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Brooke Amplifier Problem

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Tan-2 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tan-2 Quote  Post ReplyReply Direct Link To This Post Posted: 10 August 2013 at 10:40am
Sometimes we get them pain in the butt repair's that have us burning the midnight oil...it's good to take some stress free time out.

Have you measured voltage at the o/p in case there's high offset?  even after replacement's have been fitted there still might be a leaky, o/c or s/c part, them sneaky diodes or even them small short circuit trannies within it's I-limiting circuit will act up.. that mje350 would under stress from heating up this would be around it's vas stage or bias circuit.. 

I've a few repairs waiting in the work shop so it's grab a coffee time/food offering followed by the joyful comments from 'joe' public.......ie, our amp starting smoking, mmm that can't be good for it's health!
Logic will get you from A to B. Imagination will take you everywhere.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JayeJSAV Quote  Post ReplyReply Direct Link To This Post Posted: 12 August 2013 at 4:01am
So, lots of stuff replaced, done all the big resistors, cause they all showed signs of scorching, and one had a broken leg too. Just did a power up test now after those replacements (couldn't swap out the MJE350 cause Farnell missed it off the order), and instead it just decided to blow that and take out my plug fuse. quite a few darkened resistors on the power supply board also, so going to change those too.

I wish this guy had just said "I'll replace it", although I am looking forward to the happy face when I've completed it, even if it is a full rebuild! :(
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tan-2 Quote  Post ReplyReply Direct Link To This Post Posted: 12 August 2013 at 8:53am
It's looking like a psu and stage rebuild on the cards ... Just hope that none of the replacement output devices have not been damaged when that primary fuse blow.
Try hifi engine and see if service info is there you might be lucky there or it will be the case of long hours to solve this mess.. Some up load pics would be handy here so we can see things as last link did not work.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote JayeJSAV Quote  Post ReplyReply Direct Link To This Post Posted: 12 August 2013 at 2:02pm
Hifi engine?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tan-2 Quote  Post ReplyReply Direct Link To This Post Posted: 12 August 2013 at 5:45pm
It's a site to look for schematic's..
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JayeJSAV Quote  Post ReplyReply Direct Link To This Post Posted: 12 August 2013 at 11:22pm
ooooooo :)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JayeJSAV Quote  Post ReplyReply Direct Link To This Post Posted: 13 August 2013 at 5:12am
Ooooohhhhh kayyyyy

So, after repairing the power supply, I now have a nice pair of rails at +18v and -18v, and another pair at +70v and -70v. Before, I was getting a ripply +16 and -19, and then +60 and -78.

Bearing in mind that I have replaced with identical components (no alternative swap outs needed, all readily available), and that I have no kind of diagram at all, I don't even think one exists, I am hoping that they are correct.

On the photo, you can see the runs of resistors, all off a common track, feeding into one output device each. Those are the ones which were scorched, as well as the MJE350, and 340's. On magnification on the bench, I found some cracked diodes too, as well as bulging capacitors.

So I've replaced the 7 faulty output transistors, the other cracked components, and a couple of suspect ones (near by the ones which were damaged, not scorched as such but more discoloured). As they were mostly 1/4w resistors, I thought I may as well. Checked board for any stray solder and flux as per usual, and connected it back to the power supply. (After discharging PSU Caps).

Power up time!

1) Smoke.
2) 0.15 ohm resistors (at inner most side of white blocks - 5W), glowing...
3) I'm sat in bed writing this and picking their casings out of my hair.

So, tomorrow, test PSU post explosion.... and I have decided that as I have no information whatsoever, and the client STILL wants it fixing, despite rising costs, the only way forward is a complete rebuild of that channel.

I would have done some tests on it to get more info, however it blew up.

Here's a link to that picture, and hey guys, it works!!






Edited by JayeJSAV - 13 August 2013 at 5:14am
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JayeJSAV View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JayeJSAV Quote  Post ReplyReply Direct Link To This Post Posted: 13 August 2013 at 5:50am
Well after not sleeping yet and googling about, I found a spec sheet for it,  but that is literally it.

I've also seen it called a Cave CV4000 but apart from that, this amp doesn't seem to have any information at all. http://www.satsol.co.uk/impact/ProductInfo/J01953/J01953.pdf
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tan-2 Quote  Post ReplyReply Direct Link To This Post Posted: 13 August 2013 at 9:12am
It's going to be a real testing time this repair and like you say, cost is creeping up.. Now that you've got the knackered channel out the way and using the working side for reference voltages that way you have something to go with.
It would of been best to replace all o/ps due to stress as working with a mix of replacements and old ones may see this unit back on your bench and a red faced client...

Here's the thing instead of reaching for that hammer to get the stress out as it may seem you can't see the wood through the trees so to speak.. Grab your meter and carry out cold resistance mesurements between the pcb's plus when powering up said faulty side using limiting resistors in the ht rails that way it would give you time to carry out ref points instead of cooking breakfast on the heating parts...
Do you have a variac with limiter that would aid running things up instead of slamming power on and watch the fire works happen...
Logic will get you from A to B. Imagination will take you everywhere.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JayeJSAV Quote  Post ReplyReply Direct Link To This Post Posted: 13 August 2013 at 2:25pm
I don't, but I am still adding things to my bench as I go along.

Thing is, I am wary of applying the working side to the amp in case the psu isn't kicking out the right voltages, (bearing in mind nothing is labelled as to what it gives out, just VL and VH for low and high voltage).

I'm off for some bacon and components. Not necessarily in that order :)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tan-2 Quote  Post ReplyReply Direct Link To This Post Posted: 13 August 2013 at 4:13pm
Your need to run the good channel to get a clear line of volts for ref point.. The Lv line would be running op-amps/ led display, there should be a feed to relay, fan circuit per say.. Even using 47 ohm say 40w or more in the ht rail would give time to get some voltages down.


The working side will be the only clue here to see how volt lines such as long tail in put transistors or if its op/amp in put circuit followed by vas stage driver and o/p end.

A quick limiter is the old lamp in the mains plug trick this acts as a limiter via glowing bright indicates a short some where and you might have to use to 100w bulbs.. The trusty lamp limiter as served me well...

Logic will get you from A to B. Imagination will take you everywhere.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tan-2 Quote  Post ReplyReply Direct Link To This Post Posted: 14 August 2013 at 7:06pm
So was it a scrap it job due to cost or more time and parts to rebuild?
Logic will get you from A to B. Imagination will take you everywhere.
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