Batboard

Does anyone know of a source for the TDA7256, the audio amplifier in the Spectra? I was given a VHF and a UHF mid power set, but the audio amplifier in the UHF unit is dead. Shows signs of obvious heat damage, as does the speaker wire that was associated with it. Looks as though a pinch in the wire grounded the audio output, melted the wire and took out the amplifier. (I have already replaced all electrolytics). Everything else seems to work fine.
Thanks,
John
AA4TX

Yes, I saw that before I posted. It seems as though there are / were two version of this chip. A 15 pin version and an 11 pin version. The spectra uses the 15 pin version. All I can find now is the 11 pin. I was hoping that there might be some old stock hanging around out there. It looks as though with a little pin bending, I may be able to use the 11 pin part. That would be a last resort though.

John
AA4TX

Just opened the VHF Spectra - it has a TDA7255 - also a 15 pin. Is it possible that the UHF has a TDA7255 mislabled as a TDA7256? This seems very strange. Anyone with experience with the audio section here?

John
AA4TX

The spectra uses a special TDA7256 made for Motorola, the P/N is the same as the industry standard.

Thank you for the information. Does anyone have any ideas on procuring a replacement for this device, or a work around?

John
AA4TX

According to this link on Repeater Builder you can use the TDA7255 in place of the 7256.

Astro Spectra wrote:According to this link on Repeater Builder you can use the TDA7255 in place of the 7256.

No not on the later command boards. The two chips are different and require different value components, caps, ect.

The correct IC IS available.

Could you let me know where I could buy one? None of my suppliers seem to have any idea.
John
AA4TX

"Could you let me know where I could buy one?"
-----------------------------------------------------

Other than from the Motorola parts department?

"Other than from the Motorola parts department?"

Yes, perhaps I am optimistic, but at their prices, I was hoping to find someone who might be willing to let it go for a bit less. Looking at the spec sheets for both, I know I can fit the commercial version with some pin bending and a few component value changes. Just thought I would try to find one at a resonable price before I went through this. This is, after all, a Spectra, and the only life prospects it has remaining is duty on the ham bands.

Somebody on this board had a stock of them, awhile back. You might run a want ad in the ad section. I know what you mean, these radios are worth less than the chip from MOL. I would think there will be a bunch of very cheap parts grade Spectras showing up throughout the next few years, and you could just change the whole board. That's what I am waiting to do.

Not a bad idea. I am in no rush, but the board stares at me every time I go to do some other work on the bench. It would be a trivial job if I could get the parts!