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This hitachi P.S. is driving me nuts!

J

janek77

Jan 1, 1970
0
I've posted this before, but now I have some more info.
Here it is hitachi scope V1060 power supply:
http://img.photobucket.com/albums/v338/gamow/PS.gif
Seems pretty simple?
What it does, It runs fine under reduced load, ie I put 22ohms resistor in
series with the rest of the load on 55v circuit.
As is it will produce voltages 40% lower than specs.
To remove any doubt I disconnected all the loads and replaced them with
resistors.
To simmulate full load I've used :
11 ohms on 5V rail~.45A
22 ohms on12V rail~.37A
230 ohms on 55V rail~.2A
It manages to output 43V on 55V circuit , all others respectively lower too
..
Yes I've replaced all the capacitors on the primary side, actually I put 47m
instead of 39 and 100 instead of 56
Still no change.
Desoldered all the secondary diodes , They all check fine.
Checked for the ripple on the secondaries (bad caps?)
all in order.
Bgin to suspect transformer itself.
HERE I REALLY NEED HELP.
Before try to rewind the transformer , can somebody with
more experience than me look up the following waveforms?
The first one was taken with all secondary windings disconnected(I've
removed the diodes)
The second with diodes soldered back and above mentioned
resistive load reatached.
Both were taken with a scope respecive to negative of line side
capacitors(used isolation transformer ).
At point 5 (primary winding)
Here they go:
No load:
http://img.photobucket.com/albums/v338/gamow/noload-cropped.gif

Loadded:
http://img.photobucket.com/albums/v338/gamow/loadded-croped.gif

Help me please.
Thanks.
 
S

Sam Goldwasser

Jan 1, 1970
0
You could ring test the trensformer....

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.
 
R

Ross Herbert

Jan 1, 1970
0
I've posted this before, but now I have some more info.
Here it is hitachi scope V1060 power supply:
http://img.photobucket.com/albums/v338/gamow/PS.gif
Seems pretty simple?
What it does, It runs fine under reduced load, ie I put 22ohms resistor in
series with the rest of the load on 55v circuit.
As is it will produce voltages 40% lower than specs.
To remove any doubt I disconnected all the loads and replaced them with
resistors.
To simmulate full load I've used :
11 ohms on 5V rail~.45A
22 ohms on12V rail~.37A
230 ohms on 55V rail~.2A
It manages to output 43V on 55V circuit , all others respectively lower too
.
Yes I've replaced all the capacitors on the primary side, actually I put 47m
instead of 39 and 100 instead of 56
Still no change.
Desoldered all the secondary diodes , They all check fine.
Checked for the ripple on the secondaries (bad caps?)
all in order.
Bgin to suspect transformer itself.
HERE I REALLY NEED HELP.
Before try to rewind the transformer , can somebody with
more experience than me look up the following waveforms?
The first one was taken with all secondary windings disconnected(I've
removed the diodes)
The second with diodes soldered back and above mentioned
resistive load reatached.
Both were taken with a scope respecive to negative of line side
capacitors(used isolation transformer ).
At point 5 (primary winding)
Here they go:
No load:
http://img.photobucket.com/albums/v338/gamow/noload-cropped.gif

Loadded:
http://img.photobucket.com/albums/v338/gamow/loadded-croped.gif

Help me please.
Thanks.

I would be more suspicious of what is happening on the primary side.
The STK7308 could be dicky.. (looks pretty ancient)
http://www.datasheetcatalog.com/datasheets_pdf/S/T/K/7/STK7308.shtml

You say you changed the primary side electro's but did you include
C1508 (4.7uF/50V 105C) in the changes.

When loaded what is the voltage across the main input filter cap
(C1508 ?)
 
D

Dave M.

Jan 1, 1970
0
The square wave looks like what you will find in a switching power supply as
this one. If you are getting too much voltage drop, you probably either have
an excessive load or the regulation circuits are not working properly. I see
what looks like a driver regulator transistor with two zener diodes
(TR1514). You could try checking those components. I also see feedback to
what looks like a triac which would affect the voltage drop across the 10
ohm 3 watt resistor (R1501?). The 10 ohm resistor could be for initial "soft
start"/mean value etc.
 
Ive checked into that also, replaced TR1514 and zener diodes, as for
the triac it works properly , | even shorted the 10 ohm resistor while
running
to see if that will make any difference , it didn't.
 
S

Sam Goldwasser

Jan 1, 1970
0
How do I do that ? I mean whats the easiest way to do that , preferably
without desoldering it?

It's still low on the probability scale but eliminating the transformer
as a likely problem could prevent you from going down a bunch of dead
ends.

See the Flyback Testing FAQ:

http://www.repairfaq.org/sam/flytest.htm

You will probably want to desolder it though.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.
 
D

David C. Partridge

Jan 1, 1970
0
Looking at the circuit diagram annotations I think you may have driven it
slightly into over-current protection with your dummy load, and that could
explain your voltage drop.

-12V should be 0.3A ==> 40R (you don't say what you used for this)
+5V Should be .37A ==> 13R5 (say 15R) so your 11R is too low
+12 should be .45A ==> 27R so your 22R is too low
+55 should be .3A ==> 183R (say 200R or 220R) so your 230R should be OK
+110 should be .023A ==> 4K7

Dave
 
David said:
Looking at the circuit diagram annotations I think you may have driven it
slightly into over-current protection with your dummy load, and that could
explain your voltage drop.

-12V should be 0.3A ==> 40R (you don't say what you used for this)
+5V Should be .37A ==> 13R5 (say 15R) so your 11R is too low
+12 should be .45A ==> 27R so your 22R is too low
+55 should be .3A ==> 183R (say 200R or 220R) so your 230R should be OK
+110 should be .023A ==> 4K7

Dave
Well, -12V and 110V was left open, no load there.
If you add the loads together I dont think I'm overloading it.
Also dont forget when connected to the scope it overloads too.
The rest of the scope works fine.
 
If you overload any ONE output then you are overloading the entire SMPS
circuit. Standard SMPS operation dictates that each and every winding
output must remain below load. Some SMPS need a load on every output
as well.

SMPS supplies that are showing the MAXIMUM current output. Normally
you cannot simply load the outputs all at once a turn on at maximum
load as this is not how it would operate in a normal circuit.
 
D

David C. Partridge

Jan 1, 1970
0
I still think that you should use the correct dummy load values to test the
PSU - I suspect that the values quoted on the schematic may not be steady
state values, but limits, in which case your dummy load should use higher
value Rs.

I think it is likely that a capacitor in one of the load circuits has gone
(partly or completely) shorted. Measure the resistance to ground on the on
the lines to the rest of the scope with the PSU disconnected - see if you
can spot one that has an unusually low value.

It's also well worth checking the values of all the high wattage resistors
(R1501, R1502, R1512 and R1522). Also check C1511 and C1513.

Dave
 
M

Mr. Land

Jan 1, 1970
0
The second waveform you linked to - with the diodes reattached and with
the resistive loads reapplied - does that include the filtering
circuitry in the schematic, too? (C1561-3, L1562)?

If so, maybe I'm misinterpreting what I'm seeing in the scope picture,
but that semi-square wave with the ringing on the leading edge has an
amplitude of over 17V P-P. That seems excessively high to me for a
rail that's supposed to be delivering +5V DC (especially given it's got
close to 1000 mfd filtering it).

Are you sure that there's not some kind of weird grounding problem
happening here?
 
Mr. Land said:
The second waveform you linked to - with the diodes reattached and with
the resistive loads reapplied - does that include the filtering
circuitry in the schematic, too? (C1561-3, L1562)?

If so, maybe I'm misinterpreting what I'm seeing in the scope picture,
but that semi-square wave with the ringing on the leading edge has an
amplitude of over 17V P-P. That seems excessively high to me for a
rail that's supposed to be delivering +5V DC (especially given it's got
close to 1000 mfd filtering it).

Are you sure that there's not some kind of weird grounding problem
happening here?

Sorry , let me explain better.
Both waveforms are taken at the same point :
Primary windings of the transformer, probe ground was connected to
negative leg of C1509,(used isolation transformer of course)
tip of the probe to leg no 5 of the transformer.
Probe was set to 10x1 , so you have to multiply what you see by 10 ie
17Vpp should read 170Vpp.
Nothing was removed from the circuit, only loads disconnected and
resistors attached instead.

Now as far as not loading one rail while slightly overloading other,
while it may be true in most of cases,
I dont think it applies here, if you study the schematic you'll see
that theres no feedback whatsoever
from any of the secondary windings.
Theres a separate feedback winding, so loadig one or all of the
secondaries should have the same effect (within reason).
 
J

Jason D.

Jan 1, 1970
0
I've posted this before, but now I have some more info.
Here it is hitachi scope V1060 power supply:
http://img.photobucket.com/albums/v338/gamow/PS.gif

What I should do, just load one of any outputs:

for 12V positive output, I use 30 ohms 10W overrated but this is
converative to keep dummy load from overheating too much. This will
load down about .4A.

Or load 55V output I load it with 220 ohms 15W for .25A load.

By the way, I had a STK IC go soft on me, undervolting (sagging under
load causing TV to shut down on overcurrent and replace IC fixed this.

So in your situation replace ALL small caps in hot side (STK7308) and
a new STK7308.

The TR1514 is voltage regulator transistor to set specific voltage for
STK7308, Make sure this circuit is working correctly.

Also MEASURE all resistors in hot side. This sometimes fail. This
power supply is a hot side feedback regulation by monitoring the flux
density of the transmformer.

The type of waveforms under load is normal looking for this type of
STK IC with this kind of ringing on rising edge. I get this all the
time with STK 730.

Cheers, Wizard
 
J

janek77

Jan 1, 1970
0
Jason D. said:
What I should do, just load one of any outputs:

for 12V positive output, I use 30 ohms 10W overrated but this is
converative to keep dummy load from overheating too much. This will
load down about .4A.

Or load 55V output I load it with 220 ohms 15W for .25A load.

By the way, I had a STK IC go soft on me, undervolting (sagging under
load causing TV to shut down on overcurrent and replace IC fixed this.

So in your situation replace ALL small caps in hot side (STK7308) and
a new STK7308.

The TR1514 is voltage regulator transistor to set specific voltage for
STK7308, Make sure this circuit is working correctly.

Also MEASURE all resistors in hot side. This sometimes fail. This
power supply is a hot side feedback regulation by monitoring the flux
density of the transmformer.

The type of waveforms under load is normal looking for this type of
STK IC with this kind of ringing on rising edge. I get this all the
time with STK 730.

Cheers, Wizard

I really apreciate what you said, thanks.
As for TR1514 circuit , could you give me any hints how to check it
properly?
Ie what to meassure (I've allready changed both zeners and the TR itself).
If you want me to post any specific measurements/waveforms just say what ?
I've checked the zeners with the scope and they both clamping at the correct
volages.
As far as replacing STK cip , I'm having hard time finding one locally,
may have to order one online, it'll take time.
Thanks again Wizzard.
 
J

janek77

Jan 1, 1970
0
Hey, I've got good news! (its not geico)
I just replaced C1507 22/50V cap.
Guess what?
Seems to be working now , at least with my dummy load I can bring the
voltages back to normal.
It's late so I wont be hooking it up to the scope today, but I think I've
got it.
I'll report tommorow night.
Thanks guys!!
 
A

Arfa Daily

Jan 1, 1970
0
janek77 said:
Hey, I've got good news! (its not geico)
I just replaced C1507 22/50V cap.
Guess what?
Seems to be working now , at least with my dummy load I can bring the
voltages back to normal.
It's late so I wont be hooking it up to the scope today, but I think I've
got it.
I'll report tommorow night.
Thanks guys!!

I hate to say " told you so ", but when you first posted on this back on the
18th, I said to run an ESR meter over ALL of the electrolytic caps in there.
I probably didn't make it clear enough that I was referring to the little
fellas on the hot side as well as those smoothing the rails themselves,
although I did say suspect any that are near anything hot - and I bet your
culprit is. I work on switch mode power supplies of all flavours all the
time, and in at least 80% of cases of faults that are not obvious blow ups
or diode failures, the cause is an ( often primary side ) electrolytic. My
first check for a dead power supply where the fuse and startup R are ok, or
one that's doing anything odd, is to run the ESR meter over every damned
electrolytic in there. That one little test instrument has saved me so much
time and money over the years. And don't worry, that hair that you tolds us
that you tore out - it'll grow back !!

Seriously though, glad you've got it going.

Arfa
 
J

Jason D.

Jan 1, 1970
0
Hey, I've got good news! (its not geico)
I just replaced C1507 22/50V cap.
Guess what?
Seems to be working now , at least with my dummy load I can bring the
voltages back to normal.
It's late so I wont be hooking it up to the scope today, but I think I've
got it.
I'll report tommorow night.
Thanks guys!!
Another "told you so". When you have a hot power supply (touch the
heatsink right after unplugged and turned off.) Then you know
whatever to check or replace all small caps.

Good thing came out of this, you got it fixed, finish changing the
small caps first before closing scope up.

:)

Cheers, Wizard
 
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