MEP-003a high voltage once again.

[twitchit]

Before shutting me out and locking my thread, Please consider this.... I have searched and refrained from asking this until I have read everything I could find in a reasonable amount of time. Its not like I have not tried to research this. I could just simply use a little help from this very knowledgeable community.

Once again, I fired up my mep-003a and was getting about 156vac from it. I posted this in a previous thread and got one response before it was shut down. The advise I got was to replace the 2n3584 transistor (a common culprit) which I did to no avail. I searched mep-003 high voltage , but did not find much about it. I searched several key words which I thought would lead me to an answer or even a direction. I also googled it. Any advice would be greatly appreciated.

 

[Speddmon]

If the voltage is high, and you cannot adjust it with the adjustment knob on the control panel..typically the culprit is the output transistor. There is still the possibility that the transistor is bad. Just because it's new doesn't mean it was any good. It's also possible that you could have gotten it too hot when you installed it.

Another thing to check is to make sure that your CT/CVT assembly is in good working order. There is a testing procedure in the TM with a bunch of resistance readings you should be looking for on the CT/CVT.

 

[Speddmon]

And so you know, your other thread on this exact subject was not closed. You could have continued the previous thread rather than starting a new one for the exact same thing. It's reasons like this why it's so hard to find anything useful with our search function.

 

[twitchit]

Ok thank you. I saw something about reading the resistance on the cvt. in the tm. I will try that while I wait for another transistor from mouser. I will probably order a few this time. I also saw a tip, maybe from you, to someone else about using something under the transistor as a heat sink. I was real quick with the power probe but maybe I did over heat it. I do believe my problem is in the vr somewhere though. I switched control cubicles with my 002 and everything worked 4.0. Could one of the 2 smaller transistors be the culprit? Just trying to get a shopping list together for my next order. Thanks.

 

[Speddmon]

If you switched control boxes and everything worked, then there is no need to check the CV/CVT. It would have been fine. I highly doubt that it's one of the other trasistors, they don't control the output of the vr. I've been doing this kind of work for 20 years, and you would be amazed at the percentage of bad NEW parts right out of the box. As I said before, just because it's new doesn't mean it's any good.

 

[twitchit]

Ok, I swapped the 2 vrs. The one from my 002 into the 003 and vice versa. I still get the same problem from my 003 with the 002s vr in it. so, I tested the suspect vr from the 003 in my 002 and it works 4.0. Something else in the cubicle is causing the high voltage. When I swapped cubicles earlier with the 002 it worked fine. then I swapped them back a few days ago. What else in the control cubicle could cause this? I suspect t1 or t2. I will do a resistance check tomorrow. Are there any usual suspects now that I have eliminated the vr?

 

[twitchit]

Ok, I have isolated the problem to be inside the control cubicle. I have tested the components as far as I can. By swapping parts I have determined that the vr, T1, T2, R1 rheo, and the freq transducer are good. the problem is defiantly in the cubicle. I swapped the cubicle and all these parts with a known good one.I am leaning toward the wiring in the control cubicle itself. any suggestions of where to start ringing out the wires? maybe any other possibilities to look at?

 

[twitchit]

Well I found out I had a corroded connector in the wiring at T1 terminal 2 that goes to tb4-4 and then to the voltage regulator. It was corroded between the wire and the connector itself. That was a bear to find. I swapped every component in the cubicle before resolving that it was in the wiring.

 

[Speddmon]

Congratulations. Excellent job on finding the problem. Job well done!