Nad 2200 Recap and Repair

[Juljon]

Hi MBZ, I agree that shorting the cap is not an answer but was wondering if this could eliminate any other possibilities?

I'll pull Q334 and test it.

 

[Juljon]

Collector of Q338 is 0.75V. I was incorrect previously.

Checked all the earths on the board. I get 1.5ohm on all of them to the frame.

Base of Q334 remains 1.8 V no matter what the position of SVR 302. This seems like it could be part of the problem as no matter what I do with SVR 302, nothing happens anywhere in the circuit. I have removed it and it tests ok. Up to 1KV.

Q304 bce -0.8/0.2/-0.09 c should be -1.77V
Q302 bce 0.7/0.17/0.7 c should be +1.77V

 

[Juljon]

Collector of Q338 is 0.75V. I was incorrect previously.

Checked all the earths on the board. I get 1.5ohm on all of them to the frame.

Base of Q334 remains 1.8 V no matter what the position of SVR 302. This seems like it could be part of the problem as no matter what I do with SVR 302, nothing happens anywhere in the circuit. I have removed it and it tests ok. Up to 1KV.

Q304 bce -0.8/0.2/-0.09 c should be -1.77V
Q302 bce 0.7/0.17/0.7 c should be +1.77V

ignore this

Q304 bce -0.8/0.2/-0.09 c should be -1.77V
Q302 bce 0.7/0.17/0.7 c should be +1.77V

I’m testing with the power off — too late for this — need to go to bed

 

[Juljon]

That's good. How much of the board have you re-soldered? These boards had a real problem with cold solder joints and most of them looked fine but weren't. I re-soldered all of the joints that where connected to the back panel and all of the joints at the transformer. The joints looked good until you stressed the board a little bit and you could see the fractures in the joints.

I know that there where features on this amp that where unique to this amp like inverting the polarity of the low frequency input signal to draw from both rails at the same time when the signal was base heavy on right and left channels.

I have the original literature and sales brochures for this amp and the matching pre amp that I also own. They explain all of the amps features and technologies in good detail unlike today's ad campaigns that wow you with flashy images but don't tell you much. If you think it might help you I can photocopy it and post it here.

I know it was a power envelope design with loads of headroom on demand and would switch from a high current amp to a voltage amp on the fly depending on the source material. I understand that there isn't a whole lot of info available on the internet regarding the PE design so if you think it might help I will be happy to post what I have.

Hi Iamjackalope

I ave done a lot of resoldering and have gone over the boards with a magnifying glass repairing anything that looked suspicious. No change.

However during the process I found the voltage on the base of Q316, one of the large transistors, varied depending on where I put my work light. I then moved my hand around and that made changes as well. With moving the lamp around I can change the voltage on the base of this from 1.8 to 12V.

 

[irext]

That's good. How much of the board have you re-soldered? These boards had a real problem with cold solder joints and most of them looked fine but weren't. I re-soldered all of the joints that where connected to the back panel and all of the joints at the transformer. The joints looked good until you stressed the board a little bit and you could see the fractures in the joints.

I know that there where features on this amp that where unique to this amp like inverting the polarity of the low frequency input signal to draw from both rails at the same time when the signal was base heavy on right and left channels.

I have the original literature and sales brochures for this amp and the matching pre amp that I also own. They explain all of the amps features and technologies in good detail unlike today's ad campaigns that wow you with flashy images but don't tell you much. If you think it might help you I can photocopy it and post it here.

I know it was a power envelope design with loads of headroom on demand and would switch from a high current amp to a voltage amp on the fly depending on the source material. I understand that there isn't a whole lot of info available on the internet regarding the PE design so if you think it might help I will be happy to post what I have.

Dry joints on the Transformer are an amp killer in this model. Also one of the reasons for inverting one of the inputs is to make switching to Bridge mode very easy.

 

[iamjackalope]

Hi Iamjackalope

I ave done a lot of resoldering and have gone over the boards with a magnifying glass repairing anything that looked suspicious. No change.

However during the process I found the voltage on the base of Q316, one of the large transistors, varied depending on where I put my work light. I then moved my hand around and that made changes as well. With moving the lamp around I can change the voltage on the base of this from 1.8 to 12V.

So what's the outcome? Any luck?

The change in voltage is a bit odd. 1.8V to 12V is a pretty big swing. How about with the cover on it? Is it still effected or is it enough shielding?

Hope you got it working. I like these amps as well. Here is a link to a youtube video you might like. It shows the real world power of these amps.

YouTube

 

[Juljon]

So what's the outcome? Any luck?

The change in voltage is a bit odd. 1.8V to 12V is a pretty big swing. How about with the cover on it? Is it still effected or is it enough shielding?

Hope you got it working. I like these amps as well. Here is a link to a youtube video you might like. It shows the real world power of these amps.

YouTube

I've spent some time going over the different sections of the amp and have stripped the transformer, protection and power boards from the frame. I resoldered a lot of the joints and found a couple of areas where the copper strips had been damaged on the back of the PCB's. The odd voltage changes have stabilised however I now have a problem on the left channel where the output voltage is -60V. So a similar problem to what I had on the right channel initially. The outpt voltage on the right channel is now 2.45V but should be 0V. I have also found the correct schematic for the amp. I was using the standard 2200 but have since found the 2200 PE version. In this drawing I found the main transistors have 4.7ohm resistors on the base of each. I tested one and found it to be bad so have ordered a few replacements. There is a two week delivery time so will do what testing I can in the meantime.

Nice video on uTube. Wouldn't mind having a go with the dyno.... I have another 2200 which I am using in stereo. I'm hoping to fix this second one so I can set my system up with them in mono.