Tektronix 465M Power supply problem - Page 1
Forum section: electronics / repair

author: paronaram
author_rank: Regular Contributor
timestamp: May 20, 2020, 02:09:16 am
content: Hello Everybody,Trying to troubleshoot Tektronix 465M power supply issue, I am missing +95V (it measures +10V )Scope has no trace, but all lights are on, and scale illumination works.I checked all voltages and I'm missing +95V.I already replaced leaky C582 and just in case C584 (in same circuit), but still nothing. Both diodes (CR582 and CR584) are OK (in circuit) L582 -ok.I do have +51.6V after L558Any idea what else may be? Will greatly appreciate.

author: BreakingOhmsLaw
author_rank: Frequent Contributor
timestamp: May 20, 2020, 06:55:03 am
content: Open the jumper and measure again. It could be a short circuit down the line that drags the voltage down.Measure ohms resistance to ground on the load side of the jumper.

author: paronaram
author_rank: Regular Contributor
timestamp: May 21, 2020, 01:57:17 am
content: Thanks for reply.Yes, just tested with removed jumper, I got same +12V(before I replaced the capacitors it was +10V)

author: BullyBeef
author_rank: Newbie
timestamp: May 21, 2020, 08:03:30 am
content: what's the AC voltage on pin 2 of transformer T550? and with the jumper removed, the voltage on the caps C583, C584? Check out R541 & C543 - problems here could pull the volts down.

author: paronaram
author_rank: Regular Contributor
timestamp: May 24, 2020, 08:16:25 pm
content: Thank you for replysorry for delay:Pin 2 on T550 is - 0V ACC583 (do you mean C582) 24.5VC584 - 12VR541 - out of PCB - 101KC543 - out of PCB - 1.1mF on the Fluke meter, but on Multi functional tester from Amazon I get "No, Unknown or damaged part" - is it bad? Left it outside of circuit for nowThanks again

author: BullyBeef
author_rank: Newbie
timestamp: May 24, 2020, 10:15:41 pm
content: I apologize - let me try to be more clear - on the schematic you provided - with the jumper on this schematic removed -Measure the AC volts on T550 pin 2 to ground.Measure the DC volts on capacitor C582 positive terminal to ground.Measure the DC volts on capacitor C584 positive terminal to ground.Measure the DC volts on capacitor C543 positive terminal to ground.Could you scan and upload the entire schematic, please?

author: andy3055
author_rank: Super Contributor
timestamp: May 25, 2020, 02:33:24 am
content: 1. Check 32 volts DC check point on the left side of the scope motherboard.2. Check the fuse F558. If it is blown, do step 3 below:3. Break the connection from Pin 10 of the T550 transformer topin 11 of the U550 block. Make sure to insulate the lead so it won't touch the pin 11 from the transformer.4. Replace the fuse (0.25 Amp) and check the 95 volts. If it is present, you have a blown EHT section on the U550 HV block.See my thread below. You can also see the SM there.https://www.eevblog.com/forum/repair/tektronix-465m-repair-210933/msg2695668/#msg2695668

author: paronaram
author_rank: Regular Contributor
timestamp: May 25, 2020, 02:34:18 am
content: Manual:http://bama.edebris.com/manuals/tek/465m/(sorry I can't upload, file is very large)

author: andy3055
author_rank: Super Contributor
timestamp: May 25, 2020, 03:20:43 am
content: In case you have not seen my post and the thread mentioned earlier, here is the page you need.

author: andy3055
author_rank: Super Contributor
timestamp: May 25, 2020, 03:25:12 am
content: This is the left side where you can see the test points, fuse, transformer to U550 connections etc.

author: paronaram
author_rank: Regular Contributor
timestamp: May 25, 2020, 02:09:46 pm
content: Thank you for reply and all info Andy.I had all voltages on the board except +95VFuse F558 was always "OK"I soon as I disconnect pin 10 from T550, I got smoke coming from Focus pot area, and I lost all voltages on the main board.Main fuse 3A blownI can't figure out what was was smokingCan I power up this scope without "Vertical" board? Just to see if anything was smoking thereThank you.

author: andy3055
author_rank: Super Contributor
timestamp: May 25, 2020, 03:26:23 pm
content: Did you disconnect Pin 10 of the transformer from pin 11 of the HV block? Or did you disconnect the pin 10 of the HV block from the main board? Those are two different scenarios although neither of them should smoke anything. If you read my thread/post, you will see how I went about the troubleshooting procedure. BTW, have a bunch of .25 A Fast Blow fuses handy as you may need them.You can remove the Vertical assembly and power up. Just don't keep it on for too long and make sure to turn down the intensity. This is to make sure you don't burn the coating on the CRT just in case the beam is stuck in one position.I did not see a 3 Amp fuse but there is a .3 Amp fuse F 736 in the power supply section. If that is blown, there has to be a short in the 32 volt supply rail. You will have to follow that line to find what is causing it. Note that all the fuses are Fast Blow.

author: paronaram
author_rank: Regular Contributor
timestamp: May 26, 2020, 04:17:24 am
content: I did disconnected pin 10 from transformer. It the air solder joint, and when I applied power, main fuse blow up.I think this is getting very complex and I will need to sped more money to fix this, and we not even sure if it's going to be fixed afterI payed for this scope $35, I think it's cheaper to trash it ...Will start looking for better deal, deal like we all see in YouTube story's - "Swapped one cap, and I got perfectly working scope..."