ASR10 booting sometimes

Synth Repair
1

Hi Syntaurians

In a previous topic I was repairing the ASR10 PSU of my ASR suddenly not booting after serving without any problem.

Every single voltage is ok now, strictly in the standards of the service manual that I read carefully.

This is what I did in addition :

-Complete disassembly ( it’s a SCSI version )
-Checked every ribbon cable pin to pin continuity ( all OK)
-Complete disassembly and cleaning of the keyboard / keybed
-Checked the 20 pins connections on board ( even desoldering the connector and resolder and checked ) checked continuity of the ribbon between the two halves of the PCB keybed
-Checked every card, every connector, Remade cold solders after inspection with a microscopic camera ( every old solder point was eliminated with a pump and remade properly )
-Digital Board ; checked everything, even the continuity of the OTTO chip from each side of the PCB, checked the few square chips, repositionned the ram to make sure…checked every single resistor on each card
-Careful reassembly with all the screws, and every ribbon in the right place without error.

And it worked as before, responsive and with crystal clear sound and strong dynamics ) !!! :smiley: , but only for 20 minutes… :frowning:

I was playing a song by sending midi to the ASR, I could change, load, modify instruments ( from a SCSI device ) , and after a while, could’nt modify anything, as the ASR was frozen, while keeping the ability to receive and play midi notes.

I shut down, and after , it restarted later for 2 or 3 minutes before showing the same symptoms and now its over again.

Re checked psu, voltages and fuses, everything is fine, even after heating.

Do anyone knows what would cause this?
Are there some thermistors to be replaced on the digital board?
What should I check or replace ? Small condensers ?

Also have a doubt on the voltage that I should read on the analog board ( VR1 thru VR 7 ), they are silkscreenned but it’s not clear to me ( VR6 is silkscreened -15A)

Thank you.

2

hi, does the VFD screen go blank but it still responds to midi?
have you ever checked over the keybed and MPU on the keybed?
The asr-10 has three MPUs: mainboard, frontpanel and the keybed - all most be working in synchronicity

3

Hi We-Robot.

Thanks for your answer.
I’ve been off the grid for a while.

The VFD is like frozen, but not blank, , and does not change or respond to any button solicitation on the front pannel, but the ASR still work with external midi input and play notes from external device.

I have to get to the keybed again to check the MPU. I think something is wrong there.
In addition to solders is there anything else I can check and how?

Thanks

4

hi
so does the VFD respond in the diagnostics mode . i.e. you press buttons and random characters appear? Try that to exclude an issue on the front panel. This is covered in the service manual - how to place front panel in diag mode.

5

Hi

In diagnostic mode (I shut down the ASR-10 and turn it on after the symptoms mentioned above have occurred), the VFD displays all the characters indicated in the service manual, on the entire VFD from left to right. I can add that the VFD switches automatically in diagnostic mode and I never had to do any manipulation. From time to time, and especially after moving inner elements in the ASR, it can work for a few minutes.

6

Check the key bed module. My TS-10 had issue starting up. The keybed has a 555 timer that slightly delays the its microcontroller startup to allow the main board to complete the booting. In my case the capacitor driving the 555 timer circuit was bad and delaying the startup so long that the main board thinks it is faulty. Fixed it and was all good.

1 Like
7

yes keybed , the MPU (microprocessor) on there must communicate with the other two MPUs (one on the mainboard and another on the front panel)

This is a really convoluted arrangement and prone to failure

Ensoniq made great sounding products at a super competitive price but they cut corners to get those great sounding products into the hands of musicians.

1 Like
8

Hi Keyboardist.
Thank you for the advice.

I changed all the capacitors on the keybed even the one driving the 555

I checked the tantalum capacitor driving the 555 on the main board too, it is still good despite its age.

No changes, it won’t not start. Should I change the 555’s? (cant’ find the SMD version for the keybed).

But a few weeks ago, after letting the ASR heat up and switching it off for a few minutes and a restart, it worked for almost 30 minutes. It has something to do with the temperature. Anyway, I’ll recap the whole motherboard, we’ll see.

I noticed that even in self test mode (blank screen but effective characters by pressing buttons) the ASR seems to load the SCSI disk after checking the floppy ( replaced with a gotek - workin fine ).

I think the main processor does its boot routine, but it leads nowhere.

The mystery remains intact

Thx

9

try disconnecting the scsi card and try booting from floppy. I had problems with scsi - bad cable or termination which can make things go funky.
power supply tests really need a load on them before you can get proper measurements with a volt meter. regulators will give you proper voltage with no load but will go erratic if say your electrolytics are flakey, or one of the rectifiers is faulty.
the restart indicates to me that a components is getting too hot and starting to fail. you might feel around to see (feel) a component that is hot. the power supplies in the asr-10 series do get quite hot and they really need a fan to keep things cool - especially the racks.