Spectra Audio amp part number

[K3YT]

Greetings, just got a VHF A7 45 watt Spectra. Fellow I got it from said he had the caps changed when it was programmed a few years ago. I programmed it myself no problem...BUT I guess I grounded one of the audio pins since the RX aud is now low and distorted. I'm pretty sure I know how I managed it . Looked at the aud in and out with the scope and yes it is the amp IC. I searched the message board first to see if this was covered and found some good info, but...The audio amp is not a TDA7256, but a TDA 7255. Other components have 89 date codes on them. I looked for the TDA 7255 and didn't have any luck. (very obsolete) It is a 15 pin amp and the 7256 is 11 pins. Can anybody help me with a part number for the amp or give me some info on how to retrofit the 11 pin part?
BTW many years ago I worked at Mot Portable Products in Plantation, but the last time I worked in a Radio shop was 1995.

Thanks Bob K3YT

[kc7gr]

Greetings, just got a VHF A7 45 watt Spectra. Fellow I got it from said he had the caps changed when it was programmed a few years ago. I programmed it myself no problem...BUT I guess I grounded one of the audio pins since the RX aud is now low and distorted. I'm pretty sure I know how I managed it . Looked at the aud in and out with the scope and yes it is the amp IC. I searched the message board first to see if this was covered and found some good info, but...The audio amp is not a TDA7256, but a TDA 7255. Other components have 89 date codes on them. I looked for the TDA 7255 and didn't have any luck. (very obsolete) It is a 15 pin amp and the 7256 is 11 pins. Can anybody help me with a part number for the amp or give me some info on how to retrofit the 11 pin part?
BTW many years ago I worked at Mot Portable Products in Plantation, but the last time I worked in a Radio shop was 1995.

Thanks Bob K3YT

Criminys... Bob, I wonder if we ever spoke, phone-wise? I spent five years in the late 80's/early 90's at the old Motorola COSS in Emeryville, CA. I remember calling Plantation several times for advice and info, notably on the MT500 and HT600 lines.

On the audio chip. Your best bet may be a donor radio. Alternatively, you could seek out a replacement command board. It would probably be a good idea to bring the thing up to date in that manner anyway, since the older part hasn't been used for many moons.

The current chip is P/N 51-80065C19.

Happy hunting.

[K3YT]

Thank you for the information Bruce. I may have found an replacement IC, believe it or not.

So from what I gather this is one of the first REVs of the control board. This is the first Spectra I have owned. Really pleased with it. Will any control board work? I would imagine I would have to have a Conventional one of course, and try to get one used with the A7 head. But will a UHF conventional A7 control board work on a VHF A7 radio? I suppose I should invest in a service manual.

I went to work for Motorola in 1978 and was there until the mid 80's. I was WD8PLA when I came down from Ohio.

Thanks, Bob K3YT

[Will]

Motorola changed the audio amp chip, twice, to the later part that IS available.

BUT the circuit has changed several times during production. So just changing the 'chip' may (usally does) not work.

So looking for a later Command board would be good, just use your orig. MLM.

[kc7gr]

Thank you for the information Bruce. I may have found an replacement IC, believe it or not.

So from what I gather this is one of the first REVs of the control board. This is the first Spectra I have owned. Really pleased with it. Will any control board work? I would imagine I would have to have a Conventional one of course, and try to get one used with the A7 head. But will a UHF conventional A7 control board work on a VHF A7 radio? I suppose I should invest in a service manual.

I went to work for Motorola in 1978 and was there until the mid 80's. I was WD8PLA when I came down from Ohio.

Thanks, Bob K3YT

Hi, Bob,

Yes indeed... Motorola went through a few revs before getting to where they were before the analog Spectras were discontinued.

Pretty much any command board for the analog Spectras should work. The command boards are not, in the electrical sense, control-head sensitive. As Will has accurately pointed out, though, use your original MLM. Also, save a copy of your current codeplug before you start tearing things apart. It could really save your tail if something goes loopy.

You may also need to use That Software Which Must Not Be Named to reinitialize a replacement command board to your radio and MLM. You can drop me a private E-mail (outside the Batboard) for more details if you wish.

On Moto: Yep, that's just about the time I was at Emeryville. I'm pretty sure we've spoken at least twice. Small world, again...

Happy tweaking.