Tuner Issues w/Zenith H845

[tlavergne]

I have had a Zenith H845 radio. It has been a great radio. Today as I turned the tuning dial the indicator refused to move more than 1/8 of an inch in either direction (both the tuner and the indicator). I feel the same amount of resistance as I turn the dial as I usually do. It worked great last night. So, before I begin tearing into this radio I was looking for some advice for what it might be and how to fix it.
Many thanks.
Tom

[marty59]

You're gonna' have to open it up to troubleshoot and it could be more than one thing. What is the condition of the tuning string and is it slipping...is there slack it it?

Provided everything is in place can you freely move the tuning cap by it's pully does everything else moves freely with it? There may be some dry areas that may need a little lube (pivet points, needle slider, etc) but make sure the string is not slipping but should grab..even if there's resistance however stop at this point and determing what is dragging down the works.

Or if there's some slack in it if you press your finger against it and turn the shaft does everything move then? Sometimes you can reposition the dial cord string spring at the tuning cap to take up the slack.

If the string is in good shape then a soap bar rubbed over it does wonders to help make it grip at the tuning shaft.

[tlavergne]

It feels like it's slipping and not broken. I can still feel resistance when I turn the dial. Thanks for the tips...I'll start tearing it down tomorrow.

[Reece]

A little oil on the mechanical bearings is good but be sure not to get any lube on the dial string. The string needs to grip the shaft that the knob turns. A good way to do this is to rub some rosin on the part of the string that will be pulled by that shaft. Violin bow rosin would be ideal, but might be hard for a particular individual to come across. Another way is to find a pine tree and take a drip of rosin off of the bark and dissolve it in a little bit of alcohol. Paint the solution on the string and allow to dry.

[tlavergne]

Rosin eh? Sounds nice and simple. I really think the dial string is slipping and not broken. It looks fairly simple to disassemble to get to the dial string. Hope so.
Thanks for the info.

[tlavergne]

The dial string is in good shape and I don't think there is excessive slack. It is slipping on a wooden spool that is part of the tuning shaft. I don't have any rosin...soap eh? I would think soap would become a lubricant. Not so apparently.
Many thanks.
Tom

[DaveWM]

can you get a pic of that wooden part?

[marty59]

Bar soap...the wax properties is what will help it to grip. I'm wondering what you mean by "wooden spool" too.

[tlavergne]

Just behind the face of the radio the shaft goes through a small wooden spool, not unlike a spool used for thread, and then the shaft disappears into the radio. I'll try and post a photo.

[tlavergne]

If I did this correctly the image should be here.

[DaveWM]

trying to remember if this one has the cam on the AM vari cap that operates the FM slugs or are the slugs directly tuned by the tuning shaft and the AM vari cap uses a dial string and pulley.

any way I would look for a dial string that has slipped off a small pulley or some other hang up. Since you have it apart now I hope the problem become obvious. Good luck with it. Those are nice sounding radios, I have a couple of that model cabinet. I prefer the older style with the less fussy airplane prop dial.

[tlavergne]

I don't know a thing about radios, other than I really like them. But it appears to me, as seen in the photo, that the shaft disappears into the chassis and I don't know what it does from there. The dial string from the shaft turns a wheel (the bottom of which is visible in the photo) which spins a shaft that operates these fin like things that engage themselves as you turn the knob. The dial string looks fine. Like I said, I don't know much about old radios but I love the sound of this Zenith. I prefer to listen to this than my Marantz tuner and JBL speakers.

[Jeffhs]

Originally Posted by tlavergne

I don't know a thing about radios, other than I really like them. But it appears to me, as seen in the photo, that the shaft disappears into the chassis and I don't know what it does from there. The dial string from the shaft turns a wheel (the bottom of which is visible in the photo) which spins a shaft that operates these fin like things that engage themselves as you turn the knob. The dial string looks fine. Like I said, I don't know much about old radios but I love the sound of this Zenith. I prefer to listen to this than my Marantz tuner and JBL speakers.

Tom, you have an excellent radio. I have one and like it a lot. The C845 was introduced into the Zenith line of high-end table radios in 1960. It has eight tubes, one of which is an RF amplifier; this tube takes the signal from the antenna and strengthens it, before sending it to the rest of the radio's signal circuits. Today's radios do not have the sophisticated circuitry the C845 (and other radios in Zenith's 800 series, such as the C845, C835...) have, so they are not nearly as sensitive (will not pick up as many signals) as the older ones will. I live in northeastern Ohio near Cleveland, within a mile of Lake Erie, and can often hear stations on my C845 as far away as Detroit, Michigan, Toledo and Youngstown, Ohio, Erie and Pittsburgh, Pennsylvania (as well as all Cleveland stations) -- using only the radio's built-in antennas. These radios were built for DX (reception of radio signals at long distances), so I'm not surprised they work so well. Hook up one of these to an outdoor FM antenna and you may find more signals than you can imagine.

The C845, as you noted, also sounds great, rivaling most of today's plastic-cased gutless-wonder radios (often having the entire set, except the volume/tuning controls and the speaker, on one integrated circuit chip or IC) you can find for dirt-cheap prices in dollar stores and the like (I have a belt-clip FM scanning radio that is probably built this way). The reason the C845 sounds so good is, one, because it has two speakers, two, because the radio is housed in a rather large real wood cabinet (not particle board or other excuses for wood, as many radios were housed in by the late sixties-seventies), and three, the set has tone- and volume-compensation circuitry in the sound output section. These networks are designed to allow the tone control to alter the actual audio response curve, not just cut down the high frequencies (if there is a tone control in today's cheap radios, it is of the latter type and, in my opinion, not much good).

"These fin things that engage themselves as you turn the (tuning) knob" are part of a component known as a tuning capacitor or condenser. This component allows you to select AM stations on your radio; the description of its function within the set is more complicated than that, but I'm trying to make this explanation as simple as possible.

Note that I said the tuning condenser allows you to select AM stations on your C845; the condenser has nothing to do with the FM section of the radio. FM tuning on the C845 is done with a separate tuner unit, using powdered-iron slugs that are moved into and out of tuning coils in the tuner. This tuning arrangement is also used in what was Zenith's first stereo FM table radio, the MJ1035, and likely was used in most if not all of their high-end sets of the time (late '50s-early sixties).

WARNING: There is a metal plate under the chassis of all C845s (visible after the bottom plate covering the chassis is removed) that must not be disturbed unless you know exactly what you are doing, and even then there's a risk of messing things up royally if even the least little thing gets displaced under there. This plate covers the bottom of the FM tuner and is fixed in place; if it is disturbed or any of the parts under it are moved, it will affect the operation of the FM section of the radio. Fortunately, there is nothing under that cover that needs routine replacement, so as a rule there is no need to go anywhere inside it. If the tuner ever does need servicing, I'd refer such to a professional or to a person well-versed in working with these critical circuits.

Which leads me to your tuner problem. Whatever you do, don't force the tuning knob if it will only turn an eighth of an inch; if you do, you may break the dial cord or seriously damage the dial drive mechanism. As others have suggested, use a little rosin or even common bar soap on the dial cord; this will give the cord traction so it won't slip on the metal pulleys of the dial drive. Something in the dial drive mechanism is binding, almost frozen, if the knob (and the tuning condenser) will only turn a fraction of an inch; my best guess, without actually seeing the radio, is that there may be dried-out grease on the shafts on which the pulleys (a pulley is a round metal part, mounted on the tuning condenser shaft, with a groove around its perimeter that accepts the dial cord) are mounted. I'd lubricate that shaft well, as well as every other part of the dial drive. I had a problem with my C845 similar to yours as soon as I got the radio; the tuning condenser and dial pointer would not move beyond 1460 AM and 105.7 FM (local stations in my area). I simply gave it a shot of contact cleaner and that was that. The tuner has operated flawlessly across the entire AM and FM ranges ever since.

While you're at it, remove the bottom cover plate over the chassis and give the tone and volume controls a good shot of Deoxit. This is a type of contact cleaner that is preferred by VK members by far over garden-variety, generic "contact cleaner" such as is sold by Radio Shack, et al. The reason generic contact cleaner is frowned upon by us VK members is that one never knows what it may actually be, whereas with Deoxit you know it is a contact cleaner designed for that purpose. The problem with generic contact cleaners (including Radio Shack's own brand) is that it literally could be anything, from recycled motor oil to watered-down WD-40.

The C845, and many other Zenith radios of its vintage and earlier, used a component known as a selenium rectifier in the power supply circuit. This part is square in shape with fins, and is used to convert or "rectify" the AC line voltage to the DC voltage (known as B+) needed for the plates of the tubes and other parts of the radio. It is recommended that this rectifier in all vintage radios be replaced with a component known as a "silicon" rectifier, with a dropping resistor in series with it. The reason the selenium rectifier should be replaced is that when it shorts out (and it eventually will, although I've seen radios--among them my own C845 and K731--that still work well after 50 years with the original selenium "stacks", but the truth is, no one knows how long they may last after that) it will give off a toxic and very foul-smelling gas that smells of rotten eggs. This is a red flag telling you that the rectifier is defective and must be replaced at once, before the radio is used again.

Note as well that there is a terminal strip on the rear apron of the chassis of your C845 (most C845s I've seen have one as well). This has no function by itself (connect a speaker to it and you won't hear anything--at least I don't on mine), but was used in conjunction with an external stereo-FM adapter such as the Zenith model MH-902 "Stereo Multiplexer". This could conceivably be used as a standalone FM receiver, but the downside is that you would hear only one channel (not both) of a radio program broadcast in stereo. The intended effect (stereo sound) can only be achieved by using the MH-902 adapter with a Zenith radio equipped with the proper input terminals.

There is a phonograph input jack (with a radio-phono selector switch) on the rear chassis apron of most C845s, but I wouldn't use it until a part known as a blocking capacitor has been replaced. This component isolates the metal parts of the jack from the radio's chassis, which is directly connected to the AC line. In almost every radio 50 years old or more, this capacitor is defective and needs to be replaced before the phono jack can be used safely. This jack was designed for use with a 45-rpm record changer (notably RCA Victor's 45-EY-3 from the early 1950s), although some VK members have had good results with other devices, such as mp3 players, connected to it. It all depends on how much output signal the device provides at its output jacks.

Enjoy your C-845. As I said, these are well-made radios built (as were the rest of Zenith's 800 series, to say nothing of the stereo MJ-1035) with high fidelity and excellent signal-grabbing capabilities in mind; yours should give you many years of enjoyment. Correct the problem with the dial drive (which seems, to me anyway, to be the only real problem your set has at this time), replace the selenium rectifier and recap, that is, replace doubtful capacitors (or have it done if you are not comfortable with working with high voltages) at your earliest convenience, and enjoy your favorite stations in typical Zenith high fidelity. They wouldn't have put the words "high fidelity" in a script logotype on the front of the radio if the sets weren't hi-fi material.

[tlavergne]

Radio is back together and I am listening to good FM radio once again. Many thanks for the help.
TL

[DaveWM]

so was it just slipping? glad you got it back together. Yes those old Zeniths were indeed fine radios.

Besides the Y845 I have I use a H615 for AM, another fine old Zenith set.