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Old 17th Apr 2017, 8:28 pm   #61
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Default Re: Sony HP-511 - Blowing Fuses

Many thanks to Roger (RojDW48) for taking a look at the set for me. What a decent guy! A really nice collection of vintage valve gear too! Superb.

We spent several hours testing and looking over the set. Unfortunately Roger was unable to pin down the source of the problem, but hoping that by posting what we've done may spark some things to look for or ideas...

Roger: Possible contact fault. Cleaned up all contacts and switches; left & right volume control, function and speaker switch. Tightened and cleaned Phono speaker contacts. Still Left hand channel fault. Sounds like poor contact fault. Even when Left channel is running, it sounds like it is clipping.

Video of the set running here...https://youtu.be/5kXKRbSBkQ8

Or any recommendations for getting the unit repaired around Bristol and the surrounding area?
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Old 18th Apr 2017, 12:16 am   #62
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Default Re: Sony HP-511 - Blowing Fuses

Well - we did quite a few basic checks. If I had brought this item home from a sale and tried it out I would have been confident that cleaning up all the contacts would fix it! Sadly not. Doing all that made the LH channel more reliably 'on' but still distorted. All inputs produce the same problem and it happens on headphones, which makes me suspect the fault is in the pre-amp (or maybe power supply?). I am not at all confident about dealing with solid state electronics but this seems to be a well made unit which would be worth the effort of repairing and it was good to meet this enthusiastic and determined member of the forum. I really hope someone more talented than I am can help him out!
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Old 18th Apr 2017, 5:08 am   #63
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Default Re: Sony HP-511 - Blowing Fuses

Nice one Roger for having a go, sounds like you had a bit of a laugh. shame you couldn't fix it.

These's two approaches to fixing this the systematic one where you inject a signal and trace it through each stage after checking all power supply voltages. Usually you'd inject a signal just past the preamp stage to check to see if the output stage is working ok. Or you can try changing the transistors in the preamp section and hoping for the best.

The first approach is the correct one but that requires a bit more knowledge and test gear than you have Garath so short of someone else having a look at it for you, you might as well try changing the trannies in the preamp section.

I tried to download the manual but get this - see att.

Andy.
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Old 18th Apr 2017, 9:47 am   #64
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Default Re: Sony HP-511 - Blowing Fuses

I too tried downloading that - I am still waiting for the email to confirm my log in!
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Old 18th Apr 2017, 10:33 pm   #65
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Default Re: Sony HP-511 - Blowing Fuses

Thanks for the help guys. I think that this maybe as far as I am willing to go as to remove the preamp/MPX board, it appears as if I need to tackle the dial cord stringing. I will take a look into this in more detail when I get time. But if this is the case, I fear that this may be beyond my comfort zone and I may ruin the set.

If this was the case, would a damaged preamp transistor cause the output driver & output transistors to blow? I ask this as this is what happened when I plugged into the mains power previously.
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Old 18th Apr 2017, 10:44 pm   #66
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Default Re: Sony HP-511 - Blowing Fuses

I have uploaded the service manual here if this is what you guys were after?

https://drive.google.com/open?id=0B1...XpNQU9qRHZPZXc
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Old 19th Apr 2017, 9:21 pm   #67
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Default Re: Sony HP-511 - Blowing Fuses

I've managed to remove the pre-amp board, the set now looks like a skeleton! Such fabulous craftsmanship has gone into this unit and that service manual is a god send!

I've located the pre-amp transistors. They are 2SC631A and 2SC632A. These transistors are around £15 each plus postage from abroad so this could get pretty expensive. So I have a couple of questions...

The output transistors that blew were 0510 & 0509. This is the Left channel according to the markings on the power amp PCB, which is also where the sound clipping issue is. Would I be right in thinking that transistors marked 0501 & 0502 are the Left channel pre-amp Q's? (the other Q's are marked 0601 & 0602 and the power amp Q's for the Right channel are marked 0609 & 0610).

The other question and one that has been baffling me is why does the power amp have 5 output Q's? I thought it used 2 OP's per speaker output, yet there is an extra Q?


Gareth
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Old 20th Apr 2017, 12:15 am   #68
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Default Re: Sony HP-511 - Blowing Fuses

Before you spend out on more components - have we exhausted potential problems with the power supply? I am frustrated by my inability to understand solid state electronics but, at some point I recall taking a reading off the smoothing cap which, bearing in mind the LL, seemed to indicate the supply voltage was 50V or thereabouts? I remember hoping it was 25V because I could have substituted one of those. Have you identified the rectifier and regulator and taken readings with the unit working - with care, obviously and hopefully someone will be able to indicate what we should be seeing. Thanks for the manual upload by the way!
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Old 20th Apr 2017, 12:16 am   #69
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Default Re: Sony HP-511 - Blowing Fuses

And, yes, I was confused by what appeared to be a 'spare' OP transistor - surely not!?
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Old 20th Apr 2017, 6:46 am   #70
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Default Re: Sony HP-511 - Blowing Fuses

Having finally managed to see the schematic ( can't download manual) I can see a bit more what the craic is. I'm nowhere near as experienced as a lot of chaps here but the power amp looks like a quasi complementary stage, see att scn shot. I can't see what the middle Q is, but suspect it is a series pass Q used on the power supply.

Before you buy any transistors I'd get a sheet of paper and write down the voltages on the right hand side working channel, particularly at each Q's base, emmiter and collector,( be careful, its easy to slip and short out something). then do the same for the left channel and compare.

Next to see if the OP stage is ok try putting a 1khz sinewave just after C551 where R551 and R552 connect. Start with about 10mV. To do this Gareth you'll need to find a test tone online and also make a lead up say with a 3.5mm jack on one end that will plug in to your phone or PC and two of those little test probe clip thingys on the other (these - http://www.ebay.co.uk/itm/SINGLE-MIN...oAAOSwA3dYMjQC) Or I can do the 3.5mm part, you'd just need to buy and solder on the two test clips.

If your left hand side power/OP (output) stage is ok I'd go on and inject your test signal further back until you find the problem. If it were on my bench I'd test all the electrolytic caps with an ESR meter and suspect a dodgy cap in the tone or loudness section or preamp section. I'd also test the Q's in the preamp section at some point.

Andy.
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Old 20th Apr 2017, 8:47 am   #71
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Default Re: Sony HP-511 - Blowing Fuses

Looking at those diagrams, the first shows a fairly standard Baxandall type tone control followed by switchable loudness compensation, whilst the second, if I read it correctly, can be broken down as follows ; Q504 & 506 are pre-amp/driver stages,Q505 is a Vbe Multiplier. The output stages cosist of two Darlington Pairs, Q507/509 and Q508/510 respectively.

Basically I'd follow Andy (Dr. Wobble)'s suggestions
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Old 20th Apr 2017, 8:30 pm   #72
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Default Re: Sony HP-511 - Blowing Fuses

Thank you for your help once again...

Roger, I haven't taken any readings on the unit with it running yet. But thinking about what has blown and the problems we were seeing with it, it seems to be isolated to just the left channel. The right channel has had no issues besides the dirty phono connections. I still don't really know though... Maybe we can both get our heads around transistor sets with this issue and chat about it over a tea to celebrate if this blooming thing ever works properly, lord knows this has been frustrating!

Dr Wobble, when checking the voltages with the set on, where would I want to anchor the negative side of the DMM when I am checking the OP Q's for example? Is there a figure I should be seeing or is it a comparison of the working channel?.. If you could do the 3.5mm jack part of the cable that would be brilliant. Send me your paypal and I will pay for the parts & postage?
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Old 21st Apr 2017, 12:13 am   #73
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Default Re: Sony HP-511 - Blowing Fuses

Hi Gareth - I'll happily supply a 3.5mm jack and lead if you want to pop in (and I should be able to find a croc clip for anchoring the negative lead - BUT I'm away till late Monday!). Clip the -ve lead to the chassis - I don't think that changed with the advent of solid state circuitry.....or did it!?
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Old 21st Apr 2017, 5:52 am   #74
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Default Re: Sony HP-511 - Blowing Fuses

I thought those Q's in the OP stage were configured as Darlinton's but Q508 being a PNP confused me.

Rogers right, -/black lead goes to chassis. Gareth you need to do a list something like this - see below. Ignor the 50 bit on the schematic.

RHCh

* Q1 C
B
E
Q2 C
B
E etc.

LHCh
Q1 etc

It helps if you get the datasheet for each Q before taking readings and find the pinout's, so that when you come to test you know what the craic is, IE pin 1 = E, pin 2 C etc.Test the right ch first, then the left. Next if your confident and there's room, remove the black lead from chassis and with one lead on the Base and the other on the Emitter take a reading of each Q of the LHC. You should get 0.4 to 0.6v if the Q is working ok.

As Roger is sorting you a lead out, I'll hold fire. I'll try and get 10 minutes to read the manual, but usually the schematic has the voltages written on it, couldn't see them though on this one.

Andy.
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Old 24th Apr 2017, 8:14 pm   #75
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Default Re: Sony HP-511 - Blowing Fuses

Thanks Andy...

I am planning on testing the unit over at Roger's this coming Sunday and just wanted to get a bit more detail on these procedures if possible. When testing the voltages on each Q at CBE and logging, I am presuming we should be seeing very similar figures on all Q's? (I tried to see voltages on the schematic), using the set on the LL with an aux input?

When injecting the sinewave into the power amplifier (10mv) I am guessing that I need to attach the signal wires to the inner legs of resistors R551 & R552? Would polarity matter here or would it just cause an out of phase tone?

Once we have injected this sinewave and if we feel that the audio is ok, would you be able to explain where we would inject the sinewave next (loudness/tone/preamp board)?

Thank you
Gareth
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Old 25th Apr 2017, 5:55 am   #76
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Default Re: Sony HP-511 - Blowing Fuses

No worries. Yes, you should see similar voltages, but if you get something like this RHC Q2 E 1v B 1.6v C 15v LHC Q2 E 2v B 2v C 20v , aha!, something amiss with Q2 LHC. The figures are made up and have no relation in reality. But you should see a 0.4v to 0.7v difference between B and E. Take readings with no input, preferably with the input shorted, amp on for 5 minutes.

Polarity matters because your scope and probably sig gen is referenced to earth. Your black clip goes to chassis, I use a jump lead to extend my scope/sig gen ground leads if it won't reach.

I've attached a crude "inject signal here" schematic" . My skills with Gimp are zero, it's so b****y complicated, I'll print off the schematic and draw pointers in by hand that hopefully will help. It's a good idea to attach any leads etc whilst the amp is turned off. Turn amp on, let it warm up a bit, then switch on signal. Signal doesn't have to be 10mv, but its a good place to start, slowly increasing it as you go. If you get no joy with a 1v signal, forget it.

Another good fault finding technique is to put a scope on the speaker out terminals, or an old speaker, and poke it with a stick. By this I mean if you turn the amp on and give it a gentle but firm thump, and you get crackling or audio on the OP, you can get a non conductive proddy thing, like a small stick and poke around inside, like the PCB, transistors etc. This teqnique is good for finding dry joints etc.

Any other questions please ask. Drop me a PM on Friday if I havn't posted a schematic, I have a head like a sieve.

Andy.
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Old 25th Apr 2017, 11:09 am   #77
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Default Re: Sony HP-511 - Blowing Fuses

Quote:
Originally Posted by Dr Wobble View Post
Another good fault finding technique is to put a scope on the speaker out terminals, or an old speaker, and poke it with a stick. By this I mean if you turn the amp on and give it a gentle but firm thump, and you get crackling or audio on the OP, you can get a non conductive proddy thing, like a small stick and poke around inside, like the PCB, transistors etc. This teqnique is good for finding dry joints etc.
I did have an experimental poke around with the handle of a screwdriver in the hopes of surprising a cracked resistor or similar into revealing itself - Gareth only seemed slightly alarmed! That's all very helpful Andy - we shall have another go.
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Old 25th Apr 2017, 3:04 pm   #78
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Default Re: Sony HP-511 - Blowing Fuses

I'm in the Bristol area as well so I could point a scope (or even S/A) at this Gareth / Rodger - if that's any help ? This should give a better diagnosis of whats going wrong. I could probably make a few guesses but you've probably swapped enough parts already

Seriously though, a very good effort so far. And don't forget transistor power amps can be a complete devil to fix (even a 'simple looking' one like this) so to get this far is a REAL achievment !

Sadly my test gear is not portable so you would need to bring the item over to me in the east Bristol area, near M32. PM me if I can be of help.

dc
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Old 25th Apr 2017, 3:24 pm   #79
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Default Re: Sony HP-511 - Blowing Fuses

The power amps seem to have 0.1uF dc blocking capacitors on their inputs.

It would be tempting to lift the input ends of each of these and rig a couple of pieces of wire to drive each one from the opposite side's preamp.

If the distortion swaps sides, it's in the power amplifier. If it doesn't swap sides, it's in the preamp.

£18 for a transistor isn't necessary. It's quite a nice music centre as music centres go, but no rocket scientists were harmed in its development There should be several common and cheap types which ought to do the job if that's what it needs.

Fixing DC-coupled audio amplifiers is quite different to valve amps. It is neither easier or more difficult, just different. Once you start to 'see' how it works and understand its foibles, they aren't bad to fix. For the unwary, they have a nasty trick of sending the repairer round and round the same circle. There is a reason why this is so and it's not difficult to understand.

Anyway, good work so far, and you must be nearly there.

David
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Old 26th Apr 2017, 5:49 am   #80
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Default Re: Sony HP-511 - Blowing Fuses

"Seriously though, a very good effort so far." Your right there Dave, I take my hat off to Gareth for sticking with this, and your offer of help may be needed. As David says these transistor amplifier's can be tricky to fix, I've struggled with them and continue to do so, as Roger admits they're not his forte. Some help from more experienced members is welcome.

Andy.
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