Sony HP-511 - Blowing Fuses

[gazrawly]

Hello all.

I have recently inherited a 1970's record player/wireless (Sony HP-511A). The unit has great sentimental value and I am trying to repair the unit.

The system failed to power on some 15 years ago and has been sat idle since. I have removed the turntable assembly and found 2 blown glass fuses (1.6A 20mm). The unit instantly blew the fuses the I replaced.. It is probably worth mentioning that the turn table motor powers up and spins but nothing else operates.

I am just looking for some guidance on what the most logical steps would be to repair the record player. I have read that the most likely culprit is the transistors. Before I remove the amplifier board and test the transistors, is there anything you would recommend that I check?

Apologies, I am not too familiar with electrical components but I am certainly willing to put in the hours required to learn.

Thanks
Gareth

[Diabolical Artificer]

Welcome to the forum Gareth. Don't power it on again until you've found the fault. Luckily for you there is a service manual online -

http://www.hifi-manuals.com/Sony/HP-511-A/downloads

you'll need to register to download it. Posting the schematic here will help us help you. As will some good quality pictures of the inside of your music center.

Checking the OP ( shorthand for output, in this case transistors) transistors is one good first step. To do that you'll need a DMM (digital multi meter, see here -

https://www.vintage-radio.net/forum/...d.php?t=133000

for a recent thread on DMM's). These have a diode checker which is used to test if a transistor is dead. A transistor is essentially two diodes connected together. They can be tested using the DC resistance on your DMM too. There's a thread up top that details how to test transistors or there are plenty on Utube.

Though unlikely it could be your mains transformer is the culprit, again this is checked using the "ohms" range. In a nutshell you have a short circuit (SC) to ground that is causing the fuses to blow, now you have to find that SC. So

1) get service manual and read it.
2) Test OP transistors, which might mean taking apart your MC (music center)
3) If they're gone take them out and then check again that there is no SC.
4) Replace OP trannies only after you've made sure everything else is OK. See -

http://www.forum.radios-tv.co.uk/vie...php?f=3&t=6141 for info on your OP Q's (Q = transistor, which is a gob full and takes a long time to type with one finger).

Andy.

[TonyDuell]

Having looked at the schematic, I don't think it can be the mains transformer at fault, fortunately. The fuses that I blowing, I think, are the 2 that connect between the ends of the transformer secondary and the rectifier diodes (standard biphase full wave rectifier circuit). So the fault is the rectifier, or more likely something on the output side of it. And the turntable turns, the motor for that runs off the mains transformer, so the transformer is still getting mains even after the fuses have blown (which would confirm it's the fuses I think it is that have blown).

Checking the output transistors is a good idea. Also the rectifier diodes and the smoothing capacitor. In the schematic in the manual, the rectifiers are D503 and D504, the smoothing capacitor is C701

[Techman]

All good advice.

I'd be going straight to the rectifier, which it nearly always is with this type of fault on this type of unit.

[gazrawly]

Thank you so much for your useful tips and information. It's all very much appreciated.

I have taken high quality pictures of the inside here https://drive.google.com/open?id=0B1...0ptaDZfQmxFd1k

It seems as though one of the transistors has been replaced before (all but one of the transistors has L66 under the model number with a red marker line across the top)... The turntable wiring has a strange soldered joint on it too, not sure if this is an original attachment?

Thanks Techman, I will have a look into the rectifier in the service manual

[Diabolical Artificer]

Is it an actual bridge or individual diodes. In pic 120522 one diode looks blown, bit hard to be sure for all the dust. Gaz get some compressed air and blow the PCB's clean, failing that GENTLY scoosh it out with a vacuum cleaner and feather duster.

Ta for pics didn't have a good look as I have a bad head on me this morning, but.

OP Q's look original. Re the red slashes across the OP trannies, at first I thought they were where someone had marked them as dead, but the same red marker is used elsewhere so is probably factory.

BTW, to post pic's here, click "go advanced", then click "manage attachments" a pop up box appears. Choose file, click upload and wait for the magic to work, then lastly click "submit reply" but make sure it's the bottom one, there's two.

Andy.

[TonyDuell]

If the unit follows the service manual (i.e. no production changes) the rectifier is a pair of discrete diodes at one end of the amplifier PCB (the one with the power transistors on it). It's not a bridge, it's a biphase rectifier (2 diodes, centre tapped transformer secondary). The fuses that are failing are connected between the ends of the secondary and the anodes of the diodes, the cathodes of the diodes are linked and go to the +ve side of the smoothing capacitor.

[Techman]

Originally Posted by Dr Wobble

In pic 120522 one diode looks blown, bit hard to be sure for all the dust.

You're not wrong there, Andy.

That nearest diode has been blown into the next decade by the looks of it!

Job sorted! Replace them both, and the fuses, and see what happens. OK, it might be a good idea to check for any shorts after the said rectifier diodes just in case there's something else like the smoothing electrolytic that's taken them out, but it's probably just those diodes.

[gazrawly]

Thanks again for your help...

I have just managed to find some time to try and clean the PCB. I've only managed to use a crude duster attachment on a vacuum cleaner.

I'm not sure if the diode looks blown now that I've dusted it off (I am guessing the diode is the one in the picture attached?). I need to do some more reading on this but I am going to have to pull the Amplifier board regardless. This leads me onto a couple of questions.

The joints onto the board and components are some kind of winding contacts, which I seem to remembering reading about - If memory serves me correctly, this kind of contact is far superior to soldering joints onto the PCB? Since there are a number of wires joined to the board, I am considering cutting the wires and then reconnecting them with a soldered joint and shrink wrap to retain the winding to the PCB. I also thought that it would lessen the risk of damaging the board and components with heat.

Also, which type of solder/flux and soldering iron would you recommend for soldering components to the board? I really only have limited experience soldering to boards.

[TonyDuell]

Those external connections are called 'wire wrap' and are extremely reliable if done properly. To give you some idea, I have a device here over 45 years old with over 5000 such connections in it -- all original, all good.

The wire was originally wrapped with a special tool, and it looks to be larger than the common one, so you probably won't get it. You can unwrap them easily enough with pliers. Without the tool you will have to solder the wires back, to be honest you won't notice any unreliability from this in a radio/record player.

I am surprised, though, you can't get to the solder side of the PCB without disconnecting everything. There's normally enough slack in the wires to let you do this.

That diode looks fine, but of course it could still be electrically faulty. Do you have a DMM (Digital Multimeter) with a diode test range? If so (with the Sony unplugged from the mains, of course), remove the 2 fuses that blow and test the diodes with your DMM. With the fuses out, the diodes are effectively isolated at one end, the only component that could give problems would be the capacitor in parallel with the diode, but if that's faulty, you have to get to the solder side of that PCB anyway.

As for soldering, the solder you need is the normal '60/40' lead-tin alloy with a resin flux core. You don't need any other flux (and you must not use the corrosive fluxes used for plumbing, metalwork, etc). You also shouldn't use the lead free solder. For the iron, I would use a Weller TCP, but they're not cheap. I am told a Metcal (even more expensive) is better. More seriously, get a temperature-controller iron. The cheap irons sold for hobbyists are more trouble than they are worth, and it is very difficult to do some soldering jobs with one, no matter how much experience you have.

Is there anyone else near you who could let you use their soldering iron?

[gazrawly]

Hi Tony

That is a good point about pulling the board out without removing anything. I will try that when I start pulling the board out.

I do have a DMM with diode range, I've just tested both the diodes and they came back at 0 / 6 and 0 / 6 so this seems to be within range (I am assuming the 6 is a .6?)

Thanks for the heads-up on the soldering Iron. I will see if I can get hold of a temp controlled Iron, failing that I'll purchase a Weller.

[TonyDuell]

I would be very surprised if you had to undo all those wire-wraps to change components on the amplifier board. Sony are not normally that unfriendly.

I assume the '0' for the diode test means open-circuit here. If it means short-circuit then the diodes are faulty (although I've never seen a diode failure where it gives the correct 0.6 voltage drop one way and shorted the other).

The Weller TCP is a temperature controlled soldering iron (TCP = Temperature Controlled Pencil or some such). Weller make/made a large range of soldering irons (and soldering guns), the TCP is the one used by an awful lot of us here (with good reason). Be warned that the basic iron is 24V, there's a seperate 'power unit' (which is just a step-down transformer). The non-temperture-controller Weller irons are not anything like as useful for this sort of work.

You can certainly get the Weller TCP from RS or Farnell (but don't expect much change from £100 for the iron + power unit). Maplin do a cheaper temperature-controlled iron I think, but I've never tried it. Maplin, annoyingly, only sell lead-free solder now, so you won't get the solder you need there.

[Diabolical Artificer]

Your DMM is putting about 1.5v on the diodes and reading the "voltage drop" of the diode's themselves. Your diodes should conduct one way and not the other, a one way valve in other words. See here - http://www.bbc.co.uk/schools/gcsebit...entsrev6.shtml

I have a spare soldering iron you can have for the postage. It's a bog standard one not temp controlled. Think it's a half decent one.

I wouldn't disconnect any wires, that could cause all sorts of problems. One thing, when you do get it out and come to powering it up, make sure no wires or bits are touching that shouldn't be. Take your time. It would be a good idea to build yourself a lamp limiter, see here - http://www.vintage-radio.com/projects/lamp-limiter.html This will stop your amp from getting damaged if something is amiss.

Andy. .

[gazrawly]

I have tested the diodes on a decent DMM and they read OFL in one direction and 0.601v and 0.608v in the other direction (reading in one direction and not the other). This seems to be ok from what I have read but please yell at me if I'm getting confused.

I have found the smoothing capacitor as Tony mentioned in the schematics of the service manual C701 (just off the amplifier board next to the transformer) and wanted to check how to test this capacitor. I have read the capacitors need to be removed from the circuit in order to test them? Is this required to test this particular capacitor or any of the other capacitors on the amplifier PCB? The unit has not been powered on in 15 years (besides blowing a fuse instantaneously) would it make any difference to the test results from the capacitor?

Thanks for the offer on the soldering iron Andy, very kind of you. I will look into lamp limiters shortly.

This help has been brilliant, thank you so much!

Gareth

[TonyDuell]

Those diodes seem fine.

The next thing I would do is test C701 for a short circuit. At this stage the capacitance doesn't matter too much, but if C701 has failed and is internally shorted, it will blow those fuses. You can't check it in-circut because if something else has shorted (like the output transistors) you will measure that when you test the capacitor.

I would disconnect the wire(s) from one terminal of C701. Probably the positive terminal, although it doesn't matter. Then use your DMM on the lowest ohns range to measure the resistance of that capacitor. Black probe to the -ve terminal, red probe to +ve if you are using a normal DMM. You should see the resistance apparently rise (and the meter go to 'over-range') as the capacitor charges. If the resistance stays at a low value, or even 0 ohms, then C701 is shorted.

[Diabolical Artificer]

Re soldering iron. Just had a look and it's a no name Made in China jobbie, but it's a vintage iron, quite well made. It should do the job till you get an Antex, Weller or whatever. I'll pop some solder in too. Drop me a PM with your address if any use.

Andy.

[gazrawly]

I have measured the C701 with the positive disconnected on a DMM set to 200k Ohms. The reading started rising quickly from 0.15 until around 1.40 where the reading slowed down considerably. It seemed to peak off at around 1.60 with no over-range displayed on the meter.

I then noticed that the DMM also reads 2M Ohms and carried out the same test with the meter set at 2M. The reading started at around 0.350 and increased very slowly to 0.400. The reading is increasing by around 0.001 every 2 or 3 seconds. Is this normal or should the reading continue to increase quickly until the meter reads over-range? I am guessing the latter?

Thanks
Gareth

[TonyDuell]

It's likely an electrolytic capacitor like C701 will 'leak' a bit. So the meter may well never go over-range.

However, if you are getting resistances in the 100's of kOhms area then C701 is not shorted. It is not leaking enough to blow those fuses. So even if it is defective, you need to look elsewhere for the fault.

I will look at the service manual again and see if there are easy ways to check output transistors etc.

[TrevorG3VLF]

Now you have the capacitor out, check the rest of the circuit for a short.

[gazrawly]

Hi Trevor

I ran the DMM at 200k over the Amplifier board pins (the contact pins that the smoothing cap connects to) and the resistance reading is 0.002 - Is this what you mean?