Spectra 146-174 110w capacitors

[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.

Thanks a lot

[Bill_G]

http://www.repeater-builder.com/motorol ... -caps.html

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

[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?

[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.

[travisaksarben]

Thanks for your input, I'll do the replacement in any case. Just need the right parts first.

[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.

[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

[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.

[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.

[travisaksarben]

All duly noted, thanks very much, will report back (hopefully soon).

[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.

[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.

[Bill_G]

... and getting the cage off is a joy!

[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.

[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.

[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).

[travisaksarben]

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.

[jackhackett]

I believe Will used to do Spectra repairs. but it says he was last active on here in May of 2016.

[travisaksarben]

This spectra performs really well, I can now hit repeaters really far away, and it hears really far too.
Super stuff.

[travisaksarben]

Today I got the last two remaining caps replaced, the two that are in the control head.
Much to my dismay, the speaker still pops really loudly when pushing a button or when the radio begins to RX something. One cap showed signs of leakage.

I guess I got some board damage somewhere. Maybe I could post some pictures of known problem areas? thanks a lot, I had a 95 mile contact with this radio some days ago:)

[Jim202]

Let me point out that if you have a bad command board or think you do, you can replace it with one from a UHF or even an 800 Spectra. I have done this on many VHF Spectra radios. You will just have to jump through some hoops and use the service features of the bit banger to set the values of a number of addresses to allow the board from another radio to be used.

You will also need to correct the serial numbers of the command board and the MLM board if you change it also so they all match. i generally use the original radio serial number you started with. There are several web sites that provide the bit banger addresses and just what they represent.

One word of caution here in changing the boards. You will probably going to end up with an 01/82 error after you make all the changes. this is an easy fix. Read the radio without making any further changes. Then write back to the radio. This should clear up the error I mentioned.

I tend to use the clone feature to load in a good set of frequencies before trying to get rid pf the 01/82 error.

Hope this helps a few of you.

Jim

[travisaksarben]

Command board might need replacing, thanks Jim