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Old 15th Aug 2017, 2:59 pm   #41
Edward Huggins
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Default Re: Dynatron SRX25 Radiogram with Garrard 40B, Sound Issue

Reading Post #29, I'm now confused about the type of connectors you have fitted to your speakers. If they are 2 pin DIN, they will connect directly to your Dynatron.
If they have a phono plugs already fitted you will need an adaptor or just remove them and solder/screw on to 2 new DIN plugs.
It's reasonable to assume that any speaker already fitted with a phono plug is liable to be a very basic, low power handling, unit.
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Old 15th Aug 2017, 3:06 pm   #42
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Default Re: Dynatron SRX25 Radiogram with Garrard 40B, Sound Issue

Quote:
Originally Posted by paulsherwin View Post
That looks about right. Put them back in the heatsinks though.

If you measure the voltages around the output transistors again, they should have changed.
They were placed back into the heatsink

now the transistors are a tiny bit different

1 from -181.1mv to -2.08v
2 from -30.6v to -29.5v
3 from -163.3mv to -147.3
4 from -30.7v to -29.6

Thank you
Kane
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Old 15th Aug 2017, 3:14 pm   #43
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Default Re: Dynatron SRX25 Radiogram with Garrard 40B, Sound Issue

Hmm. That's bad news. Unfortunately, it's quite common for these directly coupled amps to suffer multiple failures as an initial fault cascades through the circuit, though it's very unusual for both channels to be affected identically.

I'll leave it for Michael to suggest what to try next, as he's worked on these amps and I haven't. However, you could start by measuring the voltages on the collector, base and emitter of both output transistors in both channels.
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Old 15th Aug 2017, 3:16 pm   #44
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Default Re: Dynatron SRX25 Radiogram with Garrard 40B, Sound Issue

When reporting voltages on transistors you should quote the transistors circuit reference and also indicate which transistor connection(s) the voltage(s) refer to eg: E B C (Emitter, Base, Collector)

Post Crossed.

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Old 15th Aug 2017, 3:21 pm   #45
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Default Re: Dynatron SRX25 Radiogram with Garrard 40B, Sound Issue

I'm not sure what any of that means especially post crossed?

How do I determine if it's E, B or C?
How do I quote the Circuit reference?

Thank you
Kane
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Old 15th Aug 2017, 3:33 pm   #46
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Default Re: Dynatron SRX25 Radiogram with Garrard 40B, Sound Issue

Post crossed....In this case means the Paul posted his post as I was completing and posting mine the reason I added post crossed was that he was suggesting voltage checks which is basically what I was implying as well..no worries.

EBC might be printed on the printed circuit board if not then you might have to look it up in the transistor data if it's available, most transistor data is available on line somewhere or other, failing that someone on here might know the leadout orientation.

The circuit reference will be on the schematic...VTwhatever, eg: the output pair of transistors in the schematic posted earlier gives the their circuit references as VT7 and VT8.

Lawrence.
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Old 15th Aug 2017, 3:41 pm   #47
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Default Re: Dynatron SRX25 Radiogram with Garrard 40B, Sound Issue

Crossposting is when two people post to the thread at the same time.

The circuit reference is the letter and number of the part from the circuit diagram. In many cases it is also printed on the circuit board next to the component.

Transistors have three connections: collector, base and emitter. The output transistors in this design have the collector connected to the case and the other two connections emerging as pins underneath. Here is data on them: http://www.datasheetspdf.com/PDF/NKT452/607943/1

Take care not to cause short circuits when taking measurements.
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Old 15th Aug 2017, 4:01 pm   #48
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Default Re: Dynatron SRX25 Radiogram with Garrard 40B, Sound Issue

That shows up as NKT 452 not 279, are they the same?

Thank you
Kane
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Old 15th Aug 2017, 4:06 pm   #49
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Default Re: Dynatron SRX25 Radiogram with Garrard 40B, Sound Issue

Quote:
Originally Posted by ms660 View Post
Post crossed....In this case means the Paul posted his post as I was completing and posting mine the reason I added post crossed was that he was suggesting voltage checks which is basically what I was implying as well..no worries.

EBC might be printed on the printed circuit board if not then you might have to look it up in the transistor data if it's available, most transistor data is available on line somewhere or other, failing that someone on here might know the leadout orientation.

The circuit reference will be on the schematic...VTwhatever, eg: the output pair of transistors in the schematic posted earlier gives the their circuit references as VT7 and VT8.
I don't have the Schematics unfortunately, the closest I could find had IC's on it which if I was able too I'd replace them it IC's but I don't have the full knowhow or ability to do that.

and VT7 or VT8, does that mean that the Voltage should read around 7 or 8?

Thank you
Kane
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Old 15th Aug 2017, 4:07 pm   #50
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Default Re: Dynatron SRX25 Radiogram with Garrard 40B, Sound Issue

Graham's circuit fragment in #22 shows NKT452s. They probably have the same leadout. Hopefully the Dynatron specialists will be able to comment.

VT is the component code for a transistor, so VT8 would be transistor number 8. Nothing to do with voltages.
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Old 15th Aug 2017, 4:09 pm   #51
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Default Re: Dynatron SRX25 Radiogram with Garrard 40B, Sound Issue

"that shows up as NKT 452 not 279, are they the same?"

They are not the same, the NKT 279's are the ones you wrapped the tape around, the NKT452's are the output transistors, usually its the voltages on the output transistors Emitter, Base and Collector connections that are measured and reported first.

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Old 15th Aug 2017, 4:15 pm   #52
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Default Re: Dynatron SRX25 Radiogram with Garrard 40B, Sound Issue

Quote:
Originally Posted by paulsherwin View Post
Graham's circuit fragment in #22 shows NKT452s. They probably have the same leadout. Hopefully the Dynatron specialists will be able to comment.

VT is the component code for a transistor, so VT8 would be transistor number 8. Nothing to do with voltages.
Ah right I get it now, My transistor does look identical to that in the diagram however I do not that that is luck, more a bog standard format for what they look like.

Thank you
Kane
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Old 15th Aug 2017, 4:59 pm   #53
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Default Re: Dynatron SRX25 Radiogram with Garrard 40B, Sound Issue

Quote:
Originally Posted by Kanyehobbitkind View Post
Quote:
Originally Posted by paulsherwin View Post
That looks about right. Put them back in the heatsinks though.

If you measure the voltages around the output transistors again, they should have changed.
They were placed back into the heatsink

now the transistors are a tiny bit different

1 from -181.1mv to -2.08v
2 from -30.6v to -29.5v
3 from -163.3mv to -147.3 you mean 14.73V
4 from -30.7v to -29.6

Thank you
Kane
The channel with 3 & 4 is now working ok, but you've probably miss-connected the speakers.

You need to concentrate on the other channel. ie 1 & 2.

I suggest you remove the transistors from the heatsink and then switch on, if transistor 1 now reads approx 14.5V you've still got a problem isolating those transistors. If the readings are the same then you'll have to dig a little deeper.
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Old 15th Aug 2017, 5:06 pm   #54
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Default Re: Dynatron SRX25 Radiogram with Garrard 40B, Sound Issue

Here's a layout diagram.
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Old 16th Aug 2017, 8:30 am   #55
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Default Re: Dynatron SRX25 Radiogram with Garrard 40B, Sound Issue

Quote:
Originally Posted by Michael Maurice View Post
The channel with 3 & 4 is now working ok, but you've probably miss-connected the speakers.

You need to concentrate on the other channel. ie 1 & 2.

I suggest you remove the transistors from the heatsink and then switch on, if transistor 1 now reads approx 14.5V you've still got a problem isolating those transistors. If the readings are the same then you'll have to dig a little deeper.

No it shows as -147.3mV, did I mess that up trying to fix it?
Do you mean remove ALL transistors from the headsink? as in the ones which I sellotaped?

Thank you
Kane
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Old 16th Aug 2017, 8:50 am   #56
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Default Re: Dynatron SRX25 Radiogram with Garrard 40B, Sound Issue

Quote:
Originally Posted by Station X View Post
Here's a layout diagram.
This is amazing!

Thank you
Kane
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Old 17th Aug 2017, 9:25 am   #57
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Default Re: Dynatron SRX25 Radiogram with Garrard 40B, Sound Issue

Quote:
Originally Posted by Kanyehobbitkind View Post
No it shows as -147.3mV, did I mess that up trying to fix it?
Do you mean remove ALL transistors from the headsink? as in the ones which I sellotaped?
Yes, he means the ones you taped, remove them from their heatsinks, switch on and measure the collector voltages on the four output transistors like you did previously.

Be aware that the more you fiddle about with these transistors the greater are the chances of one of their leads breaking off where they exit the encapsulation...

Lawrence.
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Old 17th Aug 2017, 3:46 pm   #58
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Default Re: Dynatron SRX25 Radiogram with Garrard 40B, Sound Issue

Okay I'm now really confused, I removed them from their heat-sinks and turned the unit on, nothing, so when I went to move the Dynatron radio I heard a bit of white noise coming out of the speakers, not sure how but yeah, so I tried to move it again to see if it worked but white noise would only come out when my thumb was touching the chassis.

So i tried to move the radio back a little and my hand slipped and flicked the cardboard at the bottom of the radio (also in the pictures)and all of a sudden
white noise like full on white noise, I re-tuned the radio and music came blaring out! now I've no idea what I did or how it's working but it is, I still have to re attach the heat-sinks and put the radio back in place but i'm worried that if I move it back into place or put the heat-sinks back onto it then it's going to not work again?

So what would be the best possible course for me moving forward now?

Thank you
Kane
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Old 17th Aug 2017, 4:01 pm   #59
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Default Re: Dynatron SRX25 Radiogram with Garrard 40B, Sound Issue

With the taped transistors still removed from their heatsinks, switch on and try and measure any voltage between the metal of those transistor cases and chassis, although you have wrapped tape around them you might be able to get to the top end of the metal cases with the meter probe, if you can't then you will have to remove the tape and any sticky stuff in order to make contact with the case with the meter probe....don't short anything out...!

The purpose of this is to see if the internal structures of those transistors are shorting or leaking to the transistors metal case as was suspected in the beginning, we need to be sure.

Lawrence.
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Old 17th Aug 2017, 4:08 pm   #60
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Default Re: Dynatron SRX25 Radiogram with Garrard 40B, Sound Issue

It could also be that there is an unrelated fault such as a bad solder joint causing a bad connection. In that case you will need to gently move things around until you find it. I'm still puzzled that both channels are affected though - maybe one of the PSU connections is intermittent.

You are making progress, though it may not feel like it.
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