Broken Neve 1272

[adc004]

Hi, I have a question about a Neve 1272 that is broken. I wired this module up a long time ago, and it was working fine. A few days ago, I decided to wire it up to have more gain (based on Geoff Tanner’s suggestions…27ohm between pin E and F, and 220ohm in series with a 100uF cap between N and E).

Everything was working correctly, but all of a sudden stopped and I have no sound. I ripped off all the mods, but now all I get is a really, really low level signal.

Did I blow the input transformer or something else? Would there still be sound then? For testing the resistors and capacitors, I was using alligator clips, and it was maybe a little clumsily wired together. some wire could have touched another one, and sent DC into pin E (have no idea though…could’ve been something else).

Anyway, I was about to pack it up and ship it off for repair, but wanted to ask you guys if you had any ideas on what it could be. I haven’t had a chance to open it up…I really didn’t feel like doing anything with it because I felt so down that it was probably me being stupid that messed it up.

Thanks!

 

[iampoor1]

You need a scope or some tool to trace the signal if you want to fix it yourself. Otherwise our guesses really dont mean much of anything as it could be absolute anything at this point.

 

[scott2000]

I really didn’t feel like doing anything with it because I felt so down that it was probably me being stupid that messed it up

Some of my best repairs were of my own mistakes...yes plural

 

[MagnetoSound]

Pin E is B- or circuit ground.
You’ve most likely shorted pin F or N directly to ground, and blown a transistor on the B183/283 board.
An easy test would be to obtain another board and substitute it.
But there are plenty of other things it could be.
Check that you still have the external links in place, B-C … K-L

 

[adc004]

Great thanks everyone! I will take a look inside the module and see what it looks like. It would be great if it were just a transistor I have to replace and not an expensive transformer. Unfortunately I don’t have another B183/283…I wish I did for stereo applications.

I don’t have a scope at the moment…I definitely should get one!

But yeah, I’ve screwed up a lot with the soldering and attempted repairs, but this is actually the first time I broke something…and possibly a transformer that is very difficult to replace. I was definitely feeling like crap for the past few days!

Another question…is Pin E supposed to be tied to Pin V? I’ve seen differing instructions on that, and I’ve also seen to connect them through a resistor.

Thanks!

 

[MagnetoSound]

No, pin V is chassis ground and should connect directly to the metalwork of the housing (rack or console frame). Pin E is B- and must go back independently to the PSU negative rail. The rail is usually grounded to the chassis close to the modules but you don’t want the module casing affected by circuit currents.

I’ve seen screens within a console tied to the link between pins E and J (the bottom of the trimmer pot), which while not strictly kosher is harmless enough for screening purposes provided the other end is left floating. It’s not a good place for a mic screen, which should be tied to the metalwork at the XLR.

 

[adc004]

Great thanks, that makes sense! Thanks for the schematic…now I see where pins E, F, and N go inside the module. Hopefully it’s just one of the transistors that got damaged.

 

[MagnetoSound]

I would check those two resistors at the top of the drawing too, just to make sure the stages are both receiving power.

 

[adc004]

Will do, thanks!

 

[adc004]

I took apart the 1272 and did some measuring. It looks like TR2 might be bad. With multimeter in diode mode, when I measure from E to C (red on E, black on C), it's showing 0.5V. All the other transistors are showing OL, which I think is correct. All other readings on TR2 seem ok, and all other readings on the other transistors seem ok.

The resistors at the top seem to be ok. With the multimeter in resistance mode, they measure 12.3 ohms and 276 ohms. When measuring voltage drops, the 270ohm one gets about a 2V drop. The 12ohm one only gets ~4.4mV, but I guess that's correct since it's only 12 ohm? Voltage from the supply is 24.3V.

I'm ordering some parts...hopefully replacing the resistor and transistor fixes my error...still praying it's not one of the transformers that went bad! Is that likely...could DC voltage harm a 10468 or LO1166?

Thanks for all the help so far, and I'll keep everyone updated on my progress!

 

[adc004]

Ugh...bad news. I think my 10468 transformer is bad. I ordered a cheap oscilloscope that finally came today.

When I play a 1kHz sine wave into the input, I see the sine wave on pin 2 and pin 5 (the input), but when I try to read pin 7 or 10 (outputs), I only get 60Hz hum. So it seems like the 10468 is bad. Looking at the schematic, I guess it's possible that I may have sent a DC voltage into pin 10 of the 10468 and fried the secondary coil?

I thought the transformers were good, because at some point, when I was testing transistors (there was nothing connected to TR2), I got a very loud, but slightly distorted output signal. Turning down the pot actually sounded great! I have no idea what that could've been...I assumed the transformers were amplifying the signal somehow (and maybe some wire was touching some other wire accidentally). I haven't been able to replicate that though.

I don't want to spend the $$ for a 10468 right now, so maybe I'll go for a cheaper replica (or maybe a 31267), but wanted to give you guys the update on my progress.

Thanks!

 

[scott2000]

I'd commit more time troubleshooting before assuming the ip transformer is goofed. 60hz hum is pretty near power supply frequency and maybe something isn't kosher somewhere else.

 

[MagnetoSound]

Are pins 3 and 4 still linked (via B and C)?

How about the secondaries (pins 8,9)?

I guess it's possible that I may have sent a DC voltage into pin 10 of the 10468 and fried the secondary coil?

How would you have done that?

 

[adc004]

Pins 3 and 4 are connected. 8 and 9 aren’t connected…I’ll try that and see if it fixes it.

For sending DC into pin 10…I’m not sure how I could’ve done that, but maybe when I was connecting N or F to pin E (through the resistors and capacitor), one of the wires touched pin E accidentally. It seems unlikely though…I can’t figure out how I would’ve done that.

You guys are right…I’ll do more troubleshooting. One thing I was thinking is that the resistor between pin 7 and 10 on the 10468 somehow got fried? Or is shorted maybe. But I definitely don’t want to replace a transformer if it’s still good.

Thanks!

 

[adc004]

Actually sorry…pin 8 and 9 on the 10468 are connected.

 

[nielsk]

Disconnect the output of the transformer and scope the transformer output to see if something further down the line is killing the signal.

 

[adc004]

Great idea, thanks! I’m going to try that after work tonight. Hopefully it’s something else and not the transformer!
Thanks!

 

[adc004]

Great news…I disconnected everything from outputs of the 10468 and measured sharing with the sine wave. The signal appears on the outputs also, so it seems like the transformer is ok. The 5.6k resistor also measures correctly.

So it looks like one of the components around TR4 is messed up…maybe TR4 itself. I’ll do some more measuring and see what I can figure out…any more hints would be greatly appreciated.

But definitely, thanks for all your help so far! This thread has made me look up everything about these Neve modules, transformers, the BA283, etc….all the best info has come from this site! I’ve learned a ton in the past few weeks!
Thanks!

 

[Voyager10]

The EZ1290 build guide here may help: https://s3.amazonaws.com/EZ1290/assembly6.pdf

Page 26 has typical base/collector/emitter voltages for all the transistors in the BA183 modules. It should at least help you figure out which of the two stages are working normally.

(From memory, the current draw of my EZ1290s was about 50mA, so I'd expect a bigger voltage drop across the 12 ohm resistor i.e. ~ 0.6V).

Good luck.

 

[adc004]

Great thanks...this is really helpful! I'll measure all of the voltages on the transistors and see if they're in the ballpark!
Thanks!