I just finished replacing all of the original Scanbe sockets with new DIPs. Little time consuming but was quite pleased with the results. I was hoping this was going to solve the problem of having both LEDs remain on constantly after start up, no blinking, but did not. I have the driver board removed and get the same result. Is there anything else that I can try? Most documents I read say I need to proceed with a test ROM or EPROM now. If so is there a good resource for these?

Thanks for the help.

You can get a test ROM from Steph http://hobbyroms.com

Once you have that it should be straightforward to debug the board on the bench with a logic probe. I used the methods from Leon's site to do the same for Williams Flash (System 4) http://pinballeon.com/williams/ewilliams.htm

Thanks very much.

Ships out of Ottawa. Decent prices. Looks good.

Quoted from Buchy

Ships out of Ottawa. Decent prices. Looks good.

Really nice guy too  ...  

...and usually gives "preferential pricing" to MAACA members.


PM me, uh..., him    

Steph

Pm'ed him... I mean you...

From my readings at both Leon's and pinrepair.com and testing done with the Leon's test IC (thanks Steph!!) I believe I have a bad PIA @ IC18; the other large 40pin IC. I have both LEDs locked on and I notice a bunch of pins on this device stuck high or low. I also have the test LED blinking when connected to pin15 of IC1 (CPU). Everywhere tells me this means a bad chip at IC18.

Does anyone have a source for these?

Thanks.

Steven

Try Dave Astill (member name astillentertainment)

Will do, thanks.

Quoted from tinyrodent

Try Dave Astill (member name astillentertainment)

Found from Dave.

Thanks again for your help here.

The chips were received from Dave (thanks again!), however changing out the suspect PIA chip did not fix the problem.

I am seeing the expected pulsing on the CPU chip on the address and data pins. I have the test LED blinking when connected to pin 15 of IC1 (CPU) which indicates that the Leon's tests program is running. I have checked the buffers/chip selection ICs and all seems to be good.

PA0-PA7 and PB0-PB7 of the PIA are all suppose to be oscillating between low and high since the test program is running. But, all of these pins remain HIGH and not alternating between states. Does anyone have any idea what is going on?

Thanks.


Steven

You should be seeing pins 22 and 24 high, pin 23 low to correctly select the device. Meanwhile there should be activity on the address and data pins. Do you have a logic probe? Did you replace and/or test the PIA socket?

This datasheet explains the operation of the PIA:

http://www.pinballpcb.com/datasheets/Mot6821.pdf

Thanks. I am using an old 60MHz oscilloscope. All sockets were recently replaced and checked to ensure no shorts between pins.

I noticed that the R/W pin of the CPU remains HIGH as the code dictates. When it goes through the buffer (IC8 ) though it is no longer constantly HIGH but oscillates at a high frequency between HIGH and LOW (~50-60% high). I removed this chip, put a socket on and tried a new 74LS367. This gives me the exact same result, so to me it must be something after this chip that is pulling the R/W signal low intermittently.

With a DMM I measure 4.1V at pin 2 of IC8 and ~2.5V at pin 3 of this chip. All the others input and output pairs are much closer than this.

Anyways any other suggestions always appreciated.

I'll take a closer look at the PIA and its datasheet.

Thanks.


Steven

edit: for the R/W issue, the only component I can see that might be causing this is IC11 the NAND gate. I removed the PIA and still have the same issue. Both 6810's and the 5101 are removed. The only other place this signal goes besides IC11 is the 40-pin header. Looks like I will try socketing this component as well.

It's at this point that I would be contacting Rottendog.

I don't know if you have looked at this but it's probably the best site for what your trying to troubleshoot and he works with Leon's chip. The recommended test is to use an led vice logic probe or oscilloscope as you will get false indications with noise on the line.

http://pinball.flippers.info/system6resources.asp

From the sounds of it your CPU is running which rules out the CPU and crystal as being the problem. PIA's should flip flop with the chip with the exception of a couple gates (see reference).

First ensure your getting clean power. The original power supply can be rebuilt to provide satisfactory power or you can go Rottendog route.

Beyond the PIA's there are IC's on the data and address busses that can also give you trouble. Again following the advanced testing techniques on the posted site will get you working through the problems systematically.

Thanks. I've been going through Mark's site. It was suggested from Leon's site as a more English friendly version hehe so I've been following that along with pinrepair.com.

I'm also running on a benchtop power supply as it is pulled from the machine, so I'm sure I have a clean source of power.

I am currently at this section:
3.4.8  The R/W line
The "R/W" line is the Read/Write line.  This the signal that the CPU generates to tell the chip it has selected whether is wants to read or write data from the chip.  This line is high for a read and low for a write.  When the test chip is running (or attempting to run), this line should be high.  It passes through the data buffer chip IC8 (pins 2 to 3).

The signal should be identical on either side of the buffer (pins 2 & 3) or constantly high. It is high on the input side but fluctuates between high and low on the output side. Chip/socket as been replaced so I am trying to figure out what else could cause this signal to be pulled low on the output side of the device. The only chip still in that receives this signal is IC11. Looks like I will replace this and then move from here.

Thanks again for the time/help.


Steven

Rottendog is an option... but I'm not quite there yet!

Replacing IC11 was no help, except it did bring something to my attention. When I was checking for continuity between pins I noticed 1.2 ohms between pins 1 and 2 ( BUS02 and R/W respectively). I double and triple checked the socket and it does not seem to be occurring here. I followed the traces and noticed they ran side by side through the 6810 RAMs and thought maybe during the socket replacement something happened here, but again double and triple checking I came up with nothing.

After completely looking through the schematic I see no reason to have such a low resistance between these 2 lines. I am hoping whatever I turn up here will be what is causing the R/W line to go low intermittently after the buffer.


Steven.

What TTL IC is data buffer IC8? I would check the logic on it. Leon's chip puts the output high on the CPU but the oscillation may be a function of the data buffer.

Pin assignment for the 6800/6808 has R/W on pin 34.

You've done the basics i.e. separated the MPU from the driver board and are testing it independently right? 40 Pin interconnect is notorious for creating issues on these systems.

Thanks again for your help.

I am using a 74LS367 as the replacement of IC8. I removed the chip and tried it only on a breadboard and I do not observe the oscillation I was noticing on board. It is very severe, down to about 60% duty cycle from 100%.

And yes, I have done all the basics, removed from driver board, replaced ALL scanbe sockets, reset (unreg 12V) modification as well as the crystal upgrade.

To me, I just see no reason for the low impedance between the R/W and BUS02 lines, and it is too much of a coincidence that the one pin on the buffer that I am having problems with is also the suspect low impedance pin (R/W). I'll gather up some more energy and get back at it tomorrow.

Cheers.


Steven