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Old 23rd May 2008, 07:49 AM   #1
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Default bose 1800series two

hi, just joined the site to see if anyone has info on the above bose amp, ive repaired it,- one of the main caps was shorting, and one of the torroid trannys was shorting the secondary to the case, it works fine now except that there is 80v on both of the speaker terminals on both channels, i really enjoy the fireworks when a loose connection touches the case ! cant find any info on this amp anywhere, (cct etc), ive worked out which is the quiescent pot but there are 3 others i was wondering what they are for, any help would be appreciated, thanks
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Old 23rd May 2008, 08:33 AM   #2
HighTec is offline HighTec  Croatia
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Default Bose 1800

Hi,

yeah, good old Bose. I had two of 1800's. They worked almost 20 years without any problem. They are retired now.
Here is a service manual and I hope it will do some help. Btw, just in case, check the output transistors.

http://rapidshare.com/files/11695052...pdf.html<br />

Regards m8
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Old 23rd May 2008, 06:29 PM   #3
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thanks, its file is titled 1801, the one i have is the 1800 series two, the 1800\1801 use npn transistors for the o\p, this has sanken complementary ones, they are mounted inside the case with a fan on the back panel
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Old 24th May 2008, 02:40 AM   #4
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i repaired a couple of series 5 amps a couple of years back with no schematics. not easy, but i was able to repair them. i haven't been able to find schematics for the 1800-series anywhere either. the ones i worked on had MJL1302/3281 output devices and the fan was inside the unit. i suspect that you will find a shorted output or driver, the drivers are probably one pair of what looks like output devices. the driver pair is at one end of the rows of outputs, and it's emitters connect to the bases of the output devices. you could also have a bad diff amp causing your offser. the easiest way to locate a shorted output device is to lift all of the output emitter leads and check each device E-C. the pots are output bias (1800's are stereo amps, so there are 2 of them) and offset controls (offset controls are usually in the +/- 500mV range, not rail-to-rail).
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Old 24th May 2008, 09:13 PM   #5
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hi, thanks for the reply, ive checked all the transistors and they appear ok, and the amp is working ok, the voltages to the caps 0v are correct but to the case there is +80 to it, ive disconnected the earth return to the 0v (earth lift switch on the rear panel) im sure if the switch was 'made' then a large bang would ensue with the demise of a fuse in the plug, i am thinking (not a good idea at my age) the -ve rail is earthed or something along thise lines as to the case i get 0v to the -ve supply and 170v to the +ve, at this moment im going for a lay down in a darkened room !!
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Old 24th May 2008, 09:13 PM   #6
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passed on the lay down, and did some more checking, the insulator was missing from the a capacitors mounting screw== geeez, thanks for your help etc, come on moderator it wasnt that bad !
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Old 25th May 2008, 09:29 AM   #7
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Glad you found it...sometimes it just takes a bit of detective work.
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