diff --git a/pymlac/MainCPU.py b/pymlac/MainCPU.py
index ec698eb..327fb96 100644
--- a/pymlac/MainCPU.py
+++ b/pymlac/MainCPU.py
@@ -175,6 +175,8 @@ class MainCPU(object):
     def execute_one_instruction(self):
         """Execute one MAIN instruction, return # cycles and a trace string."""
 
+        log('execute_one_instruction: self.running=%s, .PC=%06o'
+            % (str(self.running), self.PC))
         if not self.running:
             return (0, None)
 
@@ -189,6 +191,7 @@ class MainCPU(object):
         indirect = bool(instruction & 0100000)
         address = (instruction & 03777)
 
+        log('execute_one_instruction: running instruction')
         return self.main_decode.get(opcode, self.illegal)(indirect,
                                                           address,
                                                           instruction)
@@ -224,6 +227,7 @@ class MainCPU(object):
         return (1, tracestr)
 
     def i_JMP(self, indirect, address, instruction):
+        log('JMP handler')
         eff_address = self.memory.eff_address(address, indirect)
         self.PC = eff_address & PCMASK
         tracestr = trace.itrace(self.dot, 'JMP', indirect, address)
diff --git a/pymlac/dumpmem.test b/pymlac/dumpmem.test
index 57d26f8..dbc569e 100644
--- a/pymlac/dumpmem.test
+++ b/pymlac/dumpmem.test
@@ -1,3 +1,3 @@
-# loads executable tape and dumps 0100+4
-bootrom ptr; mount ptr dumpmem_test_c8lds.ptp; setreg pc 040; rununtil 0; dumpmem dumpmem_test.dump 0100,0110
-#bootrom tty; mount ttyin dumpmem_test_c8lds.ptp; setreg pc 040; rununtil 0; dumpmem dumpmem_test.dump 0100,0110
+# loads executable tape and dumps 0100->0107
+bootrom ptr; mount ptr dumpmem_test_c8lds.ptp; setreg pc 040; rununtil 0; checkreg ac 0177777; checkreg pc 03715; dumpmem dumpmem_test.dump 0100,0107; setreg pc 0100; rununtil 0; checkreg ac 0111; checkreg pc 0106
+#bootrom tty; mount ttyin dumpmem_test_c8lds.ptp; setreg pc 040; rununtil 0; dumpmem dumpmem_test.dump 0100,0107
diff --git a/pymlac/test_CPU.py b/pymlac/test_CPU.py
index aabf858..38738d5 100755
--- a/pymlac/test_CPU.py
+++ b/pymlac/test_CPU.py
@@ -315,13 +315,16 @@ class TestCPU(object):
         We also stop if the CPU executes the HLT instruction.
         """
 
-        log('rununtil: address=%s' % address)
         new_address = self.str2int(address)
         if new_address is None:
+            log('ABORT! rununtil: invalid stop address: %s' % address)
             return 'rununtil: invalid stop address: %s' % address
 
-        self.used_cycles= 0
+        log('rununtil: address=%s, self.cpu.running=%s' % (address, str(self.cpu.running)))
+        self.used_cycles = 0
+        self.cpu.running = True
         while self.cpu.running:
+            log('rununtil: loop top')
             (cycles, tracestr) = self.cpu.execute_one_instruction()
             if tracestr:
                 endstr = trace.itraceend(False)
@@ -332,6 +335,7 @@ class TestCPU(object):
             self.used_cycles += cycles
             if self.cpu.PC == new_address:
                 break
+            log('rununtil: bottom top, PC=%06o' % self.cpu.PC)
 
     def checkcycles(self, cycles, ignore):
         """Check that opcode cycles used is correct.