700/1 “Tim” WOPL driver board

[AngrySailor]

Just went over the driver board again looking for any bridged solder joints. Not finding anything... time for a WOPL break and fire up the sand blaster... I’m sure it’s something small...

 

[mlucitt]

You can disconnect every wire on the DCP Relay Board and do the Bring Up test again to eliminate that as a cause. Just be sure the wires are taped off. You can take the speaker binding post "DC Offset" at the disconnected Left and Right wires.

 

[AngrySailor]

You can disconnect every wire on the DCP Relay Board and do the Bring Up test again to eliminate that as a cause. Just be sure the wires are taped off. You can take the speaker binding post "DC Offset" at the disconnected Left and Right wires.

I was wondering about that, I had no DC offset but also both channels seem to be a direct short at the speaker leads left/right to ground 0.1ohm. Also wasn’t sure there would be any DC offset without outputs installed? Well I suppose looking at the schematic you would have offset due to Q11&12 right?

 

[AngrySailor]

You can disconnect every wire on the DCP Relay Board and do the Bring Up test again to eliminate that as a cause. Just be sure the wires are taped off. You can take the speaker binding post "DC Offset" at the disconnected Left and Right wires.

Done, Bais dropped to ~20V with the DCP disconneccted

 

[AngrySailor]

DC Offset 1mV each side
Left bias 228mV
Right bias 20V

 

[mlucitt]

That right Bias voltage indicates an issue with the bias transistor (Q6) or other components in the Right channel only of the Control Board.
I once accidently switched the red and brown wires on a Q6 and it gave me the same symptoms.

 

[AngrySailor]

That right Bias voltage indicates an issue with the bias transistor (Q6) or other components in the Right channel only of the Control Board.

I placed the bias transistors on the back plane and I’m sure I pinned them out the same. I’ll double check the BCE configuration on the right channel gimme a minute

 

[AngrySailor]

Right bias transistor tests ok and was installed correctly.

 

[mlucitt]

Wires to the Control Board are Red - Black - Brown?

 

[AngrySailor]

Wires to the Control Board are Red - Black - Brown?

Yeah I robbed the wires and the P straps from Linda as the 700/1 had them mounted to the driver board. I’ve got one of these component testers I used to identify the leads, the transistors are new from Lee and were well matched according to this tester, I’m not sure I followed the original color code, the BCE are going to the correct points on the board.

 

[AngrySailor]

I’m no expert but doesn’t it seem suspicious that the bias was 30V given there’s 15+/- on the driver board. I looked and looked for bridged solder but the soldering went real well and I don’t see anything bridged... weird but I’m sure we’ll find the problem.

 

[AngrySailor]

So much for sandblasting, started raining... I guess I got 142 brass taper pins to make, got a radiator needs tubes plugged. Joy...

 

[AngrySailor]

Rain let up, time to get this over with. Should be done blasting everything today.

 

[George S.]

I like the welding helmet. Are you using beach sand? Last sandblasting I did was a subframe, rear axle, and suspension pieces for my son's Saturn wagon. I love sandblasting (NO!).

 

[AngrySailor]

Nah using 50# bags of 00. $9/bag and I’m not paying.

 

[AngrySailor]

Done. 1450lbs of sand to blast that tractor. Fug me.

 

[laatsch55]

Double 00...that's big sand..

 

[AngrySailor]

Double 00...that's big sand..

Pretty sure it’s 00, it’s not real coarse though. I’ll double check the bags when I get home.

 

[laatsch55]

We usually go with20/40 on our stuff. Smaller number the bigger the sand right?

 

[George S.]

I started using a product called "Black Diamond", it's made from the coal slag waste from power plants. Has no silicon in it which is great health wise and is very, very sharp. It cuts so nice that material usage is reduced and leaves a nice toothed surface for paint adhesion. Just a much nicer abrasive then sand, and total cost is roughly equal to sand on large pieces at home if one lays a tarp out to recycle the material. It's so sharp it can be reused.
And yes, I used sand for many, many years. Never going back to sand.