Hi,

I've got a dead 50" Mitsubishi Rear Projection that I'm trying to get
working again. I'm familiar with rear projection monitors, but by no
means an expert... I've fixed 4 so far, but none have been anything
very complicated (one was a bad PIP card, another was just adjusted
wrong, one had a cable loose, and the last needed the tubes
rejuvenated). I'm very familiar with standard CRT monitors though, and
good with electronics, and I know what I can and can't touch .

Anyway, this one is on a Wave Runner arcade game (like:
http://www.klov.com/game_detail.php?...&game_id=10414 ), and when I
turn it on, I hear it click, it sounds like there's HV, then shuts down
after about a second. It's missing the back door, so I don't know what
the model number is... the only numbers I can find are PB7539 (on the
Power Supply) and PB7538 (on the HV/Deflection board). It says it was
manufactured in 1998 and it's a medium resolution monitor only (no TV
tuner). Is there any hidden place that a model number would be? Or if
I took a pic of the boards, would anyone here be able to identify what
the model is?

I'm just looking for any ideas on what I can check. I've read about a
bunch of problems with Mitsubishi monitors, mostly bad solder joints,
bad capacitors, and blown HOT, but they're always specific about which
capacitor is bad, and since this model is different, I don't know which
capacitors to check (C914 is the one I always hear about, but I don't
have a C914). I don't think the HOT is bad, since that should have
blown a fuse, and there are no blown fuses.

I've already pulled the power board and inspected/resoldered the large
pins, and that didn't help any... I've tried turning down the screen
controls (I've had one that would shut down in the past if those were
too high). I'm planning on resoldering the points on the flyback next,
but I'd like some tips on a more systematic approach to troubleshooting
this. What would cause the shutdown? I know on CRT monitors, a high
B+ would cause it, but where do I measure the B+ at on these monitors?

I'd appreciate any help or tips anyone can give me. Thanks,

Pat

Anyone have any ideas? I was just looking at it some more, it looks
like maybe the B+ is low. I found a small pin on the HV/Deflection
board marked +B, and when I turn it on, it goes up to about 60V, then
drops when it shuts down (after about 2 seconds). I tested all of the
voltage pins I could find on the power board and they all tested good.

What I guess I'm wondering is if I'm chasing the right problem with the
B+? Or does it normally take a while for it to get up to the correct
voltage, and the monitor is just shutting down too quickly? And would
a B+ being too low actually cause it to shut down (I know too high
does, I've never had too low of a B+ cause a shut down).

What is the B+ typically on one of these montors? And I assume it
comes directly from the Power board and not derived later on the
HV/Deflection board?

Oh, if this helps any, here's some pics of the monitor:
http://dogp.home.comcast.net/waverunner/DSCF0671.JPG , and
http://dogp.home.comcast.net/waverunner/DSCF0672.JPG .

Thanks,

Pat

Alright, I'm making some progress... I think. I believe that the HOT
is blown, when I tested across the Base and Emitter, it was nearly
shorted, and was the same way after I pulled it (out of circuit). I
don't have another exactly like it (the original is a 2SC5143), but I
did have one that was very close in specs to it (and same specs as ones
that were crossed to my part), so I popped it in, and it appears to
have blown the same way.

What would blow these things like that? I guess my part could have
been too weak, but it didn't act any differently, so I believe that it
blew almost instantly, meaning something is really messed up. I'm
going to be ordering a few of the correct parts soon, but what can I do
to keep these from blowing while I figure out what's blowing them?
I've heard about putting a light bulb in series, should I try that? Or
I read on one of the pages to add a 33ohm 1/4 watt resistor in parallel
with the base/emitter... is this a common modification? I know on X-Y
monitors, unhooking the yoke takes the load off the deflection
transistors, would that work the same here? Oh, btw, I did test the
yokes and they all seem to test fine.

Does anyone have any ideas? Am I in the wrong place? ;-) Thanks,

Pat

I am not going to be much help here but I think I have the same game
and I just gutted a similiar game. What about the flyback? if that
thing goes wacko isn't it going to directly affect the HOT? I just got
a Sencore HA2500 which is made to test HOTs. If it is pretty tough to
test the HOT because of the problems you mention. This thing is
suppose to help directly with this issue. I just got it so I haven't
even used it yet.
Russ



DogP wrote:
Alright, I'm making some progress... I think. I believe that the HOT
is blown, when I tested across the Base and Emitter, it was nearly
shorted, and was the same way after I pulled it (out of circuit). I
don't have another exactly like it (the original is a 2SC5143), but I
did have one that was very close in specs to it (and same specs as ones
that were crossed to my part), so I popped it in, and it appears to
have blown the same way.

What would blow these things like that? I guess my part could have
been too weak, but it didn't act any differently, so I believe that it
blew almost instantly, meaning something is really messed up. I'm
going to be ordering a few of the correct parts soon, but what can I do
to keep these from blowing while I figure out what's blowing them?
I've heard about putting a light bulb in series, should I try that? Or
I read on one of the pages to add a 33ohm 1/4 watt resistor in parallel
with the base/emitter... is this a common modification? I know on X-Y
monitors, unhooking the yoke takes the load off the deflection
transistors, would that work the same here? Oh, btw, I did test the
yokes and they all seem to test fine.

Does anyone have any ideas? Am I in the wrong place? ;-) Thanks,

Pat

Russ,

Thanks for the reply (at least I know SOMEONE is reading this ;-) ). I
don't think the flyback is bad since when I turn it on, I do get HV for
the two seconds that it turns on, but I could be wrong, which is why
I'm posting here. But it doesn't look like I'll be using an HA2500 to
test it any time soon ($2900!!! O_O). I'm used to smaller monitors
where when the flyback or HOT blows, it immediately blows a fuse (or in
the case of a G07, the flyback explodes :-P). That's why the blown HOT
threw me off in the first place.

Do your monitor boards look like the pictures that I posted? If so, do
you have the model number of the monitor (it should be on a sticker on
the back door, which is usually a pegboard sort of material). If I had
the model number, I might be able to get a schematic or service manual
from Mitsubishi.

As always, any replies are appreciated :-). Thanks!

Pat

No rear projection techs out there? I ordered some 2SC5143's and got
them yesterday... I pulled the whole chassis out and noticed that
there's another 2SC5143, and it was blown too! It looks like one goes
to the flyback, one goes to the yokes. So, I pulled both and replaced
just one, hooked it up with a light bulb in series with the main power,
and it still blew :-( . I only bought 4 replacments, thinking I only
needed 1 _.

Any idea what I could check to see what's causing these to blow? I've
checked all of the large transistors and diodes that I could find, and
made sure that none of the large capacitors were shorted. I really
don't know what else I can check, or what the next step in
troubleshooting this is.

Thanks,
Pat

"DogP" wrote in message
oups.com...
No rear projection techs out there? I ordered some 2SC5143's and got
them yesterday... I pulled the whole chassis out and noticed that
there's another 2SC5143, and it was blown too! It looks like one goes
to the flyback, one goes to the yokes. So, I pulled both and replaced
just one, hooked it up with a light bulb in series with the main power,
and it still blew :-( . I only bought 4 replacments, thinking I only
needed 1 _.

Any idea what I could check to see what's causing these to blow? I've
checked all of the large transistors and diodes that I could find, and
made sure that none of the large capacitors were shorted. I really
don't know what else I can check, or what the next step in
troubleshooting this is.

Thanks,
Pat


There are lots of us out here. Responses have more to do with whether
someone has much to contribute than whether we are here. You might get more
help if you post the model number in the subject line. Some of us don't
catch every thread from the start and I personally won't go digging up the
previous posts to see if you had the relevant info. Some Mitsubishi sets
have been known to have repeated HOT failures due to a bad coil. Not
knowing what set or chassis you have makes it impossible to search for
specific info.

In general, repeat failures in outputs in RPTV is not different from direct
view sets. Problems in the base circuit such as intermittent drive or
impedance problems or load problems such as a bad flyback or bad cap are
most likely. Typically with Mitsubishis the problems have been drive
related as opposed to load.

Apparently this is a set with separate HV and H outputs. If both are
blowing it seems pretty obvious to be looking to the drive circuits or the
power supply. Since the Mits sets are pretty unlikely to operate with
excessive B+, I'd be leaning to a h-drive problem.

Leonard

Pat,

What's the model #?

--
==========================
Jeff Stielau
Shoreline Electronics Repair
344 East Main Street
Clinton,CT 06413
860-399-1861
860-664-3535 (fax)

========================

"DogP" wrote in message
oups.com...
No rear projection techs out there? I ordered some 2SC5143's and got
them yesterday... I pulled the whole chassis out and noticed that
there's another 2SC5143, and it was blown too! It looks like one goes
to the flyback, one goes to the yokes. So, I pulled both and replaced
just one, hooked it up with a light bulb in series with the main power,
and it still blew :-( . I only bought 4 replacments, thinking I only
needed 1 _.

Any idea what I could check to see what's causing these to blow? I've
checked all of the large transistors and diodes that I could find, and
made sure that none of the large capacitors were shorted. I really
don't know what else I can check, or what the next step in
troubleshooting this is.

Thanks,
Pat

Sorry guys, this is in a Wave Runner arcade game, and it's missing the
back panel where the model number should be :-( . I have a Top Skater
with a similar monitor (model P502SG), but it's definately not the same
chassis. I have pics of the chassis he
http://dogp.home.comcast.net/waverunner/DSCF0671.JPG and
http://dogp.home.comcast.net/waverunner/DSCF0672.JPG .

The only numbers I can find are PB7539 (on the
Power Supply) and PB7538 (on the HV/Deflection board). It says it was
manufactured in 1998 and it's a medium resolution (24KHz RGB) monitor
only (no TV
tuner). If there's any place I can buy a service manual or schematic,
that'd be great, but I'd assume that I need the model of the actual
monitor, not just those boards.

I did check the voltages at all of the test points (that I saw) on the
power supply and they all tested good, and with the shorted
transistors, the B+ would climb up to only about 60V. With the shorted
transistors, I did hear HV for the couple of seconds that it stayed on
though, so I think that the flyback is good (and I don't see any
obvious signs of damage).

So you would suspect something in the H-Drive circuit? What is a
typical failure with something like this? Is there usually an IC that
goes bad, a transformer that opens/shorts, a resistor that opens, a
single transistor that shorts, or any of the above / something else?
Are they usually large components that cause it, or is there a small
signal section that could cause it? As far as I know, I've tested all
large transistors, resistors, and diodes. I haven't checked every
inductor or transformer yet.

Should I just trace back between the two large transistors and see what
is common with the two and suspect those components? Would that be a
reasonable way of troubleshooting this? Or do you have any other
suggestions, or diagrams of a circuit similar to this so I can get an
idea of what to expect?

Thanks guys, I really do appreciate the help.

Pat

I don't even recognize that chassis from any of the consumer models!

Searching my repair database for the 2SC failures you mention shows nada!

You may want to try posting these images on the rec.games.video.arcade
newsgroup to see if anyone has the service info or model cross reference.

--
==========================
Jeff Stielau
Shoreline Electronics Repair
344 East Main Street
Clinton,CT 06413
860-399-1861
860-664-3535 (fax)

========================

"DogP" wrote in message
ups.com...
Sorry guys, this is in a Wave Runner arcade game, and it's missing the
back panel where the model number should be :-( . I have a Top Skater
with a similar monitor (model P502SG), but it's definately not the same
chassis. I have pics of the chassis he
http://dogp.home.comcast.net/waverunner/DSCF0671.JPG and
http://dogp.home.comcast.net/waverunner/DSCF0672.JPG .

The only numbers I can find are PB7539 (on the
Power Supply) and PB7538 (on the HV/Deflection board). It says it was
manufactured in 1998 and it's a medium resolution (24KHz RGB) monitor
only (no TV
tuner). If there's any place I can buy a service manual or schematic,
that'd be great, but I'd assume that I need the model of the actual
monitor, not just those boards.

I did check the voltages at all of the test points (that I saw) on the
power supply and they all tested good, and with the shorted
transistors, the B+ would climb up to only about 60V. With the shorted
transistors, I did hear HV for the couple of seconds that it stayed on
though, so I think that the flyback is good (and I don't see any
obvious signs of damage).

So you would suspect something in the H-Drive circuit? What is a
typical failure with something like this? Is there usually an IC that
goes bad, a transformer that opens/shorts, a resistor that opens, a
single transistor that shorts, or any of the above / something else?
Are they usually large components that cause it, or is there a small
signal section that could cause it? As far as I know, I've tested all
large transistors, resistors, and diodes. I haven't checked every
inductor or transformer yet.

Should I just trace back between the two large transistors and see what
is common with the two and suspect those components? Would that be a
reasonable way of troubleshooting this? Or do you have any other
suggestions, or diagrams of a circuit similar to this so I can get an
idea of what to expect?

Thanks guys, I really do appreciate the help.

Pat

Its a commercial unit...Good Luck

kip
"Shoreline Electronics" wrote in message
...
I don't even recognize that chassis from any of the consumer models!

Searching my repair database for the 2SC failures you mention shows nada!

You may want to try posting these images on the rec.games.video.arcade
newsgroup to see if anyone has the service info or model cross reference.

--
==========================
Jeff Stielau
Shoreline Electronics Repair
344 East Main Street
Clinton,CT 06413
860-399-1861
860-664-3535 (fax)

========================

"DogP" wrote in message
ups.com...
Sorry guys, this is in a Wave Runner arcade game, and it's missing the
back panel where the model number should be :-( . I have a Top Skater
with a similar monitor (model P502SG), but it's definately not the same
chassis. I have pics of the chassis he
http://dogp.home.comcast.net/waverunner/DSCF0671.JPG and
http://dogp.home.comcast.net/waverunner/DSCF0672.JPG .

The only numbers I can find are PB7539 (on the
Power Supply) and PB7538 (on the HV/Deflection board). It says it was
manufactured in 1998 and it's a medium resolution (24KHz RGB) monitor
only (no TV
tuner). If there's any place I can buy a service manual or schematic,
that'd be great, but I'd assume that I need the model of the actual
monitor, not just those boards.

I did check the voltages at all of the test points (that I saw) on the
power supply and they all tested good, and with the shorted
transistors, the B+ would climb up to only about 60V. With the shorted
transistors, I did hear HV for the couple of seconds that it stayed on
though, so I think that the flyback is good (and I don't see any
obvious signs of damage).

So you would suspect something in the H-Drive circuit? What is a
typical failure with something like this? Is there usually an IC that
goes bad, a transformer that opens/shorts, a resistor that opens, a
single transistor that shorts, or any of the above / something else?
Are they usually large components that cause it, or is there a small
signal section that could cause it? As far as I know, I've tested all
large transistors, resistors, and diodes. I haven't checked every
inductor or transformer yet.

Should I just trace back between the two large transistors and see what
is common with the two and suspect those components? Would that be a
reasonable way of troubleshooting this? Or do you have any other
suggestions, or diagrams of a circuit similar to this so I can get an
idea of what to expect?

Thanks guys, I really do appreciate the help.

Pat

Jeff,

Thanks for checking your database... I'll post a message on RGVAC about
it, but every time anyone posts about rear projections in video game
groups, they seem to always send them over here :-( . I know that this
is a strange beast, so I figured I'd only get generic help, and the
tips Leonard gave me should help since I now know what section to
suspect first. Like I said, I don't have a lot of experience
troubleshooting rear projection stuff like I do standard RGB CRT
monitors, but I can usually figure this kinda stuff out, so if anyone
has any other tips, they would be greatly appreciated. Thanks,

Pat

Neither of the 2SC's you tested were bad. Standard HOT type of
transistors which those are have around a 30 ohm resistor internal
between the base and emitter and a damper diode across the collector
and emitter.

As for any service manual, given the limited type of production those
were in, you really need to contact the manufacture of the unit.

Try posting the exact symptoms the unit gives.

Wow! I think you're right! These are the kind of tips I was looking
for! I just tested one of my new ones and it tested 30 ohms across the
base and emitter. I was sure that I checked that before, but I must
not have. I wondered why a blown HOT wasn't blowing any fuses, but I
figured they had some sort of protection for that on these newer
models.

The symptoms of the unit:

Turn it on, makes a couple of clicks, has HV for about a second,
nothing shows up on the screen, then the monitor turns itself off.
Won't turn immediately back on, I have to wait about 10 seconds.

Checking the B+, it looks like it only ever gets up to about 60V (I
manually set the range on my meter trying to get a quicker reading, but
I guess it's possible that it's just not fast enough too). When it
shuts down, it seems to shut the whole thing down (I know at least +5V
shuts off to the Video/Conv board).

So far, I've tested most/all of the big caps, resistors, and
transistors on the Def/HV board, and I've checked the yokes, and all of
the voltage test points that I could find on the power supply. As far
as all that goes, everything has tested good.

I'm not really sure what else to describe. Do you have any ideas as to
what would cause those symptoms? Should I be suspecting the power
supply more than the Def/HV board? Or should I suspect the Video/Conv
board maybe shutting it down because it doesn't think there's a signal
(even though there is)? Is there usually a shutdown override somewhere
to see if the B+ ever stabilizes to the correct value, and whether
anything is displayed if it would just stay on? I assume finding the
relay that is kicking off and manually jumpering it is a bad idea?

Once again, thanks for the help, this is definately progress!

Pat

If you can turn it back on without unplugging it, that pretty much
rules out a protect shutdown situation.

Most RGB monitors use a main B+ that only runs at 60V, not the usual
130V as a typical tv set.
Use an O'scope to confirm the actual peak voltage you are getting.

Most RGB monitors will auto-shutdown if they are not getting a proper
signal that includes the H-sync and V-sync.
Probably where you need to start troubleshooting.

With the board layout of the chassis, you really need to try and buy a
service manual for it to know what to look at.
There just is not enough information you are going to be able to find
without it.

Oh, sorry, I am plugging and unplugging it to turn it on and off.
There is no manual on/off switch (that I see at least), and the remote
has never worked (the batteries are good, I've never tested the output
of the remote though). I have had it where a rear projection monitor
would shut down if the flyback controls were up too high, but I've
tried turning them all the way down and it doesn't seem to help any.

That's good to know about the B+ voltage though, and I know the game
PCB is outputting a good signal because I tested it on my test monitor,
so I'll try to somehow get a manual, and make sure all of the
connections are correct to the inputs on the front of the monitor.

There are a lot of well labeled test points on the chassis though, so
in the mean time, I'll hook it all back up and at least try probing a
bunch of them checking for anything abnormal, and lug my scope up to
the garage to check the proper B+ and any other waveforms.

Thanks a lot for the help so far, there has been a LOT of stuff cleared
up today, and I feel like I'm at least starting to go in the right
direction.

Pat

Pat,

If that's the model I'm thinking it is you may be wasting your time looking
at the wrong board.
Check all the discrete components on the convergence output board.
A couple of discrete mosfet transistors (not the outputs) like to burn up
causing this symptom.

I may be off base here but then again it doesn't hurt to check.

Good Luck,
Bill Jr


"Shoreline Electronics" wrote in message
...
Pat,

What's the model #?

--
==========================
Jeff Stielau
Shoreline Electronics Repair
344 East Main Street
Clinton,CT 06413
860-399-1861
860-664-3535 (fax)

========================

"DogP" wrote in message
oups.com...
No rear projection techs out there? I ordered some 2SC5143's and got
them yesterday... I pulled the whole chassis out and noticed that
there's another 2SC5143, and it was blown too! It looks like one goes
to the flyback, one goes to the yokes. So, I pulled both and replaced
just one, hooked it up with a light bulb in series with the main power,
and it still blew :-( . I only bought 4 replacments, thinking I only
needed 1 _.

Any idea what I could check to see what's causing these to blow? I've
checked all of the large transistors and diodes that I could find, and
made sure that none of the large capacitors were shorted. I really
don't know what else I can check, or what the next step in
troubleshooting this is.

Thanks,
Pat

Wow, Thanks! Actually, I was working on this late last night and the
more I looked at it, the more it seemed that the whole power supply was
shutting down... so I started unhooking connectors from the power
supply, and when I unhooked the power to the convergence board and it
fired up! Of course the convergence is WAY off, but that's a good
sign. I tried testing some of the components, but I was really tired,
so I didn't get a chance to dig deep into it.

Do you know which mosfets typically burn up? And do they usually short
or open? I quickly checked all of the large transistors, and I didn't
see any shorted, but I'll definately go back and check again now that
you say this is common. It's the large ones that burn up, not any of
those 50 or so small ones, correct?

Thanks again, you guys have been a huge help.

Pat

Okay, I've gotten the monitor to stay up with the convergence board
hooked up now... it ended up being an opened resistor at the -15V line
on the convergence board. It's a 2 ohm appears to be a 1W resistor,
which I didn't have, but I had lots of other low value resistors, which
I hooked up to get within the 5% allowed of the original resistor.

Anyway, now it comes up, but the convergence is WAY off. Of course
this has no manual pot adjustments, so I guess I have to adjust it all
through the menu. I do have the remote, but it doesn't seem to be
allowing me to change any of the convergence manually. It'll let me
change size and position, but when I follow the instructions for
adjusting convergence that I found online, it just sits there doing
nothing.

You can see a pic of how bad it is he
http://dogp.home.comcast.net/waverunner/DSCF0741.JPG

BTW, sorry, I assumed that this was a Mitsubishi, because the outside
looked exactly like my other Mitsubishi arcade monitors, but looking at
the remote, and the sticker on the EPROM, this is actually a Toshiba.

Does anyone know why when I hit the adjust buttons, nothing happens?
Would it be something with the new resistor I put in, or would
something else be blown, or is there some sort of protect switch or
something?

Should I make a new topic on adjusting convergence on Toshiba rear
projections? Ugh, even with how much of a pain it is adjusting the
convergence with the thousand pots on a regular old style rear
projection, I'd rather do that than go through all of the trouble I've
gone through with this "automatic" convergence stuff :-(.

Thanks again,

Pat