Hi, 9VAC is used as TOD (Time Of Day / real time clock) reference for both CIA chips. There's no hardware jumper for setting the CIA chips for 50 or 60Hz operation, this is done through register settings. 7th bit of $DC0E (for CIA#1) and $DD0E (for CIA#2). On PAL machines the 7th bit of both registe...

Thanks for the feedback !

I think there's very limited info available on the net about these expansion boards.
As I heard there are multiple revisions (maybe 3?) are exists in very limited numbers,
and they might not interchangeable freely between the different C65 mainboard revisions.

Hi, The cassette ports are handled by different chips, that could explain the symptoms. The read line of cassette port#1 (marked as "J3" on the mainboard) is connected directly (without any level conversion) to the 6522 VIA IC, while the read line of cassette port#2 (marked as "J6&quo...

Hello, I've faced the similar problem a few months back. I've bought an RGBI (CGA) to RGB adapter from gglabs ( https://gglabs.us/node/2022 ), and created a SCART adapter cable to it, so it can be used with any TV set that have RGB capable SCART input. It works nice, but doesn't looks too fancy, sin...

At the time C64 was designed to be used with TVs or video monitors. There are two basic ways to connect the 64 to a TV: - Baseband A/V: this requires an adapter cable between the C64's video connector and the TV / video monitor in this case the TV should have RCA or SCART A/V input(s), the adapter c...

Hi, This can happen when the contacts of the power switch are welded together due to the overload, so the circuit remains complete towards the primary winding of the power transformer, despite the OFF position of the switch. I'd recommend to find the root cause first, because just replacing the fuse...

I've found an image at zimmers.net which describes the jumper/DIP switch configurations: http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/pet/2001N/320351-6.gif I guess this fits for your PET2001N motherboard. If so, then it seems only SH2 DIP bank settings are need to be changed in order...

Hi,

They're pin compatible, the TMM416D-4 has a bit slower access time: 250ns vs 200ns.
IMHO the spare ICs are suitable for the RAM upgrade.

Hello, I think they're still available, or at least the IC402 (TDA2595) which was also used in TVs as well. You can make sure by checking the exact IC types on the packages and google them. IC302 is mounted adjacent to a heatsink at the centerline of main PCB, near to the rear edge of the panel, bel...

Hello, It seems the problem is probably related to one or more of the following: - missing vertical sync pulse generation, or the pulses are not reaching the vertical driver stage - vertical driver stage - missing 26 Volt power supply of the vertical driver stage - vertical deflection coil on the CR...

Well, the picture shows only a normal startup screen
At least for me this is the only picture that appears in your post.

There might be a problem with the CRTC chip memory access.

Hello, The most probably cause is weak signal from the R/W head due to the following: - wrong azimuth setting of the R/W head - the air gap of the Read core is clogged (by microscopic tape fragments) - too large air gap in the Read core of the head (mechanical wear, resulting drop in the frequency r...

I guess the RAM expansion board captured by Robert is even rarer than the C65 itself

Does someone know how many of these expansion boards are still exist ?

You will get a "?syntax error" message on the screen.

If it's not already done, I'd recommend to check all power supply voltages on the mainboard (+5V, +12V, -5V). The 4116 RAM chips are extremely sensitive to the missing negative supply, it destroys the chip in no time. Dead filter capacitors can cause fluctuating or too low voltage, causing abnormal ...