Epson LQ-510 Printer Power Supply Keeps Blowing a Fuse

[Paul678]

Here is the service manual:

http://service-manuals.waraxe.us/en/...printer/lq-510

Page 212 is for the power supply.

I got this unit from a fella who tried to test it for me.
It apparently worked at first (this was first turn on
for a while), as he slowly ramped it up with a
variac, but then he smelled something burning,
and the lights on the printer turned off.

I cracked it open, and saw the 2A fuse was
blown, so I replaced it, and it promptly blew
out again. So I removed bridge rectifier BD1
and checked the diodes for shorts, but they
were fine. Then I checked all the passive
components from the AC input to BD1, and
everything appears ok (I'm using a Russian
made ESR -micro V4.0s). No shorts, and
values are within spec.

I also checked all the large and medium sized
electrolytics on the other side of the rectifier, and
they all checked out good.

This is not exactly a simple power supply,
so I'd appreciated any advice on what and
where to check next.

Thanks in advance......

[Paul678]

Re: Epson LQ-510 Printer Power Supply Keeps Blowing a Fuse

Ok, I removed Q1, which was
a 2sc4058 in my unit, and the
Base Emitter junction was shorted
both ways.

Off to the electronics store!

BTW, I don't really see too many
power supplies that full-wave
rectify BEFORE the transformer, but
if you look at schematic on page
212, you can see they do that here.

I suppose there is enough AC still
in the rectified signal to still drive
a transformer, but I'm just wondering
why they would do this......

[budm]

Re: Epson LQ-510 Printer Power Supply Keeps Blowing a Fuse

This switching power supply, the incoming AC 120V 60Hz is converted into 170Vdc (120 x 1.414) and is fed to the transformer top leg, the botom leg of the transformer is connected to the high speed switching transistor Q1 collector and the through the Emitter resistor back top the negative side of the main DC filter cap to complete the circuits. The switching is done at about 70~100Khz, this is normal connections for switch mode power supply for converting AC to DC to High frequency AC and then it get rectified into low voltage DC as needed.
You should check the associated component attached to the BASE of Q1 to make sure they are OK.

[Paul678]

Re: Epson LQ-510 Printer Power Supply Keeps Blowing a Fuse

This switching power supply, the incoming AC 120V 60Hz is converted into 170Vdc (120 x 1.414) and is fed to the transformer top leg, the botom leg of the transformer is connected to the high speed switching transistor Q1 collector and the through the Emitter resistor back top the negative side of the main DC filter cap to complete the circuits. The switching is done at about 70~100Khz, this is normal connections for switch mode power supply for converting AC to DC to High frequency AC and then it get rectified into low voltage DC as needed.
You should check the associated component attached to the BASE of Q1 to make sure they are OK.

I suppose Q2 and Q3 make up the switching oscillator?


What do you think the opto-isolators hooked
up to +24V and +5V through the zeners
are for? I would guess they change the switching
frequency as soon as the +24 and +5 volts
have been achieved.

[budm]

Re: Epson LQ-510 Printer Power Supply Keeps Blowing a Fuse

Pin 6 of the transformer os the positive feedback loop through R3, D4, C10 for the circuit to oscillate.
D5 is for supplying the DC voltage to operate Q2 and Q3 for regulating how hard Q1 will be bias. The output DC on the secondary side are fed into the opto-isolator (transistor on the output side with current transfer Ratio (I do not know the current transfer Ratio of this Opto), the more current flow through the LED the more collector current on the output side) to control how hard Q2 will turn on, if the output voltage goes up, Q2 will conduct more so Q1 will conduct less to bring the output voltage down. The regulated point is set by IC1 PRECISION REF Diode (TL431)

[Paul678]

Re: Epson LQ-510 Printer Power Supply Keeps Blowing a Fuse

Pin 6 of the transformer os the positive feedback loop through R3, D4, C10 for the circuit to oscillate.
D5 is for supplying the DC voltage to operate Q2 and Q3 for regulating how hard Q1 will be bias. The output DC on the secondary side are fed into the opto-isolator (transistor on the output side with current transfer Ratio (I do not know the current transfer Ratio of this Opto), the more current flow through the LED the more collector current on the output side) to control how hard Q2 will turn on, if the output voltage goes up, Q2 will conduct more so Q1 will conduct less to bring the output voltage down. The regulated point is set by IC1 PRECISION REF Diode (TL431)

You mean the L5431:

http://www.digchip.com/datasheets/pa.../413/L5431.php


That's very cool, it uses a secondary coil of the transformer
as positive feedback. Awesome.

I was thinking the opto-isolators affected the
switching frequency, but the biasing level makes
more sense.

Ok, THIS BITCH WORKS NOW!!! Q1 was definitely the
problem.

This is just part 2.....I still have to make it work with
Windows 7.......

Will keep you updated.....

[Paul678]

Re: Epson LQ-510 Printer Power Supply Keeps Blowing a Fuse

Ok, this dot matrix is seen by Windows 7,
but there are errors.

It appears to always print out "@EJL 1284.4"
before every printout, and then the printout is
not centered on the page, so I lose information.

I was not able to find an Epson LQ-510 driver specifically
for Windows 7.......

[Paul678]

Re: Epson LQ-510 Printer Power Supply Keeps Blowing a Fuse

GOT IT TO WORK!

Choose your dot matrix from here:

http://esupport.epson-europe.com/Vie...GB&kbid=324521


Then "Add Printer" in Windows 7.

[budm]

Re: Epson LQ-510 Printer Power Supply Keeps Blowing a Fuse

That's great news, good job.