33 am
content: Maybe you've lost one of the deflection coils.Either bad connection or blown driver.

author: tautech
author_rank: Super Contributor
timestamp: August 08, 2014, 01:04:12 am
content: BUMPOP has attached a pic and schematics.

author: vk6zgo
author_rank: Super Contributor
timestamp: August 08, 2014, 06:25:59 am
content: Quote from: Psi on August 05, 2014, 05:49:33 amIt is Electrostatic deflection---guess "coils" was a typo!

author: mij59
author_rank: Frequent Contributor
timestamp: August 08, 2014, 06:56:22 am
content: 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 .

author: tautech
author_rank: Super Contributor
timestamp: August 08, 2014, 07:57:27 am
content: QuoteYou 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 pdfYour 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 correcttriangularwave 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.

author: christopher iles
author_rank: Regular Contributor
timestamp: August 09, 2014, 08:05:02 am
content: 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.

author: kjn4685
author_rank: Regular Contributor
timestamp: August 14, 2014, 04:30:34 am
content: 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.

author: christopher iles
author_rank: Regular Contributor
timestamp: August 14, 2014, 05:56:25 am
content: If you can put as much information as you have on here I'll take a look.Cheers,Chris.

author: kjn4685
author_rank: Regular Contributor
timestamp: August 14, 2014, 10:01:33 pm
content: here is the parts list and broad

author: christopher iles
author_rank: Regular Contributor
timestamp: August 16, 2014, 07:03:01 am
content: 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.

author: kjn4685
author_rank: Regular Contributor
timestamp: September 03, 2014, 01:37:50 am
content: 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

author: tautech
author_rank: Super Contributor
timestamp: September 03, 2014, 04:23:02 am
content: 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.

author: kjn4685
author_rank: Regular Contributor
timestamp: September 03, 2014, 06:39:38 pm
content: 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.

author: tautech
author_rank: Super Contributor
timestamp: September 04, 2014, 10:37:42 am
content: Quote from: kjn4685 on September 03, 2014, 06:39:38 pmNo 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 aschristopher ileshas 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.

author: kjn4685
author_rank: Regular Contributor
timestamp: September 04, 2014, 10:08:40 pm
content: 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 youlou

author: tautech
author_rank: Super Contributor
timestamp: September 04, 2014, 10:15:45 pm
content: 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.

author: kjn4685
author_rank: Regular Contributor
timestamp: September 04, 2014, 11:42:33 pm
content: 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

author: tautech
author_rank: Super Contributor
timestamp: September 05, 2014, 12:26:41 am
content: Quote from: kjn4685 on September 04, 2014, 10:08:40 pm2SC945 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.

author: kjn4685
author_rank: Regular Contributor
timestamp: September 05, 2014, 12:45:34 am
content: 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

author: christopher iles
author_rank: Regular Contributor
timestamp: September 07, 2014, 06:03:22 am
content: 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.

author: kjn4685
author_rank: Regular Contributor
timestamp: September 10, 2014, 01:07:20 am
content: 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

author: tautech
author_rank: Super Contributor
timestamp: September 10, 2014, 08:19:39 pm
content: Can you test the transistors?What test equipment do you have?

author: kjn4685
author_rank: Regular Contributor
timestamp: September 10, 2014, 08:54:38 pm
content: DMM with hfe tester and I have a kit I built transistor tester. can I still test my scope without this switch.

author: tautech
author_rank: Super Contributor
timestamp: September 10, 2014, 09:07:26 pm
content: Have you downloaded the datasheets for the transistors in the H-Final amp?Have you tested each transistor Hfe matches the datasheet?QuoteDid you swap the leads for correct replacement?You say :"it still does not work"Do you mean the trace is still only half way across the display?

author: kjn4685
author_rank: Regular Contributor
timestamp: September 10, 2014, 09:42:49 pm
content: No I did not switch the leads. The scope does not work at all. The power led lights but there is nothing. Ok I am at fault I did not test for the hfe. Sorry how would you test in circuit or out of circuit.

author: tautech
author_rank: Super Contributor
timestamp: September 10, 2014, 10:01:18 pm
content: QuoteThat's why it wont work at all.Remove transistors and test.

author: kjn4685
author_rank: Regular Contributor
timestamp: September 11, 2014, 11:57:45 pm
content: I have tested every transistor on that board and I got my screen back but only half a screen. Did one of the deflection plates blow. What you guys think.

author: tautech
author_rank: Super Contributor
timestamp: September 12, 2014, 12:11:22 am
content: Good. I believe the H-Final amp is OK.We must now return to a previous post to eliminate a faulty sweep as the cause.https://www.eevblog.com/forum/repair/have-a-screen-help/msg493043/#msg493043Google "CRO horizontal sweep theory" for docs for greater understanding of the next step.Can you get access to another scope ?

author: kjn4685
author_rank: Regular Contributor
timestamp: September 12, 2014, 12:28:35 am
content: No I do not anyone that has one

author: kjn4685
author_rank: Regular Contributor
timestamp: September 12, 2014, 12:45:43 am
content: I went to p53 in oscilloscope pdf and I did that.

author: tautech
author_rank: Super Contributor
timestamp: September 12, 2014, 01:00:18 am
content: Quote from: kjn4685 on September 12, 2014, 12:45:43 amIn X-Y mode, where was the dot?Did you have the Horizontal & Vertical position controls each at mid-range?If you put a country flag in your forum profile there maybe somebody on the forum that is close to you and can help with a scope.

author: kjn4685
author_rank: Regular Contributor
timestamp: September 12, 2014, 01:18:30 am
content: Yes there was spot on y and x mode. it was in the middle. It will not go any farther to left than middle.

author: kjn4685
author_rank: Regular Contributor
timestamp: September 20, 2014, 12:47:42 am
content: I am back again I would like to know if I use nte 107 instead of 2sc1907 will it work. The net 107 has a vcbo of 30v CEO is 12v ebo is 3v now the 2sc1907 has vcbo is 30v CEO is 19v ceo 2 v. Can anyone help me.

author: kjn4685
author_rank: Regular Contributor
timestamp: September 20, 2014, 03:11:19 am
content: here is a pic of 4 more transistors that I have a suspension might be a problem. what you guys think.lou

author: tautech
author_rank: Super Contributor
timestamp: September 20, 2014, 04:35:12 am
content: Quote from: kjn4685 on September 20, 2014, 12:47:42 amWhich part of the scope are they?These transistors are not a very good match, but may be OK for test purposes.BUT they have a different pin out !Quote from: kjn4685 on September 20, 2014, 03:11:19 amWhat Schematic # ? Which part of the scope circuit?What are the transistor numbers so we can look at the schematic?

author: kjn4685
author_rank: Regular Contributor
timestamp: September 20, 2014, 04:57:12 am
content: q658 q659 q660 q661 these are to-126

author: kjn4685
author_rank: Regular Contributor
timestamp: September 20, 2014, 05:07:47 am
content: q658 2sb1109c q658 sd1109c q660 2sd1609c q661 2sb1109c This is what is in the s/m. Now on the broad is q658 c1306 q659 c3423 q660 c3423 q661 c 1306.

author: tautech
author_rank: Super Contributor
timestamp: September 20, 2014, 05:09:47 am
content: Which schematic are they shown in??

author: kjn4685
author_rank: Regular Contributor
timestamp: September 20, 2014, 05:16:42 am
content: Yes you are right Tautech sorry if I spelled it wrong . these trans are above the others they are in a group of 4 they are to-126 package but the pin outs are the same as the broad here is the pic

author: kjn4685
author_rank: Regular Contributor
timestamp: September 20, 2014, 05:17:56 am
content: # 6 oscillscope pdf

author: tautech
author_rank: Super Contributor
timestamp: September 20, 2014, 09:15:30 pm
content: Quote from: kjn4685 on September 20, 2014, 04:57:12 amAre these not on the PCB?Have you have missed them !!!These are the H Final output stage transistors that have been the most likely MAIN suspects from the start.REMOVE each and test.

author: tautech
author_rank: Super Contributor
timestamp: September 20, 2014, 10:26:45 pm
content: Quote from: kjn4685 on September 20, 2014, 03:11:19 amThese are the Vertical final output amp transistors and are not related to your problem.

author: kjn4685
author_rank: Regular Contributor
timestamp: September 21, 2014, 06:17:15 pm
content: I have pulled them and when I tested them they have no hfe. So I have to change them and order.

author: tautech
author_rank: Super Contributor
timestamp: September 21, 2014, 07:25:15 pm
content: Quote from: kjn4685 on September 21, 2014, 06:17:15 pmThat cannot be correct, you have "half a screen". Get the datasheets to be sure you test correctly.Quote2SC1306 Hfe 25-200, 2SC3423 hFE classification O: 80 to 160, Y: 120 to 240

author: kjn4685
author_rank: Regular Contributor
timestamp: September 22, 2014, 09:09:09 pm
content: When I test the transistors the shows pnp or npn then it gives the pin order like ecb then the meter shows the letter k and nothing else when testing in the hfe mode. So what does that mean.

author: tautech
author_rank: Super Contributor
timestamp: September 23, 2014, 08:43:21 am
content: Quote from: kjn4685 on September 22, 2014, 09:09:09 pmI do not know what the K means on your tester.Important. Read carefully.The schematic (6) shows Q658 & Q661 asPNPand Q659 & Q660 asNPNThe 2SC3423 is NPN but TO-220 package (Q659 & Q660)The 2SC1306 is NPN and TO-126 package (Q658 & Q661)Should be PNPPlease check part numbers again, this is very wrong.There must be 2 PNP and 2 NPN.We must identify these 4 transistors correctly.Should also be the same package for all 4 transistors.

author: kjn4685
author_rank: Regular Contributor
timestamp: September 23, 2014, 11:22:07 pm
content: If I could get another scope does it have to be a analog or digital.The four transistors are just what the parts list shows. Any further I do not want to say or do.

author: tautech
author_rank: Super Contributor
timestamp: September 25, 2014, 01:09:16 am
content: Have you correctly identified the 4 output transistors in your scope (q658 q659 q660 q661) ?Are they TO-220 or TO-126?

author: kjn4685
author_rank: Regular Contributor
timestamp: September 25, 2014, 01:23:25 am
content: To 126

author: tautech
author_rank: Super Contributor
timestamp: September 25, 2014, 02:00:41 am
content: Please post the 2 transistor part numbers that are in your scope. (H-Final output)2S*****??All markings please.Carefully post them, all numbers plus any letters that might be separate to identify Hfe range.OR good photos if you can.

author: kjn4685
author_rank: Regular Contributor
timestamp: September 25, 2014, 03:06:03 am
content: Ok this is the 4 trans on the board. As you see that I have changed 2 trans they are the ones at the bottom of the pic. here is a pic. I hope that this will help you guys see what is going on.

author: tautech
author_rank: Super Contributor
timestamp: September 25, 2014, 03:51:20 am
content: From your picture:2 x 2SA1360 Y PNP Hfe 120-240 (still in PCB)(you previously posted wrongly as c1306)2 x 2SC3423 Y NPN Hfe 120-240 (shown removed)Datasheets attached.Although the datasheets list both transistors suitable for "Audio Frequency Amplifier Applications", they are used in a Video output stage.If the manufacturer made this change from the schematic you have,you are best advisedto seek thesame transistorsfor replacements.As you have substituted the NPN's and not fixed the fault,you need to check/replace the PNP's.The NTE373 is not the best substitution match for NPN 2SC3423 but should be OK to test with, then replace.

author: kjn4685
author_rank: Regular Contributor
timestamp: September 25, 2014, 04:15:08 am
content: A 1360 pnp is vcbo -150 v. -150 v -5 can you tell me what is the difference between + or-

author: tautech
author_rank: Super Contributor
timestamp: September 25, 2014, 04:22:23 am
content: Quote from: kjn4685 on September 25, 2014, 04:15:08 amCorrect.Use the full name: 2SA1360 YIf you have to get a substitute make sure it is at least -150 V rated.Some datasheets do not show the voltage as -V, only V but PNP is the important bit.

author: tautech
author_rank: Super Contributor
timestamp: September 25, 2014, 05:35:24 am
content: Quote from: kjn4685 on September 25, 2014, 04:15:08 amhttp://www.learningaboutelectronics.com/Articles/Difference-between-a-NPN-and-a-PNP-transistor

author: kjn4685
author_rank: Regular Contributor
timestamp: September 25, 2014, 05:56:54 pm
content: Again I thank you very much. I also appreciate the information that you sent me. I will do what you saidLou

author: kjn4685
author_rank: Regular Contributor
timestamp: September 27, 2014, 03:30:35 am
content: Now I have another scope. So will you guys tell me how to hook the too scope together and test my old scope to fix it. If anyone could help me I would be appreciate any helpLou

author: kjn4685
author_rank: Regular Contributor
timestamp: September 30, 2014, 12:28:11 am
content: Hi there again I seen on the forum this octopus circuit board. It has a 12v ct transfromer at 300 ma. I have a 12v ct at 3a is the anyway I can use it. If so do I need something to reduce the amps.

author: kjn4685
author_rank: Regular Contributor
timestamp: October 02, 2014, 02:29:07 am
content: I need help with my oscilloscope agian. I need to know after I hook up the too scopes what am looking for.

author: tautech
author_rank: Super Contributor
timestamp: October 02, 2014, 07:32:24 pm
content: Have you replaced the PNP output transistors?http://www.vyrian.com/part.php?part=2SA1360-Y%28Q%29There is no point in testing the scope except the sweep that I expect is working fine.It will be a sawtooth waveform that varies with the timebase setting.

author: kjn4685
author_rank: Regular Contributor
timestamp: October 02, 2014, 07:53:57 pm
content: I have already ordered the transistors. And again I thank you. You don't know how much this helps me