Russ' Phase Linear 700B Going Fully Comp!!!!!!!

[Gepetto]

Repaired the 4 backplane components that I zorched. Checking the control board to see if I wounded anything there now.

OK back at it Lee. Working on tuning the bias more. Only thing that failed on the control board was the 10 ohm in the R35 position. Fused open nicely.

 

[laatsch55]

Thank god she was a 1/4 watt..

 

[laatsch55]

Got the backplanes back in. Must have had something touching, it's ok now. Got a lot of wiring to put back on..

 

[Gepetto]

Got the backplanes back in. Must have had something touching, it's ok now. Got a lot of wiring to put back on..

OK Lee, I am done messing with the bias for a while. Here is my advice, don't populate the magic diode on the backplane in location D2. There is some strange bimodal thing going on there which is not healthy. My hunch is that it may work at the control board end but not remoted on the wires that connect the bias transistor.

 

[Gepetto]

OK Lee, I am done messing with the bias for a while. Here is my advice, don't populate the magic diode on the backplane in location D2. There is some strange bimodal thing going on there which is not healthy. My hunch is that it may work at the control board end but not remoted on the wires that connect the bias transistor.

I am now going back to see if the original values work properly now that D2 is no longer in circuit.

 

[laatsch55]

I'm still getting .2 ohms between ground and Collectors on the positive side. If the zener was shorted would I be getting that?

 

[Gepetto]

I'm still getting .2 ohms between ground and Collectors on the positive side. If the zener was shorted would I be getting that?

Unlikely Lee that it would short that hard to get that low of a reading.

Do you just have the 4 pre-drivers in? Have you disconnected your single ground wire? That trick I told you about a little while ago?


I am leaving R19 at the original 1K value Lee. I am adjusting R62 up to 2.49K. That is a value already used on the control board. It gives good range control and limits the upside bias to safe values (approx. 0.500V)

 

[Gepetto]

Unlikely Lee that it would short that hard to get that low of a reading.

Do you just have the 4 pre-drivers in? Have you disconnected your single ground wire? That trick I told you about a little while ago?


I am leaving R19 at the original 1K value Lee. I am adjusting R62 up to 2.49K. That is a value already used on the control board. It gives good range control and limits the upside bias to safe values (approx. 0.500V)

Hi Lee
I get a little over a megohm with the one chassis ground connected to the round stud on the left board. With it removed, I get off scale. So it is leakage through the caps and bridge and transformer windings that gives the megohm reading.

 

[Gepetto]

I'm still getting .2 ohms between ground and Collectors on the positive side. If the zener was shorted would I be getting that?

That kind of points to your B+ supply being tied to ground somehow. Have you taken the B+ fuses out of their fuseholders to see if it goes away?

 

[laatsch55]

When I take the Single ground from the middle of the board off the bus bar everything powers up normally. Offset-13, Bias 387 and 408 with R62 at the 5.6K and R19 at 270 ohms. This is strange.

 

[laatsch55]

Solder blob from case on BR to B+ out...jeez!!

 

[laatsch55]

Now putting R19 back to 1K and R62 to 2.49K

 

[laatsch55]

Bias adjusts now at 1:00 o'clock like normal Joe. Rest of outputs in the morning. I'm tired, chasin them damn electrons can get frustrating.. and it would have powered up the first time with no issues had I inspected the BR a little more closely after putting on the hash caps...DAYAM!!

 

[laatsch55]

gotta work this morning

 

[Gepetto]

Solder blob from case on BR to B+ out...jeez!!

That will do it every time Lee. That is why I recommended the trick to remove the B+ fuses. It separates the power source side from the power use side. You can easily find out which side of the line the short exists on. One of those debugging tricks learned over time.

 

[kevin]

WOW ! This is really getting good !.. Shows how hard this stuff really is when you and Joe have problems !! Just blows my little Hillbilly mind !

 

[Gepetto]

WOW ! This is really getting good !.. Shows how hard this stuff really is when you and Joe have problems !! Just blows my little Hillbilly mind !

The 700 is a crowded beast with lots of opportunities for making mistakes...

 

[kevin]

Joe ! Have ya got yours going ? Not been on your thread today !

 

[Gepetto]

Joe ! Have ya got yours going ? Not been on your thread today !

Sure it has been up and running for a while but I ran out of 21196 devices that I have on re-order right now so I am limited on its power output. Those should be here later this week.

As you can see in the thread, I have been tweaking with further optimization of the bias circuit values, trying to get good range of adjustment.

 

[Gepetto]

Sure it has been up and running for a while but I ran out of 21196 devices that I have on re-order right now so I am limited on its power output. Those should be here later this week.

As you can see in the thread, I have been tweaking with further optimization of the bias circuit values, trying to get good range of adjustment.

The break gives me a little time to clean up the raging mess on my lab work station