hartke LH1000 Left channel slow to come on at switch on right ok

[Arbutt]

Hello
I month or two ago i repaired an LH1000
Replaced parts in the left channel
all power transistors
R332
2 x 0.22R
tested all working gave the amp a hard test. All good
samson_lh_1000_bass_amp_sch.pdf

he brought it back this week saying not working.
turned out that left channel takes 8-9 sec to come on where the right channel takes 2 sec
he owner states he uses it on Bridged
On checking i found Q312 had blown its top. Confident i have found the fault. i replaced it. still the same
the tA7317 chip is a pcb type made by harkte with smd devices on it.
Before i change this i was hoping for any thoughts
I have replaced like for like.

many thanks A

[Enzo]

SInce you rebuilt a channel, have you since adjusted its bias and offset controls?

[nevetslab]

Actually, the TA7317 is a Toshiba part made for over-current protection, normally used to control an output relay in a power amp. I've attached the data sheet on that.

TA7317P Protection ckt.pdf

I assume there's one of these IC's on each channel. If so, it also looks like there's a time delay to control when the relay closes at turn-on. Since the two amps are not turning on at the same time, something is off on the one taking 8-9 seconds. There's information on the data sheet pertaining to that.

Both the 2SA1266 & the 2SC3198 are 50V/150mA parts. It may have been too much current was demanded of the 2SA1266 when enough current was sensed passing thru Q314, not being able to cut it off. Normally, the voltage rating of the current limiter transistors don't need to be as high as the outputs, since they're swinging on the output buss with the rest of the power & driver xstrs. Hartke/Samson's engineering staff are the ones who made the decision on using a 150mA max part for the current limiter xstrs. I wonder if changing to a higher current part there would be in order?

[Enzo]

I have repaired a zillion Hartke/Samson amps, and I don;t recall replacing many of those limiters.

Other than checking the adjustments I cited to see if the thing is idling too hot or had too much DC offset just from adjustment, I think the thing to do is scope the output buss to see if it is riding at some DC offset, or going at RF or some other clue. We need to see if the 7317 is just doing its job, or it is problematical.

The schematic just shows a box with TA7317 by it. Is it possible they have in a later revision gone back and made a small circuit board with the IC and some components to solder the whole thing in as a part? Like what PV did to replace the unavailable TL604?


In my experience, when the 7317 is actually where the problem lies, I almost always find the small electrolytics are the problem. Dried out or whatever. C315,16,17,18. Especially the two low value ones. I think I may have found one or two bad 7317 ICs in the last 30 years. One of the caps doesn't charge up well enough to keep the thing off, and the other won;t charge to keep the thing from triggering on every peak. Like that.


But really, adjust it first.

[The Dude]

There's also the possibility of operator error. You might have the customer bring in the entire rig so you can test speakers, cables, etc. Also make sure he's hooking it up correctly. There are few musicians who actually understand bridge mode.

[Jazz P Bass]

It would help if we knew where the problem is occurring.

"turned out that left channel takes 8-9 sec to come on where the right channel takes 2 sec"

Come on what?
The power supply, the relay, the signal?

[nevetslab]

The time-delay relays close to connect the amp channels to the speaker jacks.

[Arbutt]

Hi. What's the best way to set the bias on this. I have changed the caps . Still the same

Many thanks on this
Arbutt

[Enzo]

Monitor current draw from the mains. Turn the bias control so the mains current is least. Once it stops dropping stop turning. Now advance the control until the mains current JUST starts to go up. Back off a hair. That should be close. We can get into milliamps another time. If either bias control reduces mains current, it was set too high, in my view.

[Arbutt]

Hi all. Tried to adjust the bias this morning. The was Enzo said still the same. Going to the ta chip today . To be sure. Any other ideas
Arbutt

[Jazz P Bass]

Troubleshoot the problem.

Exactly what do you mean by ' left channel takes 8-9 sec to come on ' ?

[Arbutt]

when i switch on the right channel protection relay switches on in 2 secs and can be used the left channel takes 8-9 seconds before the relay switches on so it can be used.
as the left channel has been repaired there is clearly something wrong, owner stated that it never did that before it went faulty

A

[nevetslab]

Troubleshoot the problem.

Exactly what do you mean by ' left channel takes 8-9 sec to come on ' ?

Monitor the output buss, where the emitter resistors of the output stage collect (R324 thru R331), to see if there is any significant DC level present during power-up. It should look much the same as the right channel. If it is coming up without any problem, yet the TA7317 is NOT engaging the output relay, then monitor the charging line that un-mutes the chip which is controlling the output relay. That would be Pin 8 on that IC.

If you are getting DC offset at power-up, and it takes 8-9 seconds to settle near 0VDC, then enabling the protect circuit to close the relay, then we need to address that problem. You are our eyes and hands for probing and searching while we try to direct you to the cause and cure.

[g1]

In my experience, when the 7317 is actually where the problem lies, I almost always find the small electrolytics are the problem. Dried out or whatever. C315,16,17,18. Especially the two low value ones.

Did you replace those 4 caps Enzo mentioned yet?

[Arbutt]

Hi yes I have changed the caps . All 4 of them .