I have to call uncle on an issue I am having with a PL400 II. I started with a perfectly working amp (after I recapped, installed new filter caps, rectifier, op amps and large resistors) and decided to install a WA speaker protect. While messing around and before the install, I stupidly crossed two output wires. (Don't ask, it was stupid). Before going on, I put the unit back on the DBT and yup, it remained brightly lit. First I pulled one row of transistors at a time, hoping to find a bad transistor. I did find one, however, the DBT remained lit. After removing all the transistors, It remained lit.
Next, I checked every transistor, resistor, op amp and cap on the board. (I had already recapped the board, installed new resistors and opamps prior to my screwup and everything had worked fine). Still the DBT remained bright. The filter caps and rectifier were brand new as well. I tested them anyway, no issues. I discovered if I removed the wires from one of the filter caps, the DBT would work properly. I then disconnected the board from the back plane, and the dbt still remained lit. Disconnecting the filter caps, I tested the leads on the rectifier. 79 V dc came out of each rectifier lead, 122V AC was showing on the input leads to the rectifier. I disconnected the output wires and still I was stuck with a bright DBT. Finally decided to bring it up on the variac without the dbt. All three fuses blew.
I crawled all over the back plane with a magnifying grass and found nothing amiss. I also disconnected the light boards. still bright DBT.
So My thinking is that something is wrong with the transformer. although I'm a bit puzzled as to why I get a reading of 79V on the leads, and if I disconnect one of the filter capacitors, the DBT goes out and the remaining filter cap charges properly.
Hive mind thoughts PLEASE...
Next, I checked every transistor, resistor, op amp and cap on the board. (I had already recapped the board, installed new resistors and opamps prior to my screwup and everything had worked fine). Still the DBT remained bright. The filter caps and rectifier were brand new as well. I tested them anyway, no issues. I discovered if I removed the wires from one of the filter caps, the DBT would work properly. I then disconnected the board from the back plane, and the dbt still remained lit. Disconnecting the filter caps, I tested the leads on the rectifier. 79 V dc came out of each rectifier lead, 122V AC was showing on the input leads to the rectifier. I disconnected the output wires and still I was stuck with a bright DBT. Finally decided to bring it up on the variac without the dbt. All three fuses blew.
I crawled all over the back plane with a magnifying grass and found nothing amiss. I also disconnected the light boards. still bright DBT.
So My thinking is that something is wrong with the transformer. although I'm a bit puzzled as to why I get a reading of 79V on the leads, and if I disconnect one of the filter capacitors, the DBT goes out and the remaining filter cap charges properly.
Hive mind thoughts PLEASE...