Marshall VS100

[Valvehead]

Well...i forgot to check something...maybe this info well help . After pulling pcb's , fixing solder joints , and chasing the resistor problem ....i forgot to check if the amp passes audio.

It does ! it switches channels fine. One thing is , on Ch 2 od1/od2 , the controls dont work .
On the clean channel they do work . Another oddity = when touching the guitar cable end, the clean channel LED will flicker / dim with each touch .

so does that rule out certain IC's ??

[Valvehead]

I think i found it...after only the 2nd chip i checked. I unsoldered 4/8 of IC2 , and the 2 resistors do not get hot anymore !

But , i cant find any cross # for this thing , only data sheets . Can ya'll help me find a suitable chip ??

Mitsubishi 5201A , 8 pins

i do have some chips here , Tlo81 , Tlo82 , if those dont work maybe a UPC1458C ?

https://datasheet4u.com/datasheet-pd....php?id=553422

[TomCarlos]

Updated: https://www.amplifiedparts.com/produ...itch-8-pin-dip

You got it.... the pins match up.

How about this - https://www.amplifiedparts.com/produ...itch-8-pin-dip

[Enzo]

The types you are suggesting are plain old dual op amps. Now look at the schematic and compare the op amps (which are TL072 here) to the 5201. The images are different, and data sheet will also be different. The 5201 does have op amps inside, but it also includes controllable switching, and that is how it is used here. It is a signal switch or selector

A google search brings up sources. For example:
https://www.tubesandmore.com/product...itch-8-pin-dip
https://www.amplifiedparts.com/produ...itch-8-pin-dip

I'd avoid ebay parts myself.

[The Dude]

The 5201A pinout is different than a "standard" op amp and it has switching. None of the op amps you listed will work as a sub. The 5201A is discontinued as far as I know. The JRC2120 is a sub, but I believe is also discontinued. I bring it up only to widen your search parameters.

Edit: Enzo snuck in while I was typing. Well, he found sources so there you go!

[Enzo]

Tom, your link won't open for me, though it appears to be the same link as my second one

[TomCarlos]

Yes Enzo... same link to Amplified Parts. Thanks.

How about this - https://www.amplifiedparts.com/produ...itch-8-pin-dip

[Valvehead]

awesome-----Thanks guys !!...ill get one ordered and post back.

[Valvehead]

ok , 5201A ic is changed , new r20/r21.

New resistors are not over heating anymore

amp is acting the same though ...stuck on Clean / OD 1 channel , loud low freq hum.

the bi-color LED is changing and working , (green to red) going from clean to od1 , but the OD channel (ch 2) is not working--amp is not switching channels. Oddly , the clean LED always stays lit , even when going to the OD channel (ch 2) . The OD red Led (ch 2 ) is going on/ off when changing channels .

[Enzo]

So the 12v supplies have returned to 12v each? It is quite possible you have another IC bad, even if it isn't a hard short like the one you just replaced. Remember you replaced some voltage regulators. It is possible the initial regulator failure put excess voltage on the ICs and may have damaged some.. SO pick ONE of the things that are still wrong, and track it down. If you try for all of them at once it just gets confused. Also solving one may solve another in the process.

For example, your LED changes, but the function it represents des not. That suggests another 5201 - which does the actual switching - may be shot.

SO for example, clean LED stays lit no matter what? Solve that. What turns on that LED, what controls that thing,etc.

[Valvehead]

Clean Led controlled by Tr1 / Tr3 ?

right after R20 / R21 now im getting +26v / -30v

at Zd1 im seeing +6v .......... and Zd4 has +4v

Reg 1 is +26v / 0v / +12v
Reg 2 is 0v / -30v / -12v

[Valvehead]

Replaced IC5 without damaging the flimsy traces.........amp works perfect now .