Issue with Crack Voltage [solved]

[Paul Birkeland]

On your last photo, have a look at the solder joints on R2.  One of them looks very inadequately heated.

 

[lwhitit]

On your last photo, have a look at the solder joints on R2.  One of them looks very inadequately heated.

I removed the old solder and cleaned everything up again but still no change. Not sure what else to do.

 

[Paul Birkeland]

You might want to try running the amp with no 6080 and with the large Speedball board removed.  This will isolate the 12AU7 and the small PC boards that feed it, and may bring your voltages at T1 and T5 back into check.

-PB

 

[lwhitit]

You might want to try running the amp with no 6080 and with the large Speedball board removed.  This will isolate the 12AU7 and the small PC boards that feed it, and may bring your voltages at T1 and T5 back into check.

-PB

Thanks for the response

Just to confirm I remove the 6080 and disconnect the large SB board (with the heatsinks). After that do I leave the originally connecting wire unconnected or how should I orientate everything after removing the big board?

 

[Paul Birkeland]

Leave the wires that went to the big board poking up in the air, away from anything else.

 

[lwhitit]

Leave the wires that went to the big board poking up in the air, away from anything else.

Real life got in the way but I was finally able to test this out. Removing all wires to the middle pcb did regulate the voltage for #1 (75) but #5 jumped all the way to 211.

 

[Paul Birkeland]

Now swap the small boards.  This will either isolate the issue to one of the C4S boards, or half the circuit under them.

 

[lwhitit]

Now swap the small boards.  This will either isolate the issue to one of the C4S boards, or half the circuit under them.

Swapping the boards: B is the bad one 211 on #1. A jumped up a bit when I swapped it 83 on #5.

 

[Paul Birkeland]

Try again to reheat the center leg on the MJE-350 on the bad board.  Also be 100% sure that you have the correct R1 resistor installed, as swapping one of the big board R1 resistors onto a small board will leave you with high plate voltage.

 

[lwhitit]

Try again to reheat the center leg on the MJE-350 on the bad board.  Also be 100% sure that you have the correct R1 resistor installed, as swapping one of the big board R1 resistors onto a small board will leave you with high plate voltage.

You were right I swapped the resistors I triple checked this thing but sure enough. I now have 80 on #1 (bad one) and 82 on #2.

Putting it back together and powering up now I am back to where i started but with different readings. I am going to get there.

3/4 LEDS on big board lit other 4 leds are lit but very low.
Terminal Voltage
1 75-90 (67)
2 170 (76)
3 0 (0)
4 170 (75)
5 75-90 (36)
6 0
7 100 (66)
8 0
9 100 (33)
10 0
11 0
12 0
13 170 (75)
14 0
15 185 (129)
20 0
21 206 (189)

So the issue is now on the big board?

 

[Paul Birkeland]

Yes, I bet if you pull the 6080, those voltages will pop up.

Are your TIP50's properly isolated from the heatsink with the supplied hardware?

 

[lwhitit]

Yes, I bet if you pull the 6080, those voltages will pop up.

Are your TIP50's properly isolated from the heatsink with the supplied hardware?

I will check it out tonight to test. I reviewed the instructions and I did place the thermal pad (was different from instruction pic, clearish plastic looking sheet) in between the heatsinks and the tip50's. Also the fibre washer was used for each.

 

[lwhitit]

Terminal Voltage (6080 removed) Plus pictures of both TIP50's and heatsinks.
1 75-90 (79)
2 170 (222)
3 0 (0)
4 170 (222)
5 75-90 (81)
6 0
7 100 (1)
8 0
9 100 (0)
10 0
11 0
12 0
13 170 (222)
14 0
15 185 (228)
20 0
21 206 (233)

 

[Paul Birkeland]

Yeah, that indicates that there's either a short on the board, or the TIP50's are touching the heatsinks.

-PB

 

[lwhitit]

Yeah, that indicates that there's either a short on the board, or the TIP50's are touching the heatsinks.

-PB

I am not sure what to do next. Are the pics good enough to confirm if I did it correctly? If so what should I start to check on the board.

 

[Paul Birkeland]

Check the resistance between the metal tab of each TIP-50 and the screw.

-PB

 

[lwhitit]

Check the resistance between the metal tab of each TIP-50 and the screw.

-PB

I checked it out and both look good. I get a 1 (no reading) when I check both metal tabs (silver) of the tip-50's and the connected screws.

 

[Paul Birkeland]

Well, we know that the 6080 is functional, as you did pass the voltage tests with the stock circuit.  Now that you have the small PC boards working, that only leaves issues with the large PC board.  I would suspect that some adjacent pins are soldered together, causing the short that is dragging your voltages down.

 

[lwhitit]

Well, we know that the 6080 is functional, as you did pass the voltage tests with the stock circuit.  Now that you have the small PC boards working, that only leaves issues with the large PC board.  I would suspect that some adjacent pins are soldered together, causing the short that is dragging your voltages down.

Ok that gives me an idea what to look for. I will check out my soldiering on the big board and report back.

Thanks!

 

[lwhitit]

I took it apart again and redid all the connections on the big board. Powered it up and all 4 leds were lit! I can finally leave you alone. Its up and operational and everything sounds good so far.

Thanks again PB