Pete wrote:

I'll be removing one leg of most of the components to test their values over the next few days ...

🤔 Yes, that's one option, I guess....but I'd strongly advise against that!! Lots of things can go wrong with all that soldering, not to mention the mechanical stress on the components...

If you must, remove all the transistors and test them out of circuit with a multimeter -- or a transistor tester if available. Carefully compare their values between left and right channel.
Once all the transistors are out, you can easily test resistance values on the board without danger of interference by other components.
The only other components on that board that are likely to fail are the e-caps. Did you recap the board before first power-up? There's no point in messing with the resistors - they never fail except for overheating or mechanical failure.

PS: If you're unfamiliar with transistor testing with a multimeter, research it on the internet. You should find plenty of tutorials or uTubes on that!

The enduring learning curve to enthusiastically repair one channel of a shorted Beomaster 1700 amp continues..

Step:

1.Google (other search engines are available) to find similar issues/solutions

2. Find a service manual/circuit diagram/schematics et ‘al

2.Forums are your new friend

3.Try to explain everything

4.Ask the right questions 

5.Don’t expect all the answers

6.Hope for questions…

7.Photograph everything before, during and after ‘tinkering’

8.Remove components from a PCB with a sucker or wick to avoid damage to PCB - see photos

9.Research any discontinued component electrical characteristics to find valid alternatives

10.Test component values / replace if necessary

11.Learn the difference between PNP / NPN and understand that not everything is the same in component pin layout😳 ie BC556b is PNP yet has a different Base/Collector/Emitter configuration/orientation to others!

12.Don’t trust PCB screen print layouts or schematics, compare every component to other circuits and industry standards. eg Capacitor polarity😮

13.Buy new components based on above

14.Send out white flag

15.Wait

16.Turn on… 

= Success / Failure

This weekend all the defective components will be replaced to the PCB and every one checked for connection to their correct place on the PCB according to the circuit diagram. Check over many times and check again then to power up - (power supply checked!)

Wish me luck - see you on the other side

The ‘Life is too short’ option is:

HiFi 2.0 Channel Power Amplifier Board HiFi Stereo Audio Amp DIY KIT MJ15024 and hide it in the B&O case (-:

Photos illustrate chaos, frustration and incompetence, mildly mixed with enthusiasm and hope (-:

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board without TR/IC's Login to view image

PCB connections drawn based on circuit diagram due to soldering train wreck! Login to view image

what a mess Login to view imageHope this helps someone out there...

Maybe its me but it looks a bit like some of the traces are missing. and lifted.  

Honestly don't know what to make of it.  Is that supposed to be the desoldered or soldered state?  I can't see how any of that could be working.

Pete wrote:

PCB connections drawn based on circuit diagram due to soldering train wreck! Login to view image

lots of tracking had lifted so had to work out what goes where before putting transistors back. What u see is the board without transistors. Work in progress - sort of 😇

If you ask me, then what you see is a board beyond rescue.
Your soldering iron is way to hot.

Martin

You are so correct! 😳

..but i will not be beaten (-:

I've noted where all the tracks are supposed to be (see diagram with my red line markings) and plan to link all areas where I've previously destroyed them with a too hot iron and too much tugging!

The problem of removing components came quite late to me after I realised I had a solder sucker from years ago which would have made it so much easier and tidier🙂 Lesson learnt

All new components have arrived by mail/post so plan to instal them on the PCB and carefully check (twice/three times) all the links i make where there are no tracks.

But first i will check all new transistors with multimeter for irregularities, inc hfe, pin layout, dudd components - a 'kind of' quality control

This really is my last go at this. 'Lockdown' with CV brought me here to learn with time at hand 

Please don't think I'm ragging on you...

Poor technique has made a simple (ish) job rather more involved than it needed to be.  Take some time to watch a few soldering videos on YouTube.  There are also a few on desoldering.  MrCarlsonsLab   https://m.youtube.com/channel/UCU9SoQxJewrWb_3GxeteQPA  might be a good place for you to start.

Properly desoldered parts more often than not just fall out, no tugging or force required. 

A hot iron is not bad on its own, but dont dwell too long, otherwise you'll end up melting the board and resinous material, separating the the traces and pads - which is the mess you've got now. IIt might be recoverable, but you need to be patient and not continue to make the same mistakes.

Seriously, spend half an hour to an hour watching some vids on soldering technique and you'll be in a better position to complete this and will probably save yourself at least tht amount of time by not making things worse.

Thanks for the advice on soldering (-:

I’ve replaced all Electrolytic Caps/Transistors(+ic’s) and checked all joints and values of all components. Overal the values of each component on left and right channel seem symmetrical. Traced all tracks according to circuit diagram, checked continuity. 

Turned on power without pre-amp input plugged in. No heat anywhere on the PCB, tried to measure the 12mv across R221/R121 and didn’t get a value at all no matter what i set the variable resistors to. Tried to measure 30ma collector of IC101/201 to ground, equally no result. !

Just out of curiosity measured voltage across left and right channel speaker output - both at 45v dc !?

Then I plugged in Preamp output to the board, powered up and immediately R214 (27ohms) is hot and smoking !! so quickly turned everything off.

Arrrggghh what am I missing?

Please... this is driving me nuts

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It would take several defective components to make R214 start smoking.
Shorted TR201, Shorted IC200, IC201..
Or some connection on your board is now wrong.
But wasn't this the working channel?

When I said this board was beyond repair, it's partly because of all the damage it now shows, but mainly
because the board material (pertinax, which is basically made from pressed layers of cloth and lacquer) tend to
become slightly conductive if scorched.
This cannot be cleaned away. Only way is to remove the scorched material (cut holes).

I admire you persistence, but this board will never be good again.
Even if you manage to get it working, sort of, it would be a neither stabile nor presentable repair.

Martin

Thanks Martin

The channel that died when the speaker was shorted many years ago is the channel that smokes!

I daren't wire up the speakers for the other channel, esp now that i have replaced all its parts too!

I didn't know the board could become conductive, there are quite a few scorched areas ( a few more than when I started to fiddle).. I'm guessing it's very likely I've made it worse and/or maybe missed the obvious referring to the circuit diagram (and the other channel on PCB) and have killed all the new parts when soldering them in + <deleted further excuses>

There's enough parts here now to build one of these a few times over from scratch. I despair 😳 So very sad for me to have failed to repair my dear departed uncles hifi. Looks like I'll have to buy an off the shelf Chinese Quad clone amp on pcb than will run on 50 ish volts and hide it inside and probably mess that up too😠

So very depressing - yet I want to thank you and fellow BeoWorld members for their help along the way.

I daren't continue the Reel-to-Reel Beocord 1200 repair despite re-fitting all the belts successfully. Maybe when this 'lockdown' is all over I'll be able to buy ingredients for baking a cake or basket weaving😂