Voltage issues [resolved]

[Alypius]

Aloha! I've finished my straight-through Crack/Speedball assembly and, after some power supply issues, I managed to get up to the point of voltage checks, although everything lights up except the main Speedball board LEDs (the ones on the socket and smaller boards light fine). Voltages are largely ok, with some wonky out-of-tolerance ranges:

1     75-90     70
2     170        230
3     0            0
4     170        230
5     75-90     70
6     0            0
7     100        142
8     0            0
9     100       196
10   0            0
11   0            0
12   0            0
13   170        230
14   0            0
15   185        230
20   0            0
21   206        234

A1   90   0
A2   0     0
A4   0     0
A5   0     0
A6   90   70
A7   0     0
A8   0     0
A9   0     0

B1  90    70
B2  170  228
B3  100  140
B4  90    70
B5  170  229
B6  100  198
B7  0       0
B8  0       0

I (Small)  170-185   206, 227
O (Small) 75-90       70, 70

B+ (Large) 170-185    227
O (Large)   90-100      180

Although I'd checked and rechecked my joints, I have to assume that there's more that just aren't good enough. Your thoughts? Thanks for your help!

[Paul Birkeland]

Your thoughts?

Remove the Speedball, install the 4 resistors, then see if there are any lingering issues.

[Alypius]

Done, although I managed to kill a socket LED in the process. Thanks for your help, I'll post again when the replacements get soldered in.

[Alypius]

After removing the Speedball and assembling stock, the Crack worked great. All voltages in spec and sounds awesome. I shut it down and carefully reinstalled Speedball. I now have LED's on the mainboard and the left (next to the volume pot) small board. The LEDs on the other board and the A8 socket do not light.

Voltage at T1 is 185, T2 is 4 VDC. I have resoldered the center pin of the MJE350 as recommended in other posts.

ETA: The problem follows the board, so I disassembled and resoldered the small board with no improvement. I wonder if I don't have a toasted MJE350 after my power supply issues.

[Paul Birkeland]

Voltage at T1 is 185, T2 is 4 VDC. I have resoldered the center pin of the MJE350 as recommended in other posts.

This is impossible.

Are you getting either LED on the 9 pin socket to light up?  (do not resolder these LED's, in this case they will indicate whether any current is flowing through each of the small C4S boards)

You can perform these tests with the 6080 removed from the amplifier.

[Alypius]

Well, that's impressive! But yes, one LED on the 9-pin lights, the other doesn't.

[Paul Birkeland]

Alright, let me know which LED on the 9 pin socket lights, and what your current T1, T2, and T5 voltages are.

-PB

[Alypius]

After swapping the board, the symptoms followed:

T1 (O) 71
T2 (I)  184
T3        0
T4 (I)   184
T5 (O)  2.85

A8 is now lit.
Fortunately, I am a much better brewer than solderer. I owe you beer.

ETA: It looks like I have a blown 237-Ohm resistor. Radio Shack tomorrow!

[Paul Birkeland]

Excellent.  240 ohms is plenty close to 237 if that's all you can find.  Any wattage will work too.

[Alypius]

Replaced the 237 for a 220 (all RS has) and replaced both LEDs. Everything is now lit with 150 VDC at T5, probably because of the 220. I have 240's on order and will swap them out on arrival. Thanks again for your help!

[Paul Birkeland]

Replaced the 237 for a 220 (all RS has) and replaced both LEDs. Everything is now lit with 150 VDC at T5, probably because of the 220. I have 240's on order and will swap them out on arrival. Thanks again for your help!

No, 220 Ohm resistors there would make the voltage at T5 lower.

Do both LED's on the socket light up now?

[Alypius]

Yep, all LEDs are lit. Just getting 150V to the tubes (if I'm reading the schematic correctly...it's been a decade or two).

[Paul Birkeland]

OK, if both LED's on the 9 pin socket are lit, then both the boards are passing current.  The most common cause of having 150V at terminals 1 or 5 with the LED's glowing on the socket would be installing the 31.6 Ohm resistor in place of the 237 Ohm resistor by accident.

[Alypius]

Nope, all the values are correct. At this point, I'm thinking damaged MJE-350.

[Paul Birkeland]

I would replace both transistors on that board.