Marantz Model 2100 Stereophonic Tuner

This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
I find devices with a power amp, a power check gives a quick condition of the power rail capacitors. Get a 200kohm/volt voltohmeter with a 20 VAC and 200 VAC scales. Get a pair of 8 ohm (or 4 ohm depending on the units rating) >100 watt resistors, and put a maximum signal of high energy music out. Suitable sound sources are techno-house rock at a steady volume, also sine wave generators. Measure the voltage out. (V^2)/R where R is the resistance and V is the average AC voltage, gives you the power out. Compare to the specification. If power is 75% or below, on a device this old, probably the main rail capacitors are tired.
You can get an extra life by just changing power capacitors, but at some point (usually 20-30 years) a reciever gets where it doesn't have any sensitivity (ability to pull in weak stations), stereo separation, or decent flat frequency response. When an old electronic device sounds bad or doesn't work like new, I change every electrolytic capacitor in it with a new one, preferably a capacitor that is rated >3000 hours service life. I've had to replace the e-caps in my dynakit ST70 and PAS2 three times in 43 years due to poor performance, but we have the internet now, publishes the hours service life in their selector table. There is no longer a reason to buy 500 hour life capacitors just because that is what the store stocks locally. Just changing all the e-caps brought back my 197? FM radio to super sensitivity and sound quality in 2010 without any alignment tools or procedures. Perhaps you can get as lucky. The experts on here muddy the issue immediately with super techno alignment advice, IMHO, but I haven't found it necessary to go that far on a radio that worked okay when it was new. My Dynakit FM3, that I have never seen work right, is another issue. I'm putting that headache off another year, since the Reader's Digest mono radio is working so well on the 400 W High school radio station in the next county. The Sony pocket FM radio I bought new in 1997 does not have nearly the sensitivity or sound of the 197? radio, despite "digital synthesis".
The second most common failure in consumer electronics with transistors is poor controls and oxidized switches and connectors. Sometimes volume and tone controls are scratchy and have dropout due to use beyond the design life. Some units, that were hardly used by the previous owner, don't have this problem. All tin and brass connectors inside can oxidize over the years and inhibit low level signal flow, that below 50 ma and 25 V. Sometimes removing and reinstalling these connectors is good enough, sometimes spraying with contact cleaner is required. Warning, contact cleaner safe for plastics is flammable, no smoking, open flame, pilot lights, or electricity on or off within 10 m while using. Low flammable brominated hydrocarbon contact cleaners for factory use dissolve PVC and styrene plastics, so don't use them on consumer equipment.
Some types and brands of resistors are quite stable, some tend to creep up in value over the decades. It depends on what paint (water sealant) they used, and color doesn't predict this. Cheapo manufacturers perfected visual copies of the Allen Bradley- Sprague design resistor in the late 1960's, and products with the wrong ones installed have crept way off value over the years. You can test a sample of the resistors with an ohmmeter, being aware that resistors running to semiconductor pins can read way below value in circuit. Mostly, carbon comp resistors creep up in value. Resistors with a value above 100k ohms are the most likely to be off value, even the stellar military quality brands listed above.
Amateurs make a lot of soldering errors, so don't replace too many parts at once if you decide to upgrade it. I do two or three, then reassemble it enough to test it. If I just made it worse, having only two or three places to look for the problem I just caused eases the detection of the error.
Last edited:
hey Jo, well that was informative :) thanks for taking the time to write it up. I certainly will give it a good check when I get home. Hope the airport security won't mind me carrying it under the arm :) Still have to get the matching amplifier, the 1090 model. However, I have only seen one with the rack handle bars... that might pose a problem.

Properly functioning FM receivers work fine with no more antenna than a 4' rod or a folded dipole. A roof antenna that is not disconnected in every storm is a good way to melt down your PWB. Only in a valley in the mountains, far from the city transmitter, will a roof antenna be necessary, on a properly working FM radio.
The 97 Sony was an expensive imitation of a real radio. I fished a Luxman radio out of the trash from maybe 1980 that works better than the 1997 Sony using the headphone cable as antenna, all except for the unobtainable slide pot. I've bypassed the slide pot with a fixed resistor. The Luxman uses a UTCTA2003 Unisonic reception IC. The best reception and sound FM radio I ever owned was a 1980 pocket radio from GE made in Hong Kong. Unfortunately I dropped it and broke the PWB. Probably has an IC similar to the UTC.
Last edited:
Disabled Account
Joined 2012
Sony ST-S444ES

I found this really impressive spec'ed Sony FM tuner. Going to check the same things... caps etc. But those specs -- what did they use to measure them with?


Sony FM super tuner.jpg
It takes big bucks to measure the specs on your datasheet. Sensitivity, selectivity, distortion, separation. I use the comparison test. If the radio in my car will pick up a station I like, and the new Sony portable won't, and the twenty year old radio I inherited from my father won't, I put e-caps in the inherited radio (which I did) which made it okay. The only household FM radio I've ever owned that would pick up weak stations and produce stereo, was the GE pocket radio from about 1990. The Dynakit FM3 wouldn't, but the alignment manual wasn't available free until last year. (thanks diyaudio). Most FM tuners take a lot more equipment to align properly than this kit. Distortion test, I listen to classical radio stations, and if the piano solo broadcasts don't sound like a Steinway, then something is wrong. Most FM radios produce the deadly hiss/dropout on weak station. I re-e-capped the Reader's Digest radio because my two favorite FM stations in this middleburg are kind of weak, and the $35 I spent at the store on a new radio was a waste of money. The Reader's Digest radio project worked, but the unit has to have been aligned right from the factory for re-e-capping to do any good. For real alignment procedures, see the links above in post 2.
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.