emerson 557 ? - Printable Version
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+--- Thread: emerson 557 ? (/showthread.php?tid=8120)
RE: emerson 557 ? - BrendaAnnD - 01-08-2014
OK. Your IF's are then susceptible to silver mica disease. This is most common in the AM IF transformers, but can also occur in the FM ones. I'm pretty sure there is a thread somewhere on here about repairing this. It involves opening up the IF cans, removing the old built in caps and replacing them with mica disc capacitors.
RE: emerson 557 ? - Eric - 01-09-2014
Brenda
There are so far no caps mounted under the cans that I've found. cleaned the am/fm switch no change, still intermittent. I've added a picture of a resistor for Id it reads 6 ohms I think it should be 60? Baffled because the fm works great. I will check out more cans Friday.
RE: emerson 557 ? - hsusmann - 01-09-2014
IMHO, it sounds like if the radio plays for 5 seconds then goes dead
it is a capacitor charging up somewhere.
Is it possible that there is a missing or open resistor on a grid
somewhere that lets the grid end of a coupling capacitor float upwards?
Perhaps measuring some grid voltages in the audio section will
turn up something? This can be tricky, though, as sometimes
the meter will pull the line back down to where it is supposed to be.
If the radio starts playing again, however, then this is the problem.
I had this happen once on a radio long ago.
Herb S.
RE: emerson 557 ? - morzh - 01-09-2014
Eric
Do you have a spare pentagrid? 12BA7? If yes, does changing it change anything?
RE: emerson 557 ? - Eric - 01-09-2014
It doesn't go dead there is static.
Don't have another 12BA7 but I'm making a tube order up from some other radio's and will pick up another there cheap enough.
Am I right on the resistor above? there is no listing for a 6 ohm in the parts list?
RE: emerson 557 ? - morzh - 01-09-2014
I'd say first check Brenda's idea about the silver mica disease.
RE: emerson 557 ? - Eric - 01-10-2014
Have been doing research on the silver mica disease and think I will study this some more here is a link that helped a lot.
http://www.youtube.com/watch?v=h1lsWaAkCGo
probably the way to go
RE: emerson 557 ? - jerryhawthorne - 01-10-2014
Eric, it would be nice to know where your at now. You have static only which you can vary the noise level with the volume control?
What test equipment do you have? A signal generator or a scope or a signal tracer? It would help to check where your RF is being lost.
I suspect if you have static that varies in volume when you increase the volume pot, your audio section is just fine as is your power supply.
You could certainly have problems in the IF section with perhaps SMD or open coils. The only way to tell is to use a signal generator or signal tracer and find out exactly where you are loosing that nice sound. Once you locate where you loosing it, you can address the problem.
Resistance measurements of the coils in the RF, Oscillator and antenna sections would also help.
Jerry
RE: emerson 557 ? - Eric - 01-10-2014
Jerry
I do have a signal generator, right now static is minimal but if memory serves I could vary the volume but the static was constant across the dial with some popping FM still fine. Still cannot check all the values of the resistors trying to get a readable print if anybody has Volume 19.
Emerson 557 Vol 19-10 (Chassis 120018B)
Eric
RE: emerson 557 ? - jerryhawthorne - 01-10-2014
Eric, keeping in mind this is a "hot" chassis AC/DC radio, do you have an isolation transformer? If not, I would be reluctant to use your signal generator on that radio. I threw some major sparks prior to getting an isolation transformer. If you do, I would set the radio to AM and use the generator at 455KC with the modulation on and start moving it along the grids (pin 1) to ground from V3, V4, V5 and V6. Looking for the modulated hum. This could help determine where your losing your signal and allow you to focus on one area.
Regards, Jerry
RE: emerson 557 ? - Eric - 01-11-2014
Don't have a isolation trans. (yet) Let me ask was the major sparks because of touching another pin or hot lead? This chassis is pretty open and I could easily pre attach a lead out from each #1pin so as to eliminate that hazard?
RE: emerson 557 ? - jerryhawthorne - 01-11-2014
Eric, the major spark came when attaching the ground lead of my signal generator to the ground on the AC/DC chassis. Melted my ground lead connector. At a minimum, using a battery powered volt meter measure the A/C voltage between the radio chassis and ground lead of your signal generator with both plugged in. If you have 120V A/C you might try reversing one of the plugs in the wall. Be safe.
Jerry
RE: emerson 557 ? - Eric - 01-11-2014
Tomorrow I will check out the chassis and see if there is a potential between the frame and the signal gen keeping in mind the hot side of the plug as the plug is not polarized, if it looks good I will try what you have said above.
RE: emerson 557 ? - jerryhawthorne - 01-11-2014
Great Eric. Any time you work with an AC/DC radio with a hot chassis your at risk of hooking other test equipment running off of A/C. This is not to mention touching the chassis with a finger and having a decent ground on your body like standing on a concrete floor bear feet or having your other hand on something metal. Just be really careful. If you wish to work on these radios, please get an isolation transformer for your safety and that of your A/C powered test equipment. I had to go change my shorts after hooking up my signal generator to an AC/DC radio. Also had to reset the circuit breaker to my shop. I immediately went out and a nice ARF person sent me an isolation transformer for the cost of shipping.
Regards, Jerry
RE: emerson 557 ? - Eric - 01-12-2014
Hooked up everything this morning had to flip the plug as the chassis was hot to ground. Also put some 38 gauge wire in series with the chassis to signal gen to act as a fusible link no problems here are the results.
V3 - modulated hum
V4 - nothing
V5 - nothing
V6 - nothing but a slight hum like when have some loading like when you attach a meter lead not anything like when you rock the signal gen