8-bit Logic probe

Hi all,

Earlier this summer I found a logic probe on the Jameco website
www.jameco.com

They didnt even mention how the probe is powered usually by batteries so I
assumed that would be the case.

I finally got the probe and found it doesnt use a battery it seems you have
to draw the power from some other source.
Yep I found a diagram on the box :) heh heh

Well its a K & H products LP-3500 Logic Probe
it has 2 clips for the power supply lead which is 550 mm long
it has an extra IC clip lead and extra ground lead.
Of course the power lead is directly wired into the probe.
even has its own deluxe molded carrying case. :)
ewww made it TAIWAN  :-P
Okay heres more info:
Freq Range: DC to 17 mhz
minimum detectable INPUT pulse width 30 nano seconds
HIGH INPUT Impedance 1M OHMS
Wide power range 4.5 to 20 VDC
Protected up to +220V DC/AC 15 sec
Pulse flash time 500 ms

Okay there is the C64/C128 Commdore service manual does that actually show
the Low/High states of Logic chips and MOS chips hopefully to see if the
chip is good or smoked?

Still the problem that bugs me is and this is a silly question but here goes
maybe this is crazy but I dont know anything about logic probes, could I
power this somehow from the MB itself or use some other more reliable power.
The box does mention 4.5 VDC so that was my question could the probe stand
5VDC so yeah, but from what source.
I was told to draw from the C64mb power would be crazy, why?
So maybe using a PC power source and using +5VDC would be good enough?

So now I just need to look thru maybe the C128 service manual to see what
logic and MOS chips they show the pinouts and the high/low states that each
chip uses am I correct?  If one gate isnt like using a low state then that
is suspect or maybe even more that dont read like it should (high or low).

Oh yeah I do remember the Led lights have something to do with the high or
low states am I correct?

The other problem is I dont have an Oscilliscope mainly for checking for the
correct signal on the processor chips, yeah I know theres the 8502 and the
Z80 on the c128 so Im stuck with using a logic probe and a Voltage meter,
but if reading a chip with a voltage meter should that be set at OHMS to
read resistance?

BTW this 128 is DOA no power, black display.
I replaced the filter caps and the power regulator(off to the right of the
MMU).
I didnt get the needed voltages on the regulator so I replaced it too.
BUT the full wave bridge rectifier I couldnt get any voltages on it, so I
replaced that with great difficulty, the little sucker has very tight thru
holes, and right close to where one trace connects to the rectifier I
pulled that trace, so I found where that leads to and I just jumpered a
wire (from rectifier to the other end). Then I did get
the 5VDC and 9VAC (is that 9VAC right) ?
But after all of this still the 128 wont power up, dead.
but I did find one of the shorts. I set my meter to OHMS to read
resistance, from the power regulator and then I grounded to the Cartridge
port metal shield, and the meter buzzed, indicating a short. this turned
out to be one of the smallest filter caps was shorted out.  So then that
indicates that powering up the computer must have fried this little cap.  I
believe this is the smaller cap that is below the regulator. (The smallest
filter cap).  So then what circuit would fry this cap?

I also tested a few chips and then ran out of time so I didnt test but 2
chips.

Tested: 40 column Vic Display chip
I have a 128DCR Metal case U.S.A. model doesnt have carrying handle.
I popped out the original VIC Video chip and popped in the vic I needed to
test.
The results:  Black, snowy display (with suspected vic chip).
looking on Ray Carlesons website this is a faulty bad chip.

This Flat NTSC 128 uses the 6581 Sid
So I opened up a working breadbin 64 popped the Sid in powered the 64 up I
just loaded up some one CGSC Sid music tried playing a tune, but no sound.
I loaded a game and tried a joystick, that didnt work at all.
So the Sid is blown up too. :(

I really have no way of testing the DRAM but suspect that, so I already
replaced all of the DRAM chips, but pulled up 3 dang traces. I held up the
MB to a window and could see the patch of where the traces pulled up, so I
know I can use wires to jumper where the traces pulled up by soldering the
jumper wires to the solder side of the MB, on whatever RAM chip the trace
leads to.

  I cant recall the name but there is a new source for C64/C128 diagnostic
cartriges and harnesses.  So once I get this thing powering up again I can
test it more.  I have 2 of the older C128 diagnostic cartriges, were those
just different ROMS?  Which one was better?  The older diag carts will even
work with this new harness.  BTW this seller announced this on the google
groups comp.sys.cbm
forum.

I forgot to mention that I think this damage was most definitely from a
cranky power source. Beings I found 2 bad chips could all of the chips be
faulty if
the power source put out too much voltage?
Yeah I know of brown outs are harmful too, which is lower power that
computers dont like.

Terry Raymond