Motorola Radius M100 repair

[ve9jmc]

i have a Motorola Radius M100 i have to repair. The problem is, is that it is missing a diode. The diode that was there was broken leaving only the 2 ends. I am in need of a part number so i can replace this diode.(like 1n914) If anyone would have an idea of the part number and can help it would be appreciated. I am also including 2 photos where i have the spot where the diode would be. Thank you

[kcbooboo]

There are several different logic boards for the Radius radios. There should be a printed number on the board that starts with HLN. Give us that number and we may be able to help further. Also provide the radio's model number which should be on a sticker on the side or bottom of the PA heat sink.

It's probably a protection diode and not necessary for proper operation.

Bob M.

[motorola_otaku]

Looks like a trace was burnt in the process of desoldering the old diode. Hope nothing else got damaged.

[ve9jmc]

the # on the board is HLN9123A. The model number is ACD33LRA73A5BK

[Al]

That diode looks to be VR807 on my parts layout for the HLN9123A masked logic board. It's a zener, 27V, p/n 4882256C20 in my original documentation. In the schematic, it's on the switched B+ line to ground. It's still listed as being available from Motorola, but(I think) too expensive at $6.09US list. Any 27V 5% 1/2W zener diode should work in there. Bob was right, it's not necessary for the logic board to work because it's a protection diode. But you may have other more serious problems because if this diode got zapped it means that the switched B+ line went over 27V +/- the diode's tolerance.

[ve9jmc]

Thank you for the information on that diode. It is greatly appreciated. This radio was hooked to a dc line backwards. It did pop the protection diode, but on replacement of that diode discovered that on reception of anyone the radio would emit a horn or howling sound drowning out any voice. So i discovered that pin 1 of the 5v voltage regulator was shorting to ground and after trouble shooting and tracing the circuit i discovered that it was this diode that was taking pin 1 of the L487 regulator to ground. so i suspect that this may have been causing the horn or howling noise on reception. Maybe i'm way off track..but i can only fix 1 problem at a time

Thank you

[HLA]

might not be worth fixing, I didn't think that radio could do narrow band? And if not soon it won't be legal to use anyway?

[ve9jmc]

Ok just to update at the spot where that diode is supposed to go, i do get 13.67v on one side.. and the other side is going to ground. Now i also do get 13.67v on pin 1 of the 5v regulator and 5.03v on pin 5. The radio powers up fine and and receives. Now just to cure that nasty howl when receiving. Would anyone have any insight into that problem? It's not going to be used on a narrow banded system here. It's just so the owner can monitor his taxi company when at home.

Thank you to everyone that has replied.

[Al]

If he's in the US you're right, Jeff. But I think he may be in Canada, and they don't answer to the FCC.

[ve9jmc]

Yes i am in Canada...New Brunswick actually...New ststems have to be narrow banded.. but existing systems are not made to make the switch yet.

[Al]

The receive feedback(microphonic) is usually caused by something physically loose in the receive VCO circuitry if the feedback disappears or is reduced when the volume control is reduced. Pop the lid on the VCO while receiving an unmodulated on channel carrier and try tapping on the VCO components(usually the coil) until you find what's vibrating when the speaker cone is vibrating. Occasionally you'll find poor connections on the logic board to RF board connector, and sometimes the fixed part of that connector(feedthrough) screwed down to the chassis(there's a replacement for that fixed part).

[ve9jmc]

Thank you Al, i will have a look in that area and see what i discover.

[ve9jmc]

Ok no the feedback doesn't go away when the volume is turned down. The way it sounds is that when you turn the radio on you'll hear the beep nice and clearly however within a moment and as soon as a signal breaks the squelch it howls. upon turning the volume down the howl is still there just at a reduced volume. i can turn the radio completely down but the noise is still there. i have gone through the tapping process and was unsuccessful to find anything that was loose. I even proceeded to push on the board just in case it may be a bad solder joint causing it.. but again no success.

[ve9jmc]

OK another update.. i have just replaced the HLD4322B board with another working HLD4322B and the problem exists. Just to make certain it wasn't the board i put it back into my working radio and it functions fine. So i'm taking i still have a problem within the HLN9123A board.

[Will]

Check the audio at the pin from the RF board to the logic board for the microfonics.
Look at the decoupling capacitors on the DC lines.

Could be a bad RX VCO coil, common problem. Sometimes a little white glue on the coil will stop it.

[KitN1MCC]

maybe it is just time to toss it bet you could find a m100 or better on here for the cheaps

[com501]

If your radio has a connector between the rf deck and the control board and isn't soldered, separate the two boards, clean the stiff wire jumpers between the two boards and the connector.

[ve9jmc]

here is something that may help a little with diagnosing where this problem is coming from. When you first turn this radio on you hear the beep just fine... however if you hit the buttons on the front repeatedly it seems to take a moment before it starts to howl. It sounds like there is a bit of static just before it starts to howl.. i don't know if any of the helps a bit or not. but just thought i kwould add that in there.

[ve9jmc]

To get a sense of the audio problem or noise i have uploaded a video of it on youtube.. that may help better point in the right direction.

http://www.youtube.com/watch?v=hvVgabUr ... e=youtu.be

[com501]

Have you tried an external speaker instead of the internal speaker?

The audio PA or the coupling caps may be the culprit. Or, simply a bad speaker coil that doesn't like the DC bias.

That M.A.S.H. episode you were watching is a rerun, by the way.....:^)

[ve9jmc]

HA HA HA HA com501..... yea i've seen them all about 50 times.. but still enjoy them. Thanks I'll give the external speaker a try and see what happens there, and if nothing else i'll start through the Audio circuit again and see maybe if i have missed something.

[jackhackett]

From the video it sounds like a cap going bad. The large 1000uF axial lead cap near the accessory connector couples the audio amp to the speaker and is a common problem, as it tends to dry out as the radios become old. I'd check that one first, and as old as these radios are it'll be due for replacing even if it isn't the main problem.

Also, you can get the manual and revisions here (near the bottom of the page):

http://www.repeater-builder.com/maxtrac ... index.html

Besides the main manual you'll need at least the MMR005 revision, as it has the HLN9123A Logic board.