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SAE 2600 restoration/recap.....need assistance.

grateful said:
I would use onsemi MJE15033G and MJE15032G for the drivers and predrivers.
Click to expand...

What led you to believe these would be the appropriate devices to use?

I thought I would post a pic of what a SAE 2600 undergoing a recapping/repair looks like for anyone who hasn't done this. BTW, I have taken many pictures and drawn "maps" and labeled every wire to help me during reassembly.

SDC11270_zps6dfdc6da.jpg
 
I have personal experience with over 30 years as an audio repair professional. They have the correct voltage, current and bandwidth. They are available, cheap, and reliable.




Rob41 said:
What led you to believe these would be the appropriate devices to use?

I thought I would post a pic of what a SAE 2600 undergoing a recapping/repair looks like for anyone who hasn't done this. BTW, I have taken many pictures and drawn "maps" and labeled every wire to help me during reassembly.

SDC11270_zps6dfdc6da.jpg
Click to expand...
 
grateful said:
I have personal experience with over 30 years as an audio repair professional. They have the correct voltage, current and bandwidth. They are available, cheap, and reliable.
Click to expand...

Oh man, I hope I didn't come across as questioning any of that. I was just trying to glean a bit of your knowledge. I'm very thankful you're willing to share your time and knowledge with me.

I'll be ordering 8 each tonight.
 
No offense taken. I use those devices in many of my repairs. Just did a SAE 2400L The semis that I recommended worked fine in that repair.
 
I have already ordered the MJE15033G and MJE15032G semi's from Mouser. I'm sure there will be more I need to get to finish the job but it's all inexpensive too.

I've gone about as far as I can go until the good schematics and parts start arriving. The chassis, panels, brackets and faceplate have all been thoroughly cleaned and I've polished both sides of the meter windows. I will still need a few more caps, four trim pots and a bunch of resistors.
 
The first package of parts arrived today. I'm glad to finally be able to sink my teeth in and get started. The caps on the pre-driver and driver boards have now been recapped with fine gold. I discovered two broken traces which needed to be repaired. Still waiting on the rest of the caps and resistors and of course the transistors. I gotta admit, this has been a lot of fun. :D

SDC11274_zps7af5f4b6.jpg


SDC11278_zps2fab3fff.jpg
 
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I got all of my output and driver devices today along with the rest of the caps I needed. I got everything put back together and fired it up with a dim bulb tester. No shorts indicated so time to plug it in and turn it on. Everything looks good with no magic smoke escaping. I let it stay turned on for about a half hour and other than a noisy fan that will get replaced, still good.

I lost one of my 1/4" to RCA adapters so I could only test one channel at a time. The left channel sounds great. Okay, so then I did the same with the right channel and nothing. I checked all connections and they look good so I crank it way up and I can hear the music but it's really quiet.

I switched the driver boards around and the left still sounds fine and the right channel is still very quiet so the issue is not in the driver boards. I checked the drivers on the pre-driver boards but they test okay. I decided to check the DC offset and it was very high in both channels. I was only able to get the left channel down to a whopping 300mv. The right(quiet) channel was adjusted down to almost 0mv.

I didn't swap out the pre-driver pcb's because I had to solder the pin connections but I will desolder them and swap them out tomorrow to see if that's where the problem is. I'm even thinking it could have something to do with the relay for that channel. I can see the contact closing but it looks pretty beat up with a cracked case and all.

If anybody has any thought on where else I should be looking please let me know. Below are the schematics for the 2600. The first PDF is for the pre-driver and the second PDF is for the driver, main board and relay board. Please disregard my notes on the second PDF where I marked (I believe incorrectly) the emitter resistors.

Any suggestions or comments are welcome.

View attachment scan0001.pdf

View attachment scan0002.pdf
 
Did you replace the diff pairs? I see the green and black S1375/S1275 are still there a well in the last picture. That might fix your offset problems. Swapping the pre-driver boards will tell for sure.
 
Rob41,

Before you get much deeper in your rebuild, I think a Bat Signal should be bounced off the clouds calling for EchoWars to chime in here. He should be able to give you some quick pointers before any magic smoke is allowed to escape. :yes:

I am very interested in your endeavors to rebuild this SAE beast. I have one just like it, too! :thmbsp:
 
FootFungus said:
Did you replace the diff pairs? I see the green and black S1375/S1275 are still there a well in the last picture. That might fix your offset problems. Swapping the pre-driver boards will tell for sure.
Click to expand...

No I didn't but I think I need to do that. I've switched out the pre-driver boards and each channel still behaves the same with the left at full output and the right very much less. The DC offset did follow the boards however making me believe you are absolutely correct about the diff pairs.

So my diminished volume isn't from either the driver or predriver boards. What does that leave? The right channel relay, output transistors, input jack?

SAE2922 said:
Rob41,

Before you get much deeper in your rebuild, I think a Bat Signal should be bounced off the clouds calling for EchoWars to chime in here. He should be able to give you some quick pointers before any magic smoke is allowed to escape. :yes:

I am very interested in your endeavors to rebuild this SAE beast. I have one just like it, too! :thmbsp:
Click to expand...

Any input is always welcome for sure.
 
Well I think I just found the problem. I removed the relay board to check the right relay. After removing the plastic cover the coil tried to fall out. All of the plastic that holds and aligns the coil/points was broken clean off. So I will be ordering a new relay, and to get correct DC offset I'll order all of the diff pairs as well. Other than these two issues I think it would have run perfectly.
 
FootFungus said:
You could input a test signal and try to follow it. Have you checked the bias yet on either channel?
Click to expand...

I think I found the issue in the right relay. No, I haven't yet checked the bias but I know I need to. Unfortunately the service manual I have is for the 2500 rather than the 2600 and this has already led me in the wrong direction a few times. There are more than a few differences between these amps.

As soon as I get a new relay installed I'll try again. Maybe you could help me determine how to set the bias then. BTW, is the bias separate from the quiescent current?

edit: The schematics I have and posted above are the correct 2600 schematics.
 
Quiescent current and bias are the same. You'll be measuring the voltage drop across the emitter resistors, however.
 
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