The Mark IV thread....!!

[Russ]

What is the date on your PCB? I can't see it. Is that a wide chassis too? It appears you have more room between your PCB's than I do in mine. Mine seems a little more cramped inside. There is no space behind my GEQ showing where the orange wire goes.

Here's mine:

I think one of my IC's may have been changed. Check it out Shep. The red one says made in Korea I think. It doesn't seem to keep it from being a sweet amp though.

Something I wanted to ask you guys is whether or not the corner where the date on the PCB is missing on your amps too. Mine seems to have the corner carved off. It also appears as if my pentode/triode switch got hot at some time too or maybe someone got to poking around it with a hot soldering iron. It also appears as if my second grid resistor from the right got a little hot. The far right one looks slightly cooked and discolored too.

 

[Shep]

Dam!..

 

[Shep]

I think you will find that both have been changed..not 100% but I had mine out the other day and i know wish i took a picture.. i am sure that the IC on mine are hard solderd not socket like yours.. I might be wrong i will have to pull her out again.. also i know as a fact that my amp is alot more tidy than yours..so someone may have had a poke around once apon-a-time..you will see what i mean when you see picture's..

I will pull mine out and take a pic or two tomorrow..

 

[GLydian]

As I promised before here are some images of my Mark IV series A internals.

Before you guys get confused, My Mark IV is a wide/medium body 23'' wide and it is just the head.
There was a date some where and it said 92 as I remember. I think the ICs may be for the switching system, may be I am wrong :?
I don't see any significant discoloration on any components, but only few solder points have some brownish rusty color as you can see in the pictures, but I thought may be it was some kind of soldering compound they used. I just replaced one pot and checked for any swollen caps.
All in all it looks pretty clean and amp did not have any so called "Mod Works done" on it :lol:

 

[Shep]

There is mine, the IC are socketed.. but they are different to the ones in your's..

 

[jvk]

Nice MarkIV porn

About the IC sockets...

IC sockets are really cheap, £0.05 in the UK for a 14pin, whereas the TTL chips are £0.50 or whatever. When they replace an IC they'll desolder the IC, which can be done without removing the board as the holes are through plated, and they put in sockets so that in next time it happens it'll be an easy swap without soldering.

Mesa doesn't fit IC sockets at the time of manufacture, anytime you see socketed ICs you know they went dud and had to be replaced.

 

[Shep]

Nice MarkIV porn

About the IC sockets...

IC sockets are really cheap, £0.05 in the UK for a 14pin, whereas the TTL chips are £0.50 or whatever. When they replace an IC they'll desolder the IC, which can be done without removing the board as the holes are through plated, and they put in sockets so that in next time it happens it'll be an easy swap without soldering.

Mesa doesn't fit IC sockets at the time of manufacture, anytime you see socketed ICs you know they went dud and had to be replaced.

so you are saying that my mk IV had the sockets put in after it was made by mesa..or just Russ's..?

 

[Russ]

I think he is saying that our IC's went bad. Then in the repair they were socketed because Mesa doesn't socket IC's. This could be the reason for the differences between our IC's and sockets.

 

[jvk]

Yeah, I'd say that it's likely that any amp with IC / transistor sockets must've had issues with those components at some point and has had to be serviced.

You can tell straight away that both your amps are MarkIV-A by looking from the regulator ICs in front of the 30uf blue cathode caps - the IVA as 2 regulators on the mainboard, one for the 5v part of the switching buss and another for the 15v footpedal supply, whereas the IVB has a single regulator for the 5v supply. With the MarkIV-B, for reasons I don't know, Mesa added a 12V tap to the PT and moved switching subsystem powersupply from the heater taps onto this new 12v tap, and so eliminating the need for the 12v regulator.

Russ, there's a small mod on your board; a 100ohm piggy-back resistor has been added to the 470ohm resistor on the top right of the board, just by the date, in front of the '9'. 100+470 in parallel = 82ohm, close enough, on the schematic there's a 100ohm here. This resistor goes to the EQ external trigger jack. I've got some pics of later IVAs that have a 100ohm resistor here, so yours is perhaps an earlier revision. Maybe it's an official Mesa mod?

 

[Russ]

WHOA!!!! I never saw that jvk. I would have never even known. Thanks for pointing that out. Now I have to buy another A to compare... :roll: Maybe this is why I really love this amp? I doubt it though if it is only going to a switching jack. It was this way when I got it. I haven't touched it internally yet.

Mine is a pretty early A. From the inspection date on the board you can see it was 9-7-90. My serial is in the 560's. I am also wondering who KB would be. I know who MB is and who RS/RCS is. I am glad to see another board with the corner cut off too (Both Shep's and GLydian's).

 

[timv]

All the pictures I have found of mark IV's show sockets for those IC's. They probably had sockets inserted there at the place that makes the pcb's for them. It makes it much easier for replacement later. Can you imagine what those boards would look like if the average guitar amp tech got in there trying to remove those IC's without pad damage and leaving the area looking that clean? There is certain ways to remove that type of part with minimal damage and it works best if you have a special soldering iron tip.[/img]

 

[jvk]

I've got pics of mkIV As and Bs without sockets. It's possible that the newer board revisions are socketed.

 

[Shep]

mine is a 91'.. and it looks pretty darn clean to me.. i am thinking that i am one of the only owners to have a looking in side her..I bought it from the US to..that was before i was on this board...hey, how funny would it be if i bought it off someone on this board..?


So i was right , someone had had a poke around your amp Russ..

 

[timv]

The one I have now and my old one both had sockets and they were both from 91'. I haven't found any pictures without sockets, please post if you could.

 

[jvk]

The one I have now and my old one both had sockets and they were both from 91'. I haven't found any pictures without sockets, please post if you could.

Here ya go, MarkIV B without sockets

 

[Russ]

I think he meant an A. GLydian posted a wide B above.

 

[jvk]

Oh, ok. Having seen so many different variations, I just don't think Boogie installed IC sockets on MarkIVs as a rule, that's all. It's not impossible.

 

[jvk]

I made this to help me analyse the differences between the A and the B, thought I'd share it with you guys:

 

[mxr2000]

Interesting mine is a "A" version

 

[GLydian]

I think he meant an A. GLydian posted a wide B above.

No my one is wide(medium) A head.
GLydian