tek 465b  power supply problem ...plz help - Page 1
Forum section: electronics / repair

author: Naim555
author_rank: Contributor
timestamp: October 20, 2015, 02:51:40 pm
content: bref , i have a old osciloscope TEK465B it work perfect but 15 year ago, now just a spot in center , then i open cover chek for test poit for verify all point :+55v=ok+15v =ok+5v =ok-8 v =ok+110v=103v!! lowand i have shematic , i test all parts : no problemwhere is the problem i think +127v is very low for give +110v in out . i need your help plz

author: Joule Thief
author_rank: Regular Contributor
timestamp: October 20, 2015, 03:09:51 pm
content: Check the AC ripple voltage at test point 94. Higher AC voltage at this point (check service manual for normal ripple voltage) may indicate the filter capacitor for this supply requires replacement.

author: Gyro
author_rank: Super Contributor
timestamp: October 20, 2015, 03:14:52 pm
content: If you're just getting a spot in the center of the screen, then I would think that maybe the +110V rail is being load down by something else faulty. It seems unlikely that a few volts down would cause a major problem with the screen. Can you can clarify the problem you're seeing?

author: Naim555
author_rank: Contributor
timestamp: October 20, 2015, 03:51:33 pm
content: Quote from: Joule Thief on October 20, 2015, 03:09:51 pmif i read schematic diagrame the normal ripple voltage in point 94 is +150.6v but i have just127v !!probabely the capacitor ? i test it with the digital multimetter and i result it s correct

author: singapol
author_rank: Frequent Contributor
timestamp: October 20, 2015, 05:45:14 pm
content: If you see only a center spot it means the vertical deflection and horizontal has failed. Check this circuit to see what power supply voltage it uses and the vertical and horizontal deflection transistors. It could be only cracked solder joints too. Could also be the power supply?Edit: After further thought I think the sweep generator has failed as it supplies the signals to vertical and horizontal deflection circuits.

author: Joule Thief
author_rank: Regular Contributor
timestamp: October 22, 2015, 08:11:28 am
content: Quote from: Naim555 on October 20, 2015, 03:51:33 pmThe "ripple" voltage measurement I suggested should be made with your multimeter in the AC VOLTS function. Measure AC at test point 94 and post the result. I did a quick look into the 465B manual (scanned copy) and did not see any reference to an acceptable level of AC component on the 110V DC supply. I would think a few 100's of mV would be acceptable and AC ripple near 10 - 20 volts would indicate a problem with excessive load on the supply or a dried out electrolytic capacitor in the power supply.Most of the supply voltages have a removable "service link" which allows individual power rails to be disconnected from the powered circuitry. I do not believe there is a service link specifically for the 110 volt supply. The manual indicates the 110 unregulated supply is used by the CRT board. There may be a method to disconnect the 110 V from the CRT board by lifting a component on the CRT board (maybe the diode referred to in the power supply diagram).

author: MarkL
author_rank: Unknown
timestamp: October 22, 2015, 03:31:01 pm
content: How's the voltage at TP95?The voltage at TP94 builds on top of this.

author: Naim555
author_rank: Contributor
timestamp: October 26, 2015, 09:03:54 am
content: 1- thanks for you all specially friends Joule Thief and MarkL .2- excuse for the delay .3-excuse for my bad english beause i speak french and my mather language .4-no news for my problem i mesured the voltage with my multimetter in TP94 andi find127vi think replace the capacitor , bridge and mesure th resistor value ,

author: Gyro
author_rank: Super Contributor
timestamp: October 26, 2015, 12:41:46 pm
content: You still haven't come back to us with the fault symptom (other than saying "just a spot in the center"), it may well not be a power supply fault that you are looking for.Edit: Just to clarify... Is it just a spot on all timebase settings? Does it move with the horizontal and vertical position controls? Does it turn to a vertical line if you apply a Y input? That sort of thing.

author: MarkL
author_rank: Unknown
timestamp: October 26, 2015, 02:51:46 pm
content: Quote from: Naim555 on October 26, 2015, 09:03:54 amI had asked what the voltage is on TP95 (we know TP94 is 127V). I'm asking because TP95 contributes to the voltage at TP94.I tend to agree with Gyro that something is probably loading down the regulated +110V output, at least as a first theory. Does anything seem unusually hot (you can't keep your finger on it)? How about the AC volts (ripple) measurements Joule Thief suggested?You can try replacing components and you might hit the problem by luck, but we haven't even gotten into properly diagnosing where the problem might be.There's many examples in this forum (and others) of people taking the "replace whatever could be bad" approach. It often creates new and compounded problems.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: October 26, 2015, 03:36:52 pm
content: It might also help to test it in XY mode (like a sine and a cosine for a Lisajous pattern) and see if you can get the spot to move into a trace.

author: Naim555
author_rank: Contributor
timestamp: October 26, 2015, 09:09:52 pm
content: for Mr Gyro:Edit: Just to clarify... Is it just a spot on all timebase settings? Does it move with the horizontal and vertical position controls? Does it turn to a vertical line if you apply a Y input? That sort of thing.yes i can move the spot vertical and horizontal direction manualy , i rotate the delay time botton but no effect . just a spot at Y input no line

author: Naim555
author_rank: Contributor
timestamp: October 26, 2015, 09:16:05 pm
content: for Mr.MarkLI had asked what the voltage is on TP95 (we know TP94 is 127V). I'm asking because TP95 contributes to the voltage at TP94.i apdate the schematic for a new voltage value , see if can clarify the probleme .

author: tautech
author_rank: Super Contributor
timestamp: October 26, 2015, 09:31:33 pm
content: http://www.sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdf

author: Naim555
author_rank: Contributor
timestamp: October 26, 2015, 11:02:20 pm
content: Quote from: FlyingHacker on October 26, 2015, 03:36:52 pmin mode xy i see a trace but a half of screen

author: MarkL
author_rank: Unknown
timestamp: October 26, 2015, 11:50:19 pm
content: You have the scope in "Normal" trigger mode. It won't sweep until it's triggered, and the trigger LED is not lit.Can you set the trigger mode to "Auto" and the Horizontal Display to "A", please?

author: Naim555
author_rank: Contributor
timestamp: October 27, 2015, 11:39:09 am
content: Quote from: MarkL on October 26, 2015, 11:50:19 pmsee picture

author: MarkL
author_rank: Unknown
timestamp: October 27, 2015, 02:04:19 pm
content: Ok, thanks. It's important to verify the basics.I'm noticing the power LED is not on. It could be the LED (or associated resistor, connector, etc.), but it's extra suspicious because it gets its power from the +5V rail on the A7 Trigger and Sweep Board. And we're obviously having a sweep problem here.Check to see if you have +5V on one side of R7108. The other side of R7108 is connected to the power LED. This is shown on the power supply schematic even though it's on the A7 board.If you don't see +5V, start tracing backwards towards the power supply. Another good point to check is the +5V service jumper (W7291) on the A7 board.If you do have +5V on the one side of R7108, verify the other incoming power rails while you're poking around the A7 board (in the vicinity of J4541 and J4571).

author: Naim555
author_rank: Contributor
timestamp: October 27, 2015, 02:08:38 pm
content: successproblem solvedthanks for all friends

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: October 27, 2015, 02:11:26 pm
content: I see your picture, and I see that IF you have adequate signal to TRIGGER the sweep, it will not trigger. Trigger light is OFF. Reason: Your signal? is on CH1, your trigger switch is set to CH2 (use CH1), and the trigger level looks to be FAR from centered (center it), and Low Frequency Rejection is ON (best to use use AC, or DC unless you have a good reason).What is your signal amplitude, and frequency??? Please correct the settings, and try again.

author: MarkL
author_rank: Unknown
timestamp: October 27, 2015, 02:25:23 pm
content: Quote from: Naim555 on October 27, 2015, 02:08:38 pmWhat was the problem?

author: Naim555
author_rank: Contributor
timestamp: October 27, 2015, 04:33:31 pm
content: transistor Q4497 changed