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Bose 1800 Amp Spare Parts (Amp PCB)

Jon,

Yes I sorted out the power supplies to the op-amp. I'll borrow a scope from my buddy sometime here and take a look see.

Should be a good amount of stuff happening in the next few days. I put my order into Mouser for parts.

I ordered a bunch of parts, on the off chance that I'd need them. This way I wont have to put another order in and kill $10 in shipping.



I also ordered parts to
1) Finish off the last of my Kenwood 600s power supply rebuilt.
2) Recap an AudioPulse Digital Time Delay Model Two
3) Replace RCA jacks on the DBX 3BX
4) Install a protection fuse on the 12V transformer that will run the speaker protection board that should be here in a few days.

Should be a good couple of days. By the weekend the Bose should be back online. Hopefully that is.

I also found a guy on diyaudio.com who has a bunch of Motorola MPS-U10s he giving me for free. I also ordered both MJE340s and 2SC4793. I think either chip would make a suitable replacement for the U10s. When properly heatsinked both are good for 20W. Both will need leads moved around to connect up properly but that is not a big deal.

I've got some Bourns pots here from a long time ago, I can install them and adjust bias once everything is all said and done.
 
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Speaker Protection Board arrived yesterday, got it all assembled and tested. It provides a nice turn on delay too.

Some pics:
 
Another update:

Finished the installation of the protection relay. It works as advertised.

The rest of the parts should arrive Friday or Saturday, after that...with any luck it will be fully operational again. I might wait, I have a guy sending me a batch of MPS-U10s so maybe I'll put those in instead of my subs...



 
Alright parts all arrived today.

On the "good" channel I replaced Q3/Q4 as they were used in diagnosing the "bad" channel. I used the MJE340 in place of Q3 and Q4 was the same.
Im going to replace the pot with one of these Bourns models I have here and maybe the ceramic caps, and the diodes that are prone to failure on the op-amp. I did a quick power up test with it and DC offset hovered around 120mV peak.

On the bad board I replaced:
Q3, Q4,Q5
C5,6,7,8,9,12,13,17 (Replaced with either Ceramics or MLCCs)

After some messages with an eBay seller the protection board that I currently have will handle up to 150WPC. This is inadequate for this amplifier, so I moved up to a model with a more hefty relay:

http://www.ebay.com/itm/2-channel-S...ultDomain_0&hash=item3369b47074#ht_1682wt_905

The "bad" board is just about finished and ready for testing, I sent it off with a buddy of mine to finish mounting Q3 (I had to do some drilling to remove the remnant plastic screw. So tomorrow night sometime I should be able to conduct more testing.

The seller said this one should be good for 250-500WPC
 
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Repaired!

AHA SUCCESS!

Round 1 Of Testing:
No Signal Applied. No Load. 15-20 Minutes at each level.

LEFT CHANNEL:
Volume at 00 : -109mV DC Offset
Volume at 02 : -106mV DC Offset
Volume at 04 : -082mV DC Offset
Volume at 06 : -035mV DC Offset
Volume at 08 : +95~101mV DC Offset
Volume at 10 : 108-123mV DC Offset

RIGHT CHANNEL:
Volume at 00 : 127mV DC Offset
Volume at 02 : 127mV DC Offset
Volume at 04 : 119mV DC Offset
Volume at 06 : 104mV DC Offset
Volume at 08 : 086mV DC Offset
Volume at 10 : 064mV DC Offset

The right channel is the one that we've been working on for the entirety of the thread. It appears to be working correctly now. I am going to replace some key capacitors, zeners and diodes on the left channel as preventative maintenance. Apparently there are a few that are known failure points that can cause problems down the road. The repaired right channel has a much better spectrum of DC offset numbers than the left. Hopefully with these changes the left tightens up a bit.

Replacement List:
C5,C16
R13 (Bias POT)
Cr6,Cr15
C8,C9,C7,C12,C13,C17


Now I'm going to set the bias, clean the heatsinks and mount everything back up. Just about time to close the book on this repair.
 
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So I'm trying to set the bias according to the manual and I seem to be unable to see any current. Every time I adjust the pot the current spikes up then drops back down to 0 or .001mA. I assume I'm supposed to be monitoring DC current...

Here's the procedure:


Here's how I have it setup:
I removed the -85 lines and zip-tied the eyes together, then connected an alligator clip around them for the meter. I made a simple wire and attached the other alligator lead to the - terminal on the capacitor.



Same results for the other amp board.

I must be performing this procedure incorrectly...
 
Alright Bias adjust to around 89-90mA. I removed the main heatsinks, cleaned them and reapplied thermal paste.

Installed the main amp boards and everything. Connected my meters to the amp output pre-protection board and observed DC. Both channels hovered around +/-120mV without signal input. Right channel cranked went to around +80mV, Left channel went to around +22mV.

Connected up signal lines, observed the same DC offset numbers. I must have missed incompletely connected one of the wires at the protection board as I've no meter signal on the left side however there is sound output. The signal line to the meter is paralleled with the amp output line at the protection board. I'll probably leave it like this until the new larger protection board arrives. No sense in tearing it all apart twice.

To everyone who helped in this endeavor, I wish to say thank you. I've learned quite a bit about the general working of a solid state amplifier. Its been an fun time.

So lets take a look at how much I've got sunk into this amplifier:
Acquired 2007
No luck with repair. Probably shorted/blew out a lot of things trying to repair. Looking back I would suspect that Q2/3/4/24 were bad originally. Maybe op-amp supplies too.
$80 in new output transistors, misc parts

Repair in 2011
Almost two month long repair effort.
$10 in protection board
$6 transformer
$25 in parts from Mouser
$5 in parts from RadioShack
$13 in larger protection board.

Totaling: $138.

Some pics during testing, Left meter = Left channel, Right meter = Right channel

 
I ran it for about 1.5-2 hours last night on a moderate volume hooked up to the remaining Bose 141 speaker. The DC offset on the right channel remained firmly between 80mV and 120mV.

I did notice on a cold start (i.e empty caps, cold boards) the right channel will hold a near 220mV-240mV DC offset for a few seconds, then it will snap back into its normal range. Might be something with the Q3 sub I used...not entirely sure but seem ok to me.

Maybe I'll see about hooking a scope up to the output. Any special things I should do before hand? or during?
 
UPDATE:

Re-adjusted bias on right board. It was sitting around 600-700mA. Now its more near 60-70mA. I hooked up the amp to some Pioneer loaded Bose 601 speakers for more testing. I *think* I hear some minor distortion on the right channel. It might be set TOO low. We'll see after some more play time.

EchoWars mentioned a neat trick for DC offset control. Simply add a 10K pot between the -16V input and the null offset pin on the op-amp. I might try this later.

Currently both channel are hovering around 120mV at idle.

Things left to do:
1) Install New Protection Board
2) Repair connection to left channel LED meter at protection board
3) Devise some type of feet. I recall there being some threaded bosses on the bottom that I could probably get some screws for and make some kind of feet.
4) Clean faceplate, clean chassis and clean workspaces lol.

 
Nice...

:tresbon:
Great job restoring,but how does it sound?
Did you hook up some nice speakers and if so,satisfied ?
Questions,questions...
 
May 11, 2014
Everyone,
This and other threads were extremely helpful in my repair of a Bose 1801. It turned out that the MC1556 op amp was bad as determined by the -0.07 V on the positive rail to it. (It should be around +15 volts.) Initially, I replaced it with what I had - a LM301AH. This op amp drove the amp berserk! Instead of shopping around (which I did a lot of via internet), I opted to go with the DIP8 to TO99 adapter from Cimarron Technology and then try for a DIP8 op amp due to cost of the can-type op amps. (http://cimarrontechnology.com/through-holeadapters.aspx)
These adapters are about $2.75 each, plus shipping. I decided to get two - just in case! When I asked about a replacement for the MC1556, I told him that it was a fairly slow op amp and what I needed was something that would work in its place. The person I was talking with, Phil, suggested OPA134PA made by Texas Instruments (Newark Electronics for $2.94 each. http://www.newark.com/texas-instrume...9&rpsku=OPA134) and is especially designed for audio. It worked like a dream! The DC offset without any adjustments was 20 millivolts!
 
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