Maxtrac deaf until warm

wyldman · Post by **wyldman** » Fri Mar 23, 2007 5:48 am

I have an 800 Mhz maxtrac,which is totally deaf when cold.It turns on,lights up,and beeps,but then nothing.It won't even search.Search can be turned on,but it never receives anything.

Eventually as it warms up,it will start to search,and receive transmissions.They come in garbled and with lots of static at first.It will get some transmissions,and miss others.Eventually it warms up enough that is operates normally.Shutting it off even for a few mins seems to make it act up again.

I've opened it up looking for something obvious,but I can't see anything.I don't think it is a programming issue,as it has worked flawlessly up until this point.I did try reprogramming,no luck.It seems to read and write just fine even when cold.

Is there a common problem that is an easy fix ? Would like to try and narrow it down before I send it in for repair.

Max-trac · Post by **Max-trac** » Fri Mar 23, 2007 7:36 am

Try replacing C551 on the logic board, it is a weak point.
Do a search here on that number, there has been lots of discussion. I even had a GM300 that when it WARMED UP got all distorted, and it was that capacitor.

wyldman · Post by **wyldman** » Fri Mar 23, 2007 8:01 am

Does this affect just the audio circuit ? or the whole radio ?

If it is just the audio circuit,would you still not see it landing on channels when searching (numbers changing on the display) ? The radio does not seem to do this,so the problem seems to be in the receive section of the radio.

arlojanis · Post by **arlojanis** » Fri Mar 23, 2007 8:59 am

Check or replace the IF crystal.

DJP126 · Post by **DJP126** » Fri Mar 23, 2007 11:56 am

wyldman wrote:Does this affect just the audio circuit ? or the whole radio ?

If it is just the audio circuit,would you still not see it landing on channels when searching (numbers changing on the display) ? The radio does not seem to do this,so the problem seems to be in the receive section of the radio.

I never worked on the Maxtrac but from the sounds of your description, Arlojanis's suggestion of a defective IF crystal IS a good possibility. Also, look for a defective cap in the VCO circuitry (either the direct circuits or the supporting circuits).

Will · Post by **Will** » Fri Mar 23, 2007 1:19 pm

wyldman wrote:Does this affect just the audio circuit ? or the whole radio ?

If it is just the audio circuit,would you still not see it landing on channels when searching (numbers changing on the display) ? The radio does not seem to do this,so the problem seems to be in the receive section of the radio.

The C551 is in the detected audio path from the receiver to the logic board. The uP gets the data from the same path, so the radio thinks it is out of range since no trunking data is getting thru.

C551 gets leaky with age and changes the bias on the op amp causing the op amp not to pass the detected audio, or pass the detected audio with a lot of distortion.

Search: Maxtrac slow warm-up....

I replace it with a 4.7uF tantalum at 25 volts. No more problems.