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NO VIDEO Toshiba 29" Monitor, PM1745 Chassis on Astro City

trevino

trevino

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I would appreciate any advise to fix my Sega Astro City. A year ago I was playing on it when the video signal vertically shrinked. After a power cycle and waiting 5 minutes I had it up and running again.

However, now i get no video signal at all. I even tried replacing the chassis but the result is the same..

I will attach pictures shortly.

Thanks,

Trevino
 
At first it seems like a capacitor(s) in the vertical deflection section failed but the tube doesn’t turn on at all with a replacement chassis.
  • Is the replacement chassis known to work?
  • Was the original chassis re-capped?
  • Do you get an orange glow on the neck of the tube with either chassis?
 
kikaso said:
but the tube doesn’t turn on at all with a replacement chassis.
Click to expand...
Let me add:
  • Is the yoke fried?
  • Did you triple-check all your connections and are certain everything is plugged in properly on the new chassis?
 
kikaso said:
At first it seems like a capacitor(s) in the vertical deflection section failed but the tube doesn’t turn on at all with a replacement chassis.
  • Is the replacement chassis known to work?
  • Was the original chassis re-capped?
  • Do you get an orange glow on the neck of the tube with either chassis?
Click to expand...
  • I had no chance to test it because the seller didn't have the controller with pots. However, I saw a loose wire from a spool next to the flyback and tried to put it back. I don't know if it got damaged during shipping or if it was like that...
  • No chassis has been recaped
  • I haven't seen any glow at all, it's a hassle to discharge the monitor each time I test it.
 
How does one verify whether or not the yoke is fried? Asking for a friend (OP), but also for myself. ;)
 
rewrite said:
Let me add:
  • Is the yoke fried?
  • Did you triple-check all your connections and are certain everything is plugged in properly on the new chassis?
Click to expand...
How can I tell if it is fried? There is no smoke coming from the yoke.

I have tried both several times but no sucess. It is worth to mention that there was a blown fuse on the original one which i replaced but it didn't fix things at all.

Thanks
 
kazuo said:
How does one verify whether or not the yoke is fried? Asking for a friend (OP), but also for myself. ;)
Click to expand...
Test that H and V windings don't read open.

You can end up with one that's sorta-working if the values are off and corrosion has gotten to it but not severed a winding, but that's a whole different scenario. In the case of just "bad", and OP has no video at all with 2 chassis, this should be enough to rule it out for the time being.
 
At the risk of sounding very stupid, how would one go about this? Use a meter and test resistance across the pins of each winding?
 
kazuo said:
At the risk of sounding very stupid, how would one go about this? Use a meter and test resistance across the pins of each winding?
Click to expand...
Bingo. Can do it from the yoke connector itself too (and then you'd know that there's not a severed wire or corroded pin or something as well).
 
Hi all,

Thanks for the support! The PM1745 sanwa keeps blowing the 1.5A fuse.

The new one (pm1745 samsung?) has a damaged spool (one end is not wired and came off) this one however energize the monitor. I noticed it after swapping them for testing. I only need to discharge monitor with the samsung chassis when it is time to take it out.

7C94A584-1675-48BD-A0DA-822A4839FFBF.jpeg
 

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You're definitely going to need to fix that coil at a minimum, as well as probably the component that's folded over above the R461 label (looks like it's labeled 409).

Honestly if it was sold to you working, just get refunded or exchanged.
 
There are two types of pm1745 this one green PCB was made in Japan, this drive toshiba 29 tube and it is far better than the ones pm1745c yellow PCB china assembled paired with samsung tube.
Usually the damage is on psu section, there Is fuse resistor (1.5k ) and a pnp transistor often fail (2sa1091) , I will give you more detail later.
 
Mukuro_W said:
There are two types of pm1745 this one green PCB was made in Japan, this drive toshiba 29 tube and it is far better than the ones pm1745c yellow PCB china assembled paired with samsung tube.
Usually the damage is on psu section, there Is fuse resistor (1.5k ) and a pnp transistor often fail (2sa1091) , I will give you more detail later.
Click to expand...
I think i found them. The PM1745C pic is just for reference. Could this be the reason why the 1.5A fuse blows?
 

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Yes it Is the psu area usually damaged, someone here have already replaced some parts, at least two resistor which usually fail, you have to check r804, q803 , q804 and look for any short in that area, the pcb appear brand new, probably never seen one in this condition, this must be paired with samsung tube/yoke, if you want use this chassis with a toshiba tube you Must replace the heater resistor, from 2 ohm to 5 ohm, it is a big metal oxyde resistor near the hot.
 
Mukuro_W said:
Yes it Is the psu area usually damaged, someone here have already replaced some parts, at least two resistor which usually fail, you have to check r804, q803 , q804 and look for any short in that area, the pcb appear brand new, probably never seen one in this condition, this must be paired with samsung tube/yoke, if you want use this chassis with a toshiba tube you Must replace the heater resistor, from 2 ohm to 5 ohm, it is a big metal oxyde resistor near the hot.
Click to expand...

Thanks for the reply. This one is the spare i bought which doesn’t work either (damaged coil) and i have to change the oxyde resistor as you said.

The other one is packed because I was planning to send it for repair. But with your advise I will give it a try on both.

Any idea on how to repair/ replace the coil?
DD02CAC8-3802-4985-82FC-5DD339D5DC68.jpeg
 
I'd be interested to know as well, I have one with a bunch of coils that got knocked off and unwound. No clear way to source replacements other than from a donor that I am aware of.
 
If the coil is not open you can rewind the copper wire if the wire is broken you can repair by soldering but the position of the ferrite core can influence the h stage for ex ample on the h linearity, on those sanwa chassis , those coils are so fragile that they glued them on the heatsink.
If you know the spec the coil can be reproduced. It Is an odding balls job too.
 
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