Batboard

ok folks, i bought a analog VHF spectra dash mount a month ago, and had the shop set it up for everything in ham. it works, i can transmit and recieve good. but there is a higher than average amount of background noise in the audio, doesnt matter what i listen to, its there, even when decoding a carrier with 0 audio.

another problem it has, wich may be tied together is, you cant hear any beep tones from it, but tones are enabled. when you press vol up or down or any other tone related button, including the MDC pre tone, all i hear is a half second of that same background noise in place of the beep. even when theres no carrier being recieved.

any ideas?

wazz

First thing to do on a spectra, check the capacitors for leakage. This has been covered here many times, do a forum search. Bad caps will cause all kinds of weird symptoms, including audio problems.

wazzzzzzzzup wrote:ok folks, i bought a analog VHF spectra dash mount a month ago, and had the shop set it up for everything in ham. it works, i can transmit and recieve good. but there is a higher than average amount of background noise in the audio, doesnt matter what i listen to, its there, even when decoding a carrier with 0 audio.

<snippety>

This problem has received much attention in various threads. Just as a couple of examples, check this...

http://batboard.batlabs.com/viewtopic.p ... capacitors

The short summary is that there is a seris of aluminum electrolytic caps on the command and RF boards which, when they get to be about 10-12 years old, start to leak and corrode the surrounding board and other components.

If you care about preserving the radio, it is CRITICAL that damage of this nature be detected, contained and corrected as quickly as possible. The capacitor electrolyte contains anhydrous ammonia, and I'm sure I don't need to go into detail about what that stuff can do to the board's copper pads and traces, to say nothing of other components in the area.

Some telltale physical signs to look for are dull and discolored solder connections on either side of the caps, or a blackish irregular stain spreading across the board. One other sign I discovered recently is greenish-black spots on the leads of the audio PA chip.

Repair requires that you have the tools and skills to replace surface-mount parts, a through-hole desoldering unit to replace the audio PA, and the materials necessary to clean the board itself. If you have access to such, and are confident in your repair skills, just say so and I'll post some steps to take.

If not, I'm one of the folks who repairs such damage. Feel free to contact me via PM if you want to set something up.

Keep the peace(es).

That (Bruce's post) about sums up some of the Spectra problems.
Spectras as old as 4 years can have the same problems with bad caps.

I repair Spectras, and have been since they first "hit the streets" in the late 80's. And yes, I have seen some weird problems like you describe.

ok i will open the radio up to see tne extensiveness of the damage, i briefly opened it to look for date codes and it appears it was made in 95-96.

i have some spare 900 spectras collecting some dust around here, they are parts radios and i wonder if they have good audio boards, if i can swap them out? anybody know? i can compare board numbers, if it requires. EDIT..of course not the 900 PA board

i am more than up for a SMT repair as i worked in a electronics facility for many years testing and repairing circut boards, some of wich were for motorola. but it would be easier to swap a board.

thanks for the advice,

wazz

is this a problem with just the older analog spectras, or are the ASTRO spectras affected the same way?

wazzzzzzzzup wrote:is this a problem with just the older analog spectras, or are the ASTRO spectras affected the same way?

I would be leery of ANY Spectra that has those caps. One problem is that Motorola chose 'Lowest Available Bidder' when they spec'd the parts.

When I repair a Spectra with this type of damage, I don't use Motorola-bought caps. I use heavy-duty (5000 hour at 50 degrees C) parts made by Panasonic. They're the exact same size (the form factors are standardized in the industry) as the Motorola parts, and I know they're not going to leak.

Incidentally, Will is correct -- The cap issues are only one thing that can cause bizarre audio noises. It's really not possible to do a proper diagnosis over the board. I would also suggest taking a good look, with an O-scope, at the input and output lines on the audio PA (be careful NOT to ground either of the output legs), and check for low-level junk.

Since you're up for repair, the only other thing I'll add is that I've found 99% Isopropanol (aka Isopropyl Alcohol) to be an excellent cleaning agent for damage of this nature.

Happy tweaking.