Repairing MS8-29FSG

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hindered
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Re: Repairing MS8-29FSG

Postby hindered » March 22nd, 2017, 12:11 am

grantspain wrote:the cap solder link is ok

is d530 ok?


D530 meters bad in circuit, I get about .400 one way and 2.400 the other way between the same two legs. Assuming I need to test it out of circuit, I'll try to take it out when I get home from the gym. There are huge solder blobs on the parts side though so it looks like it will be tough to remove.

PrincessPrinPrin wrote:I would remove the b+ fuse and connect a light bulb to the fuse holder to see if the PSU is OK or not.


I'd have to replace the HOT as well for this, right? Isn't there an easier way to test the PSU, can't I meter it while disconnected from the chassis to see if the correct voltage is being output? The reason I'm hesitant is that while I have 2-3 more replacement HOTs available, I'm out of replacement VRs and I really don't want to blow another one until I am reasonably confident I have found and fixed the short.

Would putting the light bulb in place of the fuse add enough resistance to protect the HOT / VR from blowing again? By my quick mental math, a 120 volt 60 watt bulb would add 240 ohms of reistance, right? Those run on AC, right, and isn't fuse 902 94v DC?
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Re: Repairing MS8-29FSG

Postby PrincessPrinPrin » March 22nd, 2017, 5:20 am

With PSU I mean the part of the chassis that generates the b+. If the fuse is off it's isolated from the flyback/HOT. The VR needs to be there though or it makes no sense.
Im running games with a vga to tv converter on my Shangai Novel, with composite and it looks amazing, Im not interested in RGB or Scart.

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Re: Repairing MS8-29FSG

Postby grantspain » March 22nd, 2017, 8:12 am

i thought you had already proved the b+ by isolating the pin on the flyback and using a mains lamp as a dummy load
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Re: Repairing MS8-29FSG

Postby PrincessPrinPrin » March 22nd, 2017, 12:52 pm

The way he reported his test here I'm not sure he used a light bulb at all when doing it.
Im running games with a vga to tv converter on my Shangai Novel, with composite and it looks amazing, Im not interested in RGB or Scart.

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Re: Repairing MS8-29FSG

Postby hindered » March 22nd, 2017, 12:58 pm

PrincessPrinPrin wrote:The way he reported his test here I'm not sure he used a light bulb at all when doing it.


Correct. I have not used a light bulb yet, partly because I'm afraid of shorting out components I don't have replacements for on hand. My test was:

F902 and VR replaced. Flyback in place. Use voltmeter between the C and E pads where the HOT should be (no hot installed). 94v is present.

If I replace the HOT and put a light bulb in place of the fuse, won't the HOT and VR short themselves again? This is the part I don't understand. Does the light bulb provide extra resistance which protects the HOT and VR from being damaged due to the short circuit?

Also when you say mains bulb -- our mains are different in the US, right? Will a 60w 120v bulb do?
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Re: Repairing MS8-29FSG

Postby PrincessPrinPrin » March 22nd, 2017, 2:28 pm

hindered wrote:My test was:
F902 and VR replaced. Flyback in place. Use voltmeter between the C and E pads where the HOT should be (no hot installed). 94v is present.


You should have soldered the light bulb to C and E. If the bulb lights up there cannot be a short in either the b+ line going from PSU to flyback (through fuse) or in the line going from flyback to HOT collector (i.e. damper diode and HV poly caps not shorted). And when you put the HOT back in its place it shouldn't blow unless it's a type with uninsulated body and you forget to put the insulator in between it and the heat sink.

If you desolder the b+ pin from its pad (as suggested by grantspain) and solder the light bulb to the pad (and ground) and the bulb lights up it means the PSU (the chassis PSU!) is OK and there isn't a short in the b+ line going from PSU to flyback (through fuse) but you won't know if there is a short in the flyback itself or in the line going from the flyback to the HOT collector.
Im running games with a vga to tv converter on my Shangai Novel, with composite and it looks amazing, Im not interested in RGB or Scart.

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Re: Repairing MS8-29FSG

Postby hindered » March 23rd, 2017, 12:35 am

I'm working on processing and understanding what you guys said. I currently have pin 2 of the flyback isolated in preparation for testing with the light bulb. I'm 99% sure I'm just going to blow the bulb and short out the voltage regulator and HOT again, though, because I feel the first short is somewhere else, and developed as a result of error during my cap kit.

However, I wanted to circle back around to this:

hindered wrote:Next I tried to identify the secondary winding, putting two 9v batteries in series, as outlined in the video. When I tested pins 1-5, I was getting basically 0 volts (the meter was reading about 0.002v the whole time, whether I was making contact with a pin or not). When I tested pin 6, 7, 9, 10, I got about .392v. When I tested pin 8, I got about .447v.

Conclusion: The fact that A: I got voltage on all of the secondary pins, and b: I did not get the expected voltage on _any_ of the pins, makes me think that the secondary winding of my flyback is messed up somehow. Can anyone confirm this?

One thing that is different in my test than in the video -- my flyback was still connected to my neckboard (which was not connected to the tube). Would that affect the results of the tests above?


Does this test indicate that I have a shorted secondary winding of the flyback? Testing continuity, Pin 1-2-3 all show continuity, pins 4-5 show continuity, and pins 6-7-9-10 show continuity. Does it make sense that 6-7-9-10 all have continuity? I would expect those to be separate windings maybe? Plus, when I applied voltage to the anode cap, I got voltage on pins 6-7-8-9-10, the voltage on 8 was higher than the other pins, but I had voltage on all 5 pins. It seems bad to me that the anode cap would have connection to all 5 pins. Is this normal, or does it indicate that grantspain is right and my flyback is shorted?

If my flyback is shorted, is it normal for a flyback to just short out due to a cap kit? I think there's pretty conclusive evidence that the flyback was not shorted prior to the cap kit. If it is shorted now, WTF happened?
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Re: Repairing MS8-29FSG

Postby hindered » March 23rd, 2017, 12:44 am

PrincessPrinPrin wrote:You should have soldered the light bulb to C and E. If the bulb lights up there cannot be a short in either the b+ line going from PSU to flyback (through fuse) or in the line going from flyback to HOT collector (i.e. damper diode and HV poly caps not shorted). And when you put the HOT back in its place it shouldn't blow unless it's a type with uninsulated body and you forget to put the insulator in between it and the heat sink.


But if I do this test, and the short is something else, will I fry my VR and fuse? I'm thinking yes. Can I not just check the damper diode and HV poly caps for shorts using continuity meter / diode test without applying power?

PrincessPrinPrin wrote:If you desolder the b+ pin from its pad (as suggested by grantspain) and solder the light bulb to the pad (and ground) and the bulb lights up it means the PSU (the chassis PSU!) is OK and there isn't a short in the b+ line going from PSU to flyback (through fuse) but you won't know if there is a short in the flyback itself or in the line going from the flyback to the HOT collector.


The line from the flyback to the HOT collector is a straight line. It's flyback Pin 1 -> Hot Collector -> Yoke Header -> Other Yoke Header. So my question for this test is the same as the other test -- if I do this, and the short is in the primary winding of the flyback, great. If the short is not in the primary winding flyback, I burn out my VR and HOT and pop the fuse at F902 again.

Is there a non-destructive way to do these tests?
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Re: Repairing MS8-29FSG

Postby PrincessPrinPrin » March 23rd, 2017, 9:48 am

hindered wrote:The line from the flyback to the HOT collector is a straight line. It's flyback Pin 1 -> Hot Collector -> Yoke Header -> Other Yoke Header. So my question for this test is the same as the other test -- if I do this, and the short is in the primary winding of the flyback, great. If the short is not in the primary winding flyback, I burn out my VR and HOT and pop the fuse at F902 again.

Is there a non-destructive way to do these tests?


The HOT collector line also goes through a couple of jumpers (yellow) to the damper diode (orange) and the HV caps (pink, blue, red). You can remove the jumpers and repeat the light bulb test or just check if those components are bad.

MS8-29.jpg
Im running games with a vga to tv converter on my Shangai Novel, with composite and it looks amazing, Im not interested in RGB or Scart.

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Re: Repairing MS8-29FSG

Postby PrincessPrinPrin » March 23rd, 2017, 2:33 pm

hindered wrote:Does it make sense that 6-7-9-10 all have continuity?


Yes, they're different tappings of the same winding and 6 is ground (secondary). Pin 8 is the ABL pin and has no continuity with them. The MS8-29 schematics are not available but we can use those of the MS8-26 as a general reference:

http://wiki.arcadeotaku.com/images/4/45 ... ematic.jpg

Here on the secondary side we have 6-7-9-10 which are part of the same winding so they have continuity and 7 is used as secondary ground. Pin 8 is ABL and is connected to the contrast/brightness circuit on the chassis whereas inside the flyback it's one end of the HV winding). As I said this pin has no continuity with any other pin. Then we have 1-2-3-4 which are the primary winding and have continuity across each other but no continuity with either 6-7-9-10 or 8.

In your case you have two separate windings on the primary side (1-2-3 and 4-5) and a secondary winding (6-7-9-10) and no continuity across the three. If you had reported continuity across 1-2-3 and 4-5 then there would be a short because 1-2 (collector-B+) must be isolated from ground (5 is the primary ground, same as the negative of the big filter cap) and of course continuity across 1-2-3 and 6-7-9-10 or 4-5 and 6-7-9-10 would mean a short in the flyback as the primary and secondary grounds (5 and 6) cannot be on the same winding (and neither can B+/collector and secondary ground). So I see no indication of a shorted flyback from what you reported,
Im running games with a vga to tv converter on my Shangai Novel, with composite and it looks amazing, Im not interested in RGB or Scart.

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Re: Repairing MS8-29FSG

Postby hindered » March 24th, 2017, 12:13 am

PrincessPrinPrin wrote:The HOT collector line also goes through a couple of jumpers (yellow) to the damper diode (orange) and the HV caps (pink, blue, red). You can remove the jumpers and repeat the light bulb test or just check if those components are bad.


Thank you -- this post set of a chain reaction of understanding in my head that helped me realize that I was thinking about electricity incorrectly -- even though I logically understood the principles correctly, I was applying them incorrectly. You'll never know just how much this simple explanatory post helped my understanding of circuits.

PrincessPrinPrin wrote:
Yes, they're different tappings of the same winding and 6 is ground (secondary). Pin 8 is the ABL pin and has no continuity with them. The MS8-29 schematics are not available but we can use those of the MS8-26 as a general reference:

http://wiki.arcadeotaku.com/images/4/45 ... ematic.jpg

Here on the secondary side we have 6-7-9-10 which are part of the same winding so they have continuity and 7 is used as secondary ground. Pin 8 is ABL and is connected to the contrast/brightness circuit on the chassis whereas inside the flyback it's one end of the HV winding). As I said this pin has no continuity with any other pin. Then we have 1-2-3-4 which are the primary winding and have continuity across each other but no continuity with either 6-7-9-10 or 8.

In your case you have two separate windings on the primary side (1-2-3 and 4-5) and a secondary winding (6-7-9-10) and no continuity across the three. If you had reported continuity across 1-2-3 and 4-5 then there would be a short because 1-2 (collector-B+) must be isolated from ground (5 is the primary ground, same as the negative of the big filter cap) and of course continuity across 1-2-3 and 6-7-9-10 or 4-5 and 6-7-9-10 would mean a short in the flyback as the primary and secondary grounds (5 and 6) cannot be on the same winding (and neither can B+/collector and secondary ground). So I see no indication of a shorted flyback from what you reported,


Thank you for this as well, that all makes sense and gives me some confidence that this problem is fixable -- if the flyback was shorted, all hope would be lost, because as I understand it, there is no replacement available anymore.

I also will print out the MS8-26SU schematic as a reference, I have been wishing for a schematic for a couple of weeks and am glad there is at least _something_ available.

Has anyone reached out to Nanao to see if they have and would share the schematics for these old monitors? I know it's a long shot, but we won't know unless we try...
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Re: Repairing MS8-29FSG

Postby hindered » March 25th, 2017, 5:40 am

grantspain wrote:is d530 ok?


I was finally able to remove this component from circuit and test it. Per the datasheet, there is a diode from pin 1 to 2, and 2 to 3. Although it tests bad in circuit, It tests fine out of circuit.

I checked the HV caps for shorts using my meter, everything checked out. Doesn't the fact that I get 94v to the collector pad of the HOT with the HOT removed prove the PSU circuitry is fine? Or is the true test only when the circuit is complete (by replacing the HOT, or like PrincessPrinPrin said, solder a light bulb between the HOT collector and emitter pads)?

While trying to find the shorted component, I found this weird behavior while doing continuity testing on the VR -- While testing B to C, and C to E, I get intermittent, really short, continuity result (resistance under 10 ohm) that immediately goes away. Is this explainable? https://www.hasntfiguredouthowtoembedyoutubeproperly.com/watch?v=qazxf0ROer0 (you will need sound for this video).

I also demonstrate that the HOT pads show continuity between B and E, which PrincessPrinPrin has already explained it's OK, because they are connected by the winding at T530, which shows continuity on the pins circled in red:

T530.JPG


I haven't tried it yet, but I'm assuming isolating one/both of those pins would stop the continuity positive result between B and E of the HOT pads.
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Re: Repairing MS8-29FSG

Postby PrincessPrinPrin » March 25th, 2017, 1:44 pm

I think you should do a proper light bulb test.

Start with this:
MS8-29bulb1.jpg


and if the bulb lights up and B+ is the correct voltage try this (I've seen that you desoldered the b+ pin on the flyback so leave it like that):
MS8-29bulb2.jpg


Voltage regulator must be in and good.
Im running games with a vga to tv converter on my Shangai Novel, with composite and it looks amazing, Im not interested in RGB or Scart.

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Re: Repairing MS8-29FSG

Postby hindered » March 25th, 2017, 10:01 pm

PrincessPrinPrin wrote:I think you should do a proper light bulb test.


Alright, my friend. You (and grantspain :)) only need to tell me something 6 or 7 times before I decide to listen. :oops: ;)

I did both tests, the lightbulb lit up both times.

EDIT: I just realized I forgot to measure b+ during the first test, so I went and did it again. The typical test point for b+ (TP1) did nothing, which makes sense as it's on the other side of the fuse holder from where we are completing the circuit. THis left me to realize I don't know where to test b+ in this configuration.

The voltage across the filter cap is ~162v. The voltage across the light bulb is ~152V.

If it makes a difference, this was done without a HOT in-circuit. I don't think it matters, as, if I'm understanding correctly, the HOT doesn't come into play until after the LOPT, which we are taking out of the equation for these tests.
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Re: Repairing MS8-29FSG

Postby grantspain » March 26th, 2017, 12:38 am

to test b+ you need dc volts 200v range,negative to a capacitor ground and positive to pin 2 track of the flyback or the fuse-you can't use the heatshield as ground or the reading will be incorrect
if you are not getting 94v dc then you have a problem in the regulation circuit
and if the chassis was working before you did the caps then one of your caps is wrong or the polarity is wrong
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Re: Repairing MS8-29FSG

Postby hindered » March 26th, 2017, 5:15 am

grantspain wrote:to test b+ you need dc volts 200v range,negative to a capacitor ground and positive to pin 2 track of the flyback or the fuse-you can't use the heatshield as ground or the reading will be incorrect


Well, in the first configuration as recommended by PrincessPrinPrin, I got 150v dc across the lightbulb (fuse to filter cap negative).

MS8-29bulb with voltage.jpg


Testing the voltage of Fuse to pin 2 pad of the flyback gives 0v, which I think is expected in this configuration.

grantspain wrote:if you are not getting 94v dc then you have a problem in the regulation circuit
and if the chassis was working before you did the caps then one of your caps is wrong or the polarity is wrong


The chassis was more or less working before I did the caps. I agree the problem is most likely something that happened during my cap kit. I went and doublechecked the value and polarity of every cap -- they seem OK EXCEPT C910 is 25v instead of 50v, as previously pointed out. I also realized that C577 is original to the board, it still has rubber epoxy on it. I checked it for a short and with my ESR meter and it seemed OK. It could be a bad cap, but it doesn't seem shorted.

While I was going over the board again, I confirmed and updated the wiki here http://wiki.arcadeotaku.com/w/Nanao_MS8-29FSG with some corrections. I marked C910 as a 220 uf instead of 119 uf. I marked C446 as NP. I changed C433 to C431, they are right next to each other, and as grantspain confirmed in earlier posts, C433 is empty.
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Re: Repairing MS8-29FSG

Postby grantspain » March 26th, 2017, 1:16 pm

take the fuse out and attach the bulb there-then meter the voltage
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Re: Repairing MS8-29FSG

Postby hindered » March 26th, 2017, 2:29 pm

grantspain wrote:take the fuse out and attach the bulb there-then meter the voltage


The fuse is already out and the bulb is attached there, like in the picture in my previous post.

One thing I forgot to mention, there is one cap that is soldered into a resistor position, r556. I'm unsure I have the polarity of that cap correct because there are no polarity markings on the silk screen.
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Re: Repairing MS8-29FSG

Postby grantspain » March 26th, 2017, 2:40 pm

that cap is in sync circuit I believe so don't worry about that yet

solder the bulb to the primary side of the fuse holder-if you have removed the fuse and then added the bulb further into the circuit then the regulation circuit will not have any load
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Re: Repairing MS8-29FSG

Postby hindered » March 26th, 2017, 3:00 pm

grantspain wrote:that cap is in sync circuit I believe so don't worry about that yet

solder the bulb to the primary side of the fuse holder-if you have removed the fuse and then added the bulb further into the circuit then the regulation circuit will not have any load


Just to be clear, this is an updated picture explaining what test I did:

MS8-29bulb - Updated.jpg
Lightbulb test already performed


Are you asking me to do this instead? In other words, I'm not sure which side is the primary side of the fuse holder.

MS8-29bulb1 - grantspain.jpg
Is this what you are asking me to do instead?

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