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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
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26th May 2018, 7:16 pm | #21 |
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Re: Dynatron Elan Repair Guidance
I believe the AF115 transistor in the FM module is TR2.
20v should be enough, but remember the tin whiskers may grow again in years to come. So when you have done the test, and proved everything else is OK, if the transistor is in an inaccessible place it is best to replace with a AF125 before you finally put the radio back together.. Some FM modules and front ends can be very particular to what transistor they use, I like to prove everything else is working before swapping with a different type of transistor. Mike Last edited by crackle; 26th May 2018 at 7:27 pm. |
26th May 2018, 7:33 pm | #22 | |
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Re: Dynatron Elan Repair Guidance
Quote:
But remember to solder the 3 EBC legs together. Mike |
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27th May 2018, 9:26 am | #23 |
Hexode
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Re: Dynatron Elan Repair Guidance
Zapping it should clear the shorts. If not then let me know and I will zap an AF115 then pop it in the post to you or I can let you have a GT322b. Sorry for not following up on voltage checks for you but it totally slipped my mind. Let me know if you still want me to do that for you.
Kind regards Graham |
27th May 2018, 10:57 pm | #24 |
Octode
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Re: Dynatron Elan Repair Guidance
I've tried zapping the AF115 and it is still shorted E to C. I tested a few AF11X transistors and they were all shorted C to E. One AF117 had shorts to the screen but 20V and some vigorous tapping did not clear the shorts.
I also tested TR2 (AF178, RF amp) and it was also bad. I plan to replace both of these transistors. Thanks for the offer Radiocruncher. I will send you a PM. I've just googled the VHF front end, AE 02119, and can't find anything about it. Last edited by OldTechFan96; 27th May 2018 at 11:02 pm. |
28th May 2018, 8:23 pm | #25 |
Nonode
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Re: Dynatron Elan Repair Guidance
All these transistors are actually S/C are they? Zero ohms? I always used to check these out on a Selectest (the small one, but same sensitivity as an AVO 8) and expect to see a hundred or so ohms, but if genuinely S/C, full deflection to zero mark. Germanium transistors totally confuse most modern Chinese testers, and technicians only used to silicon devices.
Les |
29th May 2018, 11:37 pm | #26 |
Nonode
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Re: Dynatron Elan Repair Guidance
Hi!
Not normally – the "tin–whisker" syndrome is normally screen–to–collector! I think you'll find if you use an AF179 (an RF amplifier device in VHF tuners, if you can get one cheap) in the FM tuner module RF stage,and an AF178 for the remainder, you will be very gratified with the results! I would think that it's possible there could have been lightning damage at some point in the past – it doesn't have to strike anywhere near the set to cause damage, and in bad storms, sometimes very severe "atmospherics" can destroy germanium RF devices, which are only rated at 15–20V in some cases! Chris Williams
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It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed! |
30th May 2018, 12:17 am | #27 | |
Hexode
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Re: Dynatron Elan Repair Guidance
Quote:
Thanks, Peter
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BVWS and BVWTM member Last edited by marconi_pete; 30th May 2018 at 12:35 am. |
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30th May 2018, 9:02 am | #28 |
Hexode
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Re: Dynatron Elan Repair Guidance
A freshly zapped and tested AF115 will be off in the post today. It’s got short legs as it’s lived in a module for many years. Some pictures of the results on my component tester attached.
Regards Graham |
30th May 2018, 10:28 pm | #29 | |||
Octode
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Re: Dynatron Elan Repair Guidance
Quote:
B to E B to C C to E Testing the AF115 with the diode check: B to E: 0.3V B to C: 0.2V C to E: 1.9V Your post made me check the resistance between the electrodes of the AF115: B to E: 1.5KΩ B to C: 770Ω C to E: 12.5MΩ, 5.6KΩ with leads reversed. With my modern Chinese tester the AF115 tests as if it has a diode between the E and C. Quote:
Quote:
with Si transistors in the future with a different radio. I'll fit some sockets for convenience. Radiocruncher, Thanks for the transistor! I can't wait to get in on the radio!. I also bought some AF178s. |
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31st May 2018, 8:00 pm | #30 |
Nonode
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Re: Dynatron Elan Repair Guidance
OTF96, those readings do not suggest to me that the AF115 is faulty!
Les. |
1st Jun 2018, 12:22 pm | #31 | |
Octode
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Re: Dynatron Elan Repair Guidance
Quote:
I wonder if the above only applies to Si transistors? I'll assume that with Ge transistors there should be a reading between C and E? |
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1st Jun 2018, 10:32 pm | #32 |
Nonode
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Re: Dynatron Elan Repair Guidance
Germanium transistors are somewhat leaky (it's in the physics of the things) and whereas the voltage "gap" for a silicon transistor is 0.6v, it is around 0.2 to 0.3 for germanium types. If you are checking with an AVO or similar where a 1.5v battery is used on the resistance range, 0.5/1.5 looks much more leaky than 0.6/1.5 when reading across the junction.
That is why most chinese testers, designed for more modern semicons, get confused and often say faulty or why?. Les. |
2nd Jun 2018, 9:46 am | #33 |
Tetrode
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Re: Dynatron Elan Repair Guidance
if you short the base and emitter together then measure the collector to emitter leakage it should be high. the leakage current can forward bias the base if it is left floating and the transistor turns on and appears leaky during the test.
If it is truly faulty it will still be leaky even with the base and emitter shorted |
2nd Jun 2018, 5:29 pm | #34 |
Octode
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Re: Dynatron Elan Repair Guidance
I replaced the AF115 and AF178. FM now works! Well, sort of.
The only station to come in well is Classic FM. Everything else is either poor, quiet or non existent. I can't find Radio 2 on the low Mhz side of the band and I can poorly make out Smooth Radio on the high end. The tuning dial has not been reinstalled so I'm turning the tuning capacitor as carefully as possible. I'm wondering if this could be an alignment issue? The radio was hooked up to a 10M long wire aerial. |
2nd Jun 2018, 5:51 pm | #35 |
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Re: Dynatron Elan Repair Guidance
Each transistor has its own capacitive characteristics even with the same type number, this can be very critical at these VHF frequencies. This is why I always find it best to try and use the original transistors.
It does sound like you need to realign the FM front end. Mike |
3rd Jun 2018, 9:35 pm | #36 |
Octode
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Re: Dynatron Elan Repair Guidance
I would agree that an RF alignment is needed. I don't have a wobbulator but it does not look like it would be needed for the RF alignment.
I've had a look at the trader sheet and the alignment should not be a problem. |
4th Jun 2018, 5:01 pm | #37 |
Octode
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Re: Dynatron Elan Repair Guidance
I performed steps 1 to 4 of the RF alignment and it did not yield much improvement. Radio 2 can now be found at the bottom end of the band.
A full alignment is probably needed. I don't have a wobbulator to do this. |