Users may not create topics, posts, or private messages containing or relating to the following material (especially pertaining to Motorola copyrighted software, unless you want Motorola to come along and shut this site down):

  • Listing for sale or trade of, or links to sites offering for sale or trade of, or giving away, Radio
    Service Software (RSS) or Customer Programming Software (CPS)
  • Profanity, pornography, defamation, or slanderous remarks directed towards any individual or entity
  • Commercial advertising (except in the Batboard Vendors forum, as approved by the Admin/Mod Staff)
  • Any other items which may be deemed as offensive

If any topics, posts, or private messages containing or relating to the aforementioned material are brought to the attention of the Admin/Mod Staff, they will be deleted.

Additional FAQ items appear here in Forum Rules. Please review them for posting guidelines and further clarification.

Maxtrac PA board damage-Reverse Polarity diode?

The General forum is where users can discuss any topic regarding Motorola communications equipment - hardware, software, etc. There are also several focused forums on this board, so please take the time to ensure that your questions doesn't fall into one of those categories before posting here!

Moderator: Queue Moderator

Xnke
New User
Posts: 12
Joined: Sat Jul 29, 2017 7:27 pm

Maxtrac PA board damage-Reverse Polarity diode?

Postby Xnke » Fri Aug 04, 2017 2:19 pm

I have been going through my stack of these things to sort the "Parts" radios from the "projects" radios, and found a nice D51MJA9JA5AK. Clean, no dings, all the buttons there, but rattles...so before even powering it up, I popped the PA cover and found CR2170's body seperated from the leads. It appears that it ran hot enough the solder melted and the body popped free from the two leads either side of it. Looking at the service manual, it appears to be a reverse polarity protection diode...which would have worked great until it melted down and went open circuit.

The PA board is an HLB3049A, so that means 36-42Mhz, I think? Not useful to me but I'm hoping the logic board and front panel are still good-they are the 16 pin and 32 channels, and I was hoping to re-purpose them on one of my 2-channel 42-50mhz PA/RF board assemblies.

Anyone know what that diode is outside of the motorola service number? I can't seem to locate one, and more importantly, if I do locate one what are the chances that replacing it will bring the radio back to life?

User avatar
Bill_G
Posts: 3036
Joined: Thu Sep 17, 2009 5:00 am

Re: Maxtrac PA board damage-Reverse Polarity diode?

Postby Bill_G » Sat Aug 05, 2017 5:11 am

On the logic, near the 16 pin plug, there is a solder down fuse that may have blown preventing the radio from turning on, or the radio may have been set for ignition lead required by cutting the fuse out.

Xnke
New User
Posts: 12
Joined: Sat Jul 29, 2017 7:27 pm

Re: Maxtrac PA board damage-Reverse Polarity diode?

Postby Xnke » Sat Aug 05, 2017 5:42 pm

I never did power the radio up-Checking the PA transistors showed they had an emitter-base short, and 20K from base to collector.

User avatar
Bill_G
Posts: 3036
Joined: Thu Sep 17, 2009 5:00 am

Re: Maxtrac PA board damage-Reverse Polarity diode?

Postby Bill_G » Sun Aug 06, 2017 6:15 am

It's not unusual to see a ohmmeter B-E short in a class C RFPA because there may be a coil to ground. It's part of the tank circuit. Unless the transistors are obviously cooked and discolored, clip out the burnt protection diode, and apply power to the radio with a small value fuse (5A) in the mains.

User avatar
jackhackett
Posts: 1401
Joined: Tue Jun 10, 2003 8:52 am

Re: Maxtrac PA board damage-Reverse Polarity diode?

Postby jackhackett » Sun Aug 06, 2017 12:29 pm

I've seen those diodes fall apart like that many times. I think it's more from vibration than anything else, because they usually still checked okay with a diode tester.
They're not just a regular diode, they're a TVS (Transient Voltage Suppressor) diode, they protect against both reverse polarity and voltage spikes. Basically a big zener diode. The Motorola number was MR2525L.

Xnke
New User
Posts: 12
Joined: Sat Jul 29, 2017 7:27 pm

Re: Maxtrac PA board damage-Reverse Polarity diode?

Postby Xnke » Sun Aug 06, 2017 2:47 pm

That's exactly the case-the diode body checks out fine. No blown fuses, no burned traces or blown caps that would be consistant with high voltage transient or reverse polarity, just that diode broken.

Is there a modern/available replacement that should be put back in, or is it a motorola service parts number only?

This is a 36-42Mhz unit anyway-not useful to me-but it may be useful to someone else so I want it to work before I pull the logic board and front face. Someone else may need the RF board and PA someday.

User avatar
train_radio_guy
Posts: 213
Joined: Mon Sep 27, 2004 8:47 pm

Re: Maxtrac PA board damage-Reverse Polarity diode?

Postby train_radio_guy » Mon Aug 07, 2017 10:15 am

Here's the spec sheet on the MR2525L - Overvoltage Transient Supressor:
- http://pdf.datasheetcatalog.com/datasheets2/39/399377_1.pdf

As for a directly equivalent part, NTE, Mouser, & Digi-Key are turning-up nothing. Perhaps a parts radio might be a perspective donor, otherwise Motorola Parts might be your only choice.
"Trust me, I know what I'm doing!" - Sledge Hammer


Return to “General Motorola Solutions & Legacy Radio Discussion”

Who is online

Users browsing this forum: Baidu [Spider], Yahoo [Bot] and 6 guests