1994 PC78XL

[Shyguy]

Purchased this radio and was planing on doing man alignment. I have been told and researched that it is the same radio as a Cobra 29. LTD. The alignment instructions say adjust L14, except mine has no tuning slug. I also saw someone else post that their 78XL was missing the tuning slug. This radio has never been touched, a virgin everything as is when new. My question is.. how do you adjust something that never was there?

 

[Handy Andy]

Early Unidens and Cobras' had used slugs in specific radios of their chassis.

Meaning, the number of boards they did use slugs with were small, were due to different sourcing problems when the lines first came out.

Some early Cobras used 2075 while other latter versions used the more common 2078 final.

The radios the manuals refer to are those they presume use a slug, you tune with it.

Not PC78XL. Nor are they for Cobra 29 using KEPC board silkscreened on them.
(The above may look confusing - I'm referring to no slug - they did use one at L14 - L16 and even the 52MHz trap L11 - but not all radios of the same Model type used that particular coil form or slug combo - the 29Plus with the SM5123A PLL and it's controllers - as an example - had used open core - no slug - on some)

​

Some early Philippines-origin boards as well as Taiwan-origin ones had L14 forms of different wire AWG used, so their tuning range changed. To fix that, they used a slug to pass QC - and was a minor point of emission testing the FCC once had.

But why only so few? The Ronald Regan era revised Part 15 and Part 47~49 range of FCC rules and regs so the end-user became more responsible for the interference caused by their installation than the manufacturer.

So if you had a crappy TV set from ...

 

[Handy Andy]

My question is.. how do you adjust something that never was there?

The answer is - you don't.

Most of the strip was reworked in later model years and done thru a specific manufacturer to develop a supply chain model - that had not changed for decades until the Covid-19 pandemic caused a massive disruption and the subsequent Grand Resignation.

So, back then they solved certain issues with type acceptance by having a "blueprinted", a known working model, that passed and they simply template'd it and used that chassis to build from - of course they cheapened it up and slimmed down parts counts and took out the fat - like mod meter and added EL-Backlight, Sound Trasher and Weather and cheap knobs for frills.

Later on, they re-added the older, dropped features slapped in a CPU Driven LCD and called it an LX.

To Help - the slug looks to have fallen out.

Where? Don't know...check the speaker cone and wax areas.

To help further...

Locate that 52MHz slug - see how it uses a "rubber band" to snug it to the form?

IT (coil slug) has to be wedged in there somewhere - else to work around - use the slug from the 52MHz trap to get by.

​

Also, since a PC78 has not been made since 2012 or so, you cannot trust the sellers word. They don't have to say anything - for in this case the radio should have gone to QC at the factory - it would not have passed testing - but if it's chips are dated near the end of the production years this was made - it could explain the missing part - they simply ran out.

Or...

The Radio was on a shelf - and used for 1 part the seller at the store needed a new slug (Repair guy) and let this one sit.

You got it when the store closed or returned the product because it wouldn't sell.

You hold the rest of the keys to open those other doors this radio possibly went to. Read this as Wholesaled out.

 

[loosecannon]

there should absolutely be a slug in that coil.

It's the tuning adjustment for the final stage.

Why isn't the slug present?

well you might not like this answer but most likely it's because your radio is not as virgin as you were led to believe.

It is fairly common for people to remove that slug when they change the final out to a 2SC1969 which used to be a pretty popular mod for this chassis.

you might take a look and see if your final is indeed a 2SC1969 or if it's the stock 2SC2078.

even if you do find a 2078 final in there, there is a good chance that the 1969 mod was done at some point in the past, the slug was removed and lost, and then the radio was put back to stock.

they never should have been removing that slug for the 1969 mod, as removing one turn from that coil would accomplish the same thing and maintain adjustability.

if you have any other old uniden radios around, you can probably use the slug from it to replace this one.
LC

 

[secret squirrel]

The first radio I had every taken to be peaked and tuned. The tech did it in front of me. The radio was a Uniden PC66. The tech removed the tuning slug and said, "That's it, this radio is simple to tune." Lol, we all live and learn.