Bose L1, PS1 help needed – have official Bose Repair Manual

[cgoepel]

Background: I need some help from the bright minds here on the Forum. I am an EE with over 30 years experience in design and repair of electronics. I am attempting the repair of a Bose L1 sound system. I believe this is now called the “Classic”. My customer contacted Bose for repair of his “dead “ PS1 power unit. Bose support technician told the customer that the “Classic” is no longer supported and has become obsolete. The factory rep told him that they would offer him a $500 credit towards the purchase of a new system. This brave customer contacted me to attempt the repair of his dead unit. I contacted Bose and the helpful tech emailed me the full Repair Manual. Without the schematics the repair of switched mode power supplies and switched mode amplifiers would be otherwise impossible.

The problem: After checking voltages on the various boards, the main problem seems to be the Auxiliary Power Supply. All voltages from the aux power supply are 0 volts. All transistors and diodes were checked. I found one shorted component, D607, the rectifier for (-15) volts. I replaced D607 with a similar fast 3 amp switching diode. I am thinking that the ”Protect” line may be latched, but I’m not sure of the proper state of the protect circuit. Could it be active high, or active low? The protect line is common to all boards. I’m starting to feel like a cat chasing it’s own tail. I am looking for input from experienced troubleshooters here. I am supplying the schematic that I am using. Thanks in advance for your advice.

[Jazz P Bass]

Whew.
Nice power supply.

O/k. 27 volt supply/ zero volts output.
If all of the switching mosfets check good, I would look at IC501 & see if pin 6 is even running.

UC2842.pdf

[Enzo]

First, isolate the problem. The SMPS is not running, but it might be OK. Most modern SMPS have tons of protection. SO a dead power amp channel could stop it cold. Disconect the power amps completely, noting where all cables connect. Take pictures, draw maps, whatever it takes to get it back together right later. Will the SMPS power up fully now?

[drewl]

I have the modules from one of these that had the same problem.

Customer just had me convert the speakers for regular use with a power amp, so let me know if you need any power amp modules etc.

[cgoepel]

drewl,
Let me know how to contact you, as I may be interested in purchasing some of your modules

[jcdillon8267]

I need the transformer on the Aux 27volt board, any idea where I can get one?
It is TS - EC28F
1806-3665-0
China Gloria

Also, the power amp conversion for the speakers sounds like a good idea if I cant get mine fixed. At least I won't have a 2400.00 paper weight.
Thanks

[cgoepel]

Don't know where to get a spare. I don't know your electronics background. These transformers are usually very sturdy. What makes you think it's the transformer?

[drewl]

I probably have it with the other stuff buried in a box.

I'll try and dig it out.

[cgoepel]

Hey Thanks!

[drewl]

From what I researched, that aux power supply was the problem with these units.

Found three of the 27volt modules, ill keep looking for the aux.

[Jazz P Bass]

Service Manual:https://www.scribd.com/document/81452344/Bose-PS1

PDF: Bose-PS1.pdf

[drewl]

Check the part number again.
I have 1806-3666-0 on the 27v supplies.
Can't find the aux supply board.

[jcdillon8267]

Don't know where to get a spare. I don't know your electronics background. These transformers are usually very sturdy. What makes you think it's the transformer?

I had one of the large diodes shorted,( might have been 607) I replaced it.

I have no voltage that I can read on the secondary windings going into the diodes. and of course nothing out of the diodes. Other than that I see no visible damage to anything. Am I on the wrong track?

It's been a long time since I looked at anything on a board level, I worked in industrial maintenance ,on lathes and plant electrical and a few NC controlled lathes. That was in the 90’s, since then I have been an a-plus computer technician.

I am desperate to fix my Bose L1 Classic, It quit in the middle of a show. I was lucky that I had my other L1 Classic in the van and swapped out the PS1. I am now afraid to use the working system, I plan to sale it all, now that Bose is of no help at all.

I have 2 complete L1 Classics with 4 B1 bass units and a paclite power amp.

And now one of them is a very expensive paper weight.

[gis]

I had one of the large diodes shorted,( might have been 607) I replaced it.
I have no voltage that I can read on the secondary windings going into the diodes. and of course nothing out of the diodes. Other than that I see no visible damage to anything. Am I on the wrong track?

Same here. Have you managed to find the spare parts anywhere?
I tried also buying broken PS1 for parts, but didn't find anyone.
Bose told me they will not service the PSU anymore.

[Enzo]

What parts do you need to find?