ID Sega Astro City Monitor & Help Troubleshooting

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ID Sega Astro City Monitor & Help Troubleshooting

Picked up a stock Astro City. Everything appears to be original including the PSU. Here are the pics of the chassis:

https://goo.gl/photos/uHpayCndAyLjokZ38

In pic 3, silk-screened on the board is 'NANAO 05A00362G1'. Google-fu shows that it is a Nanao MS8-29FSG. Please confirm.

The issue is that the monitor is dead. I pulled the chassis and could see that fuse (F902) was burnt. A check with the multimeter confirmed this. I replaced this fuse, reconnected everything, then repowered it back up. Still nothing. No neck glow. Nothing. Retested F902 and found it was re-blown. Fuse (901) was intact before I replaced F902, and after I replaced F902.

I cannot see an ISO/stepdown transformer in this anywhere. Measuring AC voltage coming off the PSU indicates 121vac. From there, a wire connects it to the monitor. Although, I cannot measure the voltage at the monitor connection since the pins are sheathed in a very tight connector. Assuming he voltage is the same as there is no transformer in sight. I read that the PSU does the step down conversion, but why am I getting 121vac off the PSU?

Do I need to add an ISO transformer or convert 120vac to 100vac prior before powering the cab? I had a candy cab before and do not remember having to have to do this before.
 
Thanks man. Wonder how much different it is from the Nanao MS8-26SU. I see the Nanao MS8-26SU has flyback replacements. I can't find any for the Nanao MS8-29FSG. Is it possible to swap the chassis? Might be easier going forward to repair this chassis if I can swap those chassis.

I ordered a few HOT's off eBay. Will be the first time I have ever replaced a HOT. Hoping that fixes things.
 
The new HOT might blow immediately if there is a short in the collector line. You want to do your tests before putting in the new one.

Did you test the HOT or you're just assuming it's dead? What's the HOT on this?

Do a light bulb test. Get a lamp holder and solder the two wires from it to the holes where the collector and emitter of the HOT were (HOT must be off circuit). Give power (120V should be OK) and see if the bulb lights up. Chassis need not be connected to the tube so you can do this test comfortably on your working bench.
 
The HOT is a 'Toshiba 2SC4288A'. I tested it while still soldered to the board. I touched the middle pin with the black/negative lead on the multimeter. Then touched the two outer pins with the red/positive lead. I got a short in both instances. Additionally, when I touch the middle pin with the negative lead, then touch the frame with the positive, I get nothing.

I'll remove the HOT later today and test it with the diode/continuity test. I have never done the lightbulb test you mentioned. This is a Japanese monitor with really fine connector pins so that is going to be difficult to feed the monitor any power.

I'll read up on the lightbulb test now.
 
A 3 position Molex KK series .156 connector and pins, will work fine for your AC plug, remembering you only need to put in two pins/wires. Leave the middle spot unpopulated. I can't remember if this version needs an ISO or not, The 26SU series does. You may need to do more research on that.
 
A 3 position Molex KK series .156 connector and pins, will work fine for your AC plug, remembering you only need to put in two pins/wires. Leave the middle spot unpopulated. I can't remember if this version needs an ISO or not, The 26SU series does. You may need to do more research on that.

Not much info on the web for this monitor. This cab is stock as far as I can tell. I don't see an ISO anywhere and the AC coming off the PSU is ~122vac. That can't be good. I am going to get a 500w 120v-100v step down transformer for this to be safe....once I get it going of course.

Question for you SterlingRush, do you think a chassis off the 26SU you specialize in can be swapped on this monitor? I am thinking I can repair the 26SU more easily going forward as there are more readily available parts for it and you are doing great work specializing on that monitor.
 
Doesn't require an ISO. For a quick and dirty test just solder a standard power cord to the bottom of the input connector and you're good to go.

Better double check the HOT off circuit as there could be something else shorting the collector line to ground and the HOT could have survived the short. And even if the HOT is bad you should check that the through hole pad on the chassis where the middle pin was soldered is not shorted to ground.
 
Not much info on the web for this monitor. This cab is stock as far as I can tell. I don't see an ISO anywhere and the AC coming off the PSU is ~122vac. That can't be good. I am going to get a 500w 120v-100v step down transformer for this to be safe....once I get it going of course.

Question for you SterlingRush, do you think a chassis off the 26SU you specialize in can be swapped on this monitor? I am thinking I can repair the 26SU more easily going forward as there are more readily available parts for it and you are doing great work specializing on that monitor.


if you need any of the connectors i have them all on my site.
 
So I am getting ready to pull out the hot to test it. Then will give the light bulb test a shot. My first time doing both.

Question, do I put the fuse that blew out back in when I am running this test?
 
So I am getting ready to pull out the hot to test it. Then will give the light bulb test a shot. My first time doing both.

Question, do I put the fuse that blew out back in when I am running this test?

you need a good fuse in.
 
Question for you SterlingRush, do you think a chassis off the 26SU you specialize in can be swapped on this monitor? I am thinking I can repair the 26SU more easily going forward as there are more readily available parts for it and you are doing great work specializing on that monitor.

Not really sure, I don't have any experience with the MS8-29XX series monitors. From what I saw in the pics you provided, I already spotted some differences between the two types of chassis. My guess would be no, as the MS8-29 is a bigger monitor, but someone else with experience on the 29 series may be able to provide a better answer.
 
They aren't interchangeable as the yoke specs are very different.

The MS8-26:

Lh = 0.450mH

Lv = 83mH

Rh = 0.3ohm

Rv = 38ohm

The MS8-29 is in the same range as the MS9-29 which is Lh = 0.300mH and Lv = 18mH.
 
*sigh*.....I have such a nice Candy Cab which I picked up for a relative bargain. I have been reading some old posts by KenLayton and others and it is mentioned that the thing that can take out a HOT is a failing flyback. There aren't flybacks for this monitor to be found anywhere based upon my Google-fu skills.

So even if i do ever get this running by replacing the HOT which I suspect am hoping is the problem, I am on a rental with this. Pretty sad when you think about it.
 
So I took the HOT off circuit. Or at least what I think is the HOT. I tested it off circuit and it was shorted. I bought a few of these. Being anxious, I installed the new one. Skipped over the light bulb test. Again, because of anxiety. Still nothing. No neck glow. Nothing.

Pulled the chassis after reconnecting everything. Tested the "HOT" on circuit. It tested still good. I tested the fuse that blew before I removed the "HOT" and this time it was still intact. I tested the other fuse. That was still intact. I ran another test to insure I was getting AC. I can confirm AC at the plug into the chassis is good. Measures at 120vac. I bought a 100v stepdown normally recommended for Candy Cabs and will use that going forward.

So I am taking a look around the board and notice there are two other transistors connected to the chassis. Tested the two other ones on circuit. One tested good on circuit. The other tested bad on circuit. I removed the one that tested bad on circuit and tested it, and it proved to be truly bad. I ordered a replacement part from AliExpress which was the only place I could find a place for it.

So the questions now are 1) why these transistors are failing 2) Which of these transitors are HOT and and which are something else (regulators?). Am I on the right track with just replacing these? Do I truly go for the light bulb test? The flyback looks good as far as I can tell from visual inspection. If this is bad, the monitor is as good as toast as i can't find a replacement flyback anywhere. Thanks!
 

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The 2SC4157 is essential for the power supply. If that's bad nothing works.
 
The 2SC4157 is essential for the power supply. If that's bad nothing works.

I totally didn't notice the 2SC4157 the first time when I was checking the board. So I don't know if it was working prior to me replacing the "HOT", or if it was put out of commission after I replaced the "HOT". (hope I am referring to these parts correctly). Sounds like you're saying I am on the right track and need to replace this. Right?

What do you think took these transistors out of commission? I know that it is unlikely the previous owner had the cab plugged into a 100v step down transformer (this is the one I picked up). Do you think the previous owner having fed this cab US 120vac over time took these transistors out? I ask because I would hate after replacing these parts, it turns out to be the flyback. That would be awful.
 
What do you think took these transistors out of commission?

More importantly you don't want the replacements to blow again immediately so you should check that there isn't still a short on the chassis. If the pad where the middle leg of the transistor was shows a short to ground you should find what causes that short an sort it or replacing the transistor will be s waste of timeand money.

I would hate after replacing these parts, it turns out to be the flyback. That would be awful.

You should check that the flyback doesn't have its primary winding shorted to the secondary winding. If you follow the trace from the HOT collector (middle pin) you'll see that it goes to a pin of the flyback. That is the primary winding. The secondary winding is where you have the ground pin.
 
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