Hello Everyone - I’m hoping for some guidance in repairing an ESQ1 that I damaged during Eprom replacement (installed them backwards!). Since then start up (even with new, working, correctly installed eproms) causes the screen to flicker for a second and then go black. There is also no sound.
I went through all the the obvious troubleshooting steps (reseating etc) but to no avail. But i did discover that transistor Q11 gets extremely hot - about 70degC after 1 minute of the synth being powered up. So I suspect the issue is either with the transistor or something downstream drawing too much current.
So this is where I am currently - hoping some one can shed light on where to go from here (something tells me just replacing the transistor wont solve the issue)
Hi !
Do you have the means to check if your CPU (68B09) is working ?
Are there signals on the address bus and the data bus ?
What is the revision number of your main board ? E or H ?
Hello - not sure how I would check the CPU or signals - any advice welcome (I am comfortable with a multimeter) and can order an IC tester if one exists for these chips. I just checked the board and it’s the E version - which makes me wonder…does it even support firmware 3.5?
The ESQ-1 which is currently being repaired in my workshop is an E revision, it has been fitted with a 3.53 firmware from Rainer Buchty, and it works well.
Well thats reassuring - thanks. Do you have any suggestion for next steps? Do I replace the transistor and hope for the best? or its safe to say that the transistor overheating is not the cause but the symptom of a deeper problem.
Transistor Q11 generates +5V for the analog section only. Your ESQ-1 doesn’t boot (no screen display), so your problem is primarily digital. It seems unlikely that reversing the EPROMs could have damaged anything on the analog side.
I think your problem lies with the MPU, EPROM, and RAM. If your processor is working, you should start by checking the U22, U27, and U26 circuits that control the memory.
I'll check the temperature of Q11 on mine.
For your information, the temperature of my transistor Q11 was measured at 60°C. This likely indicates higher current draw in the analog section of your ESQ-1. You will need to check the functionality of each of the 8 voices after you restart.
Ok thank you both for the suggestion. So I did some voltage testing for now and noticed something interesting. All the voltages expected on page 15 of the service manual are good. Except for VBB (18-16 Display). That one should be reading 45-55VDC but only reads 20V. I tried disconnecting the display harness at which point it starts to read the expected 55VDC. Is it possible that the display is the culprit???
With connector J4 unplugged, the screen should go into self-test mode; otherwise, the 6500/11 Keypad/Display is faulty !
I’m completely confused ! I don’t see how a reversed EPROM could have destroyed the screen interface ?
Yes, it did go into self test mode originally when i started this thread. Yesterday i decided to check all the voltages and found VBB was only getting 20V instead of the 45-55V. In the process I disconnected and reconnected the display harness and after that it no longer goes into self mode but instead shows this garbled character mess. This is the case even with J4 disconnected. So - I’m thinking I now have 2 issues on hand, which is getting out of control! So I decided to sell it for repair/parts (got a buyer surprisingly quick). Appreciate all your suggestions!
