Chinese DIY EAR 834P Phono Preamp Build - What has gone wrong?

[aussievintage]

38 minutes ago, Spider27 said:

 

Thank you very much. I will check them out soon.

 

Just one quick question. Is 2K resistor correct one? Because I can see 1K3 resistor but could not see 2K resistor. I see 3K resistors just beside 1K3 resistor.

 

 

Look at the schematic.  The 2K is after the regulator, the 1K3 is before it.

[Spider27]

23 hours ago, aussievintage said:

 

 

Look at the schematic.  The 2K is after the regulator, the 1K3 is before it.

Gee. I must been blind. Thank you very much.

[Spider27]

Before checking voltage, I checked the components one more time and found a few issues.

 

1) 1K3 Resistor gone bad. When I measure it with multimeter, it shows O.L and it looks slightly burnt so need replacement.

2) Left channel 2K3 resistor is incorrect value. It should be 2K but show 0.7K as value. 

 

Good thing is that NPN Power Transistor was fine when I tested it after removing it from circuit.

 

For replacement of those two resistors, is it okay to use wire wound resistor like below linked ones? I have only used either Carbon or Metal Oxide film resistor so far and not sure if Wire Wound Resistor would be ok to use.

 

https://www.jaycar.com.au/2-2k-ohm-5-watt-wire-wound-resistor/p/RR3306

https://www.jaycar.com.au/1k-ohm-5-watt-wire-wound-resistor/p/RR3298

 

The reason for asking is that resistors in those value are sold in Wire Wounded Resistors from local store and it will be expensive to order from Mouser or RS Online for couple of resistors after adding postage and takes quite a bit of time to receive them by mail.

Edited April 25, 2021 by Spider27

[RoHo]

Looks like the 1k3 has acted like a fuse and been blown by excess current.  So you need to find out why before you replace it or it will just happen again.  And if you replace it with a higher wattage type then something else will probably take over the role of a fuse and blow.

Are you SURE the power transistor is OK?  In my experience as a tube DIYer these silly semiconductor things destroy themselves at the slightest chance.  Not like tubes which are much more robust.

Are you SURE there isn't a short from the power supply rail to ground somewhere? Check and re-check all the wiring.  Re-check all the transformer wiring.

Is the board known to be fault-free? QC on some Chinese products can be lacking.

[Spider27]

36 minutes ago, RoHo said:

Looks like the 1k3 has acted like a fuse and been blown by excess current.  So you need to find out why before you replace it or it will just happen again.  And if you replace it with a higher wattage type then something else will probably take over the role of a fuse and blow.

Are you SURE the power transistor is OK?  In my experience as a tube DIYer these silly semiconductor things destroy themselves at the slightest chance.  Not like tubes which are much more robust.

Are you SURE there isn't a short from the power supply rail to ground somewhere? Check and re-check all the wiring.  Re-check all the transformer wiring.

Is the board known to be fault-free? QC on some Chinese products can be lacking.

 

Thank you very much for your feedback.

 

I will recheck all the wiring and power supply rail.

 

Re: power NPN transistor, I followed this video and checked and seem fine.

 

 

Re: quality of the PCB board, it looks high quality & well made but not sure if it is fault free because this is the first DIY Kit from China that I am trying and probably the last given the troubles I am having comparing with other well known DIY Kit such as ACA and Elekit. 

 

 

 

 

[muon*]

On lenco heven there is a thread where many are using this board, and in some cases modifying it.

[Gryffles]

47 minutes ago, Spider27 said:

 

Thank you very much for your feedback.

 

I will recheck all the wiring and power supply rail.

 

Re: power NPN transistor, I followed this video and checked and seem fine.

 

 

Re: quality of the PCB board, it looks high quality & well made but not sure if it is fault free because this is the first DIY Kit from China that I am trying and probably the last given the troubles I am having comparing with other well known DIY Kit such as ACA and Elekit. 

 

 

 

 

Do you have a dim bulb tester for protection when turning on? You will be aware of these if your familiar with the ACA kit and related forum on DIY Audio. Might save you a lot of hassle

 

https://www.diyaudio.com/forums/power-supplies/167579-light-bulb-tester.html go to the post by member 6L6

[RCAJack]

When you say no sound, can I ask if there was any kind of hum or hiss detectable from either channel? Any sound from plugging or unplugging inputs? Did you actually test with the signal from a cartridge?
 

FWIW I notice only some of your solder joints on top of the board show solder that has flowed through from the bottom. That’s not necessarily wrong or bad, but I’d probably reflow all joints with a little extra solder to help eliminate the risk of a cold joint. 

[Spider27]

1 minute ago, RCAJack said:

When you say no sound, can I ask if there was any kind of hum or hiss detectable from either channel? Any sound from plugging or unplugging inputs? Did you actually test with the signal from a cartridge?
 

FWIW I notice only some of your solder joints on top of the board show solder that has flowed through from the bottom. That’s not necessarily wrong or bad, but I’d probably reflow all joints with a little extra solder to help eliminate the risk of a cold joint. 

 

Thank you for asking... No hum or hiss at all. No sound coming from speaker at all......

Actually Right channel was working temporarily and after soldering a few joints again, right channel also not working (no sound output at all).

 

Re: solder, I just solder from bottom of PCB and was not sure if I need to pour solder more into the hole all the way to the top of the board. I thought that just enough solder is better than too much solder 

 

When I replace those two resistors, I will put more solder to help eliminiate the chance of cold solder. 

[RCAJack]

It’s interesting that you got some sound originally on one channel. Apparently something broke after resoldering some joints. I can’t imagine you fried anything with excess heat (although maybe?) so I’m still wondering if there’s a cold joint especially since you’re not even getting hiss at the output. 

 

I’d be inclined to put in a signal and connect via an amp to a test speaker, then if voltages are ok, use a chopstick to gently tap all components including sockets and see if you hear noise or crackles.

[Addicted to music]

16 hours ago, Spider27 said:

Before checking voltage, I checked the components one more time and found a few issues.

 

1) 1K3 Resistor gone bad. When I measure it with multimeter, it shows O.L and it looks slightly burnt so need replacement.

2) Left channel 2K3 resistor is incorrect value. It should be 2K but show 0.7K as value. 

 

Good thing is that NPN Power Transistor was fine when I tested it after removing it from circuit.

 

For replacement of those two resistors, is it okay to use wire wound resistor like below linked ones? I have only used either Carbon or Metal Oxide film resistor so far and not sure if Wire Wound Resistor would be ok to use.

 

https://www.jaycar.com.au/2-2k-ohm-5-watt-wire-wound-resistor/p/RR3306

https://www.jaycar.com.au/1k-ohm-5-watt-wire-wound-resistor/p/RR3298

 

The reason for asking is that resistors in those value are sold in Wire Wounded Resistors from local store and it will be expensive to order from Mouser or RS Online for couple of resistors after adding postage and takes quite a bit of time to receive them by mail.

You have a fault condition where possibly huge Current is causing the resistor to burn out.  I’d be using the same wattage  rating resistor or lower as it acts like a “fuse” until you work out what  has drawn such current, using a higher wattage  rating resistor will only mask the issue and will not help.   So get cheap 1-2 watt resistors.   Surprise to see no fuses on the PSU on either the secondary or primary of the transformer.   If I were chasing this I would check that  I have the correct voltage >285VDC b4 it gets to the transistor MJE 13009.   This may involve removing MJE 13009 and leaving it out of the circuit and power up.  If you get  greater than 285VDC  after the 1.3k resistor than it’s obvious it’s the MJE 13009, be aware by doing this the the circuit is live and working and that the high voltage   greater than 285VDC will remain after you have switched off!  You need it to be discharged b4 you do any work.   Removing MJE 13009 will isolate the rest of the circuit from the fault condition.   If there is higher than 285V after resistor 1,3k when MJE 13009 is disconnected, which I’m assuming there is because the 1.3k resistor has gone opened, I would be checking the pins on the transistor and tracing the base/collector/emitter to ensure that the circuit pcb corresponds to the circuit diagram, this will ensure that the white print on the pcb isn’t incorrectly indicated to allow you to incorrectly place the orientation of MJE 13009.
A note on MJE13009; On semi has two styles of connection and Vishay and all others have  one,  if you have a Onsemi equivalent you need to check the data sheet to see which style you have as the pin configuration is different between style one and two;  however,  this could also be a printed error on the data sheet as I have no idea why you would have different pin configuration compared to standard.

 

 

 

Edited April 25, 2021 by Addicted to music

[RoHo]

9 hours ago, Spider27 said:

 

Thank you for asking... No hum or hiss at all. No sound coming from speaker at all......

Actually Right channel was working temporarily and after soldering a few joints again, right channel also not working (no sound output at all).

 

 

Sounds like there is a short somewhere in the left channel that caused excess current that eventually blew the 1k3 resistor.   Meanwhile, the Right channel worked fine until that resistor blew and disconnected the PS. 

Check for solder bridges between PCB tracks.

[aussievintage]

9 hours ago, Spider27 said:

Re: solder, I just solder from bottom of PCB and was not sure if I need to pour solder more into the hole all the way to the top of the board. I thought that just enough solder is better than too much solder 

 

In general, yes, less is better.  However, do you know if the circuit board has plated-through holes?  Most good boards do.  If not, however, you need to solder both sides so that the component lead makes the connection between sides of the board.

 

 

6 minutes ago, RoHo said:

Check for solder bridges between PCB tracks.

 

Definitely

 

also check the transistor pinout and orientation (and the orientation of all the diodes and capacitors)

[miyouzaic]

aussievintage is onto it !

I've played with similar looking Chinese phono boards that definitely look like through holes and are not.

A simple continuity test proved they weren't.  I soldered the top of the holes around the pins and it was all go  !

[Spider27]

13 minutes ago, miyouzaic said:

aussievintage is onto it !

I've played with similar looking Chinese phono boards that definitely look like through holes and are not.

A simple continuity test proved they weren't.  I soldered the top of the holes around the pins and it was all go  !

Thank you. I will do continuity test to see if they are through holes. It looks like they do but better check it to make sure.

[Spider27]

Ordered those resistors from local store with lower value 1K 1W & 2K 1W instead of original 3W.  Once I get those, will make sure all solder joint and PCB trace and test with those resistors. Fingers Crossed and will report back.  

[Addicted to music]

You can locate shorts to ground with power off.

 

If you have a multi meter with a continuity function, you can place a probe on the emitter of MJE 13009 that’s acting as a constant current source and ground, if there is a short it will buzz for continuity.  You then check for incorrect solder or remove components until there is no continuity, one safe and useful technique without powering up.

Edited April 26, 2021 by Addicted to music

[Spider27]

27 minutes ago, Addicted to music said:

You can locate shorts to ground with power off.

 

If you have a multi meter with a continuity function, you can place a probe on the emitter of MJE 13009 that’s acting as a constant current source and ground, if there is a short it will buzz for continuity.  You then check for incorrect solder or remove components until there is no continuity, one safe and useful technique without powering up.

 

Thank you. That is a great tip. 

 

Dumb question to ask. Should I put red probe on emitter an black probe on chassis ground?

[Spider27]

First thing first.. I just did a quick test on power transistor (I see the marking says MJE 13005) with tester and here is the outcome. 

 

Pin 1 is E, Pin 2 is C and Pin 3 is B.

 

I guess that it means that the NPN transistor face towards inward like attached is correct configuration?

 

[aussievintage]

20 minutes ago, Spider27 said:

I guess that it means that the NPN transistor face towards inward like attached is correct configuration?

Unless the board is marked EBC you will need to look at where the tracks connect to.

[Addicted to music]

25 minutes ago, Spider27 said:

First thing first.. I just did a quick test on power transistor (I see the marking says MJE 13005) with tester and here is the outcome. 

 

Pin 1 is E, Pin 2 is C and Pin 3 is B.

 

I guess that it means that the NPN transistor face towards inward like attached is correct configuration?

 

Not sure I’d trust that;

 

https://www.onsemi.com/pdf/datasheet/mje13005-d.pdf

 

pin 1 base

pins 2 collector 

pins 3 emitter 

 

Edited: if what you’re reading is correct than the transistor maybe in the wrong orientation as per the white print on the pcb.   You now need to check that the pins corresponds to the pins on the pcb by checking the continuity of other components connected to the transistor.   As per indicated in one of my above posts 

 

and yes you place the positive probe on the emitter for continuity 

Edited April 27, 2021 by Addicted to music

[muon*]

1 hour ago, Spider27 said:

Ordered those resistors from local store with lower value 1K 1W & 2K 1W instead of original 3W.  Once I get those, will make sure all solder joint and PCB trace and test with those resistors. Fingers Crossed and will report back.  

I might have missed something.

 

But why resistors of lower values, especially on power handling?

 

They should be spec'ed according to what the design calls for.

[Addicted to music]

7 minutes ago, muon* said:

I might have missed something.

 

But why resistors of lower values, especially on power handling?

 

They should be spec'ed according to what the design calls for.

There are no fuses, 

he has a fault condition that drawing current via the 1.3k,  and becuase it’s a fault condition you use the same wattage or lower until the fault is rectified.  Using a lower wattage will also prevent other components getting destroyed 

Edited April 27, 2021 by Addicted to music

[Spider27]

The PCB has black print on surface so very hard to see where the connection trace goes to where and here is what I found from PCB as below.

 

Pin 1 goes Diode section

Pin 2 goes between 1K3W resistor and 100uf/450wv cap

Pin 3 goes between 3K3W resistor and 22uf/400v cap

[Addicted to music]

1 hour ago, Spider27 said:

The PCB has black print on surface so very hard to see where the connection trace goes to where and here is what I found from PCB as below.

 

Pin 1 goes Diode section

Pin 2 goes between 1K3W resistor and 100uf/450wv cap

Pin 3 goes between 3K3W resistor and 22uf/400v cap

That would be how I read it on you schematic, you need to identify the pins on the transistor to these with the through the hole on the pcb.