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Old 14th June 2014, 05:09 AM   #21
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Well the LM339, I guess is some other chip. Or is the LM399
in the diagram one half of the real 28 pin chip?
The chip in the unit is "7kM2-T142".

The schematic shows U401A, U401B, U401C, U401D,
which look to be op amps with pins 1 - 14 used.
I've looked for a data sheet but they only show
standard op amps with buffers attached to them.

Different then this unit.

I put the chip back in and figured I'd measure J402 and see
if I got any voltage. No voltage to 60 Vac.

But I did start seeing sparks fly from the HV switch chips.
the MJE's. Not a good sign.

I guess it would correspond to U407
But instead of a TL431 with REF AK they are the MJE pair.


Yes, I"ve been testing on the variac with the board disconnected
on the bench.

Pic coming next.
-- Sync

Last edited by SyncTronX; 14th June 2014 at 05:13 AM.
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Old 14th June 2014, 05:31 AM   #22
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Board under test, 60 Vac in, limited to 15.Vac at input.
Click the image to open in full size.

Just the board layed out:
Click the image to open in full size.
-- Sync
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Old 14th June 2014, 05:50 AM   #23
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Default What gets hot?


The heat sink will get hotter than hell. Its there next to the
two cement resistors. Those are the two MJEs.

None of the 'Lytics get warm.

The L401, Red Wht Blu wired RF input choke starts smelling up and get slightly warm to the touch.

the U406 the MOC3083 also get s warm to the touch.

Not much else does.

It will start pulling current around 30 Vac.
If brought up quickly, then 25 Vac the bulb comes on.
If brought up slowly, then 30 - 35 Vac, brings the bulb on.

The soft current limiter is my friend.
-- Sync
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Old 14th June 2014, 07:31 PM   #24
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Richard, Demian,

Is the 28 pin chip and eprom chip?

something like this:

ATMEGA168 Datasheet pdf - 16K Byte self-programming Flash Program Memory, 1K Byte SRAM, 512 Bytes EEPROM, 8 Channel 10-bit A/D-converter(TQFP/MLF). debugWIRE On-chip Debug System. Up to 24 MIPS throughput at 24 MHz. 1.8 - 5.5 Volt Operation (ATmega16

or similar to this:

The RRRRRRRRRRBBA, a $3 Arduino : The ATMEGA chip IS a cheap microcontroller!

or this:

Arduino - PinMapping168

I hope it's not fried.
-- Sync
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Old 16th June 2014, 03:35 AM   #25
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The good news is I got her up and far.

The T2 board has no current draw as I tested it before reinstalling.

The buttons don't function now, but then I don't know if they
functioned before.

The Front panel display doesn't work. But the lower half does
does show the splash screen when voltage of about 80V is applied.

For about 1 second is displays "Monster HTPS 7000".

Not sure what is going on with it. I'm thinking it it came in for
service somewhere and then someone spilled a coke or a coffee
in it.

With nothing connected to the unit it is pulling
120 Volts about 1 amp
85 - 90 Volts about 1/2 amp

There are also open grounds on the first three of the first four outlets.
Not sure how that happens because all four share the same earth gound wire
and lug.

Not sure if the front panel display works on 12 Vdc or 5 Vdc and where the supply
chip is located.
-- Sync
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Old 17th June 2014, 05:54 PM   #26
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Default Theory of Operation, Current Draw

Demian & Richard,

I appreciate the assistance you've given me in getting this
pretty nice piece of gear operational.

Maybe you can suggest where to look once
the checks are complete and the main relays
turn on.

Should this filter be pulling .8 to .9 amps with
nothing connected to it?

I can't see the main T2 relays pulling the current.
If they did, then when the High Power relays switched on
they also would pull the current down, but do not.

So my next question is with the isolation transformers.
But why whould they be pulling current with nothing
attached to them?

A summary of the replacement parts is included here:
MJE13005F replaced with MJE13005, non isolated package TO-220.
MJE13003 replaced with MJE 13002, 100V lower max rating than 003.
100uf/100V 85C cap with 220uf/100V 105C cap
100uf/16V 85Ccap with 120uf/62V 105C cap
10uf/25V 85C cap replaced with 10uf/25V 105 C cap
1uf/50V cap replaced with 1uf50V 105 cap
2, 12V zeners replaced
2 1n4007 diodes replaced

On the Filter board I replaced the main filter caps
with same value 105C cap and replaced the 470uf/25V
cap with a larger 680uf/35V 105C cap.

Now on to the control and display boards.

I removed them, then spent a lot of time cleaning them with high purity
isopropal. wiped down first with 99 percent and kimwipes a few times
then washed with spray 70 percent. Blown dry. Allowed to dry in the
in the hot summer sun.

I temp wired it up and set it on top of the chassis.

To get the full display to work I was testing the EPROM chips leads
using my multimeter. Connected ground to the 5 VDC ground
pin 3 of the J208 connection and then testing the EPROM voltages on
U202 and U205. These were pins 1, 14, 15, 28, 8, 19, 20.

Then the display started to come alive.

Working around the pins then working the switch buttons.

Before I reinstall the display and control boards I'll Deoxi and lube
the switches, prelace the electrlytics on the boards and replace
the zeners on the board.

I"ll test it again before reinstalling it. It will be more difficult
to install than remove with the rest of the boards installed in
the chassis.

I'll uninstall the filter board again to find the open grounds
outlets 1 - 3.

Then put it all back together, test again before seeing how it works
in my system.

I"ve got pics of most things that I've done and will post them
here and in my gallery as the film is developed. : )
-- Sync
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Old 19th June 2014, 01:32 PM   #27
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Default Observations

The HTPS seems to pull a lot of current with nothing attached.
This is at 120 line voltage.

It also gets hot. On the T2 board, one of the design issues I see
is that the main filter cap is right next to the heat sink of the High Power
Switching Resistors. This alone should be the cause of numerous failures.

I've replaced this filter with higher temp 105C cap. It still gets warm.
I've pulled the T2 board out again and I will relocate the filter farther
away and mount is on a smaller board. There is a large ground plane
on the back side of the board to which I can mount the Cap's negative
lead. The cap will end up being parallel with the T2 board with the
rubber towards the heat sink and be about 1/2 - 3/4 inch away.
It might be better to use an axial cap as opposed to a radial cap.

Next up is replacing a few zener diodes that were the wrong
value I put in.

Finally, as Richard suggested, I try pulling banks of MOVs and
see if there is any affect on current usage. NOTE, these are a
real PITA to remove as they are fairly large, act as heat sinks when desoldering, especially being no lead soldered in to begin with.

Even with my Weller 80 watt desolder iron, set at over 820F it is hard
to get the solder to flow and suck it out. I can set at higher temp but
it will start pulling up the trace pads.

Don't get me wrong it is a nice piece of gear of consumer electronics.
As a dual sided board and I would have liked the MOV and some other
pads to have been full through hole and heavier duty would make
maintenance a lot simpler.

Now I'm wondering if I can mod the solder station I have to help it
use more current when it needs it.

I can tell you one thing, I've learned a lot about AC gear working on this.
It is really strange working on it and measuring it, a lot doesn't make
sense if your used to working on "normal" gear.

Also, you find the limit of your tools, what they can and cannot do in certain
circumstances and you learn that you need some other tools and the limits
the manufactures designed them...or perhaps I'm using them beyond their
design limits.
-- Sync

Last edited by SyncTronX; 19th June 2014 at 01:41 PM.
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Old 22nd June 2014, 07:18 AM   #28
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So, what do you do when you reach those design limits?

Do It Yourself, what we all do.

In my case I've been limited by the lack of choices for
the Weller rework station that I own. Its the WRS 3000.
When it works, it works really great. When it doesn't
it will $10 and $20 you to death. Also when working with
mid to large size through hole work or Tube amp work
you need almost hourly maintenance on it.

Fast forward, tring to desolder the big MOVs...can't be done
with any of the stock tips. I tried and pulled up three traces.

The largest tip Weller offers is the DS114 and it is too large
with an O.D. of .125 inch. The DS113 is too small, because they
have a smaller tube inside which won't enable them to go down
to the trace on a lead of .040. The next largest tip is the DS111.

The package says its size is .090 inch. I have a few that look a bit
larger so I measured them and they are larger with their O.D. .107 inch.
I drill the little tube out and end up with a hole sized about .055 inch.
Don't forget we want air space around the lead to suck out the solder.

How'd it work in practice?

Great, I'll pulled out the next 5 MOVs with out an issue in about 15 mins.

Now I've got 10 MOVs out and powered it up between and after. Neither
made a difference with the unit's current draw about .82 amps with nothing
attached to it.

I'll pull up the next four MOVs and test again.

I don't think it will make any difference, but ya never know.

At least this way I'll know for certain, as Demian mentioned
MOVs typically don't live in the mid space they either work
or don't.

However reports from some tube amp guys say sometimes
they do live in the middle zone and people don't realize why
the tone of their amps suck...until the MOV is replaced
and the tone returns.

That is a story for another day.

Thanks for the bandwidth. Pics tomorrow,
when developed unless I used my Polaroid Land camera.
-- Sync

Last edited by SyncTronX; 22nd June 2014 at 07:21 AM.
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Old 22nd June 2014, 04:06 PM   #29
RNMarsh is offline RNMarsh  United States
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Current draw you see is thru the filters and is normal.
Suggestion: You do not have to remove the MOV's to find out if they are a problem or not.... just cut a pcb trace to them will disconnect them.... later put in a jumper wire across the cut pcb gap.

Changing to 105C caps is always a good idea for longer life.


Last edited by RNMarsh; 22nd June 2014 at 04:09 PM.
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Old 22nd June 2014, 10:12 PM   #30
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Thanks Richard,

Now you tell me. I guess there is more than one way to skin the cat.

Hopefully you like pics more than just reading.
I figure I'd save more than just a couple of thousand words here:

Parts pulled and replacements
Note: The pad on the right where the original MJE was arching.
Since I didn't have a replacement I cleaned it as best as I could
then I flipped it around at least now the carbon bits are against the
heat sink on the opposite pin.
Click the image to open in full size.

Test w/o MOVs,
nothing fancy but it works.
All hooked up and the LED and cotrol board on wood for
stability and isolation. I think I've almost got it working properly.
Just a few more tweaks and we are off and running.
Click the image to open in full size.

Here the desolder tool
with the custom tip. Best thing is it works.
Click the image to open in full size.

Here are the various tips,
from left DS114, DS111, DS112, DS113, DS110,DS111
At over $10 a tip you try not to waste any but want them
to work for you. Keep 'em clean and apply solder to protect 'em.
Click the image to open in full size.
-- Sync

Last edited by SyncTronX; 22nd June 2014 at 10:22 PM.
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