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Spectra 146-174 110w capacitors

Posted: Sun Dec 31, 2017 5:16 pm
by travisaksarben
Happy new year!

I have become the proud owner of a T83FWA7HA9AK and it needs the capacitors replaced. (speaker popping, sometimes no RX)
I have never bought a capacitor before, a techie friend will do the repair while I obtain the caps.

However, I am a little confused as to exactly what I need to ask for at caps-r-us when I go shopping. Could someone please tell me exactly what I need to ask for? voltages, uf and amount. I feel like tantalums are the way to go, since they are supposed to be everlasting.
It has an A9 aka systems 9000 control head.
:o
Thanks a lot

Re: Spectra 146-174 110w capacitors

Posted: Mon Jan 01, 2018 7:09 am
by Bill_G
http://www.repeater-builder.com/motorola/spectra/spectra-caps.html

Here's a whole article about recapping Spectras, what to look for, what to buy, and how to do it.

Re: Spectra 146-174 110w capacitors

Posted: Mon Jan 01, 2018 8:55 am
by travisaksarben
Hi and thanks, I neglected to mention that I have done basic searches and of course read that article, but I still have doubts so here goes:
Control head does not need caps replaced? "Note that the A9 (sometimes called the System 9000) control head uses different style capacitors and that control head does not suffer this problem (but the radio chassis does)"

RF board: 4 caps, 10uf 16v. 1 cap, 47uF, 16v
Unknown command board, at most: 3 caps, 10uF 16v. 1 cap, 10uF, 50v.
VHF 110w PA: 1 cap, 220uF, 35v. 1 cap, 10uF 50v.

Correct?

Re: Spectra 146-174 110w capacitors

Posted: Mon Jan 01, 2018 8:59 pm
by Astro Spectra
My experience is that only a careful visual inspection will tell you if you definitely need to do replacement. Note that the converse is not true, visual inspection will not show you if you don't need replacement.

Re: Spectra 146-174 110w capacitors

Posted: Mon Jan 01, 2018 11:59 pm
by travisaksarben
Thanks for your input, I'll do the replacement in any case. Just need the right parts first.

Re: Spectra 146-174 110w capacitors

Posted: Tue Jan 02, 2018 5:15 am
by kcbooboo
If you go to www.repeater-builder.com, Motorola area, Spectra section, "Radio and Equipment Modification Articles", you will find the 2nd, 3rd, and 4th items to be rather pertinent. In particular you should avail yourself of the recap offers made by AI4JI in the 4th link.

Bob M.

Re: Spectra 146-174 110w capacitors

Posted: Mon Jan 08, 2018 1:04 pm
by travisaksarben
The caps have been replaced. Much to my dismay, the radio received normally for about 20 mins, though the audio was muted for a split second sometimes, and then the audio drifted out totally, as if the antenna had been disconnected. Now, the receive comes and goes, mostly it is completely gone. If I turn off the squelch, the speaker will blare static all the time, but signal may or may not be there. Rats.

Transmit seems fine, tested with a scanner. This thing loads my alternator hard!

Also, the speaker still pops when I press mode/volume. I believe my control head does have 2 caps after all that I have not attempted to get changed. The quote in my first post made me believe otherwise, but I see that other article now so I have to check.

I was able to check the output, it was below 40w on low, so I changed the values to this:
low relative value 72=62w
hi r v 100=90w

it would not go over 90 watts for some reason.
input appreciated, thanks a lot

Re: Spectra 146-174 110w capacitors

Posted: Wed Jan 10, 2018 4:48 am
by kcbooboo
The 2nd oscillator in the Spectra RF board is a phase-locked-loop design. There's one and only one potentiometer inside those radios and it adjusts the PLL frequency. The pots can go bad/open, and the oscillator dies or is way off frequency so you receive nothing. Play with that pot a bit.

Also read the "Miscellaneous Spectra Topics" article about half-way down as it discusses this issue.

Bob M.

Re: Spectra 146-174 110w capacitors

Posted: Wed Jan 10, 2018 5:47 am
by Bill_G
Good point Bob. That same pot area seems to attract the corrosive leakage from the caps. The feedthroughs and resistors are often damaged there. I'm also betting there are damaged feedthroughs and landings on the command board causing the audio problems. The cap rework needs to be thorough.

Re: Spectra 146-174 110w capacitors

Posted: Wed Jan 10, 2018 8:31 am
by travisaksarben
All duly noted, thanks very much, will report back (hopefully soon).

Re: Spectra 146-174 110w capacitors

Posted: Wed Jan 10, 2018 4:37 pm
by Bill_G
You're welcome. Sometimes those caps eat the landings and traces, and then migrate through the feedthroughs to the other side of the board slowly eating that side. All kinds of happiness occurs, and the guy doing the work has to inspect with a magnifying glass to find it all. Scrub scrub scrub with lots of alcohol and acid brush trimmed down to short bristles.

Re: Spectra 146-174 110w capacitors

Posted: Fri Jan 12, 2018 10:52 am
by jackhackett
Measure the voltage on the pot, it's been a while since I've done one but if I remember correctly if you touch your meter probe to the metal adjustment part of the pot you should see something like -3V. The pot gets negative bias through the surface mount resistor next to that caged in section. The feedthru hole near the edge of the board there sometimes gets corroded and loses contact with an inner board layer trace. If that happens the trace needs to be bypassed, which can be a bit tricky.

Re: Spectra 146-174 110w capacitors

Posted: Fri Jan 12, 2018 4:47 pm
by Bill_G
... and getting the cage off is a joy!

Re: Spectra 146-174 110w capacitors

Posted: Fri Jan 12, 2018 8:51 pm
by jackhackett
Don't recall if I ever had to take one off. I think the cage tended to keep the leakage out of that section.

Re: Spectra 146-174 110w capacitors

Posted: Sat Jan 13, 2018 2:18 pm
by travisaksarben
I adjusted the pot and this has cured the problem 99%. The last 1% of the time it will still lose receive, for a split second, but this is still a great improvement, I just had a nice qso over 35mi, nice and clear audio both using 100 watts.
Not been able to meter the voltage yet.

Re: Spectra 146-174 110w capacitors

Posted: Mon Jan 15, 2018 8:29 pm
by kc7gr
Clean the entire board around the capacitor areas with 99% isopropanol (Isopropyl Alcohol). Dry thoroughly. Keep in mind the RF board is at least four layer, possibly six, so if capacitor goo got into the inner layers the only thing you can do for 100% reliability is replace the RF board.

Just getting active on the board again after a very long absence. I still service the Spectras, as I did before and as at least one other person did (don't recall who).

Keep the peace(es).

Re: Spectra 146-174 110w capacitors

Posted: Tue Jan 16, 2018 2:00 am
by travisaksarben
kc7gr wrote:Clean the entire board around the capacitor areas with 99% isopropanol (Isopropyl Alcohol). Dry thoroughly. Keep in mind the RF board is at least four layer, possibly six, so if capacitor goo got into the inner layers the only thing you can do for 100% reliability is replace the RF board.

Just getting active on the board again after a very long absence. I still service the Spectras, as I did before and as at least one other person did (don't recall who).

Keep the peace(es).


Right on, next time I pick up a spectra or hopefully low band syntor, I'll probably have someone like you check it out and do maintenance, it would save me time and money. Haven't seen a spectra on for sale in 2 months, though. Glad I picked up mine.

Re: Spectra 146-174 110w capacitors

Posted: Tue Jan 16, 2018 11:18 am
by jackhackett
I believe Will used to do Spectra repairs. but it says he was last active on here in May of 2016.

Re: Spectra 146-174 110w capacitors

Posted: Thu Jan 18, 2018 1:09 pm
by travisaksarben
This spectra performs really well, I can now hit repeaters really far away, and it hears really far too.
Super stuff.