T7 [J2]circuit problem -  TDS7000 series Power Supply Martek PS2251 - Page 1
Forum section: electronics / repair

author: charlyd
author_rank: Frequent Contributor
timestamp: September 26, 2022, 05:49:38 pm
content: Hi i decided to open a new topic about the Martek Power because this PSU can be found in multiple equiptment from tektronix like TLA series and both first and second generation 7000 seriesthe Martek PS2251 - power supply. ( see attachment )here is what i already did :after i replacedallcaps with value 68uF arround the transformers. and 4x 330uf in T7 circuit andall1500uF in T10 and T7 circuit.and all small caps in the T10 circuitry, i was at the point of powering on."TiN" is talking in one of his post about connecting loads on the output.So i placed the psu on my bench. with the switch over J1/P1 and P4, where the past one is Ground/return.to make thing s visible like this: P5,6 --- 18 ohm --- gnd >>>>> +12v. P11,12 --- 18 ohm --- gnd >>>>> +5v P19 --- 18 ohm --- gnd >>>>> +3,3V[J1} P1 --- __/ ___100ohm --- gnd >>>> power switch in series with 100Ohm.my red led lit when switch is open , it goes of when #PS_ON to gnd.but doesn t lit when the switch is toggled to power off again.the secundairy side of the T7 circuitry has its own supplies for connector[ J2 ] which are not present +15v -15 v and no + and - 5 voltsMaybe i forgot to say but i already repaired my primary side.Now i am tracing the secundairy side of these famous Martek PS2251 power supply and i am curious if anybody can add info like drawings / selfmade diagrams / hand made schematics from the T7 sec. T10 sec.i am missing some voltages like. +5v -5v +15v and -15v located on J2.besides in my test configuration my [J1-p5,6] +12 is not more then +5.94V but even with a 100% working psu which i had for compare this output was as low as 5.9-6.0v or so .When i dive into this problem from a different side , my conclusion was lets try to disable the T7 circuitry by removing the F51 (5 amp) chipfuse and see if the psu is powering on now.and yes it is... so it feels to me the problem lies in T7 secundairy side...

author: alm
author_rank: Super Contributor
timestamp: September 26, 2022, 06:54:02 pm
content: You're talking about theTektronix 7000 series, but I'm pretty sure none of them used an off-the-shelf power supply. The earlier ones had a linear power supply, and the later models had a Tek-designed SMPS.

author: charlyd
author_rank: Frequent Contributor
timestamp: September 26, 2022, 09:01:50 pm
content: Tektronix uses Martek-designed SMPS models.in multiple models tek equipement like TDS,CSA & TLA.

author: alm
author_rank: Super Contributor
timestamp: September 26, 2022, 09:19:05 pm
content: Yes, but none of those are generally called the "Tektronix 7000 series". It would help if you clarify the title of this thread if you want to attract people interested in the TDS7k etc series, rather than in the 7000-series analog scopes.

author: coromonadalix
author_rank: Super Contributor
timestamp: October 01, 2022, 12:36:10 pm
content: And you should have stayed in your original threads instead of creating this one, your problems are / is in a tds 7000 scope ...

author: charlyd
author_rank: Frequent Contributor
timestamp: October 02, 2022, 07:35:41 am
content: Hello for anybody who is interrested in repairing a PS2251 power supply. the +12v on J1 pin 5,6 is in my case +5,9v as written in my first post here...i tested it on a working psu on the bench so with just 3x. 18 Ohm load and it is also arround +6v instead of 12v.so can somebody who tested this PSU on his bench with load confirm me what his output is ?

author: charlyd
author_rank: Frequent Contributor
timestamp: October 03, 2022, 06:08:39 pm
content: last weekend i continued and i am still looking for the protection parts in this supply to where is that located.and the question came to me why is my +12v output on [J1-p5,6] just arround +6v and not more.Is my connected load not enough or not ok?Do i need to feed return voltages on one or some pins on the  connector powerfail# ?who can jump into this topic with this power supply experience.

author: charlyd
author_rank: Frequent Contributor
timestamp: October 05, 2022, 09:57:12 pm
content: today i discovered that when i poweron the supply with the F51 removed and then when it is turned on, i put in the F51 fuse the supply is working 100% .at that point i can turn toggle the power and see the red led shining bright ( STDBY) or go off when the supply is on.but when it is powered off for a while and i poweron with the F51 already in. ) so with the T7 Circuitry connected.the supply does not fire up, so no output can be read on the J1 outputs. I guess because the supply goes in a sort of protect-modethen when powering off again the led doesn t shine bright red but is very dimm, nearly visible.any ideas or tips?attachment: all caps replaced circled in yellow

author: alm
author_rank: Super Contributor
timestamp: October 06, 2022, 09:37:19 pm
content: I don't have much power supply experience, but is F51 involved in the startup circuit? Or is it just connected the second set of output rails that's fed through T7? In that case, is there some sort of supervisor IC that ensures the sequencing of the different rails?Are there off-the-shelf SMPS controller ICs you can read the datasheets off? You might have to partly reverse-engineer the power supply circuit for this.There is usually a small electrolytic in there that often needs replacement, but it looks like you already replaced all electrolytics in that area.