[Nathan Slingerland]

From the Zenith service manual index (Volume II) it looks like model 10H571 corresponds to chassis 10A3.

I've attached the schematic and alignment instructions.

10H571R (chassis 10A3R) are different.

[morzh]

Thanks Nathan! Big help.

[morzh]

The photo with the FM shield removed. I can see how the recap is gonba be fuuuuuhnnnnnn ......

   



As for the initial check, well, as expected, the Candohm is bad. Not open, but 100 ohm (or close) section is 1K. The 12 ohm one is 25.

The 5Y4 tube is dead. The filament is open.

Most (all exept one) loctals tested dead first but I got suspicious with the black pins, scraped them with a scalpel and all tested good. So all tubes are good except the rectifier.

[morzh]

Nathan, you wouldn't by chance have the underchassis diagram?

[Nathan Slingerland]

Wow - that sure is a lot of capacitors! And nicely layered too....

I'm afraid it's only those two pages in the service manual - Zenith doesn't seem to provide under-chassis diagrams for the models (at least of that era).

I checked Riders and Beitman's too - but those are just schematics too. That being said I think the schematic from Beitman's might be a bit clearer - attaching that too in case that's useful.

Zenith 10H571 - Beitmans.pdf Size: 507.56 KB  Downloads: 274

[morzh]

Yeah....looks like a tube caps lasagna. Or ramen noodles.
I think 37-116 has less caps.

[Jayce]

Holy caps Batman!   That has to be the most un-Zenith like underside to a Zenith chassis that I have seen so far! One thing I have always sort of admired about Prewar Zenith radios is that they are usually pretty simple under the chassis. My late friend (who always complained about Philcos using too many caps) could rebuild an average Zenith in fairly short time, even with those belts needing replaced. The only issues he ever had was with the Robot Dials which he said was like taking apart a robot to clean things and replace the tuning belts. Maybe I don't want to find a Spinet after all...

[morzh]

Yep, there comes that monent in every restorer's life when he stands there over a chassis from H**l and asking himself if be bit a bit more than he could chew. A 37-116 was that first one for me. This is the third. The AK808 was the 2nd.

[KCMike]

Maybe I'll walk by mine another year after seeing that.   Looks like at least 25 paper caps.

[Jayce]

I need to look under an unrestored 10 tube Zenith again, but I swear that looks like they just had a case of "Ah to h*** with it!" Just grabbed a wad of capacitors and jammed them in there. That just looks like a sloppy mess under there.

[Arran]

Yep, there comes that monent in every restorer's life when he stands there over a chassis from H**l and asking himself if be bit a bit more than he could chew. A 37-116 was that first one for me. This is the third. The AK808 was the 2nd.

Mike;
  I would have figured that the AK 808 would have been first, since dear Arthur seemed to like rubber/gutta percha wire as much as Grigsby and Grunow did, but then again those didn't use that 15 tube David Grimes style modular chassis like the 37-116 did.
Regards
Arran

[morzh]

Arran

Well,

I put the 37-116 first due to the sheer complexity. No wires needed to go, or almost none, but the sheer number of caps and the access to those in the RF block are a PITA.
Now this said, it was literally the first radio of this complexity I took upon and when I lifted its 25 lbs worth of mess on the bench I got a bit of jitters. Than I followed my gramma advice, "the eyes are scared but the hands keep working" and so it worked out just fine at the end.

AK808 obviously was a mess, and I have photographs of the workplace buried under the insulation chips, literally, to prove it. But the complexity is much less. Oh, and they did use the modular chassis. That was THE pain of it, tracing cracked wires from the subassembly into the main block, changing them etc.

This one, in fact, if it weren't for the capacitors that look like the roaches in the kitchen when you turn on light 2am, would be a simple case. The space is ample, and most wires are cloth-covered, only some are rubber-coated.

[morzh]

OK, yesterday I res-stuffed the first tubular guy and took out the twist-lock cap.
The twist-lock, as it's been the case with the previous Zenith cap, in fact shows that it is not dry. It should be 5uF, and two 15uF caps, 300V and 250 and 450V. The capacitances are 8uF, 18uF and 30uF. Considering it is 40-s, and not 30-s.....
I am tempted to reform it and see how it behaves.

I need to order a bunch of the caps, like 0.1uF. I could use 0.15uF I have but as the sch is barely readable when it comes to ref designators I cannot quite see which cap goes where and so though I am sure in some places they can be used, in some others it is possible 0.1uF is preferred. If only I could have a nice readable schematic with ref designators showing clearly. Oh well, can't have it all at once.
On the other hand, this murkiness is more pronounced on the Beitman's and only in printed form, the first PDF Nathan gave is kinda readable. And yes, some of those caps should be what they are although 0.15uF would work too. Like those in teh detector circuit in the feedback bypass.

[morzh]

Tonight broke out my doubling rectifier and tried to reform the caps. Started with 400V cap. Turned the rectifier on, measured the current, started with 2mA. The current barely was going down. In several minutes it decreased by maybe 10 uA. So I decided I will restuff it.

[morzh]

The decision not to reform the cap proved to be the correct one: upon the opening inside there was lots of corrosion, so this cap would not reform well.
Tonight I will soak the cap in vinegar to remove the salts, and then dry and restuff it.