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Studiomaster 2000e repair help

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kedwardsleisure View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kedwardsleisure Quote  Post ReplyReply Direct Link To This Post Posted: 14 June 2022 at 5:00pm
no tipsy amp repairs please, it will end in tears.

1. ascertain if its an output module or something else.

(swap entire module from one side to the other)

2. either repair the 'something else' (pre amp) or

3. ascertain whether the faulty module is the switching or amp pcb

(swap boards with well-marked good side)

4. Go over the faulty board part by part. On a simple amp like this its quicker to cold check components rather than get in an endless loop with signals and offsets and long tailed pairs and whathaveyou.


Kevin

North Staffordshire

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Randy Bohannon View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Randy Bohannon Quote  Post ReplyReply Direct Link To This Post Posted: 14 June 2022 at 5:10pm
Thanks Kev, definitely no tipsy amp repairs. The weather is so glorious I’m going to be bbq’ing in the garden and not hunched over that infernal amplifier.

Your methodology makes sense, this was the better of two blown modules and so I had hoped that it would be more likely to work.

I’ll go through the other one, swap halves back and forth and see if I can get any further. Thumbs Up
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jbl_man Quote  Post ReplyReply Direct Link To This Post Posted: 20 June 2022 at 3:27pm
Any update on this Randy? 
Be seeing you.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Randy Bohannon Quote  Post ReplyReply Direct Link To This Post Posted: 21 June 2022 at 9:44pm
No update as yet I'm afraid.

I got mixed up in a Yamaha M85 and the active crossover in the car has just died and so it's gone on the back burner for now.

I'm going to rebuild the other module so I can do some swapping around, hopefully in the week.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Randy Bohannon Quote  Post ReplyReply Direct Link To This Post Posted: 31 October 2022 at 2:40pm
Suitably emboldened by the success of my other two restorations, I thought to tackle this treacherous malingerer, erm... I mean favourite old amp again...

Part of the problem with this amp was that it was badly repaired in the dim and distant by some arse who buggered up a lot of the PCB tracks. I've tried to repair what I can but given that pretty much every component was changed for brand new, I took a close look at the back of the board.

With the help of the brilliant photo that Cravings kindly posted earlier, I realised I has made a small mistake with a connection of a small compensation cap but nothing that would seem likely to cause the problems I am facing.

I would be very grateful if @Cravings, or any other kindly soul for that matter, might post large photos of the backs (and fronts if it's not too cheeky) of both amp and switching PCBs so ?I can do a sanity check and make sure my PCB repairs are correct?

The issues I'm having are:

a) 2v DC offset on the output, amplifier passes and amplifies a clean 1kHz sinewave on this offset however

b)Consequently, or by coincidence, the amplifier half of the two-PCB output module heats up like made when off the dim bulb tester. From dead cold, the fans will spin in about 30 seconds or so and go straight to full speed.


@Kevin, thanks for your help as always.

Thanks for the roadmap, replies as per below:


1. ascertain if its an output module or something else.


(swap entire module from one side to the other)

Tricky as I have two blown modules and this one is the better (!) one...

2. either repair the 'something else' (pre amp) or

I don't think bad opamps could do this, the amp would be railed if the op amps were? I've been over the other circuits and they all seem to work, I'll check each opamp output and check that they're at 0v DC.

3. ascertain whether the faulty module is the switching or amp pcb

The amp PCB is the one getting hot, the switching PCB stays ice cold, I'm thinking that means it's the amp side but class G is fairly new to me and I'm just not sure.
 
(swap boards with well-marked good side)

don't have one sadly.


4. Go over the faulty board part by part. On a simple amp like this its quicker to cold check components rather than get in an endless loop with signals and offsets and long tailed pairs and whathaveyou.


Fair shout, I mean, I think I have but it can never hurt to double check, it was the comment about the mute signal biasing them off that got me thinking whether it was them and the fact that they are original. The only amp I've seen that managed to take out it's LTP from and output stage blow up was a Yamaha M80; perhaps I should have changed them too?




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cravings View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote cravings Quote  Post ReplyReply Direct Link To This Post Posted: 01 November 2022 at 1:46pm
https://imgur.com/a/fcgdVMO

they're obviously not disassembled, and i didn't really look at the photos, just threw them up quickly. included bits that obviously fail "visual inspection" on mine.

let me know if you want anything else (that's relatively easy to do)

Edited by cravings - 01 November 2022 at 1:47pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote luton_soundman Quote  Post ReplyReply Direct Link To This Post Posted: 01 November 2022 at 4:27pm
I miss my 2000e's Cry
Sound Hire/Sales new/used equipment.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Randy Bohannon Quote  Post ReplyReply Direct Link To This Post Posted: 03 November 2022 at 9:28pm
Originally posted by cravings cravings wrote:

https://imgur.com/a/fcgdVMO

they're obviously not disassembled, and i didn't really look at the photos, just threw them up quickly. included bits that obviously fail "visual inspection" on mine.

let me know if you want anything else (that's relatively easy to do)

Thank you mate, very kind of you.

I'm going to give the other module a go and come back to this one.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Randy Bohannon Quote  Post ReplyReply Direct Link To This Post Posted: 10 November 2022 at 8:35pm
I rebuilt the other amp module completely with new semiconductors in all positions.

Plugged into the same switching board as before it Gives the same symptoms as the other amp board, I.e. gets got and oscillates. 

I note that my board doesn’t have the extra film box caps on the bottoms that appear in the photos Cravings posted above, could that be the missing piece of the puzzle?

Does anyone know their value? 




Edited by Randy Bohannon - 10 November 2022 at 8:41pm
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