700B blew one Right channel 5A supply fuse

[laatsch55]

Yep..and you rechecked the hookup wires between the board and the backwall?

 

[62vauxhall]

I have not checked any wires connected to the board except to ensure that my solder joints were secure.

Are there certain wires I should check or all of them. If all, I shall cut the zap straps holding the bundles so I can track them.

Do you mean a continuity check or a visual check?

 

[laatsch55]

Gary , just a quick check to see if the wites went back in the same place on the board....some weird shit going on there, just elomonating possibilities...

 

[62vauxhall]

Although I was certain I had them placed correctly, I just compared wire color vs connection points with the manuals diagram and they check out.

While I was at it, I took Q6 bias transistor readings at the point their wires connect to the board. Don't know if this will help or hinder determining the fault.

Q6 Left Channel
OL - red to base & black to emitter
OL - red to base & black to collector
.83 volts - red to emitter & black to base
.70 volts - red to collector & black to base
OL - red to collector & black to emitter
OL - red to emitter & black to collector

Q6 Right Channel
.72 volts - red to base & black to emitter
OL - red to base & black to collector
.62 volts - red to emitter & black to base
.62 volts - red to collector & black to base
.74 volts - red to collector & black to emitter
OL - red to emitter - black to collector

 

[62vauxhall]

Since this amp has failed 4 times that I know of, is it possible that a resistor, disc capacitor or trim pot is to blame? Minus the new components and possibly those "flying connections", the other components on the board look stock.

Might I have hooked up that bridge rectifier wrongly? Two terminals did not seem to correspond with the original so I reversed those leads.

 

[laatsch55]

Let me call in the Cavalry'...........Sir Joe....what doest thouest thinkest???

 

[laatsch55]

Since this amp has failed 4 times that I know of, is it possible that a resistor, disc capacitor or trim pot is to blame? Minus the new components and possibly those "flying connections", the other components on the board look stock.

Might I have hooked up that bridge rectifier wrongly? Two terminals did not seem to correspond with the original so I reversed those leads.

Whadda ya mean reversed the leads????????????????

 

[laatsch55]

You should check the diode in that one flying connection....

 

[laatsch55]

Gary, what leads did you reverse?

 

[62vauxhall]

Whadda ya mean reversed the leads????????????????

Around the time I received the photo you sent with capacitors in place on the rectifier bridge terminals, I remarked that the terminals markings on the old rectifier did not correspond whth those on the new one. That prompted you to comment on the "~" Tilde symbol.

I cannot locate those posts but followed the explained hookup pattern I thought correctly.

The two heavy gauge shellac insulated wires from the transformer, I attached to the same terminals, both marked with that "~" Tllde symbol. One symbol you can see in the photo and the other is diagonally opposite.

I was told the black wire went to NEGATIVE so I attached it to the terminal with the "-" sign which was diagonally opposite of where it was.

The red wire I put on the remaining terminal also diagonally opposite of where it was.

So the top left and bottom right terminals have wires from the transformer. Top Right has the black wire and bottom left the red wire. This is the reverse of how they were connected to the old bridge rectifier.

 

[laatsch55]

Ok, correct.... Gary we're gonna have to start checking every resistor and diode. Gonna have to check EVERY diode even where the oppose each other to get a reading from each one...

 

[laatsch55]

And do this with the rail fuses out...

 

[62vauxhall]

You should check the diode in that one flying connection....

ADDITIONAL: There are FIVE flying connections, Three are resistors in series. The other two is a resistor in series with a parallel pair of diodes. The oddball flying connection is in the right channel involving R4. Couldn't find it quickly on the schematic but it's orange/black/yellow which is 300K ohms. The extra resistor it's attached to has 6 color bands and I.m not familiar with those so can't calculate it's value - red/brown/orange/black/violet/yellow.

Long shot, but since it's the right channel that's affected and that's where this stray resistor is, any chance it's that simple?

And do this with the rail fuses out...

The rail fuses are now removed

we're gonna have to start checking every resistor and diode. Gonna have to check EVERY diode even where the oppose each other to get a reading from each one...


The resistors are somewhat larger than the diodes so I envision lifting one leg of each of them to test being easier than diodes. I've already replaced I think all but 3 diodes in each channel but have since checked a couple as per instructions. It was easier to replace the diode a second time than getting the cut soldered leg back into the hole.

That being the case, would you advise replacing all the diodes again only checking each one prior to mounting it?

Regarding resistors, would it be recommended to do likewise - obtain new resistors, check them and mount them.

Since this will take so much time, I'm not going to start anything tonight. I'll wait to hear back first on what you say about wholesale resistor and diode replacement.

 

[laatsch55]

No,. no need to dismount any resistors yet, and I'm braindead right now Gary, tomorrow Bud...

 

[62vauxhall]

Roger & copy that.

 

[laatsch55]

Thanks...

 

[laatsch55]

Ok Gary, are all components still on the board?

 

[62vauxhall]

I removed nothing but did separate the resistor from the diode pair in two flying connections - can reconnect quickly.

 

[laatsch55]

Was the diode Ok?

 

[62vauxhall]

Yes, they seem fine - 4 diodes in total - two per connection.