DarrenF
Well-known member
Modifying "old" 4600 chassis to support horiz. centering
So, I found Ken's details about the variations of the interface cards online: http://www.ionpool.net/arcade/tech/19K4600_pinout.txt
This explains that the P317 (which I have) includes the "highly desirable" horiz centering pot. However, I was a little disappointed when I discovered that my pot didn't effect the image at all.
It turns out that the P317, while presumably "compatible" with every version of 4600 main PCB, isn't "supported" by every 4600 main board--including mine. I dug up every 4600 schematic I could find (which turned out to be only 4 different versions). Two of them show "older" interface cards (P313, in the K4616A/4666A schems, and P305 in the K4606 schems), and two others show the P317 (4625/4626/4675 and 4625A/4626A/4675A).
On the "newer" main boards (which aren't identified differently, that I can tell), pins 1 & 2 of P202 are connected to each end of R635; of the "older" main board (including mine) those two pins are only connected up into an unpopulated area of the PCB. Also different: R635's value changed from 12K to 6.8K, and an add'l 6.8K resistor (R652) is added between R635 and P607.
So, I decided to modify my main board to support the P317 adjustment pot. I jumpered from P201 pin 1 to P502 pin 7; and from P201 pin 2 to the opposite side of R635. I swapped in a 6.8K 1/2W for R635. Finally I replaced jumper J19 with another 6.8K 1/2W resistor.
Works like a charm. Can now adjust horizontal position. Thought I'd share in case anyone else with an "old" 4600 main board ever had a P317 interface board in it and couldn't figure out why the adjustment didn't do anything (I know, slim chance...)
So, I found Ken's details about the variations of the interface cards online: http://www.ionpool.net/arcade/tech/19K4600_pinout.txt
This explains that the P317 (which I have) includes the "highly desirable" horiz centering pot. However, I was a little disappointed when I discovered that my pot didn't effect the image at all.
It turns out that the P317, while presumably "compatible" with every version of 4600 main PCB, isn't "supported" by every 4600 main board--including mine. I dug up every 4600 schematic I could find (which turned out to be only 4 different versions). Two of them show "older" interface cards (P313, in the K4616A/4666A schems, and P305 in the K4606 schems), and two others show the P317 (4625/4626/4675 and 4625A/4626A/4675A).
On the "newer" main boards (which aren't identified differently, that I can tell), pins 1 & 2 of P202 are connected to each end of R635; of the "older" main board (including mine) those two pins are only connected up into an unpopulated area of the PCB. Also different: R635's value changed from 12K to 6.8K, and an add'l 6.8K resistor (R652) is added between R635 and P607.
So, I decided to modify my main board to support the P317 adjustment pot. I jumpered from P201 pin 1 to P502 pin 7; and from P201 pin 2 to the opposite side of R635. I swapped in a 6.8K 1/2W for R635. Finally I replaced jumper J19 with another 6.8K 1/2W resistor.
Works like a charm. Can now adjust horizontal position. Thought I'd share in case anyone else with an "old" 4600 main board ever had a P317 interface board in it and couldn't figure out why the adjustment didn't do anything (I know, slim chance...)