2330b holding dim bulb and not engaging relay. spark across amp input terminals has left it in this state

[james may]

after we had the unit operating in dim bulb status, an open rca draped across the input terminals to the amp and while on 100w db, it arced across the terminals, the unit is in draw status and relay disengaged. the amp board was then removed, every component verified, the outputs verified with transistor testor, diode on meter and resistance method, as well as brand new mj's tossed in over the previous. any idea what direction to look for the constant draw the unit is doing, amp block out nothing is lighting the bulb up.

 

[dankik]

...while on 100w db, it arced across the terminals

You need to be a little more specific.

• What input terminals got shorted, the AC input to the amp or a low level audio input?
• Where did the cable get shorted to?
• What was the RCA cable connected to?

 

[james may]

You need to be a little more specific.

• What input terminals got shorted, the AC input to the amp or a low level audio input?
• Where did the cable get shorted to?
• What was the RCA cable connected to?

to the amp in yes, not preamp side. and the rca was not connected to anything. amp was connected to speakers when the arc happened as the rca was going into the amp port, the other was loose and poped the other

 

[dankik]

You seem to contradict yourself here:

1. ...and the rca was not connected to anything
2. ...when the arc happened as the rca was going into the amp port

So, the RCA cable was not connected to anything on one end AND the other end was connected to the MAIN IN jacks (what you are calling "amp port") of the amplifier.
You are saying that the open end of the RCA cable (with the other end into the MAIN IN) had arced onto what specific "terminals" of the receiver?
This is important to determine what could have been damaged. The RCA cable touched the AC line input somehow?

 

[james may]

You seem to contradict yourself here:

1. ...and the rca was not connected to anything
2. ...when the arc happened as the rca was going into the amp port

So, the RCA cable was not connected to anything on one end AND the other end was connected to the MAIN IN jacks (what you are calling "amp port") of the amplifier.
You are saying that the open end of the RCA cable (with the other end into the MAIN IN) had arced onto what specific "terminals" of the receiver?
This is important to determine what could have been damaged. The RCA cable touched the AC line input somehow?

I would check the rectifiers in the power supply

voltage was confirmed 65v from both rectifyers

 

[james may]

You seem to contradict yourself here:

1. ...and the rca was not connected to anything
2. ...when the arc happened as the rca was going into the amp port

So, the RCA cable was not connected to anything on one end AND the other end was connected to the MAIN IN jacks (what you are calling "amp port") of the amplifier.
You are saying that the open end of the RCA cable (with the other end into the MAIN IN) had arced onto what specific "terminals" of the receiver?
This is important to determine what could have been damaged. The RCA cable touched the AC line input somehow?

2330b, and yes, the ac in, or amp in side. i also had speakers engaged, without thinking i tried to connect the preamp back to the amp w/o shutting the amp off. i should know better, but here i am

 

[dankik]

Let me try to summarize what you said & measured, so we are all on the same page.
Sorry if I ask too many question, but to figure out what happened we need to be specific about what actually happened.
Use component reference numbers whenever possible when you describe what you measured. It will save time in troubleshooting.
My first question is: "Can you read a schematic?"

1. You said the RCA cable touched the AC input to the receiver. Let's assume it was the shield of the cable shorted first.
2. The 3 colored arrows (red, purple, turquoise) show points where it could have shorted. Lucky you had it on the DBT.
3. If the AC neutral was shorted to chassis ground, nothing should happen.
4. If the AC line was shorted to chassis ground, the bulb should go to full brightness.
5. If the short was the green arrow, it should have blown the fuse F001.
6. In response to @AE Bob, you measured the rectifier outputs (shaded in red) at 65VDC. I assume you measured the output of Q009 & Q010.

There are three other rectifiers in the power circuit and you did not say that you measured the voltages.

1. Q816 & Q817 (shaded in red). You can measure the DCV at C801 and C802.
2. Q818. You can measure the voltage at C817.
3. Also, check the transistor ECB voltages of Q810, Q811, Q812 of the protection circuit.

 

[james may]

Let me try to summarize what you said & measured, so we are all on the same page.
Sorry if I ask too many question, but to figure out what happened we need to be specific about what actually happened.
Use component reference numbers whenever possible when you describe what you measured. It will save time in troubleshooting.
My first question is: "Can you read a schematic?"

1. You said the RCA cable touched the AC input to the receiver. Let's assume it was the shield of the cable shorted first.
2. The 3 colored arrows (red, purple, turquoise) show points where it could have shorted. Lucky you had it on the DBT.
3. If the AC neutral was shorted to chassis ground, nothing should happen.
4. If the AC line was shorted to chassis ground, the bulb should go to full brightness.
5. If the short was the green arrow, it should have blown the fuse F001.
6. In response to @AE Bob, you measured the rectifier outputs (shaded in red) at 65VDC. I assume you measured the output of Q009 & Q010.

View attachment 3691983
There are three other rectifiers in the power circuit and you did not say that you measured the voltages.

1. Q816 & Q817 (shaded in red). You can measure the DCV at C801 and C802.
2. Q818. You can measure the voltage at C817.
3. Also, check the transistor ECB voltages of Q810, Q811, Q812 of the protection circuit.

View attachment 3691988

will get back to you on this. tyvm!

 

[12344321]

I know James and ended up having a look at the unit. To me, it is pointing to an issue in the amplifier, despite it being brand new with all parts verified.

I ended up using R801, 809, and 821 to measure the respective voltages from Q816, 817, and 818, while on a 100W DBT.

R801: 47.8V
R809: (-)47.6V
R821: 1.3V

That's looking okay there afaik.

I then measured the molex connectors to the amplifier board. The blue and yellow wires which goes to the protection relay, iirc J813, 814. measured 10mV for both.

Both channel white wires measured (-)57V. Both reds measured 58V. Therefore, both rails are intact from the filters and main rectifiers.

Is it possible that it's the driver or pre-driver stage of the amplifier causing too much draw? I know some of these units can be a bit fickle- currently it's C3503DS and its A1381 pairing for pre-drivers, MJE15032G/15033G for drivers. Brand new onsemi MJ21193G/94G outputs.