Maxtrac 900MHz Conversion

Rhino · Post by **Rhino** » Sun Oct 23, 2005 6:43 pm

I am converting Maxtrac to amateur band. I have a couple of basic questions.

1. I understand the use of the conductive pen and that to set the new frequencies, you measure the VCO steering line voltage. Where are the test points that I should use?

2. Can anyone suggest place to purchase the required front end filters for a reasonable price?

Thanks-

Ryan

n2knc · Post by **n2knc** » Sat Oct 29, 2005 1:32 pm

i can help you out with the pen,i got my filters off ebay

dave

CTAMontrose · Post by **CTAMontrose** » Sun Oct 30, 2005 6:26 am

how many filters do you need?

i think i have a few left.

kb0nly · Post by **kb0nly** » Sun Oct 30, 2005 7:58 am

A pen for the Maxtrac conversion??

I knew you had to use the conductive pen to move the VCO on the Spectra, but on the Maxtrac?

Big BOB · Post by **Big BOB** » Sun Oct 30, 2005 2:54 pm

Yep!, Have to use the pen on the Maxtrac. In fact there are 2 striplines to do, one for repeater and one for TA.

On the Spectra a lot of guys use just a 100K resistor.

HauseMan · Post by **HauseMan** » Wed Jan 25, 2006 1:48 am

Radio Shack is carrying the Caig CircuitWriter pens lately, for about $14.

I too need to know where the VCO voltage test points are. The page doesn't do a very good job of describing those. Plus, I could use two filters, if anyone has any.

N4YWG

CTAMontrose · Post by **CTAMontrose** » Wed Jan 25, 2006 5:04 am

I have some filters left over.. PM me and lets work out the details.

WB6DGN · Post by **WB6DGN** » Thu Feb 02, 2006 7:05 pm

I didn't see anyone comment on the test point for the steering line voltage. In case you need that, it is at the junction of R123 and C127 on the RF board. There is a rather large round pad on the same side as the VCO. C127 is on this side of the board also, but R123 is on the other side of the board. If you hold the RF board so that the VCO in on the left center of the board, the test point is above the VCO about an inch and a half to two inches and just SLIGHTLY to the right of the right edge of the VCO. If you still need assistance, I will try to scan that area of the pictorial and email it to you. Let me know if you find it.

73 Tom KB5DPE

HauseMan · Post by **HauseMan** » Sun Mar 19, 2006 12:25 am

Shame on me for not getting back here since half-past nearly forever....

grem467;
Thanks for the offer....I still need two, and I don't care if they're Toko's or MuRata or mixed, as long as they work (lol). Please reply here with your price, in case I don't get the profile fixed in time.

My radio is a D37, and that 30-watts is gonna be sweet if I can get the RF OUT close to that level. There's only one 900 repeater near here, and it's low-powered, so I've honestly not cared much about my project. I think in all of GA, we have 2 maybe 3 900 repeaters.

I'll be reworking my profile thingy to include my email. I have PayPal if that's good for you. It'd be great to get those, because no more can be found on Ebay, and I usually look for them weekly.

Meanwhile, produzzerguye@yahoo.com is good. I leave Yahoo IM up most of the time.

To kb5dpe/Tom:
I'd appreciate that scan/picture. I've finally bought a set of Torx drivers, and got into the radio and looked around to get familiar with those points and I should be able to do well. So with your scan/pic, I'll definitely manage. My 230-watt gun-iron should get that VCO cover loose.

BTW, is ground a common chassis ground, or should I ground elsewhere ?

I guess, in the end, I'll end up using an IFR to really tweak the sensitivity just right, but maybe the CircuitWriter pen and a VOM will get me close.

Is there a service manual anywhere in cyberland in PDF ?????? THAT would be swell.

Thanks fellas,
Paul N4YWG

kcbooboo · Post by **kcbooboo** » Sun Mar 19, 2006 4:32 am

I also have TOKO filters. $20 for a pair, and that includes shipping. Send me a PM for further details.

There are several conversion articles on repeater-builder.com. This one just went up in March and it tells you how to fool with the 900 MHz VCO:

http://www.repeater-builder.com/maxtrac ... z-vco.html

If you click on the "up one level" link at the top or bottom, you will find other articles about converting MaxTracs for 900 MHz use. There's more than enough information there between several articles to help you control the transmitter's output power and replace the front end filters.

Bob M.

HauseMan · Post by **HauseMan** » Sun Mar 19, 2006 6:14 pm

Thanks....be in touch as soon as I have the $20 (ya know how it is) and will get a pair. I skimmed-over that article, and at least NOW I know where the SL test points are, and I'm sure I can manage everything now (without an IFR !)

Paul N4YWG

kcbooboo · Post by **kcbooboo** » Sun Mar 19, 2006 6:25 pm

You definitely don't need sophisticated equipment to move the VCO down. A decent digital voltmeter or a high impedance analog voltmeter will work fine.

No problem on the filters. I have 12 at the moment and should be able to get more if need be.

Bob M.

HauseMan · Post by **HauseMan** » Fri Mar 24, 2006 9:23 pm

kcbooboo wrote:You definitely don't need sophisticated equipment to move the VCO down. A decent digital voltmeter or a high impedance analog voltmeter will work fine.

No problem on the filters. I have 12 at the moment and should be able to get more if need be.

Bob M.

Thanks Bob...my Extech or Fluke should do nicely

I"ve even got an old Xerox swing meter from probably the 1970s that was mint when I got it recently, with the original red-label Eveready's still in it, very clean.

Are you still doing $20 delivered for the pair ?? PM or IM me anytime.

HauseMan · Post by **HauseMan** » Sun Mar 26, 2006 12:08 pm

I noticed that the solder points on the bottom-side of the board look rather tricky to the eye. Are there 2 or 4 points to be unsoldered ? I can't tell because everything's so close together.

kcbooboo · Post by **kcbooboo** » Sun Mar 26, 2006 12:22 pm

There are two signal points and four mounting tab points. I can get to all of them with a 100w Weller gun with the thin tinned tip (not the big copper tip).

I use a 40w iron to unsolder the signal pins. I use the 100/140w gun to heat each mounting tab until the solder melts, then keep it there another 5 seconds so the solder on the top of the board also melts. I use a plunger-type desoldering tool to suck the solder out of the holes. They must be completely free to move; if not, reheat, add solder, and try again.

After doing a bunch, they get easier. I'd say it takes 5-8 minutes to remove the two filters on one board.

If you don't feel comfortable doing it, other arrangements can be made.

Bob M.

HauseMan · Post by **HauseMan** » Sat Apr 01, 2006 11:53 am

Yeah, my Radio Shack gun has the slot/screwdriver tip on it, and I'd have to get one like you're using. And I do have a solder sucker. So you say SIX points to get that thing out, eh ? Lots of intricate work....gotta remember to lay off the coffee before working on that thing !

Paul

kcbooboo · Post by **kcbooboo** » Sat Apr 01, 2006 11:57 am

Well, I have worked on stuff with smaller components on it, but this isn't worse than a 16-pin integrated circuit. The big problem is getting the solder to melt on both sides of the circuit board. It's thick, and the ground foils on each side tend to draw all the heat away. The small thin Weller tip works well, but you have to be careful where you put it so you only apply heat to the point of interest.

Bob M.

WB6DGN · Post by **WB6DGN** » Sat May 27, 2006 6:33 pm

"To kb5dpe/Tom:
I'd appreciate that scan/picture. I've finally bought a set of Torx drivers, and got into the radio and looked around to get familiar with those points and I should be able to do well. So with your scan/pic, I'll definitely manage. My 230-watt gun-iron should get that VCO cover loose."

HauseMan,
Sorry I never got back to you regarding the steering line metering point. Somehow I missed your post. If you still need/want the scan of the pictorial, email me at kb5dpe at arrl dot net and I will send it to you.

For ground, I just clip the neg. lead to the part of the shield that remains agter the cover is removed (the outer shield, not the VCO). Don't know if that's the recommended spot but it works.

Again, sorry I missed your post.

73 Tom KB5DPE

Maxtrac 900MHz Conversion

Maxtrac 900MHz Conversion

Maxtrac SL voltage TP

Filters

Soldering