TAC 20 ISSUE

Ok, here's the scenario. Turn power on, starter lights up after everything boots and immediately goes dead. MCC1 relay not pulling in (should pull in after CPU boots up and energizes it if it doesn't see any faults). Without MCC1 contacts made we get no control power to the starter. Ok, this all makes sense, we have a fault somewhere. Here's where it gets tricky. Shut power off, remove DLT (top terminal limit) relay, turn power back on, after CPU boots up, starter turns on nd MCC1 pulls in and we have control power. We have checked selector, it has power, it has a green flashing watchdog, and there is no red fault LED lit. On normal with power on, both DLB and DLT relays are made and contacts are good when away from respective terminal limit magnets. What are we missing?

Let me clarify that last sentence. When I say both DLB and DLT relays are made and contacts are good, that is before we kill power and remove DLT relay.

Is this a Siemens soft start? If it is I have seen the run input short on and cause this. I ended up adding a timer in the MUT contact circuit until the soft starter was replaced.

Ok, this gets even weirder. Put all relays in where they belong. Power on. Reset CPU board. Pull the MUTS relay out and we get control power on the starter. Put a call in and pump motor runs but naturally Motor Up To Speed (MUTS) can't pull in giving the CPU the MCE input allowing up valve coils to pull in and allow movement. I am now leaning towards a bad CPU 188E board as thing does really goofy Crap when you pull relays out that the CPU takes to ground.

Power supply issue? Check for ac ripple on it

You are sure the run input is not shorted on the Siemens side? This sounds almost exactly what I ran into.

The controller is going to do some goofy things when you pull relays out and try to run it. And ya, the up to speed contact on the starter is almost definitely shorted. Power to it goes through a DLT contact, up to speed picks MUTS which makes MCE go high when the car is not trying to run so it faults and drops the starter. Doesn’t fault when you pull MUTS because MCE stays low but won’t run because MCE doesn’t go high. Verify by reading resistance from 5 to 6 on the starter. You can either replace the starter logic board or open it up and break off the little surface mount capacitor under the SSR that shorts. It doesn’t need to be there.

Yes Up to speed. I forgot which one it was that had the short when I ran into this

If you still have the blue shrader relays, I'd replace them. Replace the MUTS relay also. What are the errors on IMS?

The blue relays are Finder, new brown ones are Schrader. I actually suggest that if you have the blue finder relay sockets that you keep the finder relays. The new relay pins are way smaller and I have had problems where they just won’t make a good connection in those bases. If you have blue relays in black bases, by all means, replace them with the new ones but I would save the good blue ones for when you need to replace a blue relay in a blue base. There was a time when Thyssen told everyone to replace the blue relays but I think there was just a bad lot or something. Also compare the contact size on the 2, watch how fast you smoke the new relay contacts on controllers with Maxton valves! And if you see any blue relays that say 5000 on them, they have gold plated contacts.

Please, can someone tell me what is the software able to open and edit the carEprom.dat in a tac20?
I'll appreciate it a lot.

Can confirm on the shorted/bad starter contacts. Back when I was just starting to learn TAC20's, this exact thing gave me fits. Using I/O injection I was able to force the starter to stay powered up while testing, and I could make it run, so I thought it was good. I felt pretty dumb afterwards, when it ended up being a bad contact on the internal relay in the starter. Lol. Since then I've ran into the same issue 3-4 times. I'm a fan of the Siemens starters overall, this is just something to watch for.