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 Post subject: Help with an Emerson 888
PostPosted: Feb Sun 04, 2018 3:27 am 
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Working on the subject, and have replaced all Electrolytic's, but the oscillator isn't working (2nd radio test). I verified voltages at the elements of both the mixer and oscillator Transistors, and continuity of each winding of coil L2, and all are well within spec. The only audio output is a low hiss.


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 Post subject: Re: Help with an Emerson 888
PostPosted: Feb Sun 04, 2018 4:26 am 
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Joined: May Tue 05, 2009 10:21 pm
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Location: West Windsor, NJ 08540
Hi fifties,

I would place another radio near the one your working on and see if you can hear the osc running as you tune the radio.
Also check you IF by injecting a 455 Khz signal near the high side of your tuning capacitor or just before your 1st IF amplifier to see if your IF is working.

Frank


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 Post subject: Re: Help with an Emerson 888
PostPosted: Feb Sun 04, 2018 4:54 am 
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Thx for the input, Frank. I've actually already done both exercises; "2nd radio test", and I've injected a 455 Kc tone to the base and collector elements of the first and second IF amp Transistors, which came through the set's speaker strong. Actually the IF test wasn't really necessary, since the problem exists before they would get signal.

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 Post subject: Re: Help with an Emerson 888
PostPosted: Feb Sun 04, 2018 6:09 am 
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Joined: Jun Sat 09, 2007 8:14 am
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Location: Florida
C8,9,10 ?

RRM


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 Post subject: Re: Help with an Emerson 888
PostPosted: Feb Sun 04, 2018 1:21 pm 
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Joined: May Tue 05, 2009 10:21 pm
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Location: West Windsor, NJ 08540
Retired Radio Man had a good point, it could also be any one the caps in the Osc circuit including C7 which couples the Osc signal to the emitter of the mixer.

Frank


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 Post subject: Re: Help with an Emerson 888
PostPosted: Feb Sun 04, 2018 2:26 pm 
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Joined: Feb Thu 08, 2007 2:32 pm
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Location: 06457
Frank512 wrote:
Retired Radio Man had a good point, it could also be any one the caps in the Osc circuit including C7 which couples the Osc signal to the emitter of the mixer.

Frank

Last night I also thought maybe C7, C8, and C9 should be checked after looking at it.


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 Post subject: Re: Help with an Emerson 888
PostPosted: Feb Sun 04, 2018 6:31 pm 
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Location: Utica, NY 13502 (USA)
I would try injecting a low level 455 kHz signal at test point "2" shown on the schematic using a small capacitor for DC isolation. This would verify that transistor "X1" is working since you already know that the IF amps are working.

Dave


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 Post subject: Re: Help with an Emerson 888
PostPosted: Feb Sun 04, 2018 6:36 pm 
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Thx for the input, gentlemen; I'll test as suggested and report back.

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 Post subject: Re: Help with an Emerson 888
PostPosted: Feb Mon 05, 2018 6:00 am 
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It's fixed.

I did as Dave suggested, and injected a 455 KC tone to the base of the mixer. The tone came through, and in twirling the dial around, the 1040 KC signal from my SSTrans also came through. I've been to this rodeo before, so I D/C and then reconnected the antenna coil leads, and proceeded to re-flow front end solder connections, and was able to get it to then receive a few stations, but at low volume. Distant ones came in low, stronger locals were garbled. The osc coil slug was also out of it's best position.

Connecting a small amp to ground and the high side of the VC produced normal clear signal on all stations through it, so after verifying the voltages in the audio stage, I then re-flowed solder landings, and got the radio normalized.
I did RF and IF alignments per the SAM's instructions, and the radio now receives from 540 to 1670 kilocycles, and with room filling volume on the locals. It even picked up a station in Fresno, about 200 miles north, during daylight, and another one in San Diego, about the same distance south of here.

I did this repair for a long time forum member, and I'm sure he'll be pleased.

Thanks for everyone's input. I always get sufficient help on this board to fix any set that I've ever asked about.

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 Post subject: Re: Help with an Emerson 888
PostPosted: Feb Mon 05, 2018 12:49 pm 
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Posts: 19959
Location: Utica, NY 13502 (USA)
Congratulations! It's been a while since I've worked on an 888 but I now recall that some of the solder connections on the early PC boards used in these sets were a problem.

Dave


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 Post subject: Re: Help with an Emerson 888
PostPosted: Feb Mon 05, 2018 5:26 pm 
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Joined: Feb Thu 08, 2007 2:32 pm
Posts: 11935
Location: 06457
fifties wrote:
It's fixed.

I did as Dave suggested, and injected a 455 KC tone to the base of the mixer. The tone came through, and in twirling the dial around, the 1040 KC signal from my SSTrans also came through. I've been to this rodeo before, so I D/C and then reconnected the antenna coil leads, and proceeded to re-flow front end solder connections, and was able to get it to then receive a few stations, but at low volume. Distant ones came in low, stronger locals were garbled. The osc coil slug was also out of it's best position.

Connecting a small amp to ground and the high side of the VC produced normal clear signal on all stations through it, so after verifying the voltages in the audio stage, I then re-flowed solder landings, and got the radio normalized.
I did RF and IF alignments per the SAM's instructions, and the radio now receives from 540 to 1670 kilocycles, and with room filling volume on the locals. It even picked up a station in Fresno, about 200 miles north, during daylight, and another one in San Diego, about the same distance south of here.

I did this repair for a long time forum member, and I'm sure he'll be pleased.

Thanks for everyone's input. I always get sufficient help on this board to fix any set that I've ever asked about.

Big thank you Rich, this is a keeper and you know I don't really have a collection anymore.


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 Post subject: Re: Help with an Emerson 888
PostPosted: Feb Tue 06, 2018 1:10 am 
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Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5521
Location: Indianapolis, IN
Glad you got it goin' old fella !

Amazed that many solder connections were bad---did they look okay ? I have seen sets where the component leads themselves oxidized on the surface within the solder creating a resistive or open connection---wonder if that was happening ?

John


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 Post subject: Re: Help with an Emerson 888
PostPosted: Feb Tue 06, 2018 2:31 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 19959
Location: Utica, NY 13502 (USA)
xrhonda91 wrote:
I have seen sets where the component leads themselves oxidized on the surface within the solder creating a resistive or open connection---wonder if that was happening ?

John
That's what had happened on my 888's and also other radios with early generation PC boards.

Dave


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 Post subject: Re: Help with an Emerson 888
PostPosted: Feb Tue 06, 2018 3:18 am 
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Location: SoCal, 91387
xrhonda91 wrote:
Glad you got it goin' old fella !

Amazed that many solder connections were bad---did they look okay ? I have seen sets where the component leads themselves oxidized on the surface within the solder creating a resistive or open connection---wonder if that was happening ?

John

"Old fella" - you know how to make a guy feel good, lol! This is a case where you can't tell by looks. The 60 year old solder was sort of dulled down, and grey-ish in color. The only recipe here is to heat every landing until you've done some good.

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 Post subject: Re: Help with an Emerson 888
PostPosted: Feb Tue 06, 2018 3:38 am 
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Joined: Oct Mon 26, 2009 10:02 pm
Posts: 5521
Location: Indianapolis, IN
Hey Richard,

Most of us do start getting a little dull & gray-ish around 60 ! I'm right at the doorstep and can speak from experience... Unfortunately, at that point heated landings only burn your feet...

Sorry---just needed to kid a bit...

John


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