help with this PSU schemo and problem Edit: problem solved

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pucho812

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Below is half the schemo of a Console PSU power supply. It's on arrived on my bench as the 160 left sounding good. The problem is the unit does not send out +24V. This is not good as +24V controls logic switching and Lights. The owner could give to shytes about the lights but the console logic is another story. Can't run it without it. The PSU is simple in design and each rail has it's own traces seperate from the other rails on a single PCB. The unit was powered down by the owner to do console maintanence swaping out some switches. When powering back up the +24V Led would not light this indicating a problem, PSU was not outputing +24.
In steps me. I ran it without load and it was a no go on the +24. I have tested as much as I can(caps resistors and diodes). They all test out I.E. seem to work as normal. There are no test points on said PSU. screw you Sony... :mad: :razz: The maintenance manual only lists parts that are possible subject to fail under normal operation conditions. This rules out the PSU trafo which is huge. So this leaves me down to parts Q6, Q2 both which are transistors, tip29A and parts u3 and u2. U3 is a motorola MC1723CP which is a voltage regulator IC. and U2 is a motorla Lm358N A DUAL DIFFERENTIAL INPUT OPERATIONAL AMPLIFIERS. What are the odds of these 4 componants failing. I am kind of out of ideas.
Any suggestions other then replacing the 4 componants to see if that fixes the problem. I have this suspecion that due to age the parts failed. The PSU is over 10 years and has never had maintanence on it until now.

EDIT: forgot to mention that the fuse for that section of the board works fine, tests out and ran another PSU.

SonyPSU-1.jpg
 

pucho812

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No tested with no load I.E. PSU not connected to anything. In a perfect world ALL leds's would light up if the PSU was powered and not connect to indicate PSU works as per normal operation. With it connected, the led would be on if there was no issues. At any rate the LED is on with or without load if the unit is working per normal operation...
 

walter

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I would think that something happened during the console maintanence that caused the PSU to go down. I couldn't see the values on that schemo, even printed it out. If the suspect components are used on another supply, you could borrow them to see if that fixes it.
 

pucho812

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Same maintenance has been going on and off all week as switches came in. Was working fine until bam. so I am suspecting a part faliure in the PSU with the on and off we ahve had to do. The console unlike an SSL does not have power cut switches for the bucket sections TRhe parts pulled off the console are mute switches on the large fader boards which were going in and out with console off. I seriously doubt swapping in new fader componants would cause a PSU faliure. Even if the switch was wired incorrectly, It would still work or if anything pop the fuse for +24.

[quote author="walter"]I would think that something happened during the console maintanence that caused the PSU to go down. I couldn't see the values on that schemo, even printed it out. If the suspect components are used on another supply, you could borrow them to see if that fixes it.[/quote]

I would hate to rob from peter to pay paul. I'm better off just ordering said transistors and v-reg IC's.
 

Gus

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The sense lines need to be connected to supply lines as posted above always place a small load on a power supply

I am going to guess it is maybe only one bad cap.

The 723 IIRC check the internal zener ref pin If it is not 7 something the chip might be bad.

Power supplies are often some of the easy stuff to fix

Measure and scope at the bridge note the ripple move to the pass transistors check both sides and the base with a scope.

I am going to say C18(As best I can tell it is hard to read) is bad and you have a lot of ripple on the 24VDC under load note it is using a npn pass so the base needs to be "above" the Emitter

Check or change the other caps in c18 spot

I have repaired lots of 723 based supplies over the years

That cap position is one of the higher fail parts of power supplies based on the good old 723
 

pucho812

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Gus thats good to know. I'll recheck c-18 but I could have sworn I was getting a proper capacitance with my fluke. I'll recheck it again...
whats a good way to load this down without connecting it back up to the console..

EDIT C-18 is a 330Uf/35V cap located on the traces dealing with -18. are you suggesting that c6 which is the same cap, same location, different trace(+24) may have gone bad?
 

Gus

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Ohms law and the power law are your friend

R = V/I in your case 24/ lets make it 1 amp = 24ohms( I quessed one amp what is the 24V supply rated at?)

DC Power is I X E = 1amp x 24volts =24watts

Four 100ohm 10 watts resistors in parallel should work 25ohms at 40 watts

Or two 100ohm in parallel for .5 amps and 20 watts

don't burn yourself

Load the other supplies as well

If I don't have an active load bank advaible I will make a resistor load bank.

I have a hard time reading the schematic there looks to be a crowbar(scr? circuit) on the 2nd circuit down I think I read that is the 24V. If you don't have the sense lines connected it will crowbar and you might have 1V at the 24V rail

It could be because the sense lines are not connected like the first poster wrote.

The cap is the 2nd electro from the right of the bridge that I would check or change
 

moamps

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@pucho812

A better-quality picture would be very useful here.
Also, you may wish to measure and post voltages at:
power cap, emitter and collector of both power transistors, before and after 0.01R resistor. Have you checked the crowbar triac yet?

@gus

The sense lines are connected via 100 ohm resistors to the +V and GND, which means that the PSU should power up correctly without connecting the sense pins or any significant load to the output.

Regards,
Milan
 

pucho812

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math time goodie goodie. For starters the cap to the right of the bridge you mean the big 40 V cap....

Supply rail is rated for 20 Amps


DC power 20 amps X 24 V = 480 W

I am doubting sense lines as when it first went south the owner turned it off waiting and turned it back on to see if this would fix.
I keep thinking that the LED went bad and is tied into the sense circuit or at least that is what appears to me on the schemo. I'm going to rescan a high quality image later on. You guys rock. Now I am doubting ther IC chips...
 

Gus

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I am having a very hard time reading schematic on my 15" CRT. I did not notice the 100 ohms closing the loops
 

pucho812

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[quote author="Gus"]I am having a very hard time reading schematic on my 15" CRT. I did not notice the 100 ohms closing the loops[/quote]

I hope the new scan helps Gus. From what I have seen with the other supply for the console which is the same model the LEDS will power up without load. So this is why I know it's not the console and down to the PSU itself. I ran a meter accross all the caps testing capacitance and test with in spec... I keep thinking it's one of the v-reg IC's or a faulty transister. Plus the only time that sections meets with the other PSu sections is at the cinch jones connector to go out to the console and back at the beginning comming off the power trafo. It's going to be something simple. When it first happened it was suggested to go get it looked at by Wes dooley's crew as they do it all with these boards but his crew also doesn't call back quickly...
 

pucho812

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dam 3 of my avatars mooving in sync is creepy.

Anyway After talking with another tech who has worked on said units before, he confirmed my suspicions of a faulty transistor and said that more likely transistor MJ11028. It is prone to fail out of the 2 and that the IC's are less likely to fail. Change that one first. That was one of the original parts I had planned to replace. Parts came in ysterday from newark after a minor UPS mess up. After replacing it unit is purring like a kitten. I.E. it works ike new.

Gus, everyone, thanks for the help. it's back up as new. plus saved a huge amount of money as the transistors were 6.00(us) a piece insteadt of 100.00 bench time plus parts elsewhere. when it first came up I thought I would be in over my head but after staring at the schemo for a while I was like this is easy, time to get to work. PSU was down for a week but that gave time to replace switches and such so it wasn't really downtime. again tahnks everybody...
For those of you who will be at AES I owe you a beer or two. :thumb:
 

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