Author Topic: Tektronix Scope TDS 524A LV PSU Repair Advice  (Read 659 times)

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Offline vectra_1098

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Tektronix Scope TDS 524A LV PSU Repair Advice
« on: April 06, 2019, 12:03:17 pm »
Hello,

I am working on a faulty Tek Scope TDS 524A LV PSU, the scope will not power up!
I have removed the LV power supply from the scope placed it on the bench.
Powering the PSU and monitoring the low voltage outputs at J5 & J6,
also as per the manual linking pins 3+5 of J5 together to allow start-up
The no-load outputs at J5&J6 are all zero ?
I have checked the ac input supply and filters (and fuse ) and Bridge(CR5) output and there is a
 335V dc across  C12 the Bulk capacitor.

I suspected the Standby circuit , I removed Q9 and transient suppressors  VR4 & VR5.
I have obtained new components for VR4 &VR5 ok.
Q9 in this power supply is a MJE 1320 Power switching transistor,
But they are very difficult to get hold off and other similar power supplies use the
Bu508A as Q9. I don’t think there parts are interchangeable unless the stand-by circuit is modified to take the BU508A part in this power supply ?
Is there an equivalent part for the MJE 1320 ??

**Referring to TDS524A/TDS520B service manuals for TDS 524A Scope

Advice would be nice to have.

Thanks
T

 

Offline pbarton

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Re: Tektronix Scope TDS 524A LV PSU Repair Advice
« Reply #1 on: April 07, 2019, 05:15:45 pm »
Can you identify the source of the manuals you are using, as it often helps if we are all referencing the same document?
 

Offline vectra_1098

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Re: Tektronix Scope TDS 524A LV PSU Repair Advice
« Reply #2 on: April 07, 2019, 08:51:45 pm »
Hi,
In my opion  Tek did not want anybody to repair these scope power supplies
and so to  find the correct schematics /pcb layouts is made difficult.
Ref Docs:
The Manuals reference are -
1.TDS 520B Mod Cm
Digitising Oscilloscope
Component Service Manual
070-9710-03   

2.) TDS 520A,524A,540A & 544A
Digitising Oscilloscope
070-8713-03
3.) A schematic drawing from an  EE blog, Post” Help with my TDS 520B showing a standby Supply”.
My Notes:
Ref 1:  Manual does not give component level detail although its for the TDS 524A scope.
Ref 2: Does provide schematics  which are similar but they are for the TDS 520B not the TDS 524A
Ref3:EE blog post  Standby Supply,shows a bipolar transistor Q9 type MLE 1320 and transorbs VR4/VR5.

My Power supply/custom rectifier LR40071
Zytec part number:22904701 rev g
300w,3.8A,1phase
Thanks for the reply

 

Offline Jay_Diddy_B

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Re: Tektronix Scope TDS 524A LV PSU Repair Advice
« Reply #3 on: April 07, 2019, 08:57:12 pm »
Hi.

There are at least two standby power supplies used in these TDS5xx and TDS7xx scope.
There is some useful information in this thread:

https://www.eevblog.com/forum/testgear/fixing-tek-tds684-psu/msg453682/#msg453682


This is one:



This is the other:



Regards,

Jay_Diddy_B
 

Offline Ordinaryman1971

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Re: Tektronix Scope TDS 524A LV PSU Repair Advice
« Reply #4 on: April 07, 2019, 11:48:37 pm »
I have identical problem with TDS744A, what was your replacement for VR4 and VR5... would they be the same in both power supplies?
 

Offline vectra_1098

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Re: Tektronix Scope TDS 524A LV PSU Repair Advice
« Reply #5 on: April 08, 2019, 08:43:09 am »
Hi,

=======================================================
Jay_Diddy_B Wrote Earlier :-

There are at least two standby power supplies used in these TDS5xx and TDS7xx scope.
There is some useful information in this thread:

https://www.eevblog.com/forum/testgear/fixing-tek-tds684-psu/msg453682/#msg453682
==========================================================



I can see the Stand-up supply schematic version with the Bipolar transistor  Q9 and VR4/5.
I removed these components from the PSU and checked them with a Multimeter
and other test equipment and noted their part numbers.

My test equipment does not like Q9 and VR4/5

I have obtained the Transorbs via Ebay
TVS Diode VR4=part number   1.5KE220CA St Microelectronics
TVS Diode VR5=part number   1.5KE250CA St Microelectronics

As I mentioned in an earlier post My Transistor(Q9) is a MLE 1320 which I read is obsolete ??. What Q9 do you have in your PSU ?

I am going to reverse engineer my pcb around the Standby supply area to see how close it is with the schematic
and possibly do a spice simulation for he circuit

Thanks






I can identify my bip

 

Offline Ordinaryman1971

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Re: Tektronix Scope TDS 524A LV PSU Repair Advice
« Reply #6 on: April 08, 2019, 02:28:16 pm »
I will look it up today and take some pictures.
 

Offline Ordinaryman1971

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Re: Tektronix Scope TDS 524A LV PSU Repair Advice
« Reply #7 on: April 17, 2019, 05:07:34 am »
Took few days but... here are some pictures.
Q9... I have BU508A in mine.
I've just installed the suppression diodes hoping that that's the only damage, but q9 is shorted as well. Don't have those transistors so that's the next purchase.

I hope it's good news about the replacement transistor. The BU508A are about $2 a piece.
 


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