Hi again,
Had some free time this morning, so I got the PCB (with the pots and inputs on it) out of the case and ohmed out the 0dB, -15dB, Effects Send, and Return jacks ... and they were all high resistance due to corrosion on the contacts.
Got 'em cleaned up with a small file and contact cleaner, checked the tension on 'em with the patch cable (making sure they opened and closed - several times), and rechecked the resistance: 0.40 ohms on 'em all.
Put it all back together...

It works. Still a little crackle from the Squier due to patch cord contact at the output of that bass, but the Dean sound comes through nice and clear.

Guessing the years of use before I got my hands on it was the culprit.

Thank you guys so much for your help. I really didn't know where to start, but now she's up n running and I'm happy.

Thanks!

Well, plugging into the FX loop had the same effect: crackling and popping until it just stopped. Nothing from the speaker after that. Except for a quiet hum - but you've gotta put your ear about 2-3 inches from the grille.

I've got the case open, amp sitting on a plastic crate. A closer look showed that there are globs of solder at 3 different resistors and 2 pair of the resistors are in parallel ...pretty sure they aren't supposed to be that way because of the equivalent resistance and the solder is on the wrong side of the PCB [see pics, if they attach]. Also, are the transistors supposed to have screws through them? [Phillips heads, last pic.] I installed the one with the larger washer on it because it was either missing, or shouldn't be there.

If I understand correctly, the corrosion failure in the FX loop switches MAY be contributing to this issue. If so, cleaning the corrosion off should allow a signal to pass through them. Yes?

I'm assuming that they were right on the verge of not passing a signal and by inserting the cable, the contact area may now be fouled completely.

—> I'll get that board out and try to clean them as best I can. Granted I'm assuming a few things, and we all know what happens when assumptions are made, but it's one place to start.

More details as it evolves.

Thanks!

Wow! Thanks for the quick replies!

Phil, I'll try your suggestion when I get a chance in the next few days.

Enzo, you're right, a new thread would have been a better idea (given how old this one is). But I've found so little info on this amp, I was trying to write to people well versed in it and get their attention.

I'm any case, I'll post results once I get it tested and we'll go from there.

Thanks,
Dave

Hi guys,

Hope you're still out there in the ether, and have a chance to reply to this novice's posting...

I'll try to get you guys up to speed with the basics, the quick and dirty issue I've got, and maybe we can get to the root of the problem if/when I hear back [fingers crossed].

Simple set-up:
SVT-200T
15" Bag End speaker
Custom cabinet I fabbed so the amp / cab combo would look nice collecting dust.
Squier P-Bass
Dean Edge 4
Patch cord from bass to amp
Patch cord from amp to cab
That's it (I'm an enthusiast, barely an amateur)
[Of note: I'm a veteran diagnostic tech from the car industry, but it's been more than a decade since I had to test electronics -from a schematic- at the component level. And I'm well aware of the "you could get fried working on this amp" warning.
So please be patient.]

Anyway...

The SVT-200T I've had for almost 3 years has been finicky. Worked ok-ish when I first plugged it in (see list below), took it apart to clean the attachment hardware and re-Tolex the case, and tried to renew this beast to annoy the neighbors with my loud, terrible playing.

Jan 2016:
New cab operational and I'm proud of what I've built.
Put 'em both in the living room, plugged it all together, tried it out.
The 0dB input crackled.
The 15dB input was clean.
(Or vice-versa; I can't remember ...sorry.)
Also can't remember if there was any crackling / popping when adjusting the knobs.

Fast-forward to Summer 2018
Tolex the cab.
Build a grille cover.
Paint the corner hardware.
Assemble the cab.
Set in living room and admire my hard work.
Try out the set-up.
Can't remember if it worked, but probably not too well.
Take PCB for front panel / pots out and inspect solder joints.
Input jacks (both), found solder joints are cracked.
Re-solder joints.
Notice transistors (3-pin) have either:
a) missing screws to fasten them to the PCB or
b) aren't supposed to have screws to fasten them to the PCB.
I think that's on the "heat-sink" end (?) - it's the metal tab with the hole, opposite the BCE prongs.
Project side-tracked due to noise from truck rear axle; commence rear axle rebuild.


Oct 31, 2018
Plug in the amp (for sh*#s and giggles).
Hook up the Dean.
Nothing - no sound.
Dead battery in the Dean?
Hook up the Squier - doesn't need a battery.
Nothing - no sound.

Then...
Crackles and a flickering Gain light.
Limit light (under stage volume knob) flickering.
Unsure if the two flicker at the same time, or which is flickering while the crackles come through the speaker.
Narrow down a starting point:
Gain knob causes crackling as adjusted from lowest setting to 1/4-turn up from lowest: too obnoxious to handle.
Turned everything off and tried a different wall outlet: slightly better, but essentially the same result.

Try to find schematic and pics of the internals, maybe some troubleshooting help, had very little luck (except DoktorSewage.com and this thread - with, I suspect, DoktorSewage on it).

From the pics on DoktorSewage's page, I can tell there are a few differences between my amp's guts and his, e.g. the power cable comes in from underneath on mine; his, in the back. Mine has a blue trim stripe at the bottom, where the 'input,' 'gain,' 'effects loop,' etc... labels are. I've tried to narrow down the year it was made, but the best info I've got is from the (?) serial number (?) on the back [20H-1073], and the assumption that part of the pot part numbers includes the year they were made ["8720," "8719," maybe 20th week of 1987......]. But I'm really not sure about a lot of this amp, except I know it was great once, played well for me for a while, and may be able to be brought back to life.

Thanks for reading through this - it was more than I expected to write. I hope we can get crackin' and stop that cracklin'. I'll post more info, and some pics if/when I hear back.

Thanks,
Dave