Tc electronics bass amp p/s switching problem

[bigdrums925]

I have a TC Electronics RH750 Bass amp that won't turn on. After opening it up I checked the power supply voltages that read 70VDC and -72 VDC. This using a variac and a light bulb limiter in line to the power cord. Problem is I can't find a schematic anywhere. There are 3 diagnostic LED's on the P/S board, 2 of which flash in sync with the light bulb limiter at about 2 flashes per second. The LED's are labeled 1) LD7 Mains Low, 2) LD1 protect, and 3) LD2 Amp enable. The first 2 are flashing. If I try to start this without the current limiter, the ampmeter on the variac pegs out with just a slight turn.
Can anyone give me pointers where to look for the likely problem?

[52 Bill]

So, I will assume that this has a SMPS and it doesn't like the limiter.

Before you connected the limiter and Variac, what did the amp do when it was powered on, blow fuses, smoke, nothing?

[bigdrums925]

Before I began to work on it the owner said he dropped it from about 18" after which it would not light up, turn on, or any indication thereof.
He opened it up hoping he could fix it but eventually gave up and brought it to me. When first got it nothing happened upon power up
And yes SMPS which pluses with the limiter (the bulb gets bright the dims) when inserted, but without the limiter the ampmeter pegs shortly after ramping up ~10%

[Jazz P Bass]

LED 1 trying to come on says the system is in 'Protect'.

I would start by looking at the outputs for dead shorts.

[bigdrums925]

The SMPS is not connected to anything, removed it from the chassis

[J M Fahey]

Post a power amp and supply board sharp readable picture (i.e. not a cellphone one ).
Post all PCB labels you see on it.

It´s very probably some ICE Power module.

If so, those in general are fully replced as a whole.

There is specialized people repairing them , but doubt you will send your module to Italy or Poland.

[52 Bill]

If it isn't blowing fuses, power up the power supply directly and see if the voltages are correct.

It's been a while since I saw one of these, but the last one I saw had a broken solder solder connection on one of the ac input coils, so it didn't power on at all. May not be your problem, but it could point to something caused by a physical drop.

[bigdrums925]

[ATTACH=CONFIG]40578[/ATTACH]
smps board
[ATTACH=CONFIG]40579[/ATTACH]
pcb label from smps board
[ATTACH=CONFIG]40580[/ATTACH]
believe this is power board
[ATTACH=CONFIG]40581[/ATTACH]
power board pcb label

[bigdrums925]

[ATTACH=CONFIG]40582[/ATTACH]
smps board

[J M Fahey]

Thanks.

Wow!!! a VERY complex board.

I was expecting it to be one of the ICE Power modules, many of which can be bought on EBay for a reasonable price, and about which at least some datasheets are available, that´s why I asked about the board labels, but this one seems tp be some proprietary TCE own design, so it´s available only from them.

Personally I´d do some basic SMPS troubleshooting, mainly checking switching MosFets , mains diode bridge and the secondary high speed rectifying ones, anything besides that is beyond my basic area of experience, maybe somebody with wid SMPS knowledge can suggest something else.

Just as a Plan B, ask TCE whether they can sell you a replacement board, which in fact must be the standard repair procedure, doubt many will venture beyond that

[MarkusBass]

I'm not sure whether I understand the problem you have. In the first post you wrote that you have +/-70V rails. Now, you disconnected the SMPS and you say it is not working. And you want to replace the module. But previously it was working .
I have few remarks:
- since the amp was dropped, it's clear that the problem is mechanical. I would look (with magnifying glass) at all heavy components like coils, transformers, transistors attached to heatsinks, and so on.
- you haven't proved that there is something wrong with the power supply module. All you know that it doesn't power up standalone but this may be normal. Such circuits (like this amp) usually have two power supplies. There is "helper" power supply (usually +5V) that is kind of a standby power supply. It powers up a microprocessor that checks various conditions and if everything is OK, it sends "Power_OK" signal to the big power supply. I'm not saying that this is the case but it is very common. Since you disconnected the SMPS, it does not get necessary signals. So actually you don't know whether the problem is related to the power supply or not.
I suggest (since the amp was dropped) to get a big magnifying glass and inspect the PC boards for broken tracks or pads.

Mark

[bigdrums925]

When I power up the SMPS by itself from the variac, the current meter pegs full on when I ramp up the variac to about 20%.
So I'm thinking it's probably shorted rather than an open circuit path.

[bigdrums925]

I'll try to be a little more clear. Starting with the variac, then thru a light bulb limiter, then into the SMPS removed from the rest of the circuity. I begin to ramp up the variac and the light bulb limiter pulses all the way to 120 volts, and measuring the +/- supply wires I see the DC voltages slowly rise to about +/- 70VDC.
But if I try that without the limiter there is no meter movement until about 20% on the variac at which point the amp meter slams full on. I shut it off immediately.
I tried making the same test before I removed it from the chassis and I was seeing approx. -70 and +90 at the supply wires.

I will try reinstalling the SMPS and see what I get
I have a microscope for examination of the solder joints but nothing found yet

[MarkusBass]

In such a case don't try it without the bulb limiter. The power supply looks quite simple - I would try drawing its schematic. Have you check the bridge rectifier, switching MOSFET and output diodes?

Mark

[bigdrums925]

I haven't tried drawing a schematic yet but the bridge rectifier, switching mosfets, and output diodes all seem to ck good