Motorola Digitac voter questions

[wa6jbd]

Hi all... Bear with me for a lengthy post. I've uncovered an interesting problem with a number of Digitac voters, and I'd like to see if:

a. Anyone else has seen the problem, and
b. Can anyone steer me toward a fix.

First, the problem. These digitac voters are part of a 28 channel trunked system with 5 receive sites. When a received signal is voted, and the voter then switches the selected receiver from one to another, the audio output level drops... a lot. I mean, 10-20 db. It's a rare event on some voters, much more frequent on others. It's not a receiver level problem. The levels of ALL receivers have been checked, and rechecked. A particular receiver may select and provide the proper level 10 times, and the 11th time, the audio level drops. It only changes when the voted selection changes, and only goes normal if status tone is decoded before the receiver unsquelches again.

In troubleshooting this, it was easy enough to nail it down to the QRN4306B input card. Swapping cards between comparitors, the problem follows the card. Taking this further, swapping the AGC chip (U100, U200, U300, and U400) between channels on an individual card, the problem follows the chip. The AGC chip is a digital pot, controlling the input level as directed by the card's cpu.

It would seem obvious that the AGC chip is the problem, but I'm having a hard time swallowing the possibility of DOZENS of of these chips are all developing the same problem at the same time, but that's exactly what it appears to be. We're using the QRN4306B input cards, and the AGC chip in question is the apparently discontinued 5183977M60 chip.

So... my questions are, has anyone else seen this with the digitac voters, if so, what did you do to resolve it? The input card is discontinued, and replaced with the QRN4306D. Does anyone know the differences and similarities between the 'B' and 'D' versions? Is there a different part number being used for the 77M60 AGC chip?

[GEMOTO]

For the last couple months I have been noticing some audio issues or abnormalities on my system. I have a multi-site SmartZone 4.1 system. There are 2 simulcast zones with about 4-5 sub-sites each. Each simulcast zone is mixed-mode with 6 channels analog only and 6 channels mixed mode. There are ASTRO TAC comparators for the digital audio and DigiTAC comparators for the analog audio. The base stations are Quantar's.

The thing I have noticed only occurs on analog calls as far as I can tell, I have never noticed it on an ASTRO call. It occurs on analog only and mixed-mode channels.

What happens is towards the end of a transmission it sounds like the audio gain is increased somehow. Then subscribers audio isn't increased so much that it is obnoxious but more like the background noise/line lever is increased. The small voting clicks on the subscribers de-key are also increased in level.

It is almost like the remote site level is somewhat reduced and maybe the DigiTAC is increasing the line level gain to compensate for the loss.

The sites are using a mix of microwave and T-1's to connect to the comparator. The comparator is then connected to the Zone controller at a different location.

This does not affect console transmissions, just the RF subscribers.

I will try to get an audio recording of this.

[xmo]

"...It would seem obvious that the AGC chip is the problem, but I'm having a hard time swallowing the possibility of DOZENS of of these chips are all developing the same problem at the same time..."

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Have you looked at this issue? :

MODELS AFFECTED:

Q2980A---Q2989A Digitac Comparator

MODULE AFFECTED:

QRN-4306B Input Board


The AGC IC failure is caused by high supply voltage. On some boards, the output of the 9.6V voltage regulator circuit is as high as 10.5 volts. This voltage however, is at the threshold of the maximum allowable supply voltage of the AGC IC and in some cases may have stressed the IC's which will cause degradation in the boards performance over time.

SOLUTION:

If a clear and/or coded failure occurs, first check the DC voltage output of the 9.6 volt regulator at U924-3 and make sure it doesn't exceed 10.4 volts. If it exceeds 10.4 volts, perform the following modification.

....Change chip resistor R966 from 470 ohms to 620 ohms. 620 ohm chip resistor P/N 06-11077A69 ....Change all AGC IC's U100, U200, U300, U400 on the board that displayed a failure. AGC IC P/N 51-83977M60

[GEMOTO]

Is that an FSB/SRN etc? If you do you have it in complete for or the number of it?

EDIT: Nevermind... I found it.

Code: Select all

BULLETIN MOTOROLA PRODUCT SERVICES 

LAND MOBILE PRODUCT SECTOR PSB # 767 1301 E. ALGONQUIN RD. APC # 424 SCHAUMBURG, IL. 60196 Date: MAY, 1996 (847) 576-0180 EXPIRES: 5/31/97 

Subject: Digitac Comparator AGC IC failure due to high voltage regulator output 

MODELS AFFECTED: 

Q2980A---Q2989A Digitac Comparator 

MODULE AFFECTED: 

QRN-4306B Input Board 

PROBLEM DESCRIPTION: 

It has been determined that the AGC IC's on the Digitac Input Board have been linked to clear and/or coded mode fault failures at one or more channels. These failures commonly occur after the comparator has been powered up continually over an extended period of time, usually greater than one week. SYMPTOM: When this problem occurs, the Test LED on the QRN4304B Receive Kernal Board flashes indicating a non-fatal error has occurred. If this failure occurs on any channel while status tone is present, its corresponding Fail LED on the QRN4304B will also flash and the channel will no longer be active. 

DIAGNOSTIC PRINT OUT: 

The following message will be printed on the terminal at the diagnostic port. 

Performing self-tests .......................................................... Module ID:0000 One Input Board present 

***Clear Mode Channel Faults*** This channel fault will not be displayed on the terminal until Channel 2 has a clear mode fault. the Digitac is reset. 

***Coded Mode Channel Faults*** This channel fault will not be displayed on the terminal until Channel 2 has a coded mode fault. the Digitac is reset. 

Page 2. 

Self-test complete Channels 12345678 Levels 01000000 Stat Tone 00000000 Data Path 01000000 Code Det 01000000 ML=0 G=0 R=0 C=1 TID=0000 TIME=0000 0321 ERR=0 

The AGC IC failure is caused by high supply voltage. On some boards, the output of the 9.6V voltage regulator circuit is as high as 10.5 volts. This voltage however, is at the threshold of the maximum allowable supply voltage of the AGC IC and in some cases may have stressed the IC's which will cause degradation in the boards performance over time. 

SOLUTION: 

If a clear and/or coded failure occurs, first check the DC voltage output of the 9.6 volt regulator at U924-3 and make sure it doesn't exceed 10.4 volts. If it exceeds 10.4 volts, perform the following modification. 

....Change chip resistor R966 from 470 ohms to 620 ohms. 620 ohm chip resistor P/N 06-11077A69 ....Change all AGC IC's U100, U200, U300, U400 on the board that displayed a failure. AGC IC P/N 51-83977M60 

NOTE: This problem has been corrected in all units shipping after 3/15/96. 

Authorized Motorola Service Shops will be allowed 1 hour labor time, plus travel, to do the modification in the event the above discribed problem occured. Shops should use the standard RO 21-19 claim form when submiting claims. 

[wa6jbd]

Thanks, XMO. That's just the sort of information I'm looking for. I haven't had access to any service bulletins, so was unaware of that one. It gives me a place to start. Unfortunately, the 51-83977M60 ACG IC itself is showing as "Canceled" and not available. So far, I've not been able to cross reference it to another number. But at least I have a viable explanation as to why so many chips would be failing. Any other relevant information that can be thrown this way is appreciated.

GEMOTO, it sounds as if your symptoms are opposite to what I'm seeing. Same overall cause??

[The Pager Geek]

5183977M60 shows $42.75 for a 2-pack, currently unavail with a 20day lead time.

Try the search without the -

tpg

[wa6jbd]

Funny thing... The search showed the part as "Canceled" when searching with or without the '-' until yesterday. Now I'm seeing the same thing tpg is. Motorola Online has built a web page that I'm learning to love to hate.

[d119]

Funny thing... The search showed the part as "Canceled" when searching with or without the '-' until yesterday. Now I'm seeing the same thing tpg is. Motorola Online has built a web page that I'm learning to love to hate.

Join the club, Mel. And as has always been the case, the Parts ID guys still have access to things that even top-level MOL subscribers can't see, so you've still got to call them.

[Dan562]

Hello Guys,

There is no difference between the QRN4306"B," "C" or "D" Input Modules EXCEPT Motorola used the "C" version as the First "Outsourced Module," the "D" version as the Second "Outsourced Module" have the Replacement U100 through U400 Specially Designed ICs with Carrier Boards that replaced the 5183977M60 Obsoleted Status "05" version ICs. Now I'll bet you people wonder why Motorola would let these AGC/DVC go Obsolete.

First because the mysterious "someone" in their Materials Department got a Brillaint Cost Savings Idea to remove 40 or 50 thousand of these 77M60 ICs from the warehouse stock and sell them to an unnamed outside third party vendor. Then when the factory discovered they were running short on their parts quantities in December, 2003, and the problem would STOP production in February, 2004, you guessed it, the problem turned into a "three ring circus" trying to locate that third party vendor that the 40 or 50 thousand pieces were sold too! In fact the personnel in their own Materials department couldn't remember who handled the transaction.

Secondly these Digital Volume Controls were a special design providing much more Gain than a regular DVC IC and they were manufactured by MOTOROLA's Semiconductors Segment and they destroyed the manufacturing mold under Corporate orders. Nobody is checking with Engineering or anyone else regarding needed components. Of course MOTOROLA's Semiconductors Segment was already on the Chopping Block so who could be blamed for this error?

Third, the Materials & Scheduling Departments dumped their problem right back into Engineering's lap and the "the three ring circus" continued till Engineering had developed a replacement part. And some people wonder why Motorola is so screwed up! Motorola's management philosophy is, "It's easier to re-engineer components and products than to keep the required hardware and documentation till the Product Group's personnel all agree upon Destroying and Officially Obsoleting Products, Kits, Assemblies and Components!"

Oh BTW, those 77M60 ICs Do Fail and at least they're on IC sockets!

Dan

[The Pager Geek]

...Replacement U100 through U400 Specially Designed ICs with Carrier Boards[/b] that replaced the 5183977M60 Obsoleted Status "05" version ICs.

Do you have the part number for the replacement component(s)?

tpg

[Dan562]

No, not any more. Y-O-U will be required to contact Motorola Parts Department for the replacement Component Part Number. The Parts Department personnel have access to the computer system's Module(s) break down of each Kit and IF they claim they do not, then Open A Trouble Ticket with that department. Make sure you provide the QRN4306D, the Designator U100 ~ U400, the Old Part # 5183977M60 and that you need the new replacement Part number. I would expect to Pay more money for the replacement part because it has a small Microprocessor on the Carrier Board.

Oh the other reason the Input Module became a "D" version is the Outsource Vendor could not make a big enough $$$$$$ Profit while manufacturing the Digitac comparators and modules (in the U.S.A.) so they shipped their manufacturing to Mexico or China. You people are paying for MOTOROLA's Profit Margin in a bigger fashion.

Dan

[wa6jbd]

Thanks for the additional info, Dan. There's a possibility that those 50K units disposed of may be available elsewhere. They show up on google searches at various surplus semiconductor dealers. Now, if I can get the slow wheels of local government to think outside the box, we may be able to snag some.

[wa6jbd]

Update on this, for anyone interested...

It took awhile, but I have received information from Motorola giving the part number, price, and even photos of the replacement part. Thanks to Dan562, your information proved to be quite useful in steering me in the right direction. If anyone is interested, PM me for the PDF file with the part's data.

There is also supposed to be a work around to bypass the AGC chip. I've tried this, and it works fine for a few minutes until it runs diags on itself, then fails. The trick is to fool it into thinking it passes diags. Back to the bench...!

[awyeah]

Did you ever find a way to successfully bypass the AGC chip?

[RFI-EMI-GUY]

I know this is an old thread, but I have a question. I have an 8 channel DIGITAC sitting loose on my bench, no receivers connected, thus it passes the self test fine but does show the normal fail lights. Is this enough to presume the AGC chips each passed in self test or do I need to have a status tone on each input to test? I will be checking the regulator voltages as a precaution.