Sign in   |  Join   |  Help

Beomaster 8000 Restoration

rated by 0 users
Not Answered This post has 0 verified answers | 65 Replies | 1 Follower

dahiyas
Top 500 Contributor
United States
145 Posts
OFFLINE
Bronze Member
dahiyas posted on Tue, Oct 13 2020 5:47 AM

This weekend I started on trying to restore a Beomaster 8000. 

Couple of issues before I started -

1. Three buttons missing on the panel - Martin found the replacement buttons in his dungeon and sent over the same.

2. The system has the standby light on but does not come out of standby.

3. The volume dial makes a scratching sound when turned. Looks like something is out of alignment.

So last 2 weeks were spent reading all Beomaster 8000 related messages to prep for the project. Rudy's (Belover) detailed blog was really helpful to get started.

I will also do a complete recap while trying to fix the above issues.

All Replies

dahiyas
Top 500 Contributor
United States
145 Posts
OFFLINE
Bronze Member

No problem.

I bought this used and the only thing working when I started was the standby light. After the recap I had plugged in headphones and that worked fine. (except the clicking on volume change - volume offset needs adjustment).

I have changed the connectors on the cpu/display board and that has fixed the intermittent standby/display issues.

I will proceed to checking the transistors. 

Don't have the external power supplies but we'll come to that later.

Thanks again for the inputs.

dahiyas
Top 500 Contributor
United States
145 Posts
OFFLINE
Bronze Member

Sonavor - Good news and bad news Smile

I couldn't resist connecting speakers 

Looks like the left output pcb survived (the one I was trying to adjust and saw smoke). I connected penta (minus the amp) and left side plays well.

But the right side is bad. I can hear low volume from the right side with distortion. The volume keeps fading out and coming back.

Either this pcb was bad prior to me getting the system or while I was focused on the left pcb, the right pcb would be heating up if idle current was out of spec and that killed the board. Ideally, should have worked on one board at a time - replace trimmer and adjust, then move to next board.

As indicated by Martin/You in other posts, will rebuild both the boards in any case. The TIP's and other parts are not that expensive.

Are there any equivalents that I can look for if I don't find the TIP141/TIP146?

 

sonavor
Top 25 Contributor
Texas, United States
3,715 Posts
OFFLINE
Gold Member

Well...these things happen.

I would look for TIP141 and 146 devices.  You should be able to find them.

I am a little unclear on the left channel output amplifier board. Were you able to finally adjust the no-load current on that one?

The boards shouldn't require a rebuild if you already worked on them. It sounds like there was a problem with the transistors that finally caught up to the output amplifier...once you replaced the capacitors. 

-sonavor

dahiyas
Top 500 Contributor
United States
145 Posts
OFFLINE
Bronze Member

Yes, I had replaced all the caps on all the boards.

After finishing the setting of left, I looked at the right side. I noticed that the heat sink was hot. So adjusted the idle current trimmer and also the volume offset . switched off the system and waited for 10 mins. The heat sink was cool again. Switched on the system. The heat sink did not become hot but felt heat from the output pcb. switched off again. Both the BF857s were hot.

Playing source through TP1, produced good sound from left but very low/shrill volume from right with volume fading in and out.

 

sonavor
Top 25 Contributor
Texas, United States
3,715 Posts
OFFLINE
Gold Member

I would leave the left channel output amplifier board alone then.

One nice thing about the way it turned out...If you do want to remove the whole output amplifier assembly so it is easier to check and work on, the right channel is pretty easy to remove the way I showed on the blog.  The left channel is the tricky one and has to be rotated ninety degrees to remove it out the back.

Remove and check the transistors on the right channel output amplifier assembly as a start. 

-sonavor

dahiyas
Top 500 Contributor
United States
145 Posts
OFFLINE
Bronze Member

I did pull out the transistors. All of them read 2.5v-2.8v between B-E instead of OL.

Have ordered replacements. Hopefully will be here by weekend.

What are the other components I should be checking on the output PCB ?

 

 

 

sonavor
Top 25 Contributor
Texas, United States
3,715 Posts
OFFLINE
Gold Member

Your measurements of the TIP 141 & 146 Darlington pairs seem a little odd. 
A good transistor of those type measure with a Vbe of around 1.13V.

With a failed board like that one I would check all of the semiconductor components (transistors and diodes) to be safe.

If you plan on doing more restorations it is worth it to invest in a good transistor/diode tester.

-sonavor

dahiyas
Top 500 Contributor
United States
145 Posts
OFFLINE
Bronze Member

Yes Sonavor...This is my destressing activity..so have been buying tools on need basis.

I did use a DMM to test the transistors and followed the general guidelines for testing a NPN and PNP transistors. 

I did pull out my component tester and tested all the transistors. None of them came up as "damaged component".

TIP 141 - hFE - 36/35/35 ,Ube - 996/996/970mV, Ic - 5.6/5.6/5.6mA, CE - 578/570/567mV

TIP 146 -  hFE - 27/35/31,Ube - 873/858/862mV, Ic - 5.7/5.7/5.7mA, CE - 587/575/582mV 

 

sonavor
Top 25 Contributor
Texas, United States
3,715 Posts
OFFLINE
Gold Member

That's good news then. Your IC201 through IC206 transistors are likely good.
The bad news is you will have to keep going and check the rest of the transistors on the board. 
There are eleven on the PCB itself and one small transistor on the heatsink (TR208).
Then there are twelve 1N148 diodes and one 9.1V zener diode.

-sonavor

dahiyas
Top 500 Contributor
United States
145 Posts
OFFLINE
Bronze Member

I looked at the PCB carefully and I think one of the legs of a 200uf capacitor was not soldered properly. (Lesson to others - please listen to the experts who recommend pulling out the PCB for recap.).

Can that explain the volume fading in and out ?

dahiyas
Top 500 Contributor
United States
145 Posts
OFFLINE
Bronze Member

I looked at the PCB carefully and I think one of the legs of a 200uf capacitor was not soldered properly. (Lesson to others - please listen to the experts who recommend pulling out the PCB for recap.).

Can that explain the volume fading in and out ?

dahiyas
Top 500 Contributor
United States
145 Posts
OFFLINE
Bronze Member
dahiyas replied on Tue, Nov 24 2020 11:02 PM

I de-soldered and checked all transistors and diodes. everything checks out ok.

Did the loose capacitor cause the volume and heating issue ? I was able to set the trimmers to the right specs.

Sonavor - Any other checks you can recommend before I put the board back ?

sonavor
Top 25 Contributor
Texas, United States
3,715 Posts
OFFLINE
Gold Member
sonavor replied on Tue, Nov 24 2020 11:36 PM

I can't think of any. It sounds like you checked all of the component thoroughly.
When you say you set the trimmers do you mean you did connect up power to the output amplifier and do the idle current check?

-sonavor

dahiyas
Top 500 Contributor
United States
145 Posts
OFFLINE
Bronze Member
dahiyas replied on Wed, Nov 25 2020 12:07 AM

Yes Sonavor, the trimmer settings were done prior to me pulling out the board and transistors. 18mV and 0mV. After performing the settings, I figured that the right channel was not ok.

Yes, all of the components tested ok on the component tester. 

Only thing I can think of is the bad solder joint. I had done the recap without pulling out the boards on a vertical board. Soldered all the caps again also checked the polarity again. But not sure if that would lead to the BF857 heating up so quickly.

I don't have much of a choice but to put the board back. Don't have any external power supplies (as yet) to test the board outside the system.

Will report back once done.

sonavor
Top 25 Contributor
Texas, United States
3,715 Posts
OFFLINE
Gold Member

I have a hunch it will work this time.

If you do decide to invest in some bench power supplies make sure you get ones with a current limiting feature. On my 60 VDC supplies I preset the current limit so they won't exceed what the Beomaster 8000 Output Amplifier board can take. If something is wrong on the board and it starts demanding too much current when I test it then the power supplies just shut down.

-sonavor

Page 2 of 5 (66 items) < Previous 1 2 3 4 5 Next > | RSS
Beoworld Security Certificate

SSL