FedExin said:
Hi Ken,
I believe I tested correctly on the transformer, but I got some weird voltages. I couldn't find a schematic online of the lugs on the transformer. I had my meter set to Volts AC (VAC) and had my black ground lead on a ground strip in the cab. I then probed the molex connection from the transformer to the PS board. The reads were so far off from what should be coming from the transformer it seems.
I don't know which end was Pin 1 but I went from left to right starting with the Orange lead:
Orange: 4.68 VAC
Purple: 4.54 VAC
Grey/White: 14.11
Grey/Yellow: 14.40
Green: 17.80
Grey: 10.79
Black:10.79
The other readings I'm much more sure of:
MPU board power input pins:
1 = GND
2 = GND
3 = GND
4 = key
5 = +12VDC Regulated (Actual 11.91)
6 = n/c
7 = +5VDC Regulated (Actual 5.03)
8 = +12VDC Unregulated (Actual 13.64)
9 = -5VDV Regulated (Actual -4.95)
At the Power supply output pins:
1 = -5VDC Regulated (Actual -4.94)
2 = key
3 = +12VDC Regulated (Actual 11.92)
4 = -12VDC Unregulated (Actual -14.72)
5 = +12VDC Unregulated (Actual 14.37)
6 = +12VDC Unregulated (Actual 14.37)
7 = GND
8 = GND
9 = GND
10 = GND
11 = GND
12 = +5VDC Regulated (Actual 5.03)
13 = +5VDC Regulated (Actual 5.03)
14 = +5VDC Regulated (Actual 5.03)
15 = +5VDC Regulated (Actual 5.03)
Something is amiss, and I don't think it's my questionable testing of the transformer. Some voltages seem ok, but some seem waaaay off. Do I need a new transformer?
Thanks!
- Pete
The transformer voltages are probably good. If they weren't you wouldn't be getting the correct DC voltages at the PS board and the MPU board.
When measuring AC voltages, you need to measure between the source and the sink. Unless one side is tied to ground (which they are not in the case of the Williams transformers) measuring between an AC source and ground will yield meaningless results. You actually need to measure the AC voltage between the pairs of lugs in the original message:
Lug 15 -> Lug 16 = 11.3 VAC (pin 3 to 5 on PS Input)
Lug 16 -> Lug 17 = 11.3 VAC (pin 5 to pin 1)
Lug 11 -> lug 12 = 20VAC (pin 8 to pin 9)
Lug 13 -> Lug 14 = 11.5 VAC (pin 11 to pin 12)
Since it is hard to read the numbers on the transformer, that is why I also included the pins on the power supply board.
So you would measure between pin 3 and pin 5 on the power supply input and between pin 5 and pin 1 for 11.3 VAC input. And so on for the rest of the voltages.
The regulated voltages are reasonably close to what is required to run the game. If the voltages at the ROM board are still low, then it is likely that one of the following things may need to tested/corrected:
1) the input pins on the ROM power header may need to be reflowed. There may be some cracks in the solder that are limiting the current flow which will drop the apparent voltage.
2) there may be some corrosion on pins or on the connector pins that are causing a slight resistance in the connection that will drop the voltage.
3) there may be a bad connection at either end of the power connectors. If they are the original wiring harness connectors, the wires can work their way loose from the IDC connectors and this can cause a drop in the voltages.
4) There may be a break in the wires leading to the ROM card. You need to check the continuity of the wires to check this possibility.
ken
This was from a set of PMs regarding this topic, but I thought it would be general interest if anybody was having the same issues.