Author Topic: Fixed HP1741A in a big shape but... I bet in a focus problem, and you? (Read 68347 times)

rf+tech · « **Reply #100 on:** February 15, 2016, 03:08:34 am »

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I can measure 0.0V on the twa channels but with de poisition a bit to left around 20%.

Great!

No concern about the 20%. When the alignment procedure in the manual is performed, this error will be corrected.

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near to zero I can, around 0.053mV.

If it will help to understand, the deflection plates have a sensitivity expressed in Volts per centimeter. A guess, maybe 10 Volts deflects the beam by 1 cm. One Volt will deflect the beam 1 mm. 0.1 Volt will deflect the beam 0.1 mm. 0.053 Volts will deflect the beam .053 mm. Can you see that small?

SAUL BRITTO · « **Reply #101 on:** February 15, 2016, 03:29:11 am »

Good! But I don't know if you remember: this scope don't have a visible trace.I said to you: it has just 2.8 kV when it was to have at least 5kV.

SAUL BRITTO · « **Reply #102 on:** February 15, 2016, 03:32:06 am »

I don't know right now who is the culprit, maybe fllyback or tripler ou another component in HV or LVPS.Despite I did measure all the voltages on the LVPS and all that was correct.unless a mistake my.

SAUL BRITTO · « **Reply #103 on:** February 15, 2016, 03:34:19 am »

I did see that some rectifier bridges,are very hot.I dont know the regimen of those rectfiers.

rf+tech · « **Reply #104 on:** February 15, 2016, 03:41:58 am »

Yes, I remember the tripler may be defective. The manual says the CRT cathode voltage should be -2295 Volts. Can you measure this safely?

If this voltage is correct, then the tripler is defective. But do not worry about it, I have an idea.

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I did see that some rectifier bridges,are very hot.I dont know the regimen of those rectfiers.

What CR number on the power supply schematic?

SAUL BRITTO · « **Reply #105 on:** February 15, 2016, 04:03:57 am »

I measured The cathode V and,it was around -1850V.What is CR? Is the part number of CRT?

SAUL BRITTO · « **Reply #106 on:** February 15, 2016, 04:19:45 am »

I do have a RCA 56kV probe. I will measure the cathode again.

SAUL BRITTO · « **Reply #107 on:** February 15, 2016, 04:29:39 am »

rf+tech> It shows me exactly -1832V.

SAUL BRITTO · « **Reply #108 on:** February 15, 2016, 04:57:44 am »

Ah, ok! CR= rectifiers. I think most.

rf+tech · « **Reply #109 on:** February 15, 2016, 04:59:14 am »

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What is CR? Is the part number of CRT?

CR1, CR2, CR3, CR4, CR5, CR6, CR7 are the bridge rectifiers on the power supply board schematic.

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I did see that some rectifier bridges,are very hot.I dont know the regimen of those rectfiers.

What is the CR number of the hot rectifier bridges on the power supply board?

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It shows me exactly -1832V

This cathode voltage is too low. Measure the +120 Volts on the HV power supply. And check that the "Deep Erase" switch on the rear panel is set to "Normal."

About the -1832 Volts, here is what I think. Look at the HV power supply schematic. See where the tap on the HV transformer secondary (pin 7) is less turns than the end of the secondary that becomes -2295 Volts with CR3?

If the +120 Volts is good, and the tripler is defective, the tripler may be loading the HV transformer and pulling the CRT cathode voltage down. Disconnect the lead to the tripler, from this pin 7 of the HV transformer. Measure the CRT cathode voltage again. Is it still -1832 Volts or is it now close to -2295 Volts?

SAUL BRITTO · « **Reply #110 on:** February 15, 2016, 05:42:28 am »

rf+tech is normal the UNG 15V with 24V? I know that is unregulated but...As I don't know very well this circuit...

SAUL BRITTO · « **Reply #111 on:** February 15, 2016, 05:49:35 am »

rf+tech the 120V measuring on the botton of board on the connector that goes to HV is with 123V the pin oh tripler I will do it later,because I'm almost dead tired!

SAUL BRITTO · « **Reply #112 on:** February 15, 2016, 05:51:12 am »

Here in Brazil: 2:50 until later. Thank you for all . have a good day.

SAUL BRITTO · « **Reply #113 on:** February 15, 2016, 04:42:10 pm »

rf+tech disconnecting the cable post-tripler and the GND will not be the same than disconnecting that one of pin 7?

rf+tech · « **Reply #114 on:** February 15, 2016, 05:58:12 pm »

Yes, it is the same. It is not safe. There may be an arc that damages other components or yourself.

Only if the wire to the tripler from the HV transformer is one piece without a solder or twist lock connection, should floating the tripler be attempted and only with great caution and very good insulation. In this case, be very very careful.

Here is a saying to think about:

There are old electricians, and there are bold electricians.
But there are no old, bold electricians.

SAUL BRITTO · « **Reply #115 on:** February 15, 2016, 09:45:55 pm »

Oh yes it's true!! But I wil do it as you said in another text,the correct way.I Preffer be an old not a bold.

SAUL BRITTO · « **Reply #116 on:** February 15, 2016, 10:43:10 pm »

rf+tech already managed to repair a tripler? It's possible to use another trilper as one tektronix in lacking of an original?

SAUL BRITTO · « **Reply #117 on:** February 15, 2016, 10:45:31 pm »

I know a guy here in my country that made it times ago. He fixed the tripler,was a philips one.

SAUL BRITTO · « **Reply #118 on:** February 15, 2016, 10:46:49 pm »

Look: http://www.py2bbs.qsl.br/pm3540.php

rf+tech · « **Reply #119 on:** February 15, 2016, 11:21:34 pm »

Saul,

Remember i said

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But do not worry about it, I have an idea.

Yes, it is possible to build one yourself. Here is an application note by Vishay on just this subject:

http://www.vishay.com/docs/88842/anusingr.pdf

Yes, it should be possible use almost any other scope tripler and if you are careful, you may be able to excavate and repair the HP tripler.

There are many possibilities. First, tell me about the test results.

RF+ Tech

SAUL BRITTO · « **Reply #120 on:** February 15, 2016, 11:30:59 pm »

rf+tech I was seeing a french video abouT this scope (hp) and it was fenomenal for your time.
Ok, soon I tell you the result.

SAUL BRITTO · « **Reply #121 on:** February 15, 2016, 11:53:48 pm »

rf+tech beeing it a tripler, that multiplies x3 then, the flyback generates around 1600V?

Sorry for this idiot question but,is just to be sure about a small question: "sparks," in case of disconnection of pin 7.

rf+tech · « **Reply #122 on:** February 16, 2016, 12:21:07 am »

Yes, when the HV circuit is able to supply 2295 Volts to the CRT cathode.

Can the wire to the tripler be disconnected at the HV power supply board? Or must the wire be disconnected from the tripler?

SAUL BRITTO · « **Reply #123 on:** February 16, 2016, 01:04:57 am »

it must to be disconnected from the board,has a pin on the botton of the board connected to the flyback with a kind of thermo-retractil insulator.

SAUL BRITTO · « **Reply #124 on:** February 16, 2016, 01:15:34 am »

I just can disconnect the tripler on that connection of anode of tube and the ground pin as I said before.


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Author Topic: Fixed HP1741A in a big shape but... I bet in a focus problem, and you? (Read 68347 times)

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