TTI 6 pack dimmers

[JohnHartman]

As a number of you seem to have experience with these dimmers i figured I would ask as I try and patch a lighting rig back together.. stupid lightening strike.

I have TTI 6 pack dimmer MDS-5-132 that the last channel is stuck at full. Before I pull the module I thought I would ask if anyone has any suggestions as to why only that particular channel would be stuck.

Thanks.

 

[SteveB]

Fried SCR's will fail in a closed state. thus full on and no control.

Only option is pull the module and replace the 2 SCR's.

In the process of having the shop replace the SCR's have them do a routine check of the dimming functions to make sure nothing on the firing card got zapped.

 

[JD]

2nd on an SCR being popped. If I remember right, they are 35 amp 600piv stud mount. (Two, for a full-wave rating of 70 amps.) Only takes one to fail for the "full on" effect. Replace them both anyway. TTIs were a pretty hearty unit.

 

[avkid]

I have 4 in service and tons of parts including cards.

 

[STEVETERRY]

2nd on an SCR being popped. If I remember right, they are 35 amp 600piv stud mount. (Two, for a full-wave rating of 70 amps.) Only takes one to fail for the "full on" effect. Replace them both anyway. TTIs were a pretty hearty unit.

Use silicone heatsink grease and torque the studs to 35 inch/pounds.

The stock SCR's had a very low I-squared-T rating (about 900 amp squared seconds, if I remember right). This meant that even with the expensive KAW-A-35 silver sand fuses, they got zapped all too often by shorts and lamp burnouts.

You should be able to find a replacement SCR with a 600V PIV and 63A rating that will have an I-squared-T rating of about 2500 amp squared seconds. This will be much more immune to shorts and blown lamps. With such a rating, you could get rid of the fuses, as overcurrent protection is provided by the circuit breakers.

ST

 

[jhochb]

Good Morning John
It's been ages sence I've even seen a TTI, but i do recall on some packs if 1 of the 2 SCR's shorts you won't be able to dim it bellow 50%. it will dim UP from 50-full. I've seen this a couple of times.
You should still replace both SCR's

 

[JD]

Good Morning John
It's been ages sence I've even seen a TTI, but i do recall on some packs if 1 of the 2 SCR's shorts you won't be able to dim it bellow 50%. it will dim UP from 50-full. I've seen this a couple of times.
You should still replace both SCR's

There are actually three failure modes:
Short = Full on
Open = dims from 0 to 50%
Diode = dims from 50% to 100% (kind of rare)
In the third failure mode, the gating junction goes bad and the SCR turns into a diode!

 

[northcoastlts]

Greetings!
I have a TTI MDS Model E 6-channel pack that has become surplus. If anyone needs parts, let me know. I think most of it works, although some channels have problems. You can email me at [email protected]. No charge for parts; I would like to be reimbursed for shipping costs.
Dave