"Floating" IC in GK 800RB?

[Rhodesplyr]

I opened up a GK 800RB I've been asked to take a look at and found that one of the ICs, U5, is mounted on a ~3" square of circuit board, suspended above the main input/control PCB on wires, along with a couple of resistors.

Is this a known field-mod of some sort, or is it likely that someone simply didn't have the right IC to do a repair? The other ICs on the board are LF353N. The replacement isn't.

[MarkusBass]

Most probably this is a replacement for TL604 - analog key IC that is not longer manufactured. Several companies provide a replacement module like the one you have. What is the symbol on this IC?

EDIT: you may read this: http://www.firebottle.com/fireforum/...873-000000.msg
and this: http://music-electronics-forum.com/t2196/

Mark

[Rhodesplyr]

Markus,

Just a follow-up to let you know that you were right. It is a board to adapt the DG419DJ for use in an 800RB that originally used the TL604.

The disturbing thing is that I also sent a message to G-K, and their "tech" wrote back that he had no idea what it was. Their parts department also sent me schematics and parts lists that didn't match even though I gave them all the PCB numbers they requested.

So, G-K 0 for 2, Music Electronics Forum: perfect score.

[Jazz P Bass]

That may in fact be a Peavey or similar replacement.
So it appears that GK does not have a work around for the TL604.

[MarkusBass]

Markus,
Just a follow-up to let you know that you were right. It is a board to adapt the DG419DJ for use in an 800RB that originally used the TL604.
The disturbing thing is that I also sent a message to G-K, and their "tech" wrote back that he had no idea what it was. Their parts department also sent me schematics and parts lists that didn't match even though I gave them all the PCB numbers they requested.
So, G-K 0 for 2, Music Electronics Forum: perfect score.

The problem with TL604 is a well known fact. How can they do not know it? What do they do it it fails and customer sends them an amp for fixing - start crying? . Where is this serwis - maybe I could get a job there?

Mark

[Gtr_tech]

Its just an analog switch.....there are several ways you can do a "workaround" from ICs to discrete jfet circuitry. Even reed relays would work providing you have enough current available to fire the coils....

[Ronsonic]

Markus,

Just a follow-up to let you know that you were right. It is a board to adapt the DG419DJ for use in an 800RB that originally used the TL604.

The disturbing thing is that I also sent a message to G-K, and their "tech" wrote back that he had no idea what it was. Their parts department also sent me schematics and parts lists that didn't match even though I gave them all the PCB numbers they requested.

So, G-K 0 for 2, Music Electronics Forum: perfect score.

I don't know if I'd be all that hard on the guy from GK, this does go back a bit.

Anyway, if you're interested in a TL604 PM me, there is a very limited stash available in my junk drawer / treasure chest.

[Rhodesplyr]

I don't know if I'd be all that hard on the guy from GK, this does go back a bit.

Anyway, if you're interested in a TL604 PM me, there is a very limited stash available in my junk drawer / treasure chest.

Well, at their request, I sent G-K the serial number of the amp and all the individual printed circuit board ID numbers so that they could send me the right schematic; then, they sent me the wrong one. The schematic they sent me showed the DG419 switch, not the TL604, so I couldn't figure out why someone had mounted it in such a strange way. In fact, here's what I said in my e-mail to the G-K tech, who was not the same person who sent me the schematic:

I was wondering if this was some sort of field mod necessitated by something like the original IC becoming unavailable or simply someone not having the right IC on hand.

Thus, even though I guessed the answer, their guy wrote back that he knew of no reason why someone would do that. I really just wanted to know was why this little scrap of circuit board was mounted in there. It's not the problem; it has a DG419 in it, and it works. I very much appreciate the generous offer of a TL604, but I think that the adapter board is probably sufficient. Plus, if that TL604 ever failed, I or the next tech would be up the same creek...

The actual problem with the amp was the pedestrian matter of a cracked solder joint on an input jack.

[J M Fahey]

Hi guys.
I see that today is "Lash_GK_Day".
Oh well. Maybe it's fun, if you have nothing better to do.
Fact is, our friend Mark Black posted in this very Forum, the GK supplied solution to this problem.
The post:
http://music-electronics-forum.com/t2196/
The solution: http://music-electronics-forum.com/a...-reference.doc
They don't seem to offer a dedicated board per se, as Peavey did though.
Although for all I know, they might have done so afterwards.
After all the post is from March 2007 !!
And it's not an obscure one either, the GK solution shows 187 hits.
Just because an employee sent a corrected schematic instead of the already obsolete (in 2007) one, does not qualify them as a second rate company.
My own experience with them was asking for the switching power supply for an MB150 I was repairing and getting my inbox swamped by 3 huge schematic packs covering *all* non-current-production amps, including the famous "Santana/Woodstock" one (and a couple even earlier ones).
Yes, probably some variation of a sub-variation was not present, but an immediately earlier or later one was close enough, with some interpolation.
Much better response than other companies which either answered "obsolete/early/discontinued model=not available" or "we don't send schematics to non authorized people" or even "what? .... "

Just as a reality check, this is what GK answers to TL604 problems:
>>>>>>>>>>>>>>
Service Memo
Model 400RB
Subject Power/ Preamp Boards
Date 5/7/1999
Memo # 400-02
Description of Service Issue
The 400RB has had several revisions throughout its 20 year history, resulting in several revisions of the power amp and preamp boards.
These revisions were primarily initiated to accommodate new parts that replaced out dated or discontinued parts. This memo describes conditions under which a down rev preamp or power amp has to be replaced
with a current version. This normally results from a badly burned power amp that can not be repaired, or a pot or TL604 failure in the preamp that can not be replaced. Old rev potentiometers and the TL604 are no longer available and amplifiers having problems with these parts should have the preamp replaced.
New pots can be used in place of the early units but they have to be hand wired in as described in memo SM400-01.
The TL604 is not replaceable but can be wired out as described in SM400-03.
Preamps with these problems are greater than 10 years old and it is our recommendation to replace the entire preamp board which will avoid other problems that are sure to arise due to the age of the parts. When replacing the preamp or power amp board the following guidelines should be followed. (continues)
<<<<<<<<<<
Now I see the GK employee offered the "official/company suggested" solution.