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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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15th Aug 2017, 2:59 pm | #41 |
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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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15th Aug 2017, 3:06 pm | #42 | |
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Re: Dynatron SRX25 Radiogram with Garrard 40B, Sound Issue
Quote:
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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15th Aug 2017, 3:14 pm | #43 |
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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. |
15th Aug 2017, 3:16 pm | #44 |
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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. Lawrence. |
15th Aug 2017, 3:21 pm | #45 |
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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 |
15th Aug 2017, 3:33 pm | #46 |
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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. |
15th Aug 2017, 3:41 pm | #47 |
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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. |
15th Aug 2017, 4:01 pm | #48 |
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Re: Dynatron SRX25 Radiogram with Garrard 40B, Sound Issue
That shows up as NKT 452 not 279, are they the same?
Thank you Kane |
15th Aug 2017, 4:06 pm | #49 | |
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Re: Dynatron SRX25 Radiogram with Garrard 40B, Sound Issue
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and VT7 or VT8, does that mean that the Voltage should read around 7 or 8? Thank you Kane |
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15th Aug 2017, 4:07 pm | #50 |
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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. |
15th Aug 2017, 4:09 pm | #51 |
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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. Lawrence. |
15th Aug 2017, 4:15 pm | #52 | |
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Re: Dynatron SRX25 Radiogram with Garrard 40B, Sound Issue
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Thank you Kane |
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15th Aug 2017, 4:59 pm | #53 | ||
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Re: Dynatron SRX25 Radiogram with Garrard 40B, Sound Issue
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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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15th Aug 2017, 5:06 pm | #54 |
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Re: Dynatron SRX25 Radiogram with Garrard 40B, Sound Issue
Here's a layout diagram.
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16th Aug 2017, 8:30 am | #55 | |
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Re: Dynatron SRX25 Radiogram with Garrard 40B, Sound Issue
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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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16th Aug 2017, 8:50 am | #56 |
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Re: Dynatron SRX25 Radiogram with Garrard 40B, Sound Issue
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17th Aug 2017, 9:25 am | #57 | |
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Re: Dynatron SRX25 Radiogram with Garrard 40B, Sound Issue
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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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17th Aug 2017, 3:46 pm | #58 |
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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 |
17th Aug 2017, 4:01 pm | #59 |
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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. |
17th Aug 2017, 4:08 pm | #60 |
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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. |