D9400 not powering up, high frequency chirp

SheepyChris

Member
Joined
Sep 12, 2023
Messages
71
Reaction score
57
Location
Ontario, Canada
Hey y'all,

I've recently been dealing with a non-working Wells Gardner D9400 that came in a Need for Speed Underground, upon first inspection IC301 (vertical) was blown into pieces and IC502 (optocoupler) had lots of green corrosion built upon it. Both were replaced alongside nearly all capacitors (filters, 2200uf 250v and some BPs were kept as I did not have replacements on hand) but the same behavior described in the thread's title continues to happen.

HOT tested fine but done so still in circuit (unclear to me if removal is preferred or not with this chassis), yoke tested 5.0 ohm vertical and 0.1 ohm horizontal which concerns me a tad bit knowing I've read values of 0.6 ohm elsewhere instead. I do plan to further test components in the power supply area as the relay in the degauss circuit doesn't get to click during the start up attempts either.

Has anyone faced a similar issue to this and/or have any suggestions on how to proceed? Thanks!
 

Attachments

  • 20250609_123919.jpg
    20250609_123919.jpg
    413 KB · Views: 5
  • 20250610_200005.jpg
    20250610_200005.jpg
    683.9 KB · Views: 5
  • 20250610_200012.jpg
    20250610_200012.jpg
    456.6 KB · Views: 5
  • 20250610_200022.jpg
    20250610_200022.jpg
    507.5 KB · Views: 5
It sounds like it is going into over-voltage shutdown. The first thing to check is capacitor C513 in the sense winding feedback loop.

Note: It is recommended practice to replace all the electrolytic capacitors. APAR makes it easy with this kit.

Screenshot 2025-06-10 at 10.12.25 PM.png
 
Last edited:
It sounds like it is going into over-voltage shutdown. The first thing to check is capacitor C513 in the sense winding feedback loop.
C513 has already been replaced, D506 and R506 leading to it are also within specs.

Is a service manual known to exist for this chassis? Would a bad yoke also trigger an over-voltage shutdown?
 
It sounds like you have already given it a thorough evaluation. Perhaps one more look at components in the shutdown circuit - between the transformer secondary and the Optoisolator (IC502)?

I can't say for certain with regard to the low yoke resistance triggering a shutdown, but it seems plausible. To isolate the H yoke winding from the circuit, lifting a leg of R260 should remove the SMPS output from the H coil. If the SMPS stays up at that point, then the H yoke winding is most likely at fault.

Had no luck either finding an online version of the service manual. Hopefully, someone here has access to a copy.


1749661359624.png

1749661447769.png
 
Back
Top Bottom